Bond fixation in a [14]annulene: Synthesis, characterization, and ab initio computations of furan adducts of dimethyldihydropyrene

Article abstract of DOI:10.1021/ja953795w

Furan adducts, 13, 15, and 16, of dimethyldihydropyrene are prepared in order to test the postulate that bicyclic annelations are generally effective at inducing bond localization in aromatic systems. A large 2-ppm downfield shift of the ¹H NMR shifts of the internal methyl signals in 15 compared to 16 provides a significant indicator of bond localization in 15. X-ray diffraction analysis of 13 displays regular bond length alternation. Ab initio computations that do not include dynamic electron correlation are found to be inadequate for modeling the molecular structure of 1. Density Functional Theory models 1 well and predicts bond localization in derivatives of 1 consistent with the observed NMR spectroscopic and X-ray diffraction results.

Full text of DOI:10.1021/ja953795w

J. Am. Chem. Soc. 1996, 118, 2907-2911
2907
Bond Fixation in a [14]Annulene: Synthesis, Characterization,
and ab Initio Computations of Furan Adducts of
Dimethyldihydropyrene
Reginald H. Mitchell,*,1a Yongsheng Chen,1a Vivekanantan S. Iyer,1a
Danny Y. K. Lau,1a Kim K. Baldridge,1b and Jay S. Siegel*,1c
Contribution from the Department of Chemistry, UniVersity of Victoria, P.O. Box 3055,
Victoria, British Columbia V8W 3P6, the San Diego Supercomputer Center, P.O. Box 85608,
San Diego, California, 92186-9784, and the Department of Chemistry, UniVersity of California,
San Diego, La Jolla, California 92093-0358
ReceiVed NoVember 13, 1995X
Abstract: Furan adducts, 13, 15, and 16, of dimethyldihydropyrene are prepared in order to test the postulate that
bicyclic annelations are generally effective at inducing bond localization in aromatic systems. A large 2-ppm down-
field shift of the 1H NMR shifts of the internal methyl signals in 15 compared to 16 provides a significant indicator
of bond localization in 15. X-ray diffraction analysis of 13 displays regular bond length alternation. Ab initio
computations that do not include dynamic electron correlation are found to be inadequate for modeling the molecular
structure of 1. Density Functional Theory models 1 well and predicts bond localization in derivatives of 1 consistent
with the observed NMR spectroscopic and X-ray diffraction results.
Introduction
Bicyclic annelations (e.g. bicyclo[2.1.1]hexeno2 and oxan-
orbornadieneo3 ) have been implicated as inducers of π-bond
localization in aromatic systems.4 Dimethyldihydropyrene, 1,
is an excellent test molecule for investigations of cyclic
π-electron delocalized systems, because the NMR chemical shift
of the internal methyl protons of 1, δ -4.25, is relatively
insensitive (<(0.2 ppm) to simple substituent effects, but is
very sensitive to anything that disturbs the cyclic delocaliza-
tion of its π-electrons.5,6 The methyl protons of 1 are shielded
by 5.2 ppm from those in 2; this shielding is ascribed to the
ring current caused by the cyclic delocalization of the 14
π-electrons in 1. Fusion of a strongly aromatic system such as
benzene to give 3 causes substantial bond fixation in the
macrocyclic ring of 3, which betrays itself in a reduced ring
current and reduced shielding of the methyl protons, δ -1.63
instead of δ -4.25. In contrast, the spectra of the cyclobutane
annelated systems 4 and 5, with methyl signals clustered around
-4 ppm, indicate that fusion of a nonconjugated carbocyclic
ring causes no π-bond fixation;7 there is almost no change in
methyl proton chemical shift either between 4 and 5 (∆δ 0.12
Figure 1. Annelated dihydropyrenes 6-12 and their 1H chemical shifts
(10-12 isomeric mixtures).
ppm), or between these signals and those of 1 (∆δ 0.16, 0.02
ppm), as would be expected if bond fixation were significant.
Studies on a number of other nonconjugated carbocyclic
annelated dihydropyrenes all show insignificant effects on the
ring current and thus presumably on the π-delocalization present
(Figure 1).8
X Abstract published in AdVance ACS Abstracts, March 1, 1996.
(1) (a) University of Victoria. (b) San Diego Supercomputer Center. (c)
UC-San Diego.
(2) (a) Bu¨rgi, H.-B.; Baldridge, K. K.; Hardcastle, K.; Frank, N. L.;
Gantzel, P.; Siegel, J. S.; Ziller, J. Angew. Chem., Int. Ed. Engl. 1995, 34,
1454. (b) Frank, N. L.; Baldridge, K. K.; Gantzel, P.; Siegel, J. S.
Tetrahedron Lett. 1995, 36, 4389. (c) Frank, N. L.; Baldridge, K. K.; Siegel,
J. S. J. Am. Chem. Soc. 1995, 117, 2102.
(3) Kohnke, F. H.; Mathias, J. P.; Stoddart, J. F.; Slawin, A. M. Z.;
Williams, D. J. Acta Crystallogr., Sect. C 1992, C48, 663.
(4) Such bond localization has historically been related to a so-called
“Mills-Nixon” effect. Careful reading of the original literature makes it
abundantly clear that Mills and Nixon’s work does not apply in a modern
structural context and any attribution of modern experimental observations
to “Mills-Nixon” effects is a misnomer. For a more detailed analysis, see:
(a) Siegel, J. S. Angew. Chem. Int. Ed. Engl. 1994, 33, 1721. (b) Frank, N.
L.; Siegel, J. S. AdV. Theor. Interesting Mol. 1995, 3, 209-260.
(5) Mitchell, R. H. AdV. Theor. Interesting Mol. 1989, 1, 135-199.
(6) Mitchell, R. H.; Iyer, V. S.; Khalifa, N.; Mahadevan, R.; Venugopalan,
S.; Weerawarna, S. A.; Zhou, P. J. Am. Chem. Soc. 1995, 117, 1514-
1532.
(7) Mitchell, R. H.; Slowey, P. D.; Kamada, T.; Williams, R. V.; Garratt,
P. J. J. Am. Chem. Soc. 1984, 106, 2431-2432.
0002-7863/96/1518-2907$12.00/0 © 1996 American Chemical Society

2908 J. Am. Chem. Soc., Vol. 118, No. 12, 1996
Mitchell et al.
3
Table 1. Selected C-C Bond Distance Data and Jcis Coupling
Table 2. Bond Angle Data for Part of 13 and 1
Constants for 13
bond distance (Å) 3Jcis (Hz)
bond
distance (Å) 3Jcis (Hz)
1-2
2-3
3-4
4-5
5-6
6-7
7-8
1.365
1.406
1.357
1.413
1.357
1.417
1.361
8.42
6.97
8-13
1.428
1.359
1.427
1.374
1.413
1.376
1.409
angle
(in X)
angle
(in Y)
13-14
14-15
15-16
16-17
17-18
18-1
13 (deg)
1 (deg)
13 (deg)
1 (deg)
a
b
c
d
e
f
g
h
i
119.1
119.2
115.0
117.3
123.0
122.8
123.5
117.1
117.8
124.6
121.7
118.0
113.3
119.4
120.5
122.7
125.5
116.1
116.5
123.6
1-3-2
1-3-5
1-3-4
105.9
105.3
112.1
105.9
105.2
110.6
8.79
6.93
Results
Anomalous among the spectra of derivatives of 1 are the
chemical shifts observed6 for the methyls of the two isomers
of the oxanorbornadiene fused dihydropyrenes, 13 and 14; the
signals for these methyls appear at δ -3.34, -3.51 and δ -3.29,
-3.45, respectively. A substantial reduction (16-17%) in ring
current has occurred from that of 1. Isomer 13 was purified
from the mixture by fractional crystallization, and a crystal
structure was determined (full details are deposited). The
relevant macrocyclic carbon-carbon bond distances are given
in Table 1, together with the measured 3Jcis coupling constants,
which are completely consistent with the X-ray data. Clearly,
multiple techniques support substantial bond fixation in the
macrocyclic ring of 13, and by correlation of the NMR chemical
shifts, one can deduce the same to be true for 14.
j
magnetic ring current field, and therefore any difference in
chemical shift should be due primarily to a difference in ring
current, and not a shift in position of the methyl group.
If indeed the oxanorbornadiene ring does have some special
π-bond localizing effect, then synthesis and spectral character-
ization of the bis-adducts 15 and 16 should prove this effect.
Comparison of the two resonance structures of 15A and 15B
(symmetry nonequivalent contributors) and 16A and 16B
(symmetry equivalent contributors) indicates that the π-electrons
of 15 should manifest a smaller ring current effect than those
of 16.
A further test of whether ring current is actually reduced
comes from the relationship between the chemical shift of the
internal methyl protons and H-2 of 13. For a series of aromatic
ring annelated examples, including 3, the chemical shift of the
internal methyl protons is related to the chemical shift of H-2
through the equation:6
Reaction of the dibromide 179 with NaNH2 and t-BuOK in
furan formed a 1:4 mixture of 15 and 16, three isomers of each
(total yield 62%). In the H NMR spectrum of the mixture of
1
15 and 16, one set of internal methyl protons was centered
around δ -4, while the smaller set was around δ -2.3,
consistent with an enhancement of bond localization in one
isomer type. Chromatography failed to separate the products;
however, fractional crystallization several times from methanol-
dichloromethane finally gave a sample with only the three
isomers of 16 (Figure 2) and an enriched sample of the three
isomers of 15. The gross structure of the isomeric mixture of
15 or 16 was easily proved by deoxygenation of the respective
isomeric mixture using Fe2(CO)9 in benzene to the known10
dibenzannulenes. The three isomers of 16 could not be
separated from each other, but the mixture gave a M+ at 364.148
(EI-HRMS), consistent with that required for C26H20O2 (364.146),
and more convincingly this mixture gave only the known
δ(Me) ) 17.52 - 2.69δ(H-2)
In the 1H NMR spectrum of 13, H-2 appears at δ 7.76, which
by formula corresponds to δ(Me) ) -3.31, in extremely good
agreement with the values found experimentally (-3.29 to
-3.51). Such a correspondence among spectral shifts indi-
cates that it is unlikely that the chemical shift of the meth-
yls is affected by some anisotropic or geometric effect, rather
than a ring current effect. That ring current effects are domi-
nant is supported by comparison of the X-ray data for 13
with those of 1.6 Some of the relevant data are shown in
Table 2.
Clearly, the relationship between the methyl groups and the
ring periphery in 13 is not very different from that in 1, in
particular, the distance from the methyl group (atom 1 in Y) to
the midpoint of the 3-4 bond in Y is 1.98 Å in 13 and 1. Thus,
in both compounds, the methyl group is situated at ap-
proximately the same position relative to the center of the
(9) Phillips, J. B.; Molyneux, R. J.; Sturm, E.; Boekelheide, V. J. Am.
Chem. Soc. 1967, 89, 1704-1709. Prepared by reaction of 1 with 2 equiv
of NBS in dry DMF (see: Mitchell, R. H.; Lai, Y. H.; Williams, R. V. J.
Org. Chem. 1979, 44, 4733-4735).
(10) Mitchell, R. H.; Williams, R. V.; Dingle, T. W. J. Am. Chem. Soc.
1982, 104, 2560-2571.
(8) Mitchell, R. H.; Lau, D. Y. K.; Iyer, V. S. Unpublished results.

Bond Fixation in a [14]Annulene
J. Am. Chem. Soc., Vol. 118, No. 12, 1996 2909
Table 3. Selected Structural Parameters for 15, 19, and 20 from
DFT Computations
compound
1
20
19
15
dexo (Å)
1.409
1.409
0.0
1.402
1.412
1.0
1.390
1.428
3.8
1.389
1.427
3.8
d
endo (Å)
endo-exo (pm)
ave (Å)
∆
d
1.409
1.407
1.409
1.408
of theory for derivatives of 1. This level of theory is thus
established as the minimum necessary for meaningful compari-
son with experiment.
On the basis of annelation induced bond localization effects
on benzene, systems 15 and 19 are expected to show roughly
equal degrees of bond localization, as opposed to 20, which
should show essentially no localization. DFT computations on
20, 15, and 19 substantiate this structural correlation unequivo-
cally (Table 3). Whereas the bonds of the [14]annulene in 20
all cluster around 1.40 Å and show no regular alternation in
length, the bonds in 15 (and 19) group into two sets and alternate
long-short around the annulene. Starting from the fused bond
between the macrocycle and the annelation, one can highlight
every other bond. As such, all highlighted bonds belong to the
endo set, and the others belong to the exo set. A parameter,
Figure 2. Isomers of 16 and the corresponding deoxygenation product
18.
transoid dibenzannulene 18 on deoxygenation, thus proving the
relative orientation of the annelations.
The udud and the uudd isomers of 16 are symmetrical and
1
each would be expected to display a single H NMR methyl
resonance. The two methyl groups in the uduu isomer are
however different, and thus two signals are expected for this
isomer. Indeed, four methyl signals were observed, with the
two signals of 16uduu (δ -3.80 and -4.15) being of equal
intensity, corresponding to 16uduu; the other signals (δ -3.96
and -4.01) were not specifically assigned but belong to 16uudd
and 16udud. The relative integrations of the three sets of signals
was 5:1:2. After several recrystallizations, the ratio was 14:5:
1. The 16uduu isomer is formed preferentially. Similarly, the
three isomers of 15 also give four methyl signals. Analogously,
15uduu gave signals at δ -2.17 and -2.48; the other two
isomers gave signals at δ -2.29 and -2.34. The relative
integrations of these being 2:3:1, in this case the uduu isomer
is not formed preferentially.
d(endo) - d(exo)
∑
)
∑
∆
endo-exo
n
can be defined in order to gauge the degree of bond localiza-
tion. For 20, ∆endo-exo equals ca. 1 pm and corresponds to
localization of less than 5% of a bond. In contrast, for 15 and
19, ∆endo-exo is 3.8 and 3.8 pm, respectively, corresponding to
a localization of roughly 25% of a bond. These distortions are
consistent with the kinds of distortions predicted and seen for
21 and 22.2,3
The NMR data indicate clearly that a substantial (35-40%)
reduction of ring current has occurred for 15, and almost none
for 16; 15B is predicted to be the dominant resonance contribu-
tor. Thus, the strong π-bond localizing effect of the oxanor-
bornadiene ring seems difficult to dispute.
Computational studies on 1 and derivatives are complicated
by the size of the molecules and the difficulties associated with
a correct computational description of the behavior of π-delo-
calized systems. For example, although several methods
accurately predict the structure of benzene as D6h with 1.395
Å C-C bonds, few handle the thermochemistry with sufficient
accuracy. Theoretical treatments of 1 are even more complex.
Discarding semiempirical methods due to their unreliable nature,
even restricted Hartree-Fock (RHF) levels of theory at reason-
able basis sets (DZV(d)) predict a C2 (bond localized) structure
for 1. These levels of theory describe the experimentally
observed C2h structure as a transition state structure (one
negative eigenvalue), ca. 10 kcal/mol higher in energy than the
C2 form. Haddon and Baumann11 predicted that electron
correlation would be important for delocalized systems such as
[10]annulene. Indeed, only at dynamically correlated levels of
theory such as Moller-Plesset, MP2, or Density Functional
Theory, DFT, does the structure of 1, a [14]annulene, come
into accord with experiment, thus establishing self-consistency
A perturbation analysis of the orbitals of cyclobutane interact-
ing face-to-edge with the π-system of the macrocycle reveals a
destabilizing filled-filled interaction between the σ orbitals on
the cyclobutyl fragment and the highest occupied molecular
orbital (HOMO) of the macrocycle.12 Localization of the double
bonds exo to the point of fusion reduces this destabilizing
interaction. This explanation accounts well for the distortions
in 22 and 20, but may be questioned for 15 and 21. Hydro-
genation of the double bonds in the oxanorbornadieneo anne-
lations of 13, 15, and 21 leads to 23, 24, and 25. Experimen-
tally, the chemical shift perturbation vanishes for 23 and 24.
Computationally, the bond localization is substantially reduced
in 25, and by analogy we would expect the same for 23 and
24. Therefore, 15/19 and 21/22 show similar structural distor-
tions, but the components of their physical mechanism are
potentially different. Although one can speculate that the
(11) (a) Haddon, R. C.; Raghavachari, K. J. Am. Chem. Soc. 1982, 104,
3516-3518. (b) Haddon, R. C.; Raghavachari, K. J. Am. Chem. Soc. 1985,
107, 289-297. (c) Xie, Y.; Schaefer, H. F., III; Liang, G.; Bowen, J. P. J.
Am. Chem. Soc. 1994, 116, 1442-1449. (d) Baumann, H. J. Am. Chem.
Soc. 1978, 100, 7196.
(12) For a related orbital analysis, see: (a) Jorgensen, W. L.; Borden,
W. T. J. Am. Chem. Soc. 1973, 95, 6649. (b) Gleiter, R.; Bischof, P.;
Gubernator, K.; Christl, M.; Schwager, L.; Vogel, P. J. Org. Chem. 1985,
50, 5064. (c) Gleiter, R.; Heilbronner, E.; Heckman, M.; Martun, H.-D.
Chem. Ber. 1973, 106, 28.

2910 J. Am. Chem. Soc., Vol. 118, No. 12, 1996
Mitchell et al.
and then the reaction mixture was stirred without further cooling for 2
h. Diethyl ether (200 mL) was added, and then the mixture was poured
into iceswater. The ether extract was washed well with water and
dried (MgSO4), and silica gel was added to pre-absorb the product after
evaporation. Chromatography on silica gel using ether-petroleum ether
(1:10) gave the product as the major green fraction, 1.18 g (70%), which
could be recrystallized from chloroform-methanol, mp 212-214 °C
(lit.9 mp 213-214 °C). 1H NMR (360 MHz) δ 8.69 (s, 4), 8.51 (s, 4),
-4.04 (s, 6); 13C NMR (90.6 MHz) δ 136.7, 126.8, 123.9, 118.5, 29.2,
14.2.
annelation effects in 19 act purely through σ-π interactions
and those in 15 act through a mixture of σ-π filled-filled
interaction and secondary through-space π-π and σ-π interac-
tions, a complete analysis of angle strain and orbital conjugation
is needed. In 20, none of the correct orbitals are present at an
energy which permits efficient interaction and no bond localiza-
tion is seen.
Furan Adducts 15 and 16. NaNH2 (150 mg, 3.85 mmol) and
t-BuOK (2 mg) were added to a stirred solution of dibromide 17
(122mg, 0.31 mmol) and dried furan (4 mL) in dry THF (4 mL) at 20
°C under argon. After stirring for 48 h, methanol (0.5 mL) was added
followed by silica gel (2 g), and then the solvent was evaporated. The
solid residue was placed on the top of a silica gel column and
chromatographed using first petroleum ether to elute any unchanged
bromide and then ether-petroleum ether (7:3) to elute the products 15
and 16, 70 mg (62%) as a mixture of six isomers. From the integrations
of the internal methyl protons at δ -3.80 to -4.15 (16) and at -2.12
to -2.45 (15), the ratio of 16/15 was found to be 78:22 (4:1).
Rechromatography of this mixture and fractional recrystallization
several times from dichloromethane-methanol yielded 30 mg of pure
16 as a mixture of the three isomers shown in Figure 2. MS (CI) m/z
365 (MH+): EI-HRMS M ) 364.1485, C26H20O2 requires 364.1463.
1H NMR (360 MHz): 16uduu ∂ 8.46 (s, H-1,8), 8.43-7.96 (m,
H-2,3,9,10), 7.23-7.16 (8 lines, H-6,13), 7.16-7.13 (8 lines, H-5,12),
6.59 (bs, H-4,11), 6.25 (bs, H-7,14), -3.80 and -4.15 (s, -CH3);
16udud + 16uudd ∂ 8.46 (s, H-1,8), 8.43-7.96 (m, H-2,3,9,10), 7.39-
7.36 (6 lines, H-5,12), 7.34-7.31 (6 lines, H-6,13), 6.61 (bs, H-4,11),
6.23 (bs, H-7,14), -3.96 and -4.01 (s, -CH3)ssee text. In the 13C
NMR spectrum, each type of carbon showed three resonances, e.g.,
C-4 83.97, 83.55, 83.50 and C-7 81.53, 81.31, 81.23, corresponding to
the three isomers present. Cisoid isomers 15: 1H NMR (360 MHz,
peaks after subtracting transoid isomers) ∂ 7.80 and 7.42 (s, H-1,4),
7.70-7.61 (m, H-2,3,9,10), 7.05-6.81 (m, H-6,7,12,13), 6.27 (bs,
H-8,11), 5.92 (bs, H-5,14), -2.13, -2.27, -2.31, -2.45 (s, -CH3)ssee
text.
Computational Details
The molecular structure of 1 has been determined at a variety of
theoretical methods to determine self-consistency. Reported here is
the double-ú valence DZV(d)14 basis set, employed at the restricted
Hartree-Fock (RHF) self-consistent field (SCF) level of theory. This
basis set includes a set of six d polarization functions on all heavy
atoms. These calculations were performed with the aid of the
analytically determined gradients and search algorithms contained in
GAMESS.15 Additional calculations at the MP2/6-31G(d)13 and Density
Functional Theory levels were performed to determine the effects of
dynamical correlation. The former method, a post-RHF method which
incorporates correlation in terms of Møller-Plesset theory of order 2
(MP2),16 were performed using the GAUSSIAN94 suite of programs.17
The Density Functional Theory (DFT) Methods, which inherently
incorporate effects of correlation within the Kohn-Sham formalism,
were performed with CADPAC.18 These calculations, denoted BLYP,
employ the exchange correction of Becke, which includes the Slater
exchange along with the corrections involving the gradient of the
density, and the correction function of Lee, Yang, and Parr,18c,d which
includes both local and nonlocal terms. Comparative DFT calculations
were performed on 1 and 20 with the BPW91 functional, which uses
Perdew and Wang’s 199118e gradient-corrected correlation function.
These latter calculations, performed with GAUSSIAN94, corroborate
precisely with the BLYP results.
Deoxygenation of 16 to Dibenzannulene 18. A mixture of mixed
isomers of 16 (12 mg, 0.033 mmol) and Fe2(CO)9 (29 mg, 0.080 mmol)
in benzene (4 mL, distilled from sodium, under argon) was stirred at
60 °C under Ar for 1 h. The cooled mixture was directly chromato-
graphed on SiGel (5% water deactivated), quickly using petroleum ether
as eluant. The deep blue band yielded 6 mg (55%) of 18, identical to
an authentic sample10 (MS, NMR). When mixed isomers of 15/16 were
used, both benzannulenes10 were obtained.
Experimental Section
Hydrogenation of Furan Adduct 13 to 23. Recrystallized isomer
136 (40 mg) in ethyl acetate (10 mL) was added to pre-reduced Pt (5
mg) in ethyl acetate (10 mL), and the mixture was stirred under H2 for
30 min. Direct chromatography of the product on SiGel using
petroleum ether as eluant gave 37 mg (93%) of product 23, as green
crystals from petroleum ether, mp 112-113 °C: 1H NMR (300 MHz)
∂ 8.63 (d, 1H), 8.55-8.49 (m, 5H), 8.40 (s, 1H), 8.02 (t, 1H), 6.37 (m,
1H), 5.99 (m, 1H), 2.36-2.31 (m, 2H), 1.54-1.30 (m, 2H), -4.13,
-4.23 (s, 3H each); 13C NMR (90.6 MHz) ∂ 142.2, 139.5, 139.3, 136.4,
136.1, 126.1, 124.0, 123.9, 123.3, 122.8, 122.5, 119.1, 114.4, 80.5,
78.1, 31.4, 30.3, 29.3, 27.9, 14.2, 13.7; UV (cyclohexane) λmax nm (ꢀ)
343 (60 000), 380 (23 200), 477 (4500), 640 (550); CI MS m/z 301
(MH+). Anal. Calcd for C22H20O: C, 87.96; H, 6.71. Found: C,
87.30; H, 6.76.
The general experimental conditions are as previously described.
The preparation of 13 has been reported.6
2,7-Dibromo-trans-10b,10c-dimethyl-10b,10c-dihydropyrene (17).
A solution of NBS (not recrystallized from water) (1.54 g, 8.62 mmol)
in dry DMF (70 mL) was added slowly over 20 min to a stirred solution
of dihydropyrene 1 (1.00 g, 4.31 mmol) in dry DMF (50 mL) at 0 °C
(13) (a) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1982, 28, 213.
(b) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163.
(14) (a) Dunning, T. H. J. Chem. Phys. 1971, 55, 716. (b) McLean, A.
D.; Chandler. G. S. J. Chem. Phys. 1980, 72, 5639. (c) Wachters, A. J. H.
J. Chem. Phys. 1970, 52, 1033.
(15) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Jensen, J. H.;
Koseki, S.; Gordon, M. S.; Nguyen, K. A.; Windus, T. L.; Elbert, S. T.
QCPE Bull. 1990, 10, 52.
(16) Pople, J. A.; Binkley, J. S.; Seeger, R. Int. J. Quantum Chem. Symp.
1976, 10, 1.
(17) GAUSSIAN 92, Revision C, M. J. Frisch, G. W. Trucks, M. Head-
Gordon, P. M. W. Gill, M. W. Wong, J. B. Foresman, B. G. Johnson, H.
B. Schlegel, M. A. Robb, E. S. Replogle, R. Gomperts, J. L. Andres, K.
Raghavachari, J. S. Binkley, C. Gonzalez, R. L. Martin, D. J. Fox, D. J.
Defrees, J. Baker, J. J. P. Stewart, J. A. Pople; Gaussian, Inc.: Pittsburgh,
PA, 1992.
(18) (a) Amos, R. D.; Rice, J. E. CADPAC: The Cambridge Analytic
Derivatives Pasckage, Issue 5.2, Cambridge, 1995. (b) Becke, A. D. Phys.
ReV. A 1988, 38, 3098. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B
1988, 37, 785. (d) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem.
Phys. Lett. 1989, 157, 200. (e) Perdew, J. P.; Wang, Y. Phys. ReV. B 1992,
45, 13244.
Hydrogenation of Mixed Isomers 15/16. This was carried out
exactly as described above for 13. The 1H NMR spectrum of the
product containing 24 and the corresponding transoid isomer indicated
internal methyl protons at ∂ -3.94 and -4.36 with minor isomer peaks
between -4.01 and -4.42, i.e. no peaks at higher chemical shift than
-3.94. The other protons were as expected at ∂ 8.6-8.2, 6.3, 5.9,
2.4-1.3 as for 23.
Acknowledgment. Support was provided by the National
Science Foundation (CHE9307582; ASC-9212619 and VPW
to K.K.B.) and the Canadian National Science and Engineering

Bond Fixation in a [14]Annulene
J. Am. Chem. Soc., Vol. 118, No. 12, 1996 2911
Research Council. A grant for supercomputing time was
provided by the San Diego Supercomputer Center.
in the microfilm version of the journal, can be ordered from
the ACS, and can be downloaded from the Internet; see any
current masthead page for ordering information and Internet
access instructions.
Supporting Information Available: Tables and details of
the X-ray analysis of 13 (9 pages). This material is contained
in many libraries on microfiche, immediately follows this article
JA953795W