Crystal structure, NMR and theoretical investigations on 2-(o-hydroxy-anilino)-1,4-napthoquinone

Article abstract of DOI:10.1016/j.molstruc.2009.12.029

Crystal structure, ¹H NMR and cyclic voltammetric investigations of 2-(o-hydroxy-anilino)-1,4-napthoquinone (HAN), resulting from coupling of aminophenol with 2-hydroxy-1,4-napthoquinone, have been carried out. X-ray structure reveals that the HAN ligand crystallizes in orthorhombic space group Pca2₁ with Z = 4, forming a chain via inter-molecular O2?H1A{single bond}O1 and C15{single bond}H15?O3 interactions. Both ¹H NMR and cyclic voltammetry experiments suggest the titled ligand is associated and exists as dimer in d₆-DMSO while the monomer has been predicted in CDCl₃ solution. Density functional calculations can be utilized to gauge the strength of hydrogen-bonded interactions from the ¹H chemical shifts in the NMR spectra. Self-consistent reaction field (SCRF) calculations further support the inferences drawn from cyclic voltammetry experiments.

Full text of DOI:10.1016/j.molstruc.2009.12.029

Journal of Molecular Structure 966 (2010) 144–151
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Crystal structure, NMR and theoretical investigations on
2-(o-hydroxy-anilino)-1,4-napthoquinone
a
b
Nourollah Feizi a, Rahul V. Pinjari a, Shridhar P. Gejji a, , Fareed B. Sayyed , Rajesh Gonnade ,
*
Sandhya Y. Rane a,
*
a Department of Chemistry, University of Pune, Pune 411007, India
b Centre of Material Characterization, National Chemical Laboratory, Pune 411008, India
a r t i c l e i n f o
a b s t r a c t
Crystal structure, 1H NMR and cyclic voltammetric investigations of 2-(o-hydroxy-anilino)-1,4-naptho-
quinone (HAN), resulting from coupling of aminophenol with 2-hydroxy-1,4-napthoquinone, have been
carried out. X-ray structure reveals that the HAN ligand crystallizes in orthorhombic space group Pca21
with Z = 4, forming a chain via inter-molecular O2ꢀ ꢀ ꢀH1AAO1 and C15AH15ꢀ ꢀ ꢀO3 interactions. Both 1H
NMR and cyclic voltammetry experiments suggest the titled ligand is associated and exists as dimer in
d6-DMSO while the monomer has been predicted in CDCl3 solution. Density functional calculations can
be utilized to gauge the strength of hydrogen-bonded interactions from the 1H chemical shifts in the
NMR spectra. Self-consistent reaction field (SCRF) calculations further support the inferences drawn from
cyclic voltammetry experiments.
Article history:
Received 19 September 2009
Received in revised form 8 December 2009
Accepted 14 December 2009
Available online 23 December 2009
Keywords:
Napthoquinone
1H NMR
Hydrogen bonding
Cyclic voltammetry
Density functional
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
quently results in one electron reduction of R-carbonyl group [9].
The electron acceptance sites of 2-R-5H-enzo[b]carbazole-6,11-
Quinones belong to class of unsaturated
a
,b-ketones and have
diones (BCDs), can be gauged from its molecular structure [10].
The reduced species can further be incorporated in designing
new molecules possessing enhanced biological activity. The elec-
tron-accepting capacity of these derivatives can further be modi-
fied with the substitution, for example, the phenyl group bound
to quinone which can bring about the charge transfer and result
in a gradual change in its redox properties. Intermediates of 2-hy-
droxy-1,4-napthoquinone (lawsone) [11] and amine interactions
those mimic the TPQ reactivity [12] in CAO have thus become
increasingly important [13]. With this view the amine coupling
interaction of Lawsone and o-aminophenol has been investigated
in this work. The resulting 2-(o-hydroxy-anilino)-1,4-naptho-
quinone (HAN) has further been characterized by single crystal
X-ray, 1H NMR, cyclic voltammetry experiments and density func-
tional calculations. It should be remarked here that the redox
behavior of HAN ligand should prove useful in understanding the
biological activity in CAO.
been focus of attention owing to their important role in cellular
respiration and photosynthesis [1]. The 1,4-naphthoquinone deriv-
atives are toxic metabolites yet paradoxically can either be poten-
tially carcinogenic or effective anticancer agent [2]. An electron
transport in oxidative phosphorylation in mitochondrial mem-
brane by quinones leads to transformation of NADH to ATP [3].
The biological activity of quinone derivatives are known to corre-
late well to redox potential in cyclic voltammetry experiments
[4]. Numerous electrochemical experiments have been reported
in the literature which focus on understanding the reduced species
which may be semiquinone (Qꢁꢂ) or catechol (Q2ꢂ) under mild
conditions [5]. It may further be remarked here that the redox ac-
tive copper amine oxidase (CAOs) comprising of a peptide bound
with 2,4,5 trihydroxy-/-alanine–quinone cofactor, viz., topaqui-
none (TPQ) effectively catalyzes the oxidative deamination of
primary amines [6,7]. The 2-hydroxyl group in TPQ led to
reoxidation of amino resorcinol intermediate by coupling of the
amine group with hydroxyl functionality [8]. An electron transfer
in 2-[(R-phenyl)amine]-1,4-naphthalenediones (PANs) subse-
2. Experimental
2.1. Synthesis and characterization of HAN
* Corresponding authors. Fax: +91 20 25691728.
E-mail addresses: spgejji@chem.unipune.ernet.in (S.P. Gejji), syrane@chem.
unipune.ernet.in (S.Y. Rane).
All chemicals used in the synthesis were obtained from Sigma
Aldrich Chemical Co.
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.12.029

N. Feizi et al. / Journal of Molecular Structure 966 (2010) 144–151
145
The solvents, methanol and DMSO were purified according to
the procedure cited in the literature [14]. HAN was synthesized
by adding solution of 1 mmole of 2-hydroxy-1,4-naphthoquinone
(0.174 g) dissolved in 25 ml anhydrous methanol to the stirring
solution of 1 mmole of 2-aminophenol (0.109 g) dissolved in
25 ml anhydrous methanol. The solution mixture was stirred for
96 h at room temperature until it becomes dark red. This solution
was then concentrated on Büchi rotavapour model R-200. The sep-
arated dark coloured solid (0.200 g, 75%) thus obtained was
washed with ꢃ2–5 ml of anhydrous methanol and dried in
vacuum.
relation functional using the 6-31G(d,p) basis set [20,21]. Calcula-
tions were carried out employing the GAUSSIAN 03 program [22].
The highest occupied molecular orbital (HOMO) from the Frontier
orbital was visualized using the UNIVIS-2000 code [23]. The MESP
V(r), at a point r due to a molecular system with nuclear charges
{ZA} located at {RA} and electron density q(r) is defined by
Z
N
X
ZA
jr ꢂ RA
q
ðr0Þd3r0
r ꢂ r0
VðrÞ ¼
j ꢂ
ð1Þ
A¼1
Thus, the two terms contributing to the molecular electrostatic
potential V(r) represent the bare nuclear (VN) and electronic contri-
butions (VE), respectively, as shown in the above equation. The sign
of V(r) at a given point represents whether the nuclear or elec-
tronic effects are dominant. Topological features of V(r) summa-
rized by its critical points (CPs) are well reviewed in the
literature [24–25]. Accordingly, the CPs are classified in terms of
an ordered pair, viz., rank and signature. The (3, ꢂ3) CP represents
the maxima and (3, +3) yield the minima near electronegative
atom in the molecular system. Further, the remaining (3, ꢂ1) and
(3, +1) CPs denote the saddle points in the electrostatic potential.
The set of CPs of a molecule are unique and hence their existence
and nature offer a signature of the molecular structure. In this pa-
per, the topographic features of V(r) are visualized by UNIVIS-2000
[23].
NMR chemical shifts (d) were calculated by subtracting the nu-
clear magnetic shielding tensors of protons lowest energy con-
formers of (HAN)n (n = 1–4) from those of the tetramethyl silane
(TMS) (as a reference) through the gauge invariant atomic orbital
(GIAO) [26] method at the B3LYP/6-31G(d,p) level of theory. The
Quantum Theory of Atoms in Molecules (QTAIM) [27–29] proposed
by Bader was employed to investigate the molecular electron den-
sity topography and, accordingly, the bond critical point (bcp),
characterized as (3, ꢂ1) CP, of different hydrogen bonds were lo-
cated. A program developed in our laboratory was used to calculate
MP 190 °C. Microanalysis required for C, 72.20; H, 4.19; N, 5.30.
Calc. for C16H11NO3: C, 72.38; H, 4.15; N, 5.27).
2.2. Single crystal X-ray diffraction
Single crystal of compound HAN obtained from methanol. X-ray
diffraction studies were conducted on good quality single crystals
of HAN (pale orange, 0.69 mm ꢄ 0.34 mm ꢄ 0.03 mm size) and se-
lected using Leica polarizing microscope and mounted on glass fi-
bers with epoxy cement. The intensity data measurements were
carried out at room temperature (297 K) on a Brüker SMART APEX
single crystal X-ray CCD diffractometer with graphite-monochro-
matized (Mo K
operated at 50 kV and 30 mA Hemisphere data were collected with
scan width of 0.3° at three different settings of / (0°, 90° and
a = 0.71073 Å) radiation. The X-ray generator was
x
180°) with exposure time 15 s/frame (total frames = 1271) keeping
the sample-to-detector distance fixed at 6.145 cm and the detector
position (2h) fixed at ꢂ28°. The X-ray data acquisition was moni-
tored by SMART program [15]. All the data were corrected for
lorentzian and polarization effects using SAINT programs [15]. A
semi-empirical absorption correction based on symmetry equiva-
lent reflections was applied using the SADABS program [15]. Lat-
tice parameters were determined from least squares analysis of
all reflections. The structure was solved by direct method and re-
fined by full matrix least squares, based on F2 using SHELX-97 soft-
ware package [16]. All the hydrogen atoms were located from a
difference Fourier map, and their positional coordinates and isotro-
pic thermal parameters were refined. Molecular and packing dia-
grams were generated using ORTEP-32 [17] and Mercury CSD
2.1, respectively [18]. Geometrical calculations were performed
using SHELXTL (Brüker [15] and PLATON [19]).
the density at the bcp (qbcp) in the MED topography [30]. The effect
of solvation on the relative stabilization energies of these (HAN)n,
n = 1–4 conformers were studied by employing the self-consistent
reaction field (SCRF) theory incorporating the Polarizable Contin-
uum Model (PCM), where the cavity is created via a series of over-
lapping spheres, initially devised by Tomasi and co-workers, as
implemented in the GAUSSIAN 03 program.
2.3. Spectral characterization and cyclic voltammetry studies
3. Results and discussion
The proton magnetic resonance (1H NMR) spectrum of HAN in
Amine coupling at the C2 position of unsubstituted as well as
m-/p-substituted aniline of 1,4-naphthoquinone are reported in
the literature. Martinez et al. [9,31] have investigated the unsubsti-
tuted 2-(phenyl anilino)-1,4-naphthoquinone (HPAN) and its m-/p-
CDCl3 was run at 25 °C on
a BRÜKER NMR Spectrometer
(300 MHz) model. Infrared spectrum of HAN was recorded as KBr
pellet on the FTIR-8400 Shimadzu infrared spectrophotometer.
The experimental spectrum of HAN shows IR absorptions as fol-
lows:
m
max/cmꢂ1 3280 (s)(NH), 3060 (sbr)(OH), 2700 (mbr) and
2623 (mbr)(O__Hꢀ ꢀ ꢀO)(C__Hꢀ ꢀ ꢀO), 1681(m) (C1@O2), 1612 (s)
(C4@O2), 1544 (s) (in plane NAHꢀ ꢀ ꢀO deformation).
Cyclic voltammogram (CV) was recorded on a CHI 1200A elec-
trochemical analyser (CH instruments Inc., USA). The three-elec-
trode cell includes a working electrode as a platinum or glassy
carbon referenced with an Ag/AgCl electrode, a platinum wire as
an auxiliary electrode. About 0.1 M tetraethyl ammonium perchlo-
rate (TEAP) was used as a supporting electrolyte. Purified nitrogen
atmosphere was maintained in the cell during CV run.
2.4. Theoretical calculations
Optimizations of the (HAN)n (n = 1–4) conformers were carried
out using density functional calculations incorporating Becke’s
three-parameter exchange with Lee, Yang, and Parr’s (B3LYP) cor-
Fig. 1. ORTEP diagram of HAN showing atom numbering (ellipsoids drawn at 30%
probability level) scheme with the bifurcated intra-molecular NAHꢀ ꢀ ꢀO
interactions.

146
N. Feizi et al. / Journal of Molecular Structure 966 (2010) 144–151
Table 1
Crystal data of HAN.
none and aniline in boiling hot ethanol solvents were carried out
[32,33]. Moreover m-hydroxy aniline condensed product of PAN
has also been reported recently [34]. The interaction of o-hydrox-
yaniline or o-aminophenol with 2,3-dichloronaphthoquinone re-
sulted in ring closure form phenoxazone and open form as chloro
derivative of HAN which are in equilibrium that can be greatly
influenced by pH, solvent polarity and temperature as well
[35,36]. The route for synthesis of HAN (ꢃ75% yield) in the present
work involves coupling of o-aminophenol with lawsone in soft
conditions without any side products. Such a synthesis utilizes
the reactivity of lawsone [36,37] for nucleophilic addition rooted
in the HSAB principle [38].
Empirical formula
Formula weight
Crystal system
Space group
a(Å)
C16H11N1O3
265.26
Orthorhombic
Pca21
26.477(13)
5.904(3)
7.731(4)
1208.5(10)
4
1.458
0.102
552
0.69 ꢄ 0.34 ꢄ 0.03
Multi-scan
0.9335
0.9975
99.9%
6824
2088
1862
0.0628
225
1.041
0.0439
0.1012
0.0489
0.1041
0.192 and ꢂ0.152
b(Å)
c(Å)
Volume (Å3)
Z,
Dcalc (g cmꢂ3
)
l
(mmꢂ1
F(0 0 0)
)
Crystal size (mm3)
Ab. correction
Tmin
HAN is crystallized in orthorhombic space group Pca21. The
crystal structure of the compound comprises of one molecule per
asymmetric unit. The ORTEP of HAN has been displayed in Fig. 1.
Crystallographic data has been summarized in Table 1. As may
be noticed readily from Fig. 1, the crystal comprises of bifurcated
intra-molecular H-bonded interactions incorporating carbonyl
oxygen O3 of quinone and the hydroxyl oxygen O1 of the phenol
ring thereby restricting the free rotation of phenol group. The qui-
none moiety turns out to be planar with both the rings as well as
the amide group. HAN association that stems from the hydrogen-
bonded interactions can further be noticed from the parameters re-
ported in Table 2. As shown in Fig. 2 the neighbouring molecules
are linked via OAHꢀ ꢀ ꢀO hydrogen-bonded interactions incorporat-
ing the AOH group of aniline and carbonyl O2 from the quinonoi-
dal ring with the a-glide symmetry arranged in anti-parallel
fashion diagonal to the bc-plane. This engenders a 2D planar sheet
structure facilitating the O3ꢀ ꢀ ꢀHAC15 interactions rendering sta-
bility to the (HAN)n assembly displayed in Fig 2. Here, hydrogen
bond distance turns out to be 2.560 Å. The sheets are stacked along
c-axis; with the inter-planar spacing being ꢃ3.900 Å (Fig. 3) via off-
Tmax
Completeness to h = 25°
Reflns collected
Unique reflns
Observed reflns
Rint
No. of parameters
GoF on F2
Robs
wR2obs
Rall
wR2all
D
qmax
,
D
qmin (e.Åꢂ3
)
Table 2
Hydrogen bonding parameters for HAN from X-ray crystal data.
DAH...A
d(DAH)
d(H...A)
d(D...A)
\(DHA)
O(1)AH(1A)...O(2)a
C(15)AH(15)...O(3)b
N(1)AH(1)...O(3)
N(1)AH(1)...O(1)
0.93(3)
0.88(3)
0.91(3)
0.91(3)
1.71(3)
2.56(3)
2.07(2)
2.10(2)
2.642(3)
3.319(3)
2.588(3)
2.576(3)
175.0(3)
144.0(2)
115.3(17)
111.6(17)
centered
p. . .p aromatic stacking interactions. As may readily be
noticed the Cg1. . .Cg3 has been observed to be 3.895 Å (Symmetry
code: 1/2 ꢂ x, y, ꢂ1/2 + z) and 3.924 Å (Symmetry code: 1/2 ꢂ x, y,
1/2 + z) with the Cg1 and Cg3 defining the centroids of C1AC10 and
C11AC16 rings respectively. The successive molecular layers along
the bc-plane result in the stepping of stacking of sheets, which can
be attributed to the anti-parallel stacking of molecules shown in
Fig. 4.
Symmetry transformations used to generate equivalent atoms.
a
ꢂx + 1/2, y + 1, z + 1/2.
b
ꢂx + 1/2, y ꢂ 1, z ꢂ 1.
substituted derivatives, which were synthesized by oxidation of
unsubstituted 1,4-naphthoquinone using the CeCl3 catalyst. The
condensation reaction with substituted 2,3-dichloro naphthoqui-
1H NMR of HAN was recorded in DMSO as well as in CDCl3 using
the TMS as a reference and displayed in Fig. 4S of the supporting
Fig. 2. OAHꢀ ꢀ ꢀO and CAHꢀ ꢀ ꢀO interactions in HAN (diagonal to bc-plane forming 2D planar sheet).

N. Feizi et al. / Journal of Molecular Structure 966 (2010) 144–151
147
Fig. 3. Columnar assembly of molecules showing anti-parallel stacking (viewed down b-axis).
Fig. 4. Stacking of layers in HAN.
information. Chemical shifts (dH) of aminophenol protons in HAN
are observed near 6.9–7.3 ppm in d6-DMSO. The integration area
for the 22 protons have been noticed that suggest HAN present
in associated dimeric form (HAN)2 in the d6-DMSO. A triplet of
H15 proton at dH = 7.1 ppm was observed; while the (two) H1A
protons from the ligand correspond to the signal at dH = 9.95 ppm.
As revealed from the 1H NMR spectra of HAN in CDCl3 the dH values
(7.6–8.2 ppm) represent the protons in napthoquinoid ring of the
ligand. Further the NMR signal of H15 proton upshifted to
dH = 6.9 ppm in the spectrum in CDCl3 solution as compared to that
measured in d6-DMSO. On the other hand NMR spectra of HAN in
d6-DMSO reveal a singlet for H3 at 8.69 ppm. H1A protons appears
as a singlet at dH = 7.54 ppm in CDCl3 and highly downshifted
(9.96 ppm) in DMSO due to inter-molecular hydrogen bonding in
HAN dimer. The signals of N1H1 can be noticed at 6.17 ppm and
5.72 ppm in these solvents, respectively.
The intra- and inter-molecular hydrogen-bonded interactions
influence the redox chemistry of quinones significantly [39]. CV
of HAN ligand measured in DMSO displayed in Fig. 5 shows three
waves. First irreversible wave is observed with anodic potential
Epa being ꢂ0.23 V, while second and third reversible redox couples
correspond to the half wave potential values (E1/2) of ꢂ0.735 V and
0.00010
0.00008
0.00006
0.00004
0.00002
0.00000
-0.00002
-0.00004
B
D
F
H
J
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
Potential
Fig. 5. Cyclic voltagram of HAN in 0.1 M TEAP.

148
N. Feizi et al. / Journal of Molecular Structure 966 (2010) 144–151
ꢂ0.890 V, respectively. The one electron reduction at C1O3 car-
bonyl led to second redox couple. A similar feature was also
observed in the PAN ligand, [31] this could be attributed to
localization of LUMO at C1 in the ligand [10]. It should be remarked
here that the third redox couple of HAN results from reduction
of semiquinone to catechol by the C4O2 carbonyl. Further the
reduction wave was shifted to a less negative value owing to the
inter-molecular hydrogen-bonded interactions. A separation of
varying scan rates, were 0.11 V and 0.14 V for the second and
third redox couples, respectively. This clearly indicated the reduc-
tion has been facilitated by two electrons and further suggests
dimerization to (HAN)2 in polar aprotic DMSO, resulting from the
hydrogen-bonded interactions. It should further be remarked here
that the proton coupled electron transfer were also noticed [40] in
the phenoxy/phenol couple which render stability to phenoxy
radical in polar solvents. As may further be noticed here the poten-
reduction (Epc) and oxidation (Epa) potentials,
D
E obtained by
tial difference of Epa and E1/2 of C4O2 bond amounts to 0.66 V and
1
Fig. 6. Optimized geometries of (a) HAN (b) (HAN)2 (c) (HAN)3 and (d) (HAN)4.

N. Feizi et al. / Journal of Molecular Structure 966 (2010) 144–151
149
Table 4
further led to the estimation of interaction energy for the dimer to
be 0.66 V or 63.7 kJ molꢂ1
0
Selected B3LYP/6-31G(d,p) optimized geometry parameters (bond distances in AÅ and
anglesꢀ) in the (HAN)n, n = 1–4 along with the inter- and intra-molecular hydrogen
bonding interactions.
.
Electronic structure, charge distribution and the NMR chemical
shifts of HAN ligand have been derived within the framework of
B3LYP/6-31G(d,p) theory. Optimized geometries of (HAN)n, n = 1–
4 thus obtained are displayed in the Fig. 1S; the selected lower en-
ergy conformers are shown in Fig. 6. Different hydrogen bonding
patterns and orientation of phenol ring in HAN lead to four con-
formers for monomer. The lowest energy conformers ‘A’ and ‘B’
possess the hydrogen-bonded interactions facilitated by the phe-
nolic hydroxyl group (cf. Fig. 6a). Furthermore the bifurcated
hydrogen-bonded interaction from H1 leads to the lowering of en-
ergy in the conformer ‘A’ of HAN. The minimum energy structure
thus obtained match well with that derived from the single crystal
X-ray data (cf. Fig 1).The conformer ‘B’ turns out to be 1.5 kJ molꢂ1
higher in energy than the lowest energy ‘A’ conformer. A destabili-
zation >10 kJ molꢂ1 can be noticed in the ‘C’ and ‘D’ conformers,
where the hydrogen-bonded interactions are absent. The (HAN)2
conformers were generated from the lowest energy monomer,
resulted B3LYP optimized structure. As may readily be noticed the
B-(HAN)2 has been destabilized by 2.4 kJ molꢂ1 over the lowest
energy A-(HAN)2 conformer (Fig. 6b). Selected geometrical param-
eters in the minimum energy conformers ‘A’ of (HAN)2 are given
in Table 3. Relatively strong O1AH1Aꢀ ꢀ ꢀO2 (1.691 Å) and
C15AH15ꢀ ꢀ ꢀO3 interactions prevail in the lowest energy A-
(HAN)2 conformer. The O1AH1Aꢀ ꢀ ꢀO3 (1.814 Å) inter-molecular
interactions are present in the B-(HAN)2 conformer. The absence
of either or both of the O1AH1Aꢀ ꢀ ꢀO3 and C15AH15ꢀ ꢀ ꢀO3 interac-
tions can be noticed in ‘C’ or ‘D’ conformers of (HAN)2. Six conform-
ers of HAN trimer were derived from either ‘A’ or ‘B’ conformers of
(HAN)2. The conformer A-(HAN)3 possessing O1AH1Aꢀ ꢀ ꢀO3 and
C15AH15ꢀ ꢀ ꢀO3 interactions turn out to be minimum energy con-
former. Likewise conformer B-(HAN)3 that results from the interac-
tion of monomer ‘A’ with B-(HAN)2 turns out to be 6.3 kJ molꢂ1
higher in energy than A-(HAN)3. As is seen from the Fig. 6c, both
these (HAN)3 conformers represent extensions of the lower energy
A-(HAN)2 or B-(HAN)2. The rest of the (HAN)3 conformers do not
possess one or both the for mentioned interactions and are largely
destabilized (84.6 kJ molꢂ1). Similarly (HAN)4 yield five conformers
(Fig. 6d). As already been noticed in case of dimer or trimer of HAN,
the lower energy ‘A’ and ‘B’ conformers in (HAN)4 possess the
OAHꢀ ꢀ ꢀO and CAHꢀ ꢀ ꢀO intra-molecular interactions. B3LYP opti-
mized geometric parameters of (HAN)n, n = 1–4, are compared
with those determined from X-ray crystal structures in Table 4.
The average bond distances, bond angles along with those of inter,
intra-molecular hydrogen bond distances in the respective HAN
units compare fairly well with the corresponding parameters
determined from the X-ray crystal data. The dimerization of HAN
in DMSO can be explained from the hydrogen-bonded interactions
of HAN with the solvent. The energies of 1:1 complexes of HAN
with CHCl3 and DMSO in different conformations were calculated.
The corresponding optimized geometries of these complexes are
displayed in Fig. 2S and Fig. 3S, in the supporting information. As
may readily be inferred, CHCl3 possessing hydrogen bond acceptor
A-HAN
A-(HAN)2 A-(HAN)3 A-(HAN)4 Expt.
r(C1O3)
r(C4O2)
r(C12O1)
r(C2N1)
r(C11N1)
r(O1H1A)
a(C2C1O3)
a(O2C4C3)
a(C2N1C11)
a(C11C12O1)
d(C1C2N1H1)
d(C11C16N1H1)
d(C1C2N1C11)
1.228
1.232
1.370
1.361
1.399
0.966
119.3
121.6
131.3
115.9
7.7
1.230
1.234
1.357
1.357
1.401
0.993
1.230
1.234
1.356
1.356
1.401
0.995
1.229
1.234
1.355
1.356
1.401
0.996
1.219
1.252
1.359
1.331
1.391
0.930
119.5
119.5
119.6
119.1
122.0
131.9
116.4
8.7
122.1
132.1
116.4
8.3
122.1
132.0
116.4
8.5
121.6
134.6
115.9
1.3
158.3
176.4
160.6
177.2
176.6
161.3
176.3
174.8
160.4
177.2
175.5
178.9
179.0
176.1
d(C11C12O1H1A) 175.4
r(O3ꢀ ꢀ ꢀH1)
2.078
2.232
2.079
2.077
2.078
2.070
r(O1ꢀ ꢀ ꢀH1)
2.219
2.098
2.184
2.216
2.096
2.156
2.097
2.175
2.22
2.100
r(O30ꢀ ꢀ ꢀH10)
r(O10ꢀ ꢀ ꢀH10)
r(O300ꢀ ꢀ ꢀH100)
r(O100ꢀ ꢀ ꢀH100)
r(O3000ꢀ ꢀ ꢀH1000
r(O1000ꢀ ꢀ ꢀH1000
r(O2ꢀ ꢀ ꢀH1A0)
2.100
2.168
2.100
2.163
2.099
2.182
1.670
1.661
1.673
)
)
1.691
1.677
1.680
1.710
r(O20ꢀ ꢀ ꢀH1A00)
r(O200ꢀ ꢀ ꢀH1A000
)
(Cl) as well as donors (sufficiently acidic H) facilitates more num-
ber of hydrogen-bonded interactions with HAN in solution. On the
other hand, the only hydrogen bond acceptor (S or O) in DMSO
yield relatively less number of hydrogen-bonded interactions. Fur-
thermore, the relative stabilization energies (DERel) of all 6 con-
formers of HAN–CHCl3 turn out to be less than 21 kJ molꢂ1. Thus
Table 5
1H NMR Chemical shifts (dH) in the (HAN)n, n = 1–2, conformers. I and II represent the
corresponding monomer unit in A-(HAN)n conformers.
A-HAN A-(HAN)2
B-(HAN)2
II
3.74 11.27 9.00 9.00 3.82 10.67 3.65 3.87
C-(HAN)2
D-(HAN)2
Proton
I
I
II
I
I
II
I II
H1A
H1
H3
H13
H14
H15
H16
3.67
7.95
6.36
6.54
6.95
7.04
7.55
8.39
7.04
6.54
7.06
8.18
8.03
8.32 7.43 7.43 8.21
6.44 6.49 6.49 6.50
7.13 6.90 6.90 6.61
6.92 6.99 6.99 7.09
6.85 6.92 6.92 7.13
7.44 7.38 7.38 7.60
8.63 8.31 8.18
6.41 7.18 6.35
7.29 6.45 6.62
7.03 6.79 6.97
6.97 7.72 7.11
7.53 8.33 7.58
Table 3
B3LYP calculated stabilization energies (
trimer and tetramer of HAN.
D
Erel in kJ molꢂ1) of the monomer, dimer,
Monomer
D
ERel Dimer
D
ERel Trimer
D
ERel Tetramer
D
ERel
A-(HAN)
B-(HAN)
C-(HAN)
D-(HAN)
0.0
1.5
10.0
39.9
A-(HAN)2
B-(HAN)2
C-(HAN)2 12.8
D-(HAN)2 43.0
0.0
2.4
A-(HAN)3
B-(HAN)3
C-(HAN)3 16.8
D-(HAN)3 21.5
E-(HAN)3 44.3
F-(HAN)3 84.6
0.0
6.3
A-(HAN)4
B-(HAN)4
C-(HAN)4
D-(HAN)4
0.0
6.0
21.0
31.0
E-(HAN)4 129.3
Fig. 7. Hydrogen bond distances vs. dH of all O18ꢀ ꢀ ꢀH27ꢀ ꢀ ꢀO19 protons involved in
inter-molecular H-bonding in lowest Energy (HAN)n Conformers.

150
N. Feizi et al. / Journal of Molecular Structure 966 (2010) 144–151
all but two conformers of HAN–DMSO complexes are largely desta-
bilized (more than 31.7 kJ molꢂ1). This supports the inference of
presence of the HAN monomer in chloroform.
(HAN)n series. The H15 protons from C15AH15ꢀ ꢀ ꢀO3 hydrogen
bond exhibit the largest deviation of dH values in these conformers.
For example, compared to HAN monomer the H15 proton of unit ‘I’
in the A-(HAN)4 the H15 proton has been downshifted to
dH = 8.19 ppm, the dH values of H14 and H16 in the tetramer are
not significantly different from those in the HAN monomer. Like-
wise the dH values of H1 protons in the terminal units of trimer
or tetramer is nearly same. Furthermore, O1H1A protons those par-
ticipate in inter-molecular hydrogen-bonded interactions exhibit
large downshift in dH values those range from 11.27 ppm to
11.98 ppm. A larger downshift for dH of H1A was also observed
in the experimentally recorded 1H NMR spectra in d6-DMSO. From
the NMR and CV experiments it was concluded that the dimer,
(HAN)2 is present in DMSO. To verify this conclusion the chemical
shifts of all the protons in different (HAN)2 conformers were calcu-
lated, which are reported in Table 5. It should be noted that only
the conformer ‘B’ of (HAN)2 yields the two set of equivalent pro-
tons validating its presence in DMSO.
In the following we discuss how hydrogen-bonded interactions
influence the chemical shifts in the calculated NMR spectra of
(HAN)n, n = 1–4, conformers. Hydrogen-bonded interactions from
the hydroxyl group lead to deshielding of proton and engenders
a downshift in dH for it in the NMR spectra. The strength of hydro-
gen bond can, therefore, be correlated to chemical shift of the pro-
ton (dH) involved in hydrogen bonding. Calculated dH values of the
hydroxyl (H1A) as well as other aromatic protons in the lowest en-
ergy ‘A-’ conformers of (HAN)n are reported in Table 1S. The chem-
ical shifts of aromatic protons are largely influenced along the
A plot of the O1AH1Aꢀ ꢀ ꢀO2 hydrogen bond distances in the low-
est energy (HAN)n, n = 2–4, conformers as a function of dH values
for the respective proton from the hydrogen bond displayed in
Fig. 7 yields a straight line. This indicates that the dH values directly
depend on the hydrogen bond distance. The electron density at the
bond critical point (qbcp) in the molecular electron density (MED)
topography provides a measure of strength of the bond. Further-
more, in order to correlate the chemical shifts dH with the strength
of hydrogen bond a plot of chemical shifts the electron density at
the bond critical point of the corresponding hydrogen bond plotted
as a function of the chemical shift dH has been displayed in Fig 8. As
may be inferred the large qbcp value (correspond to stronger hydro-
gen bond) leads to more downshifted dH.
The charge distribution in (HAN)n, n = 1–4 has been analyzed
using the molecular electrostatic potential (MESP) and its
Fig. 8. qbcp vs. dH of all protons involved in O18ꢀ ꢀ ꢀH27ꢀ ꢀ ꢀO19 interactions in the
lowest energy (HAN)n.
Fig. 9. MESP isosurface (ꢂ186.42 kJ molꢂ1) of the lowest energy (HAN)n (n = 1–4) conformers.

N. Feizi et al. / Journal of Molecular Structure 966 (2010) 144–151
151
topography. MESP isosurface (V = ꢂ186.4 kJ molꢂ1) in the lowest
energy conformers of (HAN)n shown in Fig 9. MESP brings about
the effective localization of electron-rich regions in the molecular
system. It is evident that largely electron-rich region are localized
near O2 of the HAN unit that do not participate in hydrogen bond-
ing, and facilitate further growth of HAN assembly via this end.
MESP values at the minima (representing potential site for the
binding of electrophile) near oxygens have been reported in
Table 2S. The X1 minima near the O2 turn out to be deeper
(ꢂ262.8 kJ molꢂ1) in the terminating units (IV in case of tetramer)
as compared to that in monomer. On the contrary, minima in the
unit I get shallower as the number of HAN units in self assembly
increases. In consonant with the conclusions based on the electro-
static potential, the Hirshfeld atomic charges reported in Table 3S
in the lowest energy (HAN)n, n = 1–4 conformers reveal that charge
on oxygen O2 increases from ꢂ0.260 a.u. in HAN monomer to
ꢂ0.267 a.u. in (HAN)4 and turns out to be more electron rich. The
residual charge on the rest of the oxygens is nearly unchanged. A
decrease in the positive charge from 0.185 a.u. to 0.120 a.u. for
H1A from top unit (I) to the bottom unit (IV) has been noticed.
These inferences clearly support the ‘charge percolation’ through
H1A to O2, which has further been seen from HOMO localized over
the terminating HAN unit in the lowest energy conformers of A-
(HAN)n, n = 1–4 (Fig. 5S in supporting material).
from the CCDC, 12 Union Road, Cambridge CB21EZ, UK. Torsion an-
gles, bond distances and bond angles are deposited as supplemen-
tary material (Fax: +44 01223 336 033; E-mail address:
deposit@ccdc.cam.ac.uk).
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2009.12.029.
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aminophenol was characterized by the X-ray crystal structure, 1H
NMR and Cyclic voltammetry. Self organized molecular assemblies
of (HAN)n, result from the CAHꢀ ꢀ ꢀO and OAHꢀ ꢀ ꢀO hydrogen bond-
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Appendix A. Supplementary data
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Crystallographic data of HAN have been deposited with the
Cambridge Crystallographic Data Centre and may be obtained on
request quoting the deposition number CCDC-724554, respectively