Three oxime ether derivatives: Synthesis, crystallographic study, electronic structure and molecular electrostatic potential calculation

Article abstract of DOI:10.1016/j.molstruc.2017.02.089

Three oxime ether derivatives, (E)-3-methoxy-4-(prop-2-ynyloxy)-benzaldehyde-O-prop-2-ynyl-oxime (C₁₄H₁₃NO₃) (2), benzophenone-O-prop-2-ynyl-oxime (C₁₆H₁₃NO) (3) and (E)-2-chloro-6-methylquinoline-3-c

Full text of DOI:10.1016/j.molstruc.2017.02.089

Journal of Molecular Structure 1137 (2017) 615e625
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Three oxime ether derivatives: Synthesis, crystallographic study,
electronic structure and molecular electrostatic potential calculation
,
*
Tanusri Dey a, Koduru Sri Shanthi Praveena b, Sarbani Pal b, Alok Kumar Mukherjee a
a Department of Physics, Jadavpur University, Kolkata 700032, India
b Department of Chemistry, MNR Degree and PG College, Kukatpally, Hyderabad 500085, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Three oxime ether derivatives, (E)-3-methoxy-4-(prop-2-ynyloxy)-benzaldehyde-O-prop-2-ynyl-oxime
(C14H13NO3) (2), benzophenone-O-prop-2-ynyl-oxime (C16H13NO) (3) and (E)-2-chloro-6-
methylquinoline-3-carbaldehyde-O-prop-2-ynyl-oxime (C14H11ClN2O) (4), have been synthesized and
their crystal structures have been determined. The DFT optimized molecular geometries in 2e4 agree
closely with those obtained from the crystallographic study. An interplay of intermolecular CeH/O,
Received 18 October 2016
Received in revised form
17 January 2017
Accepted 23 February 2017
Available online 24 February 2017
CeH/N, CeH/Cl and CeH$$$p(arene) hydrogen bonds and p$$$p interactions assembles molecules
into a 2D columnar architecture in 2, a 1D molecular ribbon in 3 and a 3D framework in 4. Hirshfeld
surface analysis showed that the structures of 2 and 3 are mainly characterized by H/H, H/C and H/O
contacts but some contribution of H/N and H/Cl contacts is also observed in 4. Hydrogen-bond based
interactions in 2e4 have been complemented by calculating molecular electrostatic potential (MEP)
surfaces. The electronic structures of molecules reveal that the estimated band gap in 3, in which both
aldehyde hydrogen atoms of formaldehyde-O-prop-2-ynyl-oxime (1) have been substituted by two
benzene rings, is higher than that of 2 and 4 with only one aldehyde hydrogen atom replaced.
© 2017 Elsevier B.V. All rights reserved.
Keywords:
Oxime ether derivative
X-ray powder diffraction
Hirshfeld surface analysis
Molecular electrostatic potential
Electronic structure
1. Introduction
(PXRD) has been reported for organic systems with considerable
molecular flexibility [14e17]. It should, however, be noted that
Intermolecular interactions, in particular, hydrogen bonds, have
been a topic of considerable importance due to their role in crystal
engineering and biological recognition process [1e3]. Many of the
synthons identified in supramolecular chemistry involve N/
OeH/O/N hydrogen bonds, which provide the required selectivity
and directionality to control molecular aggregation [4,5]. In addi-
tion to these relatively strong hydrogen bonds, weak interactions
structural crystallography with PXRD is significantly more chal-
lenging than that of its single crystal counterpart [18] because, first,
the information content of a powder diffractogram is markedly
lower, and second, it is far more difficult to extract structural in-
formation from a PXRD pattern due to systematic as well as random
overlapping of peaks. This is reflected in the Cambridge Structural
Database (version 5.37, update 2, CSD 2015 release) [19] search
conducted among the organic compounds, which revealed that out
of total 350196 entries only 1842 (~0.5%) structures have been
solved from PXRD (including both laboratory and synchrotron X-
ray data) without referring to an isotypic single crystal structure.
Since structure determination from PXRD cannot establish the
positions of hydrogen atoms unambiguously, consideration of
geometrical criteria alone as obtained from the PXRD analysis
without any supplementary evidence is unlikely to be reliable for
assessing the hydrogen bonds. In this context, molecular electro-
static potential (MEP) [20e22] mapped onto a molecular surface
can provide further insights into the nature of intermolecular in-
teractions. This approach utilizes the calculated MEP surfaces
around the molecule, in which the potential maxima and minima
such as, C-H … X (X ¼ O, N, Cl), C-H …
p and p … p stacking are also
important in describing the self-assembly process in molecular
solids [6,7]. Single crystal X-ray diffraction (SXRD) is generally the
method of choice for determining crystal structures of molecular
compounds and the study of intermolecular interactions in the
solid state has focused on geometrical criteria such as, D(donor) …
A(acceptor) distance and D-H … A angle that can be directly
measured from the SXRD analysis [8,9]. With recent advances in
the direct space approaches for structure solution [10e13], ab-initio
crystal structure determination from powder X-ray diffraction
* Corresponding author.
E-mail address: akm_ju@rediffmail.com (A.K. Mukherjee).
http://dx.doi.org/10.1016/j.molstruc.2017.02.089
0022-2860/© 2017 Elsevier B.V. All rights reserved.

616
T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
correspond to hydrogen bond donor and acceptor sites, respec-
tively. Several attempts have been made relating MEP surfaces to
crystal packing via intermolecular interactions [23e26].
In the current study we focus our attention to three oxime ether
derivatives, (E)-3-methoxy-4-(prop-2-ynyloxy)-benzaldehyde-O-
prop-2-ynyl oxime (2), benzophenone-O-prop-2-ynyl oxime (3)
atmosphere. The progress of reaction was monitored by checking
TLC at regular intervals. After completion of reaction, acetone was
distilled out followed by addition of water and the compounds were
extracted with ethyl acetate (3 ꢁ 15 mL). The combined organic
extracts were washed with 25 mL brine solution and dried over
anhydrous sodium sulphate. The crude products were purified by
column chromatography to yield microcrystalline powders of (E)-3-
methoxy-4-(prop-2-ynyloxy)-benzaldehyde-O-prop-2-ynyl oxime
(C14H13NO3) (2), benzophenone-O-prop-2-ynyl oxime (C16H13NO)
(3) and (E)-2-chloro-6-methylquinoline-3-carbaldehyde-O-prop-2-
ynyl oxime (C14H11ClN2O) (4).
and
(E)-2-chloro-6-methylquinoline-3-carbaldehyde-O-prop-2-
ynyl oxime (4), modified by replacing the CH2 group in formalde-
hyde-O-prop-2-ynyl oxime (1) (Scheme 1). Since our attempts to
grow single crystals suitable for X-ray analysis resulted in assem-
blies of microcrystals, structure determination of 3 and 4 was
accomplished from PXRD analysis. To examine the contribution and
influence of intermolecular interactions on crystal packing, the
Hirshfeld surfaces [27], associated 2D fingerprint plots [28] and
enrichment ratios [29] have been calculated for the listed com-
pounds and some related systems retrieved from the CSD. The
intermolecular interactions in 2e4 have been correlated with the
MEP surface analysis. The study also includes electronic structures
of 2e4 via DFT calculations. It should be noted that the present
contribution is the second example of propargyloxime aldehyde/
ketone after 2-methyl-N-(prop-2-yn-1-yloxy)-5,6-dihydro-1,3-
benzothiazol-7(4H)-imine (COWXET) [19], available in the CSD.
2.3. Spectroscopic data
2.3.1. (E)-3-Methoxy-4-(prop-2-ynyloxy)-benzaldehyde-O-prop-2-
ynyl oxime (C14H13NO3) (2)
Colorless solid; yield 90%; mp 91(1) ꢀC; mass (m/z) 243 (Mþ,
100%); 1H NMR (400 MHz, CDCl3):
d 8.07 (s, 1H), 7.27 (d, J 1.8 Hz,
1H), 7.06e7.00 (m, 2H), 4.79 (d, J 2.2 Hz, 2H), 4.77 (d, J 2.2 Hz, 2H),
3.93 (s, 3H), 2.54 (t, J 2.2 Hz, 1H), 2.52 (t, J 2.2 Hz, 1H); 13C NMR
(100 MHz, DMSO-d6): d 149.7, 149.2, 148.3, 124.9, 120.9, 113.5, 109.0,
80.2, 78.9, 78.5, 77.4, 61.1, 55.9, 55.4; elemental analysis: found C
69.25, H 5.40, N 5.69%, calculated for C14H13NO3: C 69.13, H 5.36, N
5.76%.
2. Experimental section
2.1. Materials and general methods
2.3.2. Benzophenone-O-prop-2-ynyl oxime (C16H13NO) (3)
Colorless solid; yield 98%; mp 61(1) ꢀC; mass (m/z) 236 (Mþ,
All chemicals were obtained from commercial sources. Solvents
were dried using standard methods, and chromatographic purifi-
cation was performed using silica gel (100e200 mesh). Elemental
analysis was carried out with a Perkin-Elmer 240C elemental
analyzer. Fourier-transform infrared (FTIR) spectra were measured
as KBr pellets using a Perkin-Elmer RX1 spectrometer. 1H and 13C
NMR spectra (300 MHz and 400 MHz) were recorded at 25 ꢀC on a
Varian-Gemini 300/400 MHz spectrometer using CDCl3/DMSO-d6
as solvent. Melting points were determined by open glass capillary
method with a Sisco melting point apparatus and were uncorrec-
ted. Mass spectra were recorded on a HP 5989 instrument with
electron ionization potential 70 eV. Reactions were monitored by
thin layer chromatography (TLC) on pre-coated silica gel plates.
100%); 1H NMR (400 MHz, CDCl3):
d 7.51e7.49 (m, 2H), 7.44e7.41
(m, 3H), 7.39e7.25 (m, 5H), 4.76 (d, J 2.4 Hz, 2H), 2.46 (t, J 2.4 Hz,
1H), 13C NMR (100 MHz, CDCl3):
d 158.3, 136.1, 132.9, 129.6, 129.0,
128.3, 80.0, 74.4, 61.9, IR (KBr) nmax/cmꢂ1: 3283, 3063, 3029, 2919,
1493, 1444, 1424, 1355, 1328, 1053, 1003, 967, 922, 862, 773, 692;
elemental analysis: found C 81.52, H 5.47, N 5.88%, calculated for
C16H13NO: C 81.70, H 5.53, N 5.96%.
2.3.3. (E)-2-Chloro-6-methylquinoline-3-carbaldehyde-O-prop-2-
ynyl oxime (C14H11ClN2O) (4)
Colorless solid; yield 93%; mp 125(1) ꢀC; mass (m/z) 259 (Mþ,
100%); 1H NMR (400 MHz, CDCl3):
d 8.61 (s, 1H), 8.60 (s,1H), 7.89 (d,
J 8.4 Hz, 1H), 7.61 (d, J 10.8 Hz, 1H), 7.58 (d, J 2.0 Hz, 1H), 4.85 (d, J
2.4 Hz, 2H), 2.56 (t, J 2.4 Hz, 1H), 2.18 (s, 3H); 13C NMR (100 MHz,
2.2. Synthesis
CDCl3):
d 148.0, 146.5, 146.4, 137.7, 135.3, 133.8, 127.9, 127.0, 126.8,
123.7, 79.1, 75.1, 62.2, 21.6, IR (KBr) nmax/cmꢂ1: 3273, 3061, 2920,
1625, 1600, 1500, 1225, 1120, 830; elemental analysis: found C
64.91, H 4.19, N 10.88%, calculated for C14H11ClN2O: C 65.00, H 4.26,
N 10.83%.
Primary oximes (2b, 3b and 4b) were synthesized by treating
corresponding aldehydes (2a and 4a, 1 mmol) or ketone (3a,
1 mmol) with hydroxyl amine hydrochloride (1.2 mmol) and so-
dium hydroxide (5 mmol) in ethanol (5 mL) at 25 ꢀC followed by
neutralization with acid. Crude oximes, thus obtained, were filtered
and used without further purification. For the synthesis of com-
pounds 2, 3 and 4 (Scheme 2), equi-molar quantities of corre-
sponding oximes (1 mmol of 2b, 3b and 4b), anhydrous potassium
carbonate (0.14 g, 1 mmol) and propargyl bromide (0.12 g, 1 mmol)
were added to 15 mL of dry acetone and the resulting mixture was
refluxed with vigorous magnetic stirring under anhydrous
2.4. Single crystal X-ray analysis of C14H13NO3 (2)
Single crystal suitable for X-ray structure analysis was obtained
by slow evaporation of a solution of 2 in a mixture of ethyl acetate
and isopropyl alcohol (2:1). Intensity data were collected at 293(2)
K on a Bruker Smart APEX II CCD area detector using graphite
monochromated Mo K
a
radiation(
l
¼ 0.7107 Å). Data reduction
was performed with SAINT [30] and an absorption correction was
applied using SADABS [31]. The crystal structure was solved by
direct methods with SHELXS97 [32] and refined using SHELXL97
[32] with anisotropic displacement parameters for all non-
hydrogen atoms. The positions of hydrogen atoms were located
from difference Fourier maps and refined with isotropic displace-
ment parameters. The molecular view and crystal packing diagrams
were generated using the Mercury (version 3.8) program [33].
Geometrical calculations were carried out with PLATON [34].
Scheme 1. Chemical diagram of formaldehyde O-prop-2-ynyl oxime (1).

T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
617
Scheme 2. Synthesis of C14H13NO3 (2), C16H13NO (3) and C14H11ClN2O (4).
2.5. X-ray powder diffraction analysis of C16H13NO (3) and
as the initial structural models of 3 and 4 for Rietveld refinement
[37], which was carried out using the GSAS program [38]. A pseudo-
Voigt peak profile function was used during refinement and the
background of the PXRD patterns of 3 and 4 was modeled by a
shifted Chebyshev function of the first kind with 20 points regularly
C
14H11ClN2O (4)
Powder X-ray diffraction (PXRD) data of 3 and 4 were recorded
at ambient temperature [293(2) K] using a Bruker D8 Advance
diffractometer operating in the Bragg-Brentano geometry, with Cu
distributed over the entire 2q range. The profile parameters were
K
a
radiation (
l
¼ 1.5418 Å). The PXRD patterns of 3 and 4 were
refined initially followed by the refinement of positional co-
ordinates of all non-hydrogen atoms. Standard restraints were
applied to bond lengths and bond angles, and planar restraints
were used for phenyl and quinoline groups. While the refinement
of a common isotropic displacement parameter (Uiso) for all non-
hydrogen atoms in 4 was successful, the corresponding refine-
ment of 3 diverged, which indicated possibility of wrong space
group assignment. Structure solution of 3 was repeated in space
group P21 with two molecules in the asymmetric unit and the
refinement of common Uiso values for non-hydrogen atoms
converged successfully in the non-centrosymmetric space group.
Hydrogen atoms in molecules of 3 and 4 were placed in calculated
positions with fixed Uiso values. In the final stages of refinement, a
preferred orientation correction (generalised spherical harmonic
model) was applied. The final Rietveld plots of 3 and 4 (Fig. 1)
showed good agreement between the observed PXRD profile and
indexed using EXPO 2014 [35] into monoclinic (in 3) and triclinic
(in 4) unit cells. Given the volume of the unit cell and consideration
of density, the number of formula units in the unit cell of 3 and 4
turned out as 4 (in 3) and 2 (in 4), respectively. Although the correct
space group for 3 could not be assigned unambiguously on the basis
of systematic absences, statistical analysis of PXRD data using the
FINDSPACE module of EXPO 2014 [35] indicated probable space
group as P21/n. The space group chosen for 4 was P1. Structure
solution of 3 and 4 was carried out by global optimization of
structural models in direct space, based on a Monte-carlo search
using the simulated annealing technique (in parallel tempering
mode), as implemented in the program FOX [11]. The optimization
of isolated molecules was performed using the energy gradient
method as incorporated in MOPAC 9.0 [36].
The best solution (i.e., structure with the lowest Rwp) was used

618
T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
Fig. 1. Final Rietveld plots of C16H13NO (3) and C14H11ClN2O (4). The intensity in the high angle region has been multiplied by a factor 10.
calculated powder diffraction pattern. The molecular views of 2e4
with atom labeling scheme are shown in Fig. 2. A summary of
crystal data and relevant refinement parameters for 2e4 is listed in
Table 1.
2.6. Hirshfeld surface analysis
The Hirshfeld surfaces [39] and associated 2D fingerprint plots
[28] were calculated using Crystal Explorer [40]. Bond lengths to
hydrogen atoms were set to typical neutron values (CeH ¼ 1.083 Å
and NeH ¼ 1.009 Å). For each point on the Hirshfeld isosurface, two
distances de, the distance from the point to the nearest nucleus
external to the surface, and di, the distance to the nearest nucleus
internal to the surface, are defined. The normalized contact dis-
tance (dnorm) based on de and di is given by
di ꢂ rvi dW
de ꢂ rvedW
dnorm
¼
þ
(1)
rvedW
rvi dW
where rvi dW and revdW are the van der Waals radii of the atoms. The
value of dnorm can be negative or positive depending on whether
the intermolecular contacts are shorter or longer than the van der
Waals separations. The parameter dnorm displays a surface with a
redewhiteeblue color scheme, where the bright red spots high-
light shorter contacts, the white areas represent contacts around
the van der Waals separation, and the blue regions are devoid of
close contacts.
2.7. Electrostatic potential calculation
The molecular electrostatic potential (MEP) is an effective tool
for identifying and ranking the hydrogen bond donating and
accepting sites in organic compounds [27,30]. The electrostatic
!
potential at any point r in the space surrounding a molecule can be
expressed by
ꢁ
ꢂ
!
r0 dr0
Z
r
X
ZA
!
Vð r Þ ¼
ꢂ
(2)
r ꢂ !r0 j
!
jꢀR!A ꢂ r
j
!
A
j
ꢀ!
!
where ZA is the charge of the nucleus A located at RA and
r
ð r Þ is
!
the molecular electron density function. The sign of Vð r Þ at a
particular region depends upon whether the effect of the nucleus or
the electrons is dominant there. The MEP surfaces of 2e4 were
generated with BLYP [41,42] correlation functional and a double
numeric plus polarization (DNP) basis set using isolated molecule
DFT calculations. All calculations including the electron densities
and esp charges were carried out using the Dmol3 code [43]. The
starting atomic coordinates for property calculations were obtained
by geometry optimization of structures from the final X-ray
Fig. 2. Molecular views with atom labeling scheme for C14H13NO3 (2), C16H13NO (3)
and C14H11ClN2O (4).

T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
619
Table 1
Crystal data and structure refinement parameters for C14H13NO3 (2), C16H13NO (3) and C14H11ClN2O (4).
Chemical formula
Mol. Wt.
C14H13NO3(2)
243.26
C16H13NO(3)
235.27
C14H11ClN2O(4)
258.70
Temperature (K)
Wavelength (Å)
Crystal system
a (Å)
b (Å)
c (Å)
293(2)
0.7107
293(2)
1.5418
293(2)
1.5418
Triclinic
6.9005(2)
9.9146(5)
10.4540(5)
109.628(2)
95.317(4)
100.980(4)
651.8(1)
Monoclinic
25.844(3)
4.1166(4)
24.109(3)
90
95.531(3)
90
2553.0(5)
C2/c, 8
Monoclinic
20.0296(14)
5.9291(4)
11.3749(7)
90
98.881(3)
90
1334.7(2)
P21, 4
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
Volume (Å3)
Space group, Z
P1, 2
Density (g/mL)
1.266
0.090
1.171
0.577
1.318
2.503
m
(mmꢂ1
)
F (000)
Refinement
range (ꢀ)
1024
496
268
Full matrix least squares
3.16 to 50.00
0.180 and ꢂ0.173
0.0421
0.1207
1.160
Rietveld method
7.00 to 100.00
Rietveld method
7.00 to 100.00
2
q
Largest peak and hole (e/Å3)
R1(all data)/Rp
0.0430
0.0582, 0.0901
4.772
0.0226
0.0309, 0.0639
1.132
wR2(all data)/Rwp, R(F2)
GOF/c2
refinement cycles of 2e4 in the solid state with the same correla-
tion functional and basis set. The dispersion correction was carried
out with DFT-D approach using the TS scheme [44]. The electro-
static potentials were plotted on 0.017 au electron density isosur-
face [45]. The MEP surfaces have been mapped with a rainbow color
scheme with red representing the highest negative potential region
while blue representing the highest positive potential region.
3. Results and discussion
3.1. Structure description
In the title compounds (2e4), one hydrogen atom of the ter-
minal CH2 group of formaldehyde O-prop-2-ynyl oxime (1) has
been replaced by a substituted phenyl ring in 2 and a chlor-
omethylquinoline moiety in 4, while in 3, both CH2 hydrogen atoms
of 1 have been substituted by benzene rings. The E configuration of
molecules has been established by the torsion angle O1-N1-C4-C5
of 177.3(1)ꢀ in 2 and -178.8(6)ꢀ in 4. The linear propyne groups
(C12-C14 atoms in 2 and C1-C3 atoms in 4) are inclined to the
planar cyclic fragment of molecules; the dihedral angle between
the least-squares plane defined by C4-C10/O2/O3 atoms and the
least-squares line through C12-C14 atoms in 2 is 57.0(1)ꢀ; the cor-
responding angle between the planar (C4-C14/N2/Cl1 atoms) and
linear (C1-C3 atoms) fragments is 69.4(2)ꢀ in 4. Two molecules (A
and B) in the asymmetric unit of 3 are related by a pseudo inversion
center about (0.243, 0.348, 0.252). A superposition of two mole-
cules A and B in 3 (Fig. 3) reveals an almost identical conformation
except the linear prop-2-ynyl fragment. This observation is
consistent with the fact that although it was possible to obtain a
model structure of 3 in the space group P21/n, the same could not
be refined in the centrosymmetric space group (Uiso values of some
of the non-hydrogen atoms were unrealistically large). The oxime-
bridged phenyl rings in 3 are inclined to each other by 86.6(3)ꢀ in A
and 89.1(3)ꢀ in B. The orientation of the prop-2-ynyl oxime moiety
with respect to the benzene rings in A and B is established by the
torsion angles O1A-N1A-C4A-C5A of ꢂ158.3(11)ꢀ, N1A-C4A-C5A-
C6A of ꢂ19.6(11)ꢀ, O1B-N1B-C4B-C5B of 168.6(12)ꢀ and N1B-C4B-
C5B-C6B of 30.3(15)ꢀ, respectively. An overlay of molecular con-
formations of 2e4 as determined by the X-ray analysis and theo-
retical calculations (solid state DFT) is shown in Fig. 4. The r.m.s.
deviations between the geometrically optimized bond lengths,
Fig. 3. Overlay of two molecules (pink: A, black: B) in the asymmetric unit of C16H13NO
(3). (For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
bond angles (Table S1) and the corresponding crystallographically
determined values are 0.02 Å, 0.5ꢀ in 2, 0.02 Å, 1.7ꢀ in 3A/3B and
0.03 Å, 2.2ꢀ in 4. Close agreement between the X-ray analyzed
structure and that obtained via quantum-mechanical calculations
probably indicates that the compounds studied are stable
conformers.
3.2. Crystal packing analysis
The crystal packing in 2e4 exhibits weak intermolecular
CeH/O, CeH/N, CeH/Cl and CeH/p hydrogen bonds and
p
$$$ interactions (Table 2). While the intermolecular C1eH1/O2
p
hydrogen bond connects molecules of 2 into a one-dimensional
C11(11) chain, the C14eH14/O1 hydrogen bonds form a spiral col-
umn along the [010] direction. The combination of polymeric chain
and column generates a fused two-dimensional columnar structure
propagating along the ½110ꢃ direction in 2 (Fig. 5). The molecules A
and B in the asymmetric unit of 3 are linked through CeH/
p
hydrogen bonds (Table 2) to form a one-dimensional chain along

620
T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
dimensional framework. The interplanar spacing between parallel
quinoline rings (C5-C13, N2 atoms) is 3.539(1) Å with ring-centroid
separations for two heterocyclic six-membered rings (P: C5-C9, N2
atoms) of 3.896(1) Å, and between ring P and phenyl moiety (Q: C7,
C8, C10-C13 atoms) of 3.953(1) Å. The corresponding centroid offset
values for P:P and P:Q are 1.629 Å and 1.761 Å, respectively. The
Hirshfeld surfaces of 2e4 are illustrated in Fig. 8. The red spots
labeled as ‘a/a0’ in Fig. 8(i) and ‘b0’ in Fig. 8(ii) are due to CeH/O (in
2) and CeH/N (in 4) hydrogen bonds. Other visible red patches (c/
c0) in Fig. 8(ii) correspond to CeH/Cl interaction in 4. The Hirshfeld
surfaces for molecules A and B in 3, Fig. 8(iii), are devoid of any
significant red spots, which is consistent with Table 2 showing only
weak CeH/p interactions. In the 2D fingerprint plot, Fig. 9(i), two
sharp spikes (‘a’ and ‘a0’) of almost equal length in the region 2.2
<de þ di < 2.6 Å are characteristic of C1eH1/O2 bonded C11(11)
chain in 2. The spikes due to C14eH14/O1 hydrogen bond in 2 are
masked within the spikes a/a0 in Fig. 9(i). The corresponding
C1eH1/N2 interactions in 4 appear as sharp spikes (labeled as ‘b’
and ‘b0’) in the region 2.3 <de þ di < 2.8 Å in Fig. 9(ii). Additional
spikes (‘c’ and ‘c0’) in Fig. 9(ii) are attributable to the CeH/Cl
interaction in 4. An intense green patch in the central part of
Fig. 9(ii) represents
p$$$p interactions [27] in 4. Lack of any C/
NeH/O hydrogen bond in 3 is reflected in the absence of sharp
spike in Fig. 9(iii). The wings marked with black circles in Fig. 9(iii)
represent the CeH/p interactions in 3A and 3B. The intermolec-
ular H/H contacts comprising of 50.7% in 3A and 52.4% in 3B of the
total number of contacts, are major contributors to the crystal
packing in 3. This is reflected by the central spikes extending up to
(di, de) region of (1.0 Å, 1.0 Å) in 3A and 3B.
The enrichment ratio (E) [29], which is defined as the ratio be-
tween the proportion of actual contacts in the crystal and the
Fig. 4. Superposition of molecular conformations as obtained from X-ray structure
analysis (blue) and solid state DFT calculation (magenta) for C14H13NO3 (2), C16H13NO
(3) and C14H11ClN2O (4). (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
Table 2
Hydrogen bonds and
p/p interactions in C14H13NO3 (2), C16H13NO (3) and C14H11ClN2O (4).
Interaction
D-H/Å
H/A/Å
D/A/Å
D-H/A/ꢀ
Symmetry code
C14H13NO3 (2)
C6-H6-N1
C1-H1/O2
C14-H14/O1
C1-H1/O3
C12-H12B/O3
0.96(2)
0.94(2)
0.89(2)
0.94(2)
0.97(2)
2.63(2)
2.38(2)
2.44(3)
2.62(2)
2.71(2)
2.905(2)
3.278(2)
3.251(2)
3.380(2)
3.589(2)
97(1)
x, y, z
161(2)
152(2)
138(2)
151(1)
1/2 þ x, ꢂ1/2 þ y, z
1/2-x, 1/2 þ y, 1/2ꢂz
1/2 þ x, ꢂ1/2 þ y, z
x, ꢂ1þy, z
C
16H13NO (3)
C6A-H6A/N1A
C6B-H6B/N1B
C3A-H3A1/Cg(4)
C3B-H3B1/Cg(2)
C15A-H15A/Cg(3)
C15B-H15B/Cg(1)
0.93
0.93
0.93
0.93
0.93
0.93
2.59
2.67
2.90
2.84
2.99
2.71
2.883(15)
2.929(18)
98
97
158
133
154
159
x, y, z
x, y, z
x, y, ꢂ1þz
x, y, 1 þ z
x, y, z
x, y, z
Cg(1) ¼ C5A-C10A; Cg(2) ¼ C11A-C16A; Cg(3) ¼ C5B-C10B; Cg(4) ¼ C11B-C16B
C
14H11ClN2O (4)
C6-H6/N1
C1-H1/N2
C3-H3B/Cl1
Cg(1)/Cg(1)
Cg(1)/Cg(1)
Cg(1)/Cg(2)
Cg(1)/Cg(2)
0.93
0.94
0.95
2.54
2.44
2.81
2.824(6)
3.246(6)
3.537(4)
3.836(1)
3.896(1)
3.732(1)
3.953(1)
98
144
134
x, y, z
ꢂ1þx, ꢂ1þy, z
ꢂx, ꢂy, ꢂz
ꢂx, 1ꢂy, 1ꢂz
1ꢂx, 1ꢂy, 1ꢂz
ꢂx, 1ꢂy, 1ꢂz
1ꢂx, 1ꢂy, 1ꢂz
Cg(1): N2, C5-C9 atoms; Cg(2): C7, C8, C10-C13 atoms
the [001] direction (Fig. 6). In 4, the centrosymmetrically related
molecules are joined via pair of CeH/Cl hydrogen bonds forming a
cyclic ring with an R22(16) graph-set motif [46]. The propagation of
R22(16) synthon through intermolecular C1eH1/N2 hydrogen
bonds generates a one-dimensional chain with fused R22(16) and
R44(16) rings along the [110] direction (Fig. 7). The chains in 4 are
theoretical proportion of random contacts, has been determined for
the intermolecular contacts in 2, 3 (for two independent molecules
A and B) and 4 (Table S2) to study the propensity of two chemical
species to be in contact. The value of E is greater than unity for pair
of elements with higher propensity to form contacts, while pairs
which tend to avoid contacts yield E values less than unity. In 2, the
total Hirshfeld surface area is dominated by H/H and H/C
weakly linked by aromatic p$$$p interactions (Table 2) into a three-

T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
621
Fig. 5. Two dimensional columnar architecture formed by CeH/O hydrogen bonds in C14H13NO3 (2).
Fig. 6. One dimensional molecular ribbon formed by CeH$$$
p hydrogen bonds in C16H13NO (3).
Fig. 7. One dimensional molecular chain formed by CeH/N and CeH/Cl hydrogen bonds in C14H11ClN2O (4).
contacts, comprising of 38.4% and 33.9%, respectively. The corre-
sponding enrichment ratios, however, show an increased pro-
pensity of H/C contacts to form (EHC ¼ 1.15), and the H/H
contacts are less favored (EHH ¼ 0.88). It should be noted that H/O
contacts are more favored in 2 (EHO ¼ 1.35). This is consistent with
the crystallographic results showing all three oxygen atoms (O1-
O3) participating in intermolecular hydrogen bond in 2 (Table 2).
The EHH values of 0.90 in 3A and 0.91 in 3B, indicate an almost
identical propensity to form H/H contacts for two crystallo-
graphically independent molecules in 3, and these contacts
contribute about 50% of the total Hirshfeld surface (Fig. 10). Slightly
increased propensity to form H/C and H/N contacts has been
observed in 3A (EHC ¼ 1.29 and EHN ¼ 1.26) compared to that in 3B
(EHC ¼ 1.27 and EHN ¼ 1.23). This can be attributed to marginally
higher percentage of H/C and H/N contacts to the total surface
area in 3A that in 3B, and an almost identical random contacts for

622
T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
both molecules in 3. The EHO values for two independent molecules
in 3 with identical random contacts (RHO ¼ 3.3%) are larger than
unity (1.36 and 1.33), indicating that H/O contacts have an
increased propensity to form. The distribution of main intermo-
lecular contacts on the total Hirshfeld surface area of 4 is similar viz.
H/C (18.9%), H/Cl (15.7%), C/C (10.8%), H/N (10.0%) and H/O
(6.2%) except H/H contacts, which appear to be the major
contributor (34.9%). The enrichment ratios reveal that H/H
(EHH ¼ 0.96), H/N (EHN ¼ 1.35), H/Cl (EHCl ¼ 1.51) and H/O
(EHO ¼ 1.68) contacts are more favored, and C/C contacts with
ECC ¼ 2.25 are even more favored in 4. High enrichment ratio for
C/C contacts (ECC ¼ 2.25) is a consequence of several
teractions in 4 (Table 2).
p$$$p in-
The relative contribution of different interactions to the Hirsh-
feld surfaces of 2e4 as well as a few closely related oxime derivatives
(Tables S3eS9) retrieved from the CSD such as, (E)-4-hydroxy-3-
methoxybenzaldehyde oxime (VIMRUE) [47], (E)-phenyl(m-tolyl)
methanone O-methyl oxime (HIFYIG) [48], benzophenone oxime
(XULKUK) [19] and 6-chloro-3-ethyl-4-isobutylisoxazolo [4,5-c]
quinoline (NOLCUN) [49] is shown in Fig. 10. Due to replacement of
both hydroxyl H atoms in VIMRUE by propargyl (-CH2CCH) groups in
2, the H/O contribution to the Hirshfeld surface reduces from 23.0%
in VIMRUE to 15.8% in 2 with a corresponding increase in the H/C
interactions from 18.8% in VIMRUE to 33.9% in 2. The compound 3
bears a close structural resemblance with benzophenone oxime
(XULKUK). With different substitutions in the XULKUK skeleton, a
Fig. 8. Hirshfeld surfaces of (i) C14H13NO3 (2), (ii) C14H11ClN2O (4) and (iii) C16H13NO
(3).
Fig. 9. Fingerprint plots of (i) C14H13NO3 (2), (ii) C14H11ClN2O (4) and (iii) C16H13NO (3).

T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
623
Fig. 10. Relative contribution of different interactions to the Hirshfeld surfaces of C14H13NO3 (2), C16H13NO (3) and C14H11ClN2O (4) and a few related structures from the CSD.
propargyl group replacing the hydroxyl H atom of XULKUK in 3 and
that a methyl group in HIFYIG, the molecular interactions are pre-
dominantly of H/H and H/C types, which can account for about
85% (82.7e88.4% in XULKUK, 89.2e90.1% in 3, and 89.1e89.5% in
HIFYIG) of the Hirshfeld surface area. Incidentally, these three
benzophenoneoxime compounds crystallized with Z' ¼ 2.
H14 in 2, H1A in 3A, H1B in 3B and H1 in 4) carry most positive
charge among the hydrogen atoms due to electron withdrawing
nature of adjacent alkyne carbon atoms. Due to this charge redis-
tribution, the dipole moments of 2, 3A, 3B and 4 are 0.57, 0.32, 0.29
and 1.57 a.u., respectively. The electrostatic potential maxima and
minima (Vs,max, Vs,min) associated with different donor and acceptor
atoms can serve as good indicators of hydrogen bond validation in
2e4. While the alkyne hydrogen atoms in 2 (H1 and H14) are
associated with two most positive potential values of 45 and
40 kcal/mol, respectively, the phenoxy O2 and O3 atoms corre-
spond to the maximum negative potential of ꢂ40 kcal/mol. Other
relatively high positive/negative potentials in 2 around H12A
(31 kcal/mol), H12B (30 kcal/mol) and N1 (ꢂ28 KCal/mol) atoms are
attributable to intra/intermolecular interactions involving these
atoms. This is consistent with hydrogen bonds in 2 (Table 2) ob-
tained via crystallographic analysis. In 3, the two most negative
potentials (Vs,min) associated with molecules 3A (ꢂ35 kcal/mol for
N1A and ꢂ32 kcal/mol for O1A) and 3B (ꢂ34 kcal/mol for N1B
and ꢂ32 kcal/mol for O1B) are due to intramolecular CeH/O and
CeH/N interactions. The corresponding positive potentials
(Vs,max) around the hydrogen atoms involved in intramolecular
interactions are 21, 20, 18 and 18 kcal/mol for H3B2, H3A2, H12A
and H12B, respectively. The presence of negative potentials asso-
ciated with centers of phenyl rings viz, C5A-C10A (ꢂ16 kcal/mol),
C11A-C16A (ꢂ20 kcal/mol), C5B-C10B (ꢂ16 kcal/mol), C11B-C16B
(ꢂ19 kcal/mol) and H3A1 (26 kcal/mol), H3B1 (25 kcal/mol),
H15A (22 kcal/mol), H15B (22 kcal/mol) can be rationalized in
3.3. Molecular electrostatic potential
The MEP surfaces of 2e4 (Fig. 11) have been analyzed in terms of
intra- and inter-molecular hydrogen bonds. The MEP derived
charges with the density functional BLYP using DMol3 program
indicated negative charges on the oxygen (O1-O3) and nitrogen (N1
and N2) atoms. The terminal H atoms of the propargyl group (H1,
terms of C-H …
p interactions in 3. It should, however, be noted
that the alkyne hydrogen atom (H1A and H1B) in both molecules of
3 with highest positive potential of 39 kcal/mol for 3A and 3B does
not participate in hydrogen bond. In 4, the hydrogen bond acceptor
is characterized by the most negative potential around the quino-
line N2 atom (ꢂ39 kcal/mol) and the corresponding donor atom
(alkyne H1) is linked with the maximum positive potential of
43 kcal/mol. The relatively moderate negative potentials around O1
(ꢂ24 kcal/mol) and N1 (ꢂ22 kcal/mol) atoms are due to intra-
molecular hydrogen bonds in 4. The chlorine atom (Cl1) in 4,
associated with slightly negative potential (ꢂ4 kcal/mol), acts as a
weak acceptor and forms weak intermolecular interaction with
Fig. 11. MEP surfaces of C14H13NO3 (2), C16H13NO (3) and C14H11ClN2O (4).

624
T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
H3B; the corresponding positive potential around H3B atom is
29 kcal/mol (Table S10).
atom, adjacent CeC bond and the two benzene rings, while the
HOMO and HOMO-1 level contributions are on the O1 atom and
N1eC4 bond in addition to the phenyl rings. A striking feature in
the electronic structure of 3 is the occurrence of almost degenerate
states for both HOMO and LUMO levels. Since no symmetry con-
straints are imposed in such a large molecular structure, both
HOMO and LUMO levels can be considered degenerate [50]. This
reflects the fact that the inherent symmetry is preserved and the
energy levels are not split. Consequently a higher HOMO-LUMO gap
is expected for 3 than that of 2 and 4.
Energy eigen values EHOMO and ELUMO calculated using a BLYP
correlation functional are ꢂ4.71 and ꢂ1.74 eV in 2, ꢂ5.16
and ꢂ1.82 eV in 3 and ꢂ5.51 and ꢂ2.78 eV in 4, which indicate that
the energy gap of 3.34 eV in 3 as the highest among the three oxime
ether derivatives. It is widely accepted that the energy difference
between HOMO and LUMO can be considered as a rough estimate
of band gap i.e. the transition energy required to excite electrons
from the ground state to the first dipole-allowed excited state
[51,52]. The band gap in 3 with both aldehyde hydrogen atoms of
formaldehyde O-prop-2-ynyl oxime (1) being substituted by two
benzene rings is higher by 0.37 eV/0.61 eV than that of 2 and 4, in
which only one aldehyde hydrogen atom of 1 has been replaced by
a substituted phenyl or quinoline moiety. This behavior is consis-
tent with the expected higher reactivity of aldoximes compared to
3.4. Electronic structure
The frontier molecular orbitals HOMO (highest occupied mo-
lecular orbital), LUMO (lowest unoccupied molecular orbital),
HOMO-1 (second highest occupied molecular orbital) and LUMOþ1
(second lowest unoccupied state) of 2e4 are depicted in Fig. 12,
where colors on the isosurface are to distinguish the phase of the
wave function. These frontier orbitals are the most involved states
in electronic transitions. With substituted phenyl (in 2) and quin-
oline (in 4) rings replacing one of the hydrogen atoms of the CH2
group in formaldehyde O-prop-2-ynyl oxime (1) skeleton, the
HOMO electrons in 2e4 are mostly localized on the oxygen (O1-O3
in 2 and O1 in 4) and quinoline nitrogen (N2 in 4) atoms in addition
to the CeC bonds of the aromatic rings showing bonding-
antibonding patterns characteristic of a
p-conjugated ring sys-
tem. The occupied levels have a bonding character on the C4eN1
double bond. The prop-2-ynyl chain (eCH2eC^CH) in 2e4 had
hardly any HOMO or LUMO population. The LUMO level in 2 and 4
has more contributions to the N1 atom, C4eC5 bond as well as the
ring atoms (C6, C8, C10 in 2 and N2, C6, C8, C10, C12, C13 in 4). In 3,
both hydrogen atoms of the CH2 group in 1 have been replaced by
phenyl rings, thus making the molecule approximately symmetric
about the C4eN1 bond. The frontier orbitals of 3 shown in Fig. 12
indicate that the LUMO and LUMOþ1 levels are located on the N1
ketoximes [53]. The chemical potential (
(EHOMO þ ELUMO)/2, is ꢂ3.2, ꢂ3.5 and ꢂ4.1 eV for 2, 3 and 4,
respectively. High HOMO-LUMO energy difference and negative
m), expressed as
m
¼
m
Fig. 12. Molecular orbitals of C14H13NO3 (2), C16H13NO (3) and C14H11ClN2O (4).

T. Dey et al. / Journal of Molecular Structure 1137 (2017) 615e625
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Acknowledgements
The authors thank Mr. Rajdip Roy, Department of Organic
Chemistry, IACS, Kolkata-700032, India, for helping in single crystal
X-ray data collection of 2. Financial support from the Council for
Scientific and Industrial Research, New Delhi, India, for a senior
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