An experimental and theoretical study of the substituent effects on the redox properties of 2-[(R-phenyl)-amine]-1,4-naphthalenediones in acetonitrile

Article abstract of DOI:10.1021/jo990186o

We synthesized and analyzed 19 compounds of 3'- (meta-) and 4'-(para-) substituted 2-[(R-phenyl)amine]-1,4-naphthalenediones (PANs) R = p-MeO, p- Me, p-Bu, p-Hex, p-Et, m-Me, m-Et, H, p-Cl, p-Br, m-F, m-Cl, p-COCH₃, m-CN, m-NO₂, m-CO

Full text of DOI:10.1021/jo990186o

3684
J . Org. Chem. 1999, 64, 3684-3694
An Exp er im en ta l a n d Th eor etica l Stu d y of th e Su bstitu en t Effects
on th e Red ox P r op er ties of
2-[(R-p h en yl)a m in e]-1,4-n a p h th a len ed ion es in Aceton itr ile|
M. Aguilar-Mart´ınez,*,† G. Cuevas,‡ M. J ime´nez-Estrada,‡ I. Gonza´lez,§
B. Lotina-Hennsen,| and N. Mac´ıas-Ruvalcaba†
Universidad Nacional Auto´noma de Me´xico, Facultad de Qu´ımica, Departamentos de Fisicoquı´mica y
Bioquı´mica; Instituto de Quı´mica, 04510 Me´xico, D.F., Me´xico, and Universidad Auto´noma
MetropolitanasIztapalapa, Departamento de Quı´mica, Apartado Postal 55-534,
09340 Me´xico D.F., Me´xico
Received February 1, 1999
We synthesized and analyzed 19 compounds of 3′- (meta-) and 4′- (para-) substituted 2-[(R-phenyl)-
amine]-1,4-naphthalenediones (PANs) R ) p-MeO, p-Me, p-Bu, p-Hex, p-Et, m-Me, m-Et, H, p-Cl,
p-Br, m-F, m-Cl, p-COCH3, m-CN, m-NO2, m-COOH, and p-COOH. Despite the fact that the nitrogen
atom, which binds the quinone with the meta- and para-substituted ring, interferes with the direct
conjugation between both rings, the UV-vis spectra of these compounds show the existence of an
intramolecular electronic transfer from the respective aniline to the p-naphthoquinone moiety. In
accordance with this donor-acceptor character, the cyclic voltammograms of these compounds
exhibit two, one-electron reduction waves corresponding to the formation of radical-anion and
dianion, where the half-wave potential values vary linearly with the Hammett constants (σx). The
analysis of the different voltammetric parameters (e.g., voltammetric function, anodic/cathodic peak
currents ratio, and the separation between the anodic and cathodic potential peaks) show that
with the exception of the carboxylic PAN derivatives, all compounds present the same reduction
pathway. We investigated the molecular and electronic structures of these compounds using the
semiempirical PM3 method and, within the framework of the Density Functional Theory, using
the Becke 3LYP hybrid functional with a double ú split valence basis set. Our theoretical calculations
predict that, with the exception of the p-nitro compound, all the compounds are planar molecules
where the conjugation degree of the nitrogen lone pair with the quinone system depends on the
position and magnitude of the electronic effect of the substituent in the aniline ring. The Laplacians
2
of the critical points (∇ F), for the C-O bonds, show that the first reduction wave corresponds to
the carbonyl group in R-position to the aniline, and that the second one-electron transfer is due to
the C4-O2 carbonyl reduction. Thus, the higher reaction constant value (F) obtained for the second
one-electron transfer is due to the fact that the displacement of the nonshared electrons of the
amino nitrogen merely modifies the electron density of C4-O2 bond. The positive correlation between
the LUMO energy values calculated for these compounds and the E1/2 potentials corresponding to
the C1-O1 carbonyl reduction show that the electron addition takes place at the lowest unoccupied
molecular orbital, supporting the fact that this wave is also prone to the substituent effect.
In tr od u ction
of these species.3 The ability of the quinones to accept
one or two electrons depends directly on their chemical
structures.4 The electron-accepting capacity of these
substances can be modified by directly adding a substitu-
ent to the quinone system5 or by adding a substituted
phenyl to the quinone ring.6 For these types of com-
pounds, the attracting or donor effects of the substituents
are very important in affecting the redox properties of
the quinone system, either facilitating or interfering with
the charge transfer to the quinone. However, for some
applications, gradual changes of these redox properties
are required. To achieve such a gradual change, mol-
ecules of the type quinone-X-substituted phenyl have
The quinone structure is found in many naturally
occurring compounds and is associated with diverse
biological activities.1 Because of the inevitable exposure
of humans to quinones and their inherent reactivity,
many studies have focused on the chemistry and toxicol-
ogy of these compounds.2 In most cases, the biological
activity of the quinones is related to their capacity to
accept one or two electrons to form the corresponding
radical-anion or dianion and to the acid-base properties
* To whom correspondence should be addressed. Fax: (525) 6 16
22 17; e-mail: marthaa@servidor.unam.mx. Present address: Instituto
de Qu´ımica, Universidad Nacional Auto´noma de Me´xico, 04510,
Me´xico, D.F., Me´xico.
(3) Wolstenholm, G. E. W.; O’Conner, C. M., Eds. Quinones in
Electron Transport; Churchill: London, 1961.
(4) Zuman, P. Substituents Effects in Organic Polarography; Plenum
Press: New York, New York, 1967.
(5) Huntington, J . L.; Davis, D. G. J . Electrochem. Soc. 1971, 118
57-62.
(6) Li, C. Y.; Caspar, M. L.; Dixon, D. W. Electrochim. Acta 1980,
25, 1135-1142. Qureshi, G. A.; Ireland, N. Bull. Soc. Chim. Belg. 1981,
90, 223-226.
† Facultad de Qu´ımica, Universidad Nacional Auto´noma de Me´xico.
‡ Instituto de Qu´ımica, Universidad Nacional Auto´noma de Me´xico.
§ Universidad Auto´noma MetropolitanasIztapalapa.
| Contribution no. 1691 of the Instituto de Quim´ıca, UNAM.
(1) Morton, R. A., Ed. Biochemistry of Quinones; Academic Press:
New York, New York, 1965.
(2) Monks, T. J .; Hanzlik, R. P.; Cohen, G. M.; Ross, D.; Graham,
D. G. Toxicol. Appl. Pharmacol. 1992, 112, 2-16.
10.1021/jo990186o CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/28/1999

Redox Properties of 2-[(R-Phenyl)amine]-1,4-naphthalenediones
J . Org. Chem., Vol. 64, No. 10, 1999 3685
Ta ble 1. Str u ctu r e of
2-[(R-P h en yl)a m in e]-1,4-n a p h th a len ed ion es Syn th esized
in Th is Wor k
of the substituents on the electronic properties of the title
compounds.
Through theoretical calculations using the semiem-
pirical PM3 method and in the frame of the Density
Functionals Theory (DFT), we performed the complete
optimization of the geometry for some of the PANs
studied experimentally. We also determined the Wiberg
bond indexes, the natural charges, the densities at critical
bond points, Laplacians, and ellipticities. Besides defin-
ing the spatial array of the neutral PAN molecules, these
findings help clarify how the substituents in the aniline
ring modify the electronic properties of the quinone
system.
Since the biological activity of quinone compounds is
related to the redox potentials of the quinone moiety, a
systematic investigation of the substituent effects in
PAN-like molecules could provide clues to the mecha-
nisms of their biological activity. Such information will
be useful for designing new molecules with greater and
more specific biological activities.
compound
PAN
R1
R2
H
H
H
H
H
H
p-MeOPAN
p-MePAN
CH3O
CH3
n-C4H9
C2H5
H
p-BuPANa
p-EtPANa
m-MePANa
m-EtPANa
p-HexPANa
p-ClPAN
CH3
C2H5
H
H
n-C6H13
Cl
H
p-BrPAN
H
F
Br
H
m-FPANa
m-ClPAN
Cl
H
m-COOHPAN
p-COOHPAN
p-COCH3PAN
p-CF3PANa
m-CNPANa
m-NO2PANa
p-NO2PAN
COOH
H
H
H
COOH
COCH3
CF3
H
H
NO2
Resu lts a n d Discu ssion
H
Sp ectr oscop ic Resu lts. PAN and its derivatives were
insoluble in water. PANs containing electron-withdraw-
ing substituents were found to be less soluble than the
PANs with electron-releasing groups in both acetonitrile
and ethanol. All the derivatives exhibited orange to dark-
red colored solutions in ethanol. Dissolved compounds in
EtOH had similar UV-vis spectra, with a band in the
240-272 nm region corresponding to the intense benzene
and quinone π-π* electron transitions. We observed one
band transfer at about 335 nm and a very broad, low-
energy band in the visible region centered between 375
and 480 nm. We assume this second band is due to the
n-π* transition of the carbonyl groups in the quinone.
The p-NO2PAN compound showed an additional, very
intense band at 785 nm. Comparing the PAN spectrum
with that of naphthoquinone (NQ), there is a significant
shift in the λmax absorption for the n-π* transition. This
is an indication of the strong influence of the substituted
aniline group at C2 position of the naphthoquinone. The
PAN derivatives show a similar electronic effect to that
of PAN. The λmax value, corresponding to the n-π*
transition, was modified by the substituent in the aniline
ring. We found that the electron donor groups (auxo-
chromes) caused changes in the absorption of the n-π*
transition at the longest wavelengths (batochromic ef-
fect), while the electron-accepting groups (chromophores)
changed the absorption at shorter wavelengths (hipso-
chromic effect) (Table 2).
CN
NO2
H
a
These compounds have not been previously described, see
Experimental Section.
been suggested,7,8 with X being a heteroatom. The pres-
ence of the heteroatom allows modulation of the sub-
stituent’s effect on the electronic properties of the quinone
system, as well as modification of the geometry of the
neutral molecules and of their reduction intermediates.8
1,4-Naphthoquinones, possessing an amine or a sub-
stituted amine group in the 2-position, have been the
subject of study for many years due to their use in a
variety of medical and biological applications such as
antituberculars,9 antimalarials,10 antibacterials,11 anti-
tumor agents,12 larvicides,13 molluscicides,13 herbicides,14
and fungicides.15 Our work reports on the synthesis and
analysis of a series of 19 2-[(R-phenyl)amine]-1,4-naph-
thalenediones (Table 1), nine of which have not been
previously described. These compounds were character-
1
ized by H and 13C NMR, IR, UV-visible spectroscopy,
mass spectrometry, and cyclic voltammetry. To analyze
the influence of the N-substituted phenyl group in
quinone properties, we also studied the related quinone
(naphthoquinone NQ). Through these analyses, we de-
fined the influence of the donor and acceptor properties
Plotting the 1/λmax values obtained for each compound
against the Hammett substituent constants σx, produced
a linear correlation (eq 1).
(7) Stradins, J .; Glezer, V.; Turovska, B.; Markava, E.; Freimanis,
J . Electrochim. Acta 1991, 36, 1219-1225. Glezer, V.; Turovska, B.;
Stradins, J .; Freimanis, J . Electrochim. Acta 1990, 35, 1933-1940.
(8) Illescas, B.; Martin, N.; Segura, J . L.; Seoane, C.; Orti, E.;
Viruela, P. M.; Viruela, R. J . Org. Chem. 1995, 60, 5643-5650.
(9) Oeriu, I.; Benesch, H. Bull. Soc. Chim. Biol. 1962, 44, 91-100.
Oeriu, I. Biokhimiya 1963, 28, 380-383.
1/λmax (nm-1) )
1.43 × 10-4 σx + 0.00214 (n ) 18, r ) 0.9667) (1)
(10) Prescott, B. J . Med. Chem. 1969, 12, 181-182.
(11) Silver, R. F.; Holmes, H. L. Can. J . Chem. 1968, 46, 1859-
1864.
This correlation indicates that even though the sub-
stituent is on the aniline group, the electronic properties
of the quinone system are affected by the nature and
position of the substituent. Theoretical studies explain
this topic extensively. The σx constants used in this work
are the standard Hammett values16 and are included in
Table 2.
(12) Hodnett, E. M.; Wongwiechintana, C.; Dunn, W. J .; Marrs, P.
J . Med. Chem. 1983, 26, 570-574.
(13) Lopez, J . N. C.; J ohnson, A. W.; Grove, J . F.; Bulhoes, M. S.
Cienc. Cult. (Sao Paulo) 1977, 29, 1145-1149.
(14) U.S. Rubber Co., British Patent 862 489, 1959. Takeda Chemi-
cal Industry Co. Ltd, J apanese Patent 18 520, 1963. Ube Industries
Ltd. J apanese Patent 126 725, 1979. Shell Internationale Research
Maatschappij B. V., British Patent 1 314 881, 1973.
(15) Clark, N. G. Pestic. Sci. 1985, 16, 23-32.

3686 J . Org. Chem., Vol. 64, No. 10, 1999
Aguilar-Mart´ınez et al.
Ta ble 2. Electr och em ica l P a r a m eter sa a n d th e Lon gest Wa velen gth Absor p tion Ba n d b of
2-[(R-P h en yl)a m in e]-1,4-n a p h th a len ed ion es (P ANs)
ipcv-1/2c-1 × 104
(AV-1 s1/2 mol-1 cm3)
ipa/ipc
wave II
∆Ep (mV)
E1/2 (mV)
c
compound
NQ
σx
λmax (nm)
wave I
wave II
wave I
wave I
wave II
wave I
wave II
d
0.79
0.75
0.81
0.81
0.76
0.75
0.69
0.72
0.77
0.66
0.70
0.75
0.76
0.77
0.66
0.69
0.72
0.74
0.70
0.63
0.71
0.62
0.64
0.67
0.71
0.68
0.70
0.67
0.72
0.63
1.01
1.00
0.99
0.95
1.05
1.02
0.98
0.92
0.99
1.08
1.01
1.06
1.00
0.98
0.93
1.11
0.89
0.76
0.71
0.72
0.83
0.76
0.94
0.90
0.62
0.78
0.92
0.93
0.96
0.97
73
69
67
64
70
64
73
75
70
65
61
70
70
68
70
97
73
74
124
86
68
70
81
80
69
65
59
82
64
66
63
74
-1036
-1236
-1216
-1217
-1215
-1218
-1213
-1216
-1209
-1173
-1176
-1163
-1145
-1126
-1147
-1133
-1104
-1067
-880
-1495
-1809
-1773
-1770
-1720
-1749
-1685
-1665
-1685
-1608
-1642
-1567
-1520
-1554
-1602
-1612
p-MeOPAN
p-MePAN
p-BuPAN
p-HexPAN
p-EtPAN
m-MePAN
m-EtPAN
PAN
-0.27
-0.17
-0.16
-0.16e
-0.15
-0.07
-0.07
0.0
0.23
0.23
0.34
0.37
0.50
0.54
0.56
0.71
0.78
0.37
0.45
480.0
473.1
472.9
474.6
472.4
468.3
469.1
465.5
460.9
463.4
456.4
456.8
459.1
452.0
448.0
444.4
443.1
459.5
459.5
p-ClPAN
p-BrPAN
m-FPAN
m-ClPAN
p-COCH3PAN
p-CF3PAN
m-CNPAN
m-NO2PAN
p-NO2PAN
m-COOHPAN
p-COOHPAN
0.82
0.68
1.08
0.84
f
f
f
f
115
108
162
341
39
-1312
f
f
f
f
f
f
f
f
f
f
0.29
0.14
0.90
64
-1211
f
f
f
-917
Measured by cyclic voltammetry (mV vs Fc/Fc+), 0.1 M Et4NBF4/acetonitrile with Pt electrode (3.14 mm2). In ethanol, corresponding
a
b
to the n-π* transition of the quinone carbonyl group. c The standard Hammett values were taken from ref 16. Not observed. e Determined
d
value in this work. f Because the waves were ill-defined, these values could not be accurately determined.
wave potential values E1/2 for both waves were evaluated
from the voltammograms obtained at a sweep rate of 100
mVs-1, as E1/2 ) (Epa+Epc)/2, where Epa and Epc cor-
respond to anodic and cathodic peak potentials, respec-
tively, for each wave.
With the exception of the m-COOHPAN, p-COOHPAN,
m-NO2PAN, and p-NO2PAN compounds, which presented
more complex cyclic voltammograms, the electrochemical
behavior for all the other PAN derivatives and also for
NQ was similar to that shown in Figure 1. In all PANs,
the cathodic peak current (ipc) vs the square root of the
sweep rate (v1/2), produced a linear relationship with zero
intercept for both peaks, indicating the lack of detectable
chemical kinetic complications.17 This behavior was
confirmed by consistency of the voltammetric function
(ipcv-1/2c-1) with the sweep rate. Due to the different
F igu r e 1. Typical cyclic voltammogram of 1 mM PAN in 0.1
solubilities of the PANs in acetonitrile, the concentration
used for the voltammetric studies varied. Voltammetric
function values were standardized for concentration and
reported as ipcv-1/2c-1, where ipc represents the cathodic
peak current of the first or second reduction peak, v is
the scan rate, and c is the concentration of compound in
mol/cm3.
Table 2 shows that the values of the current function,
ipcv-1/2c-1, for both waves are approximately the same.
This indicates the one-electron transfer for each wave and
that the diffusion coefficients are approximately equal
for the compounds analyzed. Such a result is to be
expected since the molecules are quite similar in size and
shape. Furthermore, the reversibility degree is indicated
by the relationship ipa/ipc, which is close to one in value
as described for reversible systems. The values of ∆Ep
(Epa - Epc) also approach the theoretical value of 60 mV
reported for one-electron reversible systems.18 The E1/2
values (Table 2) for the first one-electron transfer,
corresponding to the formation of the radical-anions, are
in the potential range of -1036 to -1236 mV. For the
M Et4NBF4/acetonitrile obtained in Pt electrode (3.14 mm2),
scan rate 100 mV/s. The cathodic (c) and anodic (a) peaks are
indicated in the figure.
Electr och em ica l Resu lts. The redox potentials of the
PAN compounds determined in this work were measured
by cyclic voltammetry at room temperature using a
platinum electrode in acetonitrile solvent and 0.1 M
tetraethylamonium tetrafluoroborate as the supporting
electrolyte. The voltammograms were recorded in the
potential range from 0.0 to -2.4V vs Fc/Fc+. Figure 1
shows the typical electrochemical behavior of PAN, which
proceeded in two one-electron diffusion stages, PAN + e
h PAN•- and PAN•- + e h PAN2-. The same behavior
was observed within the sweep range of 50 to 1000 mV
s-1. At scan rates higher than 1000 mVs-1, however,
small distortions were detected in the cyclic voltammo-
grams that made determination of the corresponding
electrochemical parameters difficult. For this reason, in
our discussion of the results only the data obtained
between 50 and 1000 mVs-1 were considered. The half-
(17) Bard, A. J .; Faulkner, L. R. Electrochemical Methods. Funda-
mentals and Aplications; J ohn Wiley & Sons: New York, 1980.
(18) Heinze, J . Angew. Chem., Int. Ed. Engl. 1984, 23, 831-847.
(16) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165-
195.

Redox Properties of 2-[(R-Phenyl)amine]-1,4-naphthalenediones
J . Org. Chem., Vol. 64, No. 10, 1999 3687
second one-electron transfer, the E1/2 values, leading to
the formation of the corresponding dianions, fall within
the range of -1312 to -1809 mV.
the aniline ring, proved to be more powerful electron-
acceptors than the trifluoromethyl and halogens. The
magnitudes of the observed anodic shifts for these
compounds, with respect to PAN (p-COCH3PAN, 83 mV;
m-CNPAN, 76 mV; m-NO2PAN, 105 mV; p-NO2PAN, 142
mV) were larger than those for p-CF3PAN (62 mV) and
for halogens. The nitro group in meta-position was found
to be a weaker electron-accepting group than the same
group in para-position, indicating that in this case the
resonance effect is more pronounced that the inductive,
even when there is not a direct electron displacement in
these compounds.
The electron density, as induced by their substituents
and measured as a function of E1/2 for wave I, increases
in the following order: p-NO2 < m-NO2 < p-COMe <
m-CN < m-Cl < p-CF3 < m-F < p-Cl < p-Br < H < m-Me
< p-Hex < p-Me < p-Bu, m-Et < p-Et < p-MeO.
To establish a quantitative measure of the substituent
effect over the electrochemical reduction of the unsub-
stituted PAN system, the ∆E1/2 potentials were correlated
with the σx Hammett constants, where ∆E1/2 is the
difference in half-wave potentials between the substi-
tuted quinone and the parent reference compound, PAN.
The ∆E1/2 for the transformation of Q to Q•- varies
linearly with σx Equation 2 represents the linear regres-
sion obtained.
The differences in voltammetric behavior observed for
the m-COOHPAN and p-COOHPAN compounds as com-
pared to the other PANs indicate that for these com-
pounds there must be an additional effect on the electrode
process. Since carboxylic acids tend to liberate a hydrogen
ion easily, the autoprotonation reaction of the different
19
species in solution can actually take place.
The complexity of the cyclic voltammograms observed
for m-NO2PAN and p-NO2PAN indicates that the nitro
group is also electroactive in the cathodic zone studied.
The reduction potentials for the nitro and the quinone
groups unfortunately are similar enough so that dif-
ferentiation of the independent stages from the overall
reduction process is difficult. Because of this we were
unable to assess all the voltammetric parameters for
these derivatives.
Based on the similarities in the voltammetric mea-
surements (Table 2), we can presume that all these
quinones are reduced by the same mechanism.4 So being,
one would expect to find consistency among these sub-
stances for other molecular properties such as substituent
electronic effects (Hammett substituent constant σx),
spectroscopic parameters, and molecular-orbital calcula-
tions.
Su bstitu tion Effects. The introduction of the 3′-
(meta-) and 4′- (para-) substituted anilines on the 2-posi-
tion of 1,4-naphthoquinone (NQ), produces a considerable
cathodic shift for the two, one-electron steps (Table 2).
Even though the substituent is not directly conjugated
with the quinone group, the substitution effect of the
aniline system on the electrochemical reduction of the
naphthoquinones was evident. The electron-attracting
groups (fluoro, chloro, bromo, cyano, nitro, acetyl, and
trifluoromethyl) displaced the E1/2 of PAN to less negative
values. The electron-donor groups (methoxy, methyl,
ethyl, butyl, and hexyl) made the reduction of quinone
more difficult than that of PAN.
The four alkyl side chains in the compounds m-
MePAN, p-MePAN, m-EtPAN, p-EtPAN, p-BuPAN, and
p-HexPAN proved to be similar electron-donors since the
magnitude of the observed cathodic shift with respect to
that of PAN for the first wave was roughly equal. The
values for each were as follows: p-methyl, 7 mV; p-ethyl,
9 mV; m-methyl, 4 mV; m-ethyl, 8 mV; p-butyl, 8 mV;
p-hexyl, 6 mV. The methoxy group, as expected, was
consistently a more powerful electron-donor than the
alkyl groups, as it exerted a cathodic shift of 27 mV, a
value approximately four times that recorded for the
alkyl groups.
∆E1/2(mV) ) 139 σx + 3.71 (n ) 16, r ) 0.9771) (2)
In the regression analysis, the compounds m-COO-
HPAN and p-COOHPAN were far outside the trend of a
linear relationship shown by the other compounds in the
series and so were not considered for the linear regression
treatment. The results confirm that these compounds
undergo a different reduction mechanism,4 which, as
mentioned above, is due to an autoprotonation process.
The good correlation between the electroreduction po-
tentials for the first one-electron reversible stage with
the Hammett’s σx constants for all the other PANs
substantiates that the electrochemical reduction mech-
anism is the same for all of them.
In the Hammett-Zuman context, the slope of eq 2, 139
mV, corresponds to the reaction constant, Fπ, which is
characteristic of a given reaction and denotes the sensi-
tivity of the reaction to the electronic effects of the various
substituent groups studied. The positive value of Fπ
implies that the reaction is facilitated by a low electron
density on the electroactive group, and indicates that the
electron-accepting ability of these PAN derivatives bears
a linear relationship to the substituents electronic per-
turbation. From PAN and p-HexPAN E1/2 potentials
obtained for wave I (Table 2) and using eq 2, we
estimated the σp Hammett value for the hexyl substituent
(σp ) -0.16), which had not been previously reported.
The σp value obtained for the hexyl group substituted in
the para-position is very close to the σp values reported
for similar alkyl groups.16
The chloro and bromo substituents in para-positions
exerted approximately equal anodic shifts (p-chloro, 36
mV and p-bromo, 33 mV). However, the anodic shift was
greater with halogens in meta-positions (m-FPAN, 46 mV
and m-ClPAN, 64 mV). This confirmed that the inductive
effect of the halogen groups at this position is much more
pronounced than their resonance effect.16
To establish the influence of the substituent on the
radical-anion (Q•-) formed during the first reduction of
the PAN derivatives, the variation of ∆E1/2 of the second
reduction peak is presented as a function of σx. To assess
correctly the effect of the substituents in this type of
Substituents such as cyano, acetyl, and nitro, which
are strongly unsaturated at the point of attachment with
(19) Gonza´lez, F.; Aceves, J . M.; Miranda, R.; Gonza´lez, I. J .
Electroanal. Chem. 1991, 310, 293-303. Ortiz, J . L., Delgado, J ., Baeza,
A., Gonza´lez, I., Sanabria, R.; Miranda, R. J . Electroanal. Chem. 1996,
411, 103-107.
•-
reaction, σx constants for radical-anions should be used.
•-
Since the σx values for the compounds we studied are
not available, we used the σx values as an approximation

3688 J . Org. Chem., Vol. 64, No. 10, 1999
Aguilar-Mart´ınez et al.
Ta ble 3. Geom etr y of NQ, p-NO2P AN, p-CNP AN, p-F P AN,
P AN, p-MeP AN, p-MeOP AN w ith th e P M3 Meth od
Ta ble 4. Geom etr y of NQ, p-NO2P AN, p-CNP AN, p-F P AN,
p-CF 3P AN, P AN, p-MeP AN, p-MeOP AN a t Beck e3LYP /
6-31G(d ,p) Level
bond
NQ
NO2
CN
F
H
Me MeO
bond
NQ NO2 CN
CF3
F
H
Me OMe
C1-O1
1.219 1.218 1.220 1.220 1.220 1.220 1.221
1.486 1.506 1.513 1.513 1.513 1.513 1.513
1.334 1.347 1.352 1.353 1.353 1.354 1.354
1.481 1.473 1.471 1.470 1.470 1.469
1.218 1.221 1.222 1.222 1.222 1.222
1.489 1.488 1.489 1.489 1.490 1.490 1.490
1.395 1.393 1.394 1.394 1.395 1.395 1.395
1.393 1.393 1.392 1.392 1.392 1.392 1.392
1.388 1.389 1.389 1.389 1.389 1.389 1.389
1.393 1.392 1.392 1.392 1.392 1.391
1.395 1.396 1.397 1.397 1.397 1.397
1.405 1.403 1.402 1.402 1.402 1.402 1.402
1.433 1.408 1.405 1.403 1.403 1.401
0.998 0.999 0.999 0.999 0.999 0.999
1.428 1.422 1.472 1.428 1.429 1.431
1.409 1.414 1.412 1.414 1.411 1.409
1.384 1.383 1.383 1.389 1.385 1.386
1.401 1.400 1.402 1.395 1.397 1.399
1.493 1.423 1.343 1.095 1.485 1.381
1.402 1.400 1.399 1.398 1.398 1.400
1.386 1.399 1.390 1.392 1.390 1.388
1.400 1.394 1.397 1.388 1.393 1.401
120.4 121.2 120.5 120.6 120.6 120.7 120.6
122.3 120.2 119.8 119.7 119.7 119.7 119.6
117.1 114.1 114.2 114.3 114.3 114.3
112.5 114.6 114.7 114.8 114.8 114.8
123.5 132.6 132.6 132.6 132.6 132.7
122.3 120.2 123.3 123.4 123.5 123.4 119.6
11.7 112.8 112.6 112.6 112.6 112.5
120.5 120.9 121.0 120.5 120.7 121.2
120.5 120.5 120.6 120.1 120.2 120.6
116.5 117.9 117.9 117.9 117.9 117.9
153.4 180.0 180.0 180.0 180.0 180.0
C1-O1
1.226 1.228 1.229 1.229 1.229 1.229 1.229 1.229
1.485 1.513 1.517 1.517 1.517 1.517 1.516 1.516
1.343 1.363 1.364 1.365 1.368 1.368 1.368 1.370
1.462 1.461 1.459 1.456 1.456 1.455 1.454
1.229 1.230 1.231 1.232 1.232 1.233 1.233
1.429 1.498 1.497 1.497 1.499 1.499 1.499 1.499
1.398 1.395 1.395 1.395 1.395 1.395 1.395 1.395
1.393 1.395 1.395 1.395 1.395 1.395 1.395 1.395
1.399 1.399 1.399 1.399 1.399 1.399 1.399 1.399
1.393 1.392 1.392 1.392 1.392 1.392 1.392
1.400 1.401 1.401 1.401 1.401 1.401 1.401
1.409 1.407 1.406 1.406 1.406 1.406 1.406 1.406
1.369 1.368 1.367 1.362 1.362 1.361 1.360
1.018 1.020 1.019 1.019 1.019 1.018 1.018
1.392 1.391 1.395 1.400 1.400 1.400 1.402
1.411 1.412 1.409 1.410 1.409 1.407 1.405
1.385 1.383 1.387 1.388 1.389 1.398 1.391
1.396 1.407 1.397 1.391 1.397 1.401 1.400
1.463 1.431 1.502 1.349 1.085 1.510 1.365
1.408 1.407 1.406 1.404 1.404 1.404 1.407
1.389 1.390 1.391 1.395 1.396 1.393 1.389
1.393 1.403 1.396 1.387 1.393 1.400 1.400
120.5 118.9 118.9 119.0 119.1 119.1 119.1 119.2
122.2 120.5 119.9 119.8 119.8 119.7 119.8 119.8
110.6 109.8 109.8 109.9 109.9 110.0 110.0
111.1 109.8 109.9 110.0 110.1 110.1 110.1
132.0 134.8 134.9 134.7 134.8 134.8 134.8
122.2 120.5 122.6 122.7 122.7 122.8 122.8 119.8
116.9 115.4 115.3 115.3 115.1 115.1 115.1
120.8 121.2 121.0 121.3 120.9 121.0 121.7
120.1 120.2 120.0 120.3 119.9 120.0 120.4
118.2 118.5 118.5 118.5 118.5 118.5 118.4
159.9 180.0 180.0 180.0 180.0 180.0 180.0
C1-C2
C1-C2
C2-C3
C2-C3
C3-C4
C3-C4
C4-O2
C4-O2
C4-C4a
C4-C4a
C4a-C5
C4a-C5
C5-C6
C5-C6
C6-C7
C6-C7
C7-C8
C7-C8
C8-C8a
C8-C8a
C4a-C8a
C2-N
C4a-C8a
C2-N
N-H
N-H
N-C1′
N-C1′
C1′-C2′
C1′-C2′
C2′-C3′
C2′-C3′
C3′-C4′
C3′-C4′
C4′-R
C4′-R
C1′-C6′
C1′-C6′
C6′-C5′
C6′-C5′
C5′-C4′
C5′-C4′
O1-C1-C2
C1-C2-C3
C1-C2-N
C2-N-H
C2-N-C1′
C2-C3-C4
H-N-C1′
C1′-C2′-C3′
C1′-C6′-C5′
C8a-C1-C2
C2-N-C1′-C2′
O1-C1-C2
C1-C2-C3
C1-C2-N
C2-N-H
C2-N-C1′
C2-C3-C4
H-N-C1′
C1′-C2′-C3′
C1′-C6′-C5′
C8a-C1-C2
C2-N-C1′-C2′
O1-C1-C2-N 0.0
H-N-C2-C1
C1-C2-C3-C4 0.0
C2-C3-C4-C4a 0.0
C2-C1-C8a-C8 180.0 178.1 180.0 180.0 180.0 180.0 180.0 180.0
C8a-C1-C2-N 180.0 178.8 180.0 180.0 180.0 180.0 180.0 180.0
1.46 0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
O1-C1-C2-N 0.0
H-N-C2-C1
C1-C2-C3-C4 0.0
C2-C3-C4-C4a 0.0
C2-C1-C8a-C8 180.0 163.8 180.0 180.0 180.0 180.0 180.0
C8a-C1-C2-N 180.0 168.2 180.0 180.0 180.0 180.0 180.0
C1-C2-N-C1′
O1-C2-C4-O2 0.0
O1-H(N)
11.4 0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
6.3
2.6
0.0
0.0
0.0
0.0
8.6
1.8
0.0
0.0
14.7 0.0
C1-C2-N-C1′
O1-C2-C4-O2 0.0
O1-H(N)
173.7 180.0 180.0 180.0 180.0 180.0 180.0
62.2 180.0 180.0 180.0 180.0 180.0 0.0
2.034 1.983 1.985 1.993 1.997 1.997 1.995
2.027 1.827 1.832 1.824 1.827 1.827 1.831
130.3 180.0 180.0 180.0 180.0 180.0
2.4 0.0 0.0 0.0 0.0 0.0
2.377 2.274 2.277 2.280 2.282 2.280
H3-H6′
of the substituent effect, as suggested by Hammett.20 The
∆E1/2 from the reduction of Q•- to Q2- also showed an
acceptable linear relationship with the Hammett con-
stants (eq 3).
Ta ble 5. Na tu r a l Ch a r ges a t Beck e3LYP /6-31G(d ,p)
Level
R2
C1
NQ
NO2
CN
CF3
F
H
Me
MeO
0.51
C2 -0.25
0.54
0.15
0.54
0.15
0.54
0.15
0.54
0.15
0.54
0.15
0.54
0.15
0.54
0.15
C3
C4
-0.35 -0.34 -0.35 -0.36 -0.36 -0.36 -0.37
0.50 0.50 0.50 0.50 0.50 0.50 0.50
0.09 -0.08 -0.09
∆E1/2 ) 319σx - 0.27 (n ) 15, r ) 0.8536) (3)
C4a -0.12 -0.09 -0.09 -0.09 -0.09
The value of the slope is higher than the one obtained
for the Q/Q•- reduction, indicating that the radical-anions
are more intensely affected by the substituents than the
corresponding PANs. This will be discussed in detail in
the theoretical section, below.
For the m-COOHPAN, p-COOHPAN compounds, where
it was impossible to include the ∆E1/2 values in the
relationship of 2 and 3 because of their complex electro-
chemical behavior, the (1/λmax vs σx) relationship for these
compounds (eq 1) establishes that the substituent effect
shows the same behavior as for the other PANs.
Th eor etica l Ca lcu la tion s. To understand the experi-
mental observations reported above, we performed the
complete geometrical optimization of p-MeOPAN, p-
MePAN, PAN, p-FPAN, p-CF3PAN, p-CNPAN, p-NO2-
PAN, and the naphthoquinone (NQ) (Tables 3 and 4)
using the semiempirical PM3 method within the frame-
C5 -0.19 -0.19 -0.19 -0.19 -0.19 -0.20 -0.20 -0.20
C6 -0.22 -0.21 -0.21 -0.21 -0.21 -0.21 -0.21 -0.21
C7
C8
C8a
O1
O2
N
-0.23 -0.23 -0.23 -0.23 -0.23 -0.23 -0.23
-0.18 -0.18 -0.18 -0.18 -0.18 -0.18 -0.18
-0.13 -0.13 -0.13 -0.13 -0.13 -0.13 -0.13
-0.55 -0.55 -0.55 -0.55 -0.55 -0.56 -0.56
-0.53 -0.54 -0.54 -0.55 -0.55 -0.55 -0.55
-0.57 -0.57 -0.57 -0.56 -0.56 -0.56 -0.56
C1′
0.19
0.18
0.18
0.15
0.16
0.15
0.14
C2′ -0.51 -0.26 -0.26 -0.25 -0.25 -0.26 -0.25 -0.24
C3′
C4′
C6′
C5′
-0.20 -0.18 -0.20 -0.29 -0.22 -0.22 -0.31
0.31
0.04 -0.19 -0.19
0.41 -0.25 -0.04
-0.27 -0.26 -0.26 -0.25 -0.26 -0.26 -0.25
-0.19 -0.17 -0.24 -0.29 -0.22 -0.21 -0.26
work of the Density Functional Theory21 with the
Becke3LYP hybrid functional, by using a double ú split
valence basis set. The relevant geometric data are
included in Tables 3 and 4. Tables 5 and 6 show the
natural charges and the Wiberg bond indexes, calculated
with the NBO program22 at Becke3LYP/6-31G(d,p) level,
as well as the densities of the relevant critical points,
(20) Hammett, L. P. Physical Organic Chemistry; McGraw-Hill:
New York, 1940.

Redox Properties of 2-[(R-Phenyl)amine]-1,4-naphthalenediones
J . Org. Chem., Vol. 64, No. 10, 1999 3689
Ta ble 6. Wiber g Bon d In d exes (WBI), a n d P r op er ties of
th e Releva n t Bon d Cr itica l P oin ts, in th e Electr on ic
Den sity of th e Refer r ed Qu in on es a t Beck e3LYP /
6-31G(d ,p) Level
According to previously published studies of N-phenyl-
substituted p-quinones,8 the PM3 calculation predicts
strong distortions in the quinone ring which take it out
of planarity and pyramidalize both the amine nitrogen
atom and the CdO groups.
2
R2
enlace
WBI
F
∇ (F)
ꢀ
NQ
C1-C2
C2-C3
O1-C1
C1-C2
C2-C3
C3-C4
O1-C1
O2-C4
C2-N
N-C1′
O-H
1.05
1.08
1.74
1.0
1.54
1.14
1.71
1.67
1.20
1.06
0.157
0.163
0.259
0.261
0.324
0.286
0.394
0.393
0.317
0.290
0.028
0.015
0.261
0.324
0.286
0.395
0.393
0.317
0.290
0.028
0.015
0.261
0.325
0.285
0.395
0.393
0.316
0.291
0.028
0.015
0.261
0.325
0.285
0.395
0.393
0.316
0.291
0.028
0.015
0.261
0.326
0.284
0.395
0.394
0.314
0.295
0.029
0.015
0.261
0.327
0.283
0.395
0.395
0.313
0.297
0.029
0.015
0.263
0.328
0.283
0.395
0.395
0.313
0.298
0.026
0.012
-0.100
0.084
0.064
-0.632
-0.905
-0.741
0.168
0.240
1.082
0.471
0.099
0.310
0.155
0.029
0.054
0.096
0.095
0.231
0.104
0.098
0.311
0.152
0.030
0.054
0.092
0.078
0.232
0.103
0.098
0.312
0.149
0.031
0.054
0.090
0.073
0.232
0.104
0.098
0.313
0.150
0.031
0.054
0.091
0.089
0.226
0.104
0.098
0.315
0.143
0.031
0.055
0.084
0.070
0.218
0.107
0.098
0.316
0.139
0.032
0.055
0.080
0.072
0.214
0.108
0.096
0.314
0.137
0.035
0.056
0.074
0.070
0.273
0.078
The geometry of the molecules considered in this study
was calculated according to the PM3 method. In this case,
for example, for the p-NO2PAN, the O1-C1-C2-N dihe-
dral angle is 11.4°, the C2-N-C1′-C2′ angle is 153.4°,
and the C2-C1-C8a-C8 angle is 163.8°. For the remain-
ing quinones, the PM3 calculation predicts planar mol-
ecules. The C2-C3 distance is in agreement with a located
double bond. A strong electronic delocalization was
detected in the benzene ring fused to the quinone moiety.
Illescas et al.8 supports the break of planarity of this
system with the published geometry of p-benzoquinone
at -160 °C24 and of p-naphthoquinone.25 However, the
distortion suggested by the experiment is small compared
to the distortion shown by p-NO2PAN.
Unlike the previous calculations, the geometry of the
p-NO2PAN at Becke3LYP/6-31G(d,p) level is practically
planar in the naphthoquinone moiety with a small
distortion of 1.46° in the O1-C1-C2-N angle and of 2.6°
in the C1-C2-C3-C4 angle (Table 4). This is in agree-
ment with the experimental data.24,25 The C2-C3-C4-
C4a angle is 0.0° and not 14.7° as predicted by the PM3
calculation. Unlike the other quinones, where the para-
substituted aromatic ring remains in the plane of the
quinone, in p-NO2PAN, the C2-N bond is rotated, taking
the phenyl ring out of the plane. The C1-C2-N-C1′ angle
is 173.7°.
MeO
Me
H
0.078
-0.855
-0.816
0.100
H-H
0.052
C1-C2
C2-C3
C3-C4
O1-C1
O2-C4
C2-N
N-C1′
O-H
1.0
-0.638
-0.910
-0.739
0.171
1.55
1.13
1.71
1.66
1.19
1.07
0.084
-0.868
-0.820
0.100
H-H
0.052
C1-C2
C2-C3
C3-C4
O1-C1
O2-C4
C2-N
N-C1′
O-H
0.99
1.55
1.13
1.71
1.68
1.19
1.07
-0.637
-0.912
-0.737
0.172
0.088
-0.872
-0.826
0.099
H-H
0.052
F
C1-C2
C2-C3
C3-C4
O1-C1
O2-C4
C2-N
N-C1′
O-H
1.0
-0.637
-0.912
-0.737
0.170
1.55
0.13
1.71
1.68
1.19
1.07
Because the PM3 method is incapable of predicting the
p-NO2PAN geometry, the parameters used by this method
for calculating quinones are unreliable. We will, there-
fore, limit our discussion to the results obtained according
to the Density Functional Theory.
0.088
-0.863
-0.836
0.100
The nitrogen atom, which binds the quinone and the
para-substituted phenyl ring, prevents the direct conju-
gation between the two rings, and interacts with one or
the other, determined by the competitive interaction
between the two. This is established by the pattern in
the C1′-N-C2-C3-C4-O2 bonds which must be carefully
analyzed. In the NO2 f CN f CF3 f F f H f Me f
OMe series (where the electron-donating properties suc-
cessively increase), we observe substantial elongation of
the C1′-N bond, contraction of the N-C2 bond, lengthen-
ing of the C2-C3 bond, shortening of the C3-C4 bond, as
well as slight elongation of the C4-O2 bond (Table 4).
Elongation of the N-C1 bond, also apparent in the same
sequence, is compensated by an increase in the angle of
the C2-N-C1′ bond, which is 134°, remarkably greater
than the expected 120° and which diminishes the steric
repulsion between the hydrogen atoms in the C3-H and
C6′-H positions.
H-H
0.053
CF3
CN
NO2
C1-C2
C2-C3
C3-C4
O1-C1
O2-C4
C2-N
N-C1′
O-H
1.0
-0.636
-0.919
-0.732
0.172
1.57
1.12
1.709
1.69
1.17
1.09
0.099
-0.873
-0.849
0.101
H-H
0.052
C1-C2
C2-C3
C3-C4
O1-C1
O2-C4
C2-N
N-C1′
O-H
1.0
-0.637
-0.923
-0.729
0.172
1.58
1.11
1.71
1.69
1.16
1.10
0.105
-0.871
-0.856
0.101
H-H
0.052
C1-C2
C2-C3
C3-C4
O1-C1
O2-C4
C2-N
N-C1′
O-H
1.0
-0.647
-0.931
-0.728
0.171
1.59
1.11
1.71
1.70
1.16
1.09
Analysis of the natural charges at C3 and C1 and the
Wiberg bond indexes (Tables 5 and 6) establish that the
0.111
-0.884
-0.876
0.095
(22) NBO 4.0. Glendening, E. D.; Badenhoop, J . K.; Reed, A. E.;
Carpenter, J . E.; Weinhold, F. Theoretical Chemistry Institute,
University of Wisconsin, Madison, WI, 1994. Reed, E. A.; Weinstock,
R. B.; Weinhold, F. J . J . Chem. Phys. 1985, 83, 735-746. Reed, E. A.;
Weinhold, F. J . J . Chem. Phys. 1985, 83, 1736-1740. Reed, E. A.;
Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899-926.
(23) Biegler-Koenig, F. W.; Bader, R. F. W.; Tang, T. H. J . Comput.
Chem. 1982, 3, 317-328.
H-H
0.049
and the Laplacians and ellipticities determined with the
proaimv program.23
(21) Malkin, V. G.; Malkina, O. L.; Eriksson, L. A.; Salahub, D. R.
In Modern Density Functional Theory. A Tool for Chemistry; Seminario,
J . M., Politzer P., Eds.; Elsevier: Amsterdam, 1995.
(24) van Bolhuis, F.; Kiers, C. Th. Acta Crystallogr. B 1978, 34,
1015-1016.
(25) Gaultier, J .; Hauw, Ch. Acta Crystallogr. 1965, 18, 179-183.

3690 J . Org. Chem., Vol. 64, No. 10, 1999
Aguilar-Mart´ınez et al.
Both interactions generate two ring critical points in such
a way that the topological relation of Poincare`-Hopf is
accomplished. An important difference between these two
critical points is that, in the specific case of the critical
point defining the hydrogen bridge, the major ellipticity
axes are practically parallel to the ring plane. This is
considered as an index of electronic delocalization.27 In
the critical point generated by the H-H steric repulsion,
however, the axes are perpendicular to the annular plane.
The densities of the critical points studied here strongly
depend on the distance between the related attractors,
where the density of the critical point diminishes with
increasing distance. These critical points are also char-
acterized by a positive Laplacian, which is associated
with interactions between closed shell systems, ionic
bonds, hydrogen bonds, and van der Waals bonds.28
2
∇ (F) is very sensitive to electronic delocalization. This
fact is evident in the carbonyl fragments of the com-
pounds studied, since they allow us to effectively dif-
ferentiate the two quinone carbonyls. The Laplacians of
the critical points of the C-O bonds indicate a raised
ionic character (Table 6). The C1-O1 bond is more
electrophilic than the C4-O2 bond. The hydrogen bridge,
on the other hand, polarizes the CdO group, and the
donating aminic nitrogen makes the reduction to non-
conjugated carbonyl more susceptible, protecting the C4-
O2. The Laplacians of critical bond points support the
participation of the resonant forms shown in Figure 2a.
F igu r e 2. Dominant hybrids of PANs according with the
electronic properties of the substituents. (a) Electron delocal-
ization in PANs, (b) effect of the electron-accepting (EA)
groups, (c) effect of the electron-donor (ED) groups at the
aniline moiety.
geometric behavior is associated with the charge transfer
from the para-substituted aniline group to the quinone
ring, according to the resonant hybrids described in
Figure 2a.
Table 7 includes the energies of the frontier molecular
orbital, as well as absolute hardness (η), defined as
(ELUMO - EHOMO)/2. For the substituted naphthoquinones,
the NBO analysis established that the HOMO orbital
corresponds to the lone pairs of one of the heteroatoms.
In the p-MeOPAN, HOMO orbital corresponds to one of
the OMe unshared electronic pairs, the np type, and the
HOMO-1 orbital corresponds to the ns type orbital. For
the p-MePAN, the HOMO corresponds to the unshared
pair of the np type of the O1 atom. In the reference
molecule, PAN, the HOMO corresponds to the np type
orbital of the oxygen atom, which forms the hydrogen
bridge with the NH group. When R is CF3, the HOMO
orbital corresponds to an np orbital associated with one
of the group’s fluorine atoms. When R is F, the HOMO
corresponds to the np orbital of the fluorine atom; for
p-CNPAN, the HOMO is the np orbital of the nitrogen
atom in the nitrile group. When R is NO2, the HOMO
orbital corresponds to an unshared electron pair belong-
ing to one of the oxygen atoms of the nitro group and is
of the np type. In all the cases, LUMO corresponds to
the Rydberg orbital of the sp type located at C1. A linear
relationship occurs between the HOMO and LUMO
orbital energy of these molecules and the experimental
σp Hammett parameter (eqs 4 and 5).
In the p-NO2PAN quinone, the nitrogen atom bond to
the quinone interacts strongly with the nitro group. The
increase in the C2-N-C1 angle apparently is insufficient
to compensate the H3-H6 steric repulsion caused by the
shortening of the N-C1 bond. The p-nitrophenyl group
leaves the plane of the quinone, and the C2-N rotates.
The aromatic ring shows a geometric pattern such as is
expected for strong electron-accepting groups. The ge-
ometry shows the participation of the resonant hybrids
(Figure 2b) which contribute to the delocalization of the
electronic density at the nitrogen atom avoiding its
displacement in the quinone ring, while the electron-
donating groups, resonant hybrids in Figure 2c, domi-
nate, allowing its interaction with the quinone.
We determined the density at bond critical points of
the compounds studied according to the Topological
Theory of Atoms in Molecules.26 These densities (Figure
3) agreed with the electronic displacement previously
suggested, where the benzene ring of the quinone keeps
its aromatic character, and the quinone segment, conju-
gated with the nitrogen atom, is influenced by the
substituent of the aniline-para-substituted group.
Figure 3 shows two additional, unexpected bond paths.
One of them corresponds to the hydrogen bond between
the amine proton and the quinone carbonyl group. The
second unexpected critical point corresponds to an inter-
action line between the attractors of steric origin. These
types of interactions have been described by Cioslowski,27
and the interaction distance (H3-H6′ distance) in the
compounds studied here agrees with those reported.27
EHOMO(eV) )
-0.2102σp - 5.1481 (n ) 7, r ) -0.9619) (4)
E
LUMO(eV) )
-0.1388σp - 2.5321 (n ) 7, r ) -0.9150) (5)
(26) Bader, R. F. W. Atoms in Molecules -A Quantum Theory;
Clarendon Press: Oxford, 1990. Bader, R. F. W. Acc. Chem. Res. 1985,
18, 9-15. Bader, R. F. W. Chem. Rev. 1991, 91, 893-928. Bader, R. F.
W.; Slee, T. S.; Cremer, D.; Kraka, E. J . Am. Chem. Soc. 1983, 105,
5061-5068.
(27) (a) Cioslowski, J .; Mixon, S. T.; Edwards, W. D. J . Am. Chem.
Soc. 1991, 113, 1083-1085. (b) Cioslowski, J .; Mixon, S. T. J . Am.
Chem. Soc. 1992, 114, 4382-4387.
Elimination of the molecule with the nitro group
increases the correlation. From the conformational point
(28) Cremer, D.; Kraka, E. Croat. Chem. Acta 1985, 57, 1259-1281.

Redox Properties of 2-[(R-Phenyl)amine]-1,4-naphthalenediones
J . Org. Chem., Vol. 64, No. 10, 1999 3691
F igu r e 3. Bond and ring critical points in the density of quinones: p-MeOPAN, p-MePAN, PAN, p-FPAN, p-CNPAN, p-NO2-
PAN. The values of F were obtained into the frame of the topological Theory of Atoms in Molecules.
Ta ble 7. En er gy of th e F r on tier Or bita l a n d Th eir Neigh bor s for th e Releva n t Qu in on es (en er gy in h a r tr ees)
R2
ELUMO + 1
ELUMO
EHOMO
EHOMO - 1
η
total
OMe
Me
H
-0.03534
-0.03741
-0.03911
-0.04092
-0.04710
-0.05791
-0.10699
-0.10253
-0.10471
-0.10647
-0.10855
-0.11461
-0.11941
-0.13762
-0.19873
-0.20759
-0.21268
-0.21341
-0.22553
-0.23131
-0.25070
-0.2443
0.0481
-0.05144
0.05371
-0.05243
0.05546
0.05595
0.05654
-936.07804
-860.87440
-821.55405
-920.78393
-1158.5897
-913.79575
-1026.05554
-0.24698
-0.24899
-0.25106
-0.25745
-0.26166
-0.28032
F
CF3
CN
NO2
of view, the minimum of this molecule is different because
it is not a planar molecule. Its conformation thus modifies
electronic displacement and the transmission of the
substituent’s electronic effect. This fact is confirmed by
UV-vis experimental data.
The linear relationships (eqs 4 and 5) illustrate that
inclusion of the electron-donating group in the aniline
ring increases the energy of the border orbitals.
According to Figure 2a, the displacement of the un-
shared electrons of the aminic nitrogen modifies primarly
the electronic density of the C2-C3, C3-C4, and C4-O2
bonds with less effect on the electronic density of the C1-
O1 bond. These results explain the greater susceptibility
of the second reduction wave to the substituent effect (eq
3).
Considering that an electrochemical reduction involves
an electron flux from the electrode (cathode) to the
substrate (chemical species in solution), the electrons
should be gained in the unoccupied molecular orbital of
lower energy (LUMO). Hence, when we apply potentials
at more negative values, the energies of the electrons
increase and eventually they reach sufficiently high
energy levels to occupy vacant states over the species in
solution. So, the lower the LUMO energy, the easier it
will be to achieve the energy level for electrode-solution
electron transfer (Figure 4). From the LUMO energy
values calculated for the different PANs studied here, we
predict that the reduction facility will follow the order:
p-NO2 > p-CN > p-CF3 > p-F > H > p-Me > p-MeO. The
reduction order agrees with the E1/2 potentials (Table 2)
obtained by cyclic voltammetry for the reduction of PANs
in aprotic media. We observed a good linear correlation
of the LUMO energy with the corresponding E1/2 for Q
to Q•- reduction (eq 6). This explains how the E1/2
potentials, corresponding to the C1-O1 carbonyl reduc-
tion, were also subject to the effects of the substituent.
Con clu sion s
We synthesized 19 2-[(R-phenyl)amine]-1,4-naphtha-
lenediones, nine of which were previously unreported.
These compounds are quinone-NH-substituted phenyls
(PAN type).
For PAN type molecules, the amine group located
between the quinone and the substituted aryl group
interferes with direct transmission of the substituent
effect on the quinone system. One would thus expect the
electronic properties at the quinone radical-anion, gener-
ated in the first reduction step, to be distributed solely
in the quinone system. However, our analysis of the effect
of the substituents on the E1/2 potentials for wave I
demonstrates that the substituent effect is transmitted
through the amine group.
For the compounds studied, we determined the pa-
rameters associated with electronic properties (1/λmax and
∆E1/2) of the substituent effect which can be assessed by
σx. Surprisingly, we obtained a linear variation of these
electronic properties as a function of σx. This variation
indicates a direct influence of the donor-acceptor proper-
ties of the substituent in the aniline ring on the electronic
properties of the quinone ring.
E1/2(mV) )
-172.79ELUMO(eV) -1707.82 (n ) 5, r ) -0.9855)
(6)

3692 J . Org. Chem., Vol. 64, No. 10, 1999
Aguilar-Mart´ınez et al.
F igu r e 4. Relationship between energy of HOMO and LUMO molecular orbitals with the donating-acceptor electron properties
(oxidation and reduction capability), related to E1/2 for first reduction process, in mV.
119.58 (C6′), 103.30 (C3), 21.42 (CH3); CIMS m/z 263, 248, 234,
220, 218, 206, 191, 158, 130, 105, 91, 77, 57, 43, 41. Anal. Calcd
for C17H12O2N: C, 77.56; H, 4.94; N, 5.32. Found: C, 77.18;
H, 5.05; N, 5.30.
Exp er im en ta l Section
Syn th esis. NMR spectra were recorded as solutions in
CDCl3 at 25 °C on 200 or 300 MHz spectrometers with TMS
as reference.
2-[(3′-Eth ylp h en yl)a m in e]-1,4-n a p h th a len ed ion e (m -
EtP AN). Recrystallization from ethanol gave 43% yield; mp
119-120 °C; IR (KBr, cm-1) 3304, 3042, 2960, 1672, 1598,
1568, 1484, 1242; UV-vis (EtOH, nm) 272 (54034), 469
(10432); 1H NMR (CDCl3) δ 8.11 (dt, 2H, J ) 7.5, J ) 1.4 Hz,
H5, H8), 7.77 (td, J ) 7.5, J ) 1.4 Hz, H6), 7.66 (td, J ) 7.5, J
) 1.4 Hz, H7), 7.60 (sb, 1H, NH), 7.32 (t, J ) 7.5, J ) 1.4 Hz,
H5′), 7.11 (sb, 1H, H6′), 7.10 (d, 1H, J ) 7.5 Hz, H4′), 7.06 (m,
1H, J ) 7.5 Hz, H2′), 6.42 (s, 1H, H3), 2.67 (q, 2H, J ) 7 Hz,
CH2), 1.26 (t, 3H, J ) 7 Hz, CH3); 13C NMR (CDCl3) δ 183.89
(C4), 182.09 (C1), 146.12 (C2), 144.72 (C1′), 137.37 (C3′), 134.85
(C6), 133.24 (C10), 132.26 (C7), 130.33 (C9), 129.54 (C5′), 126.47
(C8), 126.11 (C5), 125.22 (C4′), 121.98 (C2′), 119.98 (C6′), 103.30
(C3), 28.73 (CH2), 15.40 (CH3); CIMS m/z 277, 260, 248, 234,
220, 206, 204, 172, 165, 144, 130, 105, 91, 77, 51, 43, 41. Anal.
Calcd for C18H15O2N: C, 77.98; H, 5.41; N, 4.95. Found: C,
77.37; H, 5.37; N, 4.95.
Gen er a l P r oced u r e for th e P r ep a r a tion of Su bstitu ted
2-[(R-p h en yl)a m in e]-1,4-n a p h th a len ed ion es (P ANs). All
compounds were prepared by addition of the appropriate
aniline to the unsubstituted 1,4-naphthoquinone in ethanol
followed by oxidation according to the procedure described by
Mohammed et al.,29 modified by the addition of 0.1 mmol
cerous chloride heptahydrate/mol naphthoquinone. CeCl3‚
7H2O was powdered and combined with the naphthoquinone
before the amine was added. It was reported that the cerium
ion catalyzes the addition reaction of p-nitroaniline to 1,4-
naphthoquinone in the same way as in the reactions of
quinolinequinones with aromatic amines.30 The reaction mix-
ture was left at room-temperature overnight. Crystals of
different colors, precipitated from the dark-colored reaction
mixtures, were collected by filtration and washed with ethanol
until the wash became almost colorless. The residual solids
were dried and recrystallized from appropriate solvents.
We only report the spectroscopic characterization of the
compounds which have not been previously described (see
Table 1).
2-[(4′-Eth ylp h en yl)a m in e]-1,4-n a p h th a len ed ion e (p-Et-
P AN). Recrystallization from ethanol gave 63% yield; mp 150-
152 °C; IR (KBr, cm-1) 3444, 3284, 3070, 2962, 1680, 1596,
1588, 1516, 1494, 1348, 1296; UV-vis (EtOH, nm) 272 (27514),
2-[(3′-Meth ylp h en yl)a m in e]-1,4-n a p h th a len ed ion e (m -
MeP AN). Recrystallization from ethanol gave 89% yield; mp
173-175 °C; IR (KBr, cm-1) 3436, 3312, 1670, 1628; UV-vis
1
472 (4981); H NMR (CDCl3) δ 8.10 (dt, 2H, J ) 7.5, J ) 1.4
Hz, H5, H8), 7.76 (td, 1H, J ) 7.5, J ) 1.4 Hz, H7), 7.65 (td,
1H, J ) 7.5, J ) 1.4 Hz, H6), 7.52 (sb, 1H, NH), 7.21 (ddq, 4H,
J ) 7.5, 1.4 Hz, H2′, H3′, H5′, H6′), 6.37 (s, 1H, H3), 2.67 (q,
2H, J ) 7 Hz, CH2), 1.25 (t, 3H, J ) 7 Hz, CH3); 13C NMR
(CDCl3) δ 183.92 (C4), 182.11(C1), 144.99 (C2), 141.99 (C1′),
135.00 (C4′), 134.85 (C6), 133.27 (C4′), 133.27 (C10), 132.22 (C7),
130.35 (C9), 129.02 (C2′, C6′), 126.44 (C5), 126.13 (C8), 122.94
(C3′), 122.87 (C5′),103.11 (C3), 28.35 (CH2), 15.54 (CH3); CIMS
m/z 277, 262, 248, 234, 220, 204, 172,116,105, 77, 43, 41. Anal.
Calcd for C18H15O2N: C, 77.97; H, 5.41; N, 5.05. Found: C,
76.87; H, 5.34; N, 4.77.
1
(EtOH, nm) 272 (21183), 469 (3712); H NMR (CDCl3) δ 8.12
(dt, 2H, J ) 7.5, J ) 1.4 Hz, H5, H8) 7.75 (td, 1H, J ) 7.5, J )
1.4 Hz, H7), 7.64 (td, 1H, J ) 7.5, J ) 1.4 Hz, H6), 7.54 (sb,
1H, NH); 7.30 (tb,1H, H5′), 7.10 (sb, 1H, H2′), 7.02 (db, 2H, J
) 7.5 Hz, H4′, H6′), 6.42 (s, 1H, H3), 2.4 (s, 3H, CH3); 13C NMR
(CDCl3) δ 183.92 (C4); 182.06 (C1), 144.69 (C2), 139.73 (C1′),
137.31 (C2), 134.22 (C7), 133.22 (C10), 132.27 (C6), 130.33 (C9),
129.45 (C5′), 126.41 (C4′, C8), 126.11 (C5), 123.05 (C2′, C3′),
(29) Mohammed, R. A.; Ayad, M. A.; Chaaban, A. I. Acta Pharm.
J ugoslav 1976, 26, 287.

Redox Properties of 2-[(R-Phenyl)amine]-1,4-naphthalenediones
J . Org. Chem., Vol. 64, No. 10, 1999 3693
2-[(4′-n -Bu tylp h en yl)a m in e]-1,4-n a p h th a len ed ion e (p-
Bu P AN). Recrystallization from ethanol gave 61% yield; mp
112-114 °C; IR (KBr, cm-1) 3284, 2922, 1680, 1590, 1566; UV-
for C16H10O4N2. Calcd. 294.0655, found 294.0641. Anal. Calcd
for C16H10O4N2: C, 65.30; H, 3.40; N, 9.52. Found: C, 65.01;
H, 3.27; N, 9.43.
1
vis (EtOH, nm) 272 (30400), 472 (4700); H NMR (CDCl3) δ
Electr och em ica l P r oced u r e. Solven t a n d Su p p or tin g
Electr olyte. Acetonitrile (AN) (Aldrich) was dried overnight
with CaCl2 (Merck) and purified by distillation on P2O5 (Merck)
under vacuum.31 Traces of water in the solvent were elimi-
nated by contact with a molecular sieve 3 Å (Merck) in the
absence of light. Tetraethylammonium tetrafluoroborate (Et4-
NBF4) (Fluka) was dried under vacuum at 60 °C.
8.10 (dt, 2H, J ) 7.5, J ) 1.4 Hz, H5, H8), 7.78 (td, 1H, J )
7.5, J ) 1.4 Hz, H7), 7.65 (td, 1H, J ) 7.5, J ) 1.4 Hz, H6),
7.52 (sb,1H, NH), 7.21 (m, 4H, H2′, H3′, H5′, H6′), 6.37 (s, 1H,
H3), 2.67 (t, 2H, J ) 7 Hz, CH2), 1.60 (q, 2H, J ) 7 Hz, CH2),
1.35 (q, 2H, J ) 7 Hz, CH2), 1.25 (t, 3H, J ) 7 Hz, CH3); 13C
NMR (CDCl3) δ 183.75 (C4), 182.13 (C1), 145.08 (C2), 140.71
(C1′), 134.97 (C4′), 134.38 (C6), 133.38 (C10), 132.17 (C7), 130.46
(C9), 129.59 (C2′, C6′), 126.42 (C5), 126.13 (C8), 122.75 (C3′, C5′),
103.11 (C3), 35.08 (C7′), 33.47 (C8′), 22.24 (C9′), 13.85, (C10);
CIMS m/z 305, 277, 262, 248, 235, 204, 178, 116, 89, 77, 57,
43. Anal. Calcd for C20H19O2N: C, 78.68; H, 6.22; N, 4.59.
Found: C, 78.64; H, 6.21; N, 4.48.
Electr od es, Ap p a r a tu s, a n d In str u m en ta tion . Cyclic
voltammetry measurements were carried out in a conventional
three-electrode cell. A polished Pt-disk electrode with an area
of 3.14 mm2 was used as a working electrode. Prior to
measurements, this electrode was cleaned and polished with
0.05 µm alumina (Buehler), wiped with a tissue, and sonicated
in distilled water for 2-4 min. The counter electrode consisted
of a piece of platinum wire. The reference electrode was an
aqueous saturated calomel electrode (SCE) isolated from the
main cell body by a Luggin tube filled with 0.1 M Et4NBF4/
acetonitrile.
2-[(4′-n -Hexylp h en yl)a m in e]-1,4-n a p h th a len ed ion e (p-
HexP ANQ). Recrystallization from ethanol gave 62% yield;
mp 100-101 °C; IR (KBr, cm-1) 3450, 3274, 2922, 1690, 1620,
1596, 1568, 1516, 1412; UV-vis (EtOH, nm) 272 (33600), 474
1
(5500); H NMR (CDCl3) δ 8.00 (dt, J ) 7.5 Hz, H5), 7.72 (td,
1H, H8), 7.6 (td, J ) 7.5, J ) 1.4 Hz, H7), 7.43 (td, J ) 7.5, J
) 1.4 Hz, H6), 7.25 (m, 4H, H2′,H3′,H5′,H6′), 6.41 (s, 1H, H3),
2.61(t, 2H, J ) 7 Hz, CH2), 1.62 (m, 4H, 2CH2), 1.39 (m, 4H,
2CH2), 1.28 (t, 3H, J ) 7 Hz, CH3); CIMS m/z 333, 262, 248,
235, 178, 116, 105, 89, 77, 43. Anal. Calcd for C22H22O2N: C,
79.27; H, 6.90; N, 4.20. Found: C, 79.02; H, 7.00; N, 4.15.
The half-wave potentials were measured at room temper-
ature in acetonitrile solutions using 0.1 M Et4NBF4 as the
supporting electrolyte. The concentration for the PAN solutions
varied from 0.2 mM to 1.0 mM, depending on their solubility
in the solvent. Voltammetric curves were recorded using a BAS
100B/W Electrochemical Analyzer of Bioanalytical Systems
interfaced with a Gateway 2000 personal computer. Measure-
ments were made over a potential range between 500 to -2000
mV with a sweep rate from 10 to 8000 mV/s. Prior to the
experiments, solutions were purged with nitrogen, which was
presaturated with the appropriate solvent containing 3 Å
sieves. All potentials were determined under the same condi-
tions in order to obtain a consistent data set. To establish a
reference system with the experimental conditions of our
particular system, the redox potentials reported in this paper
refer to the ferrocene/ferrocinium (Fc/Fc+) pair, as recom-
mended by IUPAC.32 In this case the potential for the
ferrocene/ferrocinium (Fc/Fc+) redox pair, determined by vol-
tamperometric studies, was 399 mV vs SCE.
2-[(3′-F lu or op h en yl)a m in e]-1,4-n a p h th a len ed ion e (m -
F P AN). Recrystallization from ethanol gave 53% yield; mp
196-198 °C; IR (KBr, cm-1) 3448, 3316, 3074, 1666, 1640,
1590; UV-vis (EtOH, nm) 276, 456; 1H NMR (CDCl3) δ 8.1
(dt, 2H, J ) 7.5, J ) 1.4 Hz, H5, H8), 7.77 (td, 1H, J ) 7.5, J
) 1.4 Hz, H6), 7.67 (td, 1H, J ) 7.5, J ) 1.4 Hz, H7), 7.59 (sb,
1H, NH), 7.40 (td, 1H, J ) 7.5, J ) 1.4 Hz, H5′), 7.08 (sb, 1H,
H2′), 7.06 (dt,1H, J ) 7.5, J ) 1.4 Hz, H4′), 6.91 (td, 1H, J )
7.5, J ) 1.4 Hz, H6′), 6.46 (s, 1H, H3); 13C NMR (CDCl3) δ
183.91 (C4), 181.76 (C1), 160.00 (C3′), 144.10 (C2), 137.65 (C1′),
134.99 (C7), 132.50 (C6), 130.85 (C5′), 127.06 (C9), 126.58 (C8),
126.20 (C5), 117.88 (C2′) 112.51 (C6′), 109.78 (C4′), 104.27 (C3);
CIMS m/z 267, 266, 239, 238, 222, 211, 185, 183, 162, 149,
129, 105, 83, 69, 57, 55, 43, 41. HRMS for C16H10O2NF calcd
267.0696, found 267.0702. Anal. Calcd for C16H10O2NF: C,
71.91; H, 3.74; N, 5.24. Found: C, 71.69; H, 3.74; N, 5.24.
2-[(3′-Cya n op h en yl)a m in e]-1,4-n a p h th a len ed ion e (m -
CNP AN). Recrystallization from acetonitrile gave 34% yield;
mp 296-298 °C; IR (KBr, cm-1) 3306, 3182, 3070, 2226, 1676,
1601, 1575; UV-vis (EtOH, nm) 273, 448; CIMS m/z 274, 257,
246, 245, 229, 218, 190, 169, 146, 105, 104, 77, 76, 57, 43, 41.
HRMS for C16H10O2N2 calcd 274.0745, found 274.0742. Anal.
Calcd for C16H10O2N2: C, 74.45; H, 3.64; N, 10.21. Found: C,
74.12; H, 4.02; N, 9.83.
2-[(4′-(Tr iflu or om et h yl)p h en yl)a m in e]-1,4-n a p h t h a -
len ed ion e (p-CF 3P AN). Recrystallization from acetonitrile
gave 87% yield; mp 185-186 °C; IR (KBr cm-1) 3440, 3234,
3072, 1676, 1634, 1622, 1600, 1574, 1528; UV-vis (EtOH, nm)
271 (35460), 452 (5160) 1H NMR (CDCl3) δ 8.16 (dt,1H, H5 or
H8), 8.11 (dt,1H, H8 or H5), 7.80 (td, 1H, J ) 7.5, J ) 1.4 Hz,
H7), 7.69 (td, 1H, J ) 7.5, J ) 1.4 Hz, H6), 7.65 (bs, 1H, NH),
7.51 (vbs, 4H, H2′, H3′, H5′, H6′), 6.43 (s, 1H, H3); 13C NMR
(CDCl3) δ 183.90 (C4), 181.70 (C1), 144.25 (C2), 138.30 (C1′),
135.07 (C7), 133.04 (C10), 132.62 (C9), 132.04 (C6), 130.37 (C3′),
126.66 (C8), 126.31 (C4′, C5), 125.48 (C5′), 122.08 (C2′), 119.24
(C6′), 104.23 (C3), 104.06 (C7′); CIMS m/z 317, 300, 298, 296;
288, 272, 248, 241, 220, 212, 146, 145, 105, 76, 69, 57, 43, 41.
HRMS for C17H9O2NF3 calcd 317.0664, found 317.0661. Anal.
Calcd for C17H9O2NF3: C, 64.15; H, 3.15; N, 4.41. Found: C,
63.87; H, 3.09; N, 4.36.
Com p u ta tion a l Meth od s. Full geometry optimization
(without symmetry constraints) on the complete structures of
p-MeOPAN, p-MePAN, PAN, p-FPAN, p-CF3PAN, p-CNPAN,
p-NO2PAN, and naphthoquinone (NQ) were performed at the
PM3 level (Table 3) and according to the DFT at Becke3LYP/
6-31G(d,p) level (Table 4) with the Gaussian 92 Program
(G92).33 The Becke3LYP hybrid functional defines the ex-
change function as a linear combination of Hartree-Fock,
local, and gradient-corrected exchange terms.34 The exchange
function is combined with a local and gradient-corrected
correlation function. Substituent groups at the para-position
in the aniline group were chosen in order to avoid conforma-
tional difficulties.
The correlation function used is actually C*ECLYP + (1-C)-
*ECVWN, were LYP is the correlation functional of Lee, Yang,
and Parr,35 and includes both local and nonlocal terms. VWN
is the Vosko, Wilk, and Nusair 1980 correlation functional
fitting the RPA solution to the uniform gas, often referred to
(30) Pratt, Y. T. J . Org. Chem. 1962, 27, 3905-3910.
(31) Coetzee, J . F.; Cunningham, D. K.; Mc. Guire, D. K.; Pad-
manabban, A. Anal. Chem. 1962, 34, 1139-1143.
(32) Gritzner, G. and Ku¨ta, J . Pure Appl. Chem. 1984, 4, 462-466.
(33) G92: Gaussian 92/DFT, Revision G.2. Frisch, M. J .; Trucks,
G. W.; Schlegel, H. B.; Gill, P. M. W.; J ohnson, B. G.; Wong, M. W.;
Foresman, J . B.; Robb, M. A.; Head-Gordon, M.; Replogle, E. S.;
Gomperts, R.; Andres, J . L.; Raghavachari, K.; Binkley, J . S.; Gonza´lez,
C.; Martin, R. L.; Fox, D. J .; Defrees, D. J .; Baker, J .; Stewart, J . J . P.;
Pople, J . A. Gaussian, Inc., Pittsburgh, PA, 1993.
(34) Stephens, P. J .; Devlin, F. J .; Chabalowski, C. F.; Frisch, M. J .
J . Phys. Chem. 1994, 98, 11623-11627. Becke, A. D. J . Chem. Phys.
1993, 98, 1372-1377, 5648-5652.
(35) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. 1988, B37, 785-789.
Miehlich, B.; Savin, A. Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989,
157, 200-206.
2-[(3′-Nit r op h en yl)a m in e]-1,4-n a p h t h a len ed ion e (m -
NO2P AN). Recrystallization from acetonitrile gave 50% yield;
mp 258-260 °C; IR (KBr, cm-1) 3442, 3288, 3214, 3074, 1676,
1604, 1576, 1528, 1352; UV-vis (EtOH, nm) 271 (23600), 447
1
(4000); H NMR (DMSO) δ 8.25 (bs, 1H, NH), 7.7 to 8.1 (m,
8H, aromatics), 6.3 (s, 1H, H3); CIMS m/z 294, 277, 265, 248,
247, 219, 191, 189, 165, 146, 129, 105, 76, 57, 43, 41. HRMS

3694 J . Org. Chem., Vol. 64, No. 10, 1999
Aguilar-Mart´ınez et al.
as Local Spin Density (LSD) correlation.36 VWN is used to
provide the excess of local correlation required since LYP
contains a local term essentially equivalent to VWN.34
The orbital basis set, 6-31G(d,p), we used adds polarization
functions to heavy atoms and hydrogens. Natural Bond Orbital
Analyses (NBO) were carried out with version 3.1, which is
included in G92.22 Densities computed at Becke3LYP/6-31G-
(d,p) from the G92 output were used with the AIMPAC23 set
of programs to calculate the properties of critical points (cps)
Ack n ow led gm en t. We are grateful to Direccio´n
General de Servicios de Co´mputo Acade´mico, Univer-
sidad Nacional Auto´noma de Me´xico, DGSCA, UNAM,
for their computational support, as well as for the
generous gift of supercomputer CPU time, and we thank
Consejo Nacional de Ciencia y Tecnolog´ıa (CONACyT)
for the financial support given via grants No. 3279P-
E9607 and 400313-5-28016E, and Magdalena Kuthy
and Anne Sturbaum for careful revision of this manu-
script.
2
in the charge density, density (F), Laplacians (∇ F), and
ellipticities (ꢀ). Semiempirical PM337 full geometrical optimiza-
tions of the referred quinones were determined with G92.33
J O990186O
(36) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J . Phys. 1980, 58, 1200-
1211.
(37) Stewart, J . J . P. J . Comput. Chem. 1989, 10, 209-220, 221.