Synthesis, crystallographic characterization, DFT and TD-DFT studies of Oxyma-sulfonate esters

Article abstract of DOI:10.1007/s12039-017-1354-7

Abstract: Three oxyma sulfonate esters were prepared using dichloromethane-water (two-phase method) in the presence of sodium carbonate for scavenging HCl. The products were characterized by FT-IR, NMR (¹H and ¹³C), UV-Vis spectra and elemental analysis. X-ray single crystal diffraction experiments proved the molecular structures of three esters. Their molecular structures were also calculated using DFT/B3LYP method. The optimized structures agreed well with the X-ray structures. Time-dependent density functional theory (TD-DFT) was used to assign the electronic absorption bands observed experimentally. Pyridine derivative showed two bands at shorter λ _max compared to the others, both experimentally and theoretically. The NMR chemical shifts were computed for protons and carbons using GIAO method, which correlated well with the experimental data. Natural charges, dipole moments and chemical reactivity of these molecules, as well as their non-linear optical activity, were computed and compared. Graphical Abstract:: SYNOPSIS An eco-friendly method was used to synthesise three oxyma-sulfonate esters using two-phase (dichloromethane-water) method in presence of sodium carbonate for scavenging HCl. The oxyma sulfonate esters were characterized using different spectroscopic techniques (FT-IR, NMR, UV-Vis) as well as X-ray single crystal diffraction analysis. The electronic and spectroscopic properties of these esters were computed using DFT/B3LYP method[Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-017-1354-7

J. Chem. Sci.
© Indian Academy of Sciences
DOI 10.1007/s12039-017-1354-7
REGULAR ARTICLE
Synthesis, crystallographic characterization, DFT and TD-DFT
studies of Oxyma-sulfonate esters
SAIED M SOLIMANa,b,∗, HAZEM A GHABBOURc,d, SHERINE N KHATTABb,
MOHAMMED R H SIDDIQUIe and AYMAN EL-FAHAMb,e,∗
aDepartment of Chemistry, Rabigh College of Science and Art, King Abdulaziz University, P.O. Box 344,
Rabigh 21911, Saudi Arabia
bDepartment of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria
21321, Egypt
cDepartment of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi
Arabia
dDepartment of Medicinal Chemistry, Faculty of Pharmacy, University of Mansoura, Mansoura 35516, Egypt
eDepartment of Chemistry, College of Science, King Saud University, P. O. Box 2455, Riyadh 11451, Saudi
Arabia
E-mail: Saied1soliman@yahoo.com; aymanel_faham@hotmail.com
MS received 8 March 2017; revised 19 June 2017; accepted 7 July 2017
Abstract. Three oxyma sulfonate esters were prepared using dichloromethane-water (two-phase method) in
the presence of sodium carbonate for scavenging HCl. The products were characterized by FT-IR, NMR (1H and
13C), UV-Vis spectra and elemental analysis. X-ray single crystal diffraction experiments proved the molecular
structures of three esters. Their molecular structures were also calculated using DFT/B3LYP method. The
optimized structures agreed well with the X-ray structures. Time-dependent density functional theory (TD-
DFT) was used to assign the electronic absorption bands observed experimentally. Pyridine derivative showed
two bands at shorter
compared to the others, both experimentally and theoretically. The NMR chemical
λ
max
shifts were computed for protons and carbons using GIAO method, which correlated well with the experimental
data. Natural charges, dipole moments and chemical reactivity of these molecules, as well as their non-linear
optical activity, were computed and compared.
Keywords. Oxyma; sulfonate ester; X-ray crystallography; TD-DFT; NLO; NBO.
1. Introduction
ditions or severe conditions such as using trifluo-
romethanesulfonic anhydride (TfO). Recently milder
and more efficient method for the synthesis of sul-
fonamide by activating sulfonic acid group to the
corresponding sulfonate ester of the ethyl 2-cyano-
2-(hydroxyimino)acetate (Oxyma, 1; Figure 1) was
reported.3
Sulfonate ester of 1-hydroxybenzotriazole (HOBt 2)
derivatives has been synthesized and used for peptide
coupling.9,10 The reactivity of these sulfonate esters was
affected by the presence of electron-withdrawing sub-
stituent in both the benzotriazole and the sulfonic acid
moieties.11–14 Later, 7-Aza-1-hydroxybenzotriazole
(HOAt 3)has been reported to be more efficient than
HOBt 2 due to the electronic effect caused by the pyri-
dine ring.15,16 Because of the explosive report of HOBt3
Sulfonate esters are considered as important precur-
sors for the synthesis of sulfonamides, which exhibit
a wide range of biological activities.1,2 The differ-
ences in their reactivity have been exploited in selective
sulfonamide formation.3 A comprehensive literature
survey of the synthesis of sulfonamides revealed sev-
eral synthetic strategies, which includes the methods
for activation of the sulfonic acids to the correspond-
ing 3-methylimidazoliumtriflates,4 pentafluoropheno-
lates,5 sulfonyl benzotriazoles,6 p-nitrophenolate
esters,7 and trichlorophenolates.8 However, all the
reported methods need either prolonged heating con-
*
For correspondence
Electronic supplementary material: The online version of this article (doi:10.1007/s12039-017-1354-7) contains supplementary material,
which is available to authorized users.

Saied M Soliman et al.
magnetic resonance spectra (1H NMR and 13C NMR spec-
tra) were recorded on a JEOL ECP-400 MHz spectrometer
(JEOL Ltd., Tokyo, Japan) using CDCl3 or DMSO-d6 as sol-
vent and reported in δ-units (Figures S1–S3, Supplementary
data). Fourier transform infrared spectroscopy (FT-IR) spec-
tra were recorded on Nicolet 6700 spectrometer (Thermo
Scientific, Fishers, IN, USA) using KBr discs. Elemental
analyses were performed on Perkin-Elmer 2400 elemental
analyzer (Perkin Elmer Inc.,Waltham, MA USA). The sol-
vents used were of HPLC reagent grade and all the chemicals
were purchased from Sigma-Aldrich (Steinheim, Germany),
Fluka (Steinheim, Germany). The reactions and the purity of
the compounds were followed by TLC on silica gel-protected
aluminum sheets (Type 60 GF254, Merck Millipore, Bil-
lerica, MA, USA) using UV lamp for spot visualization.
The electronic spectra of the studied compounds were mea-
sured in different solvents such as acetonitrile, methanol and
dichloromethane using UV-Vis spectroscopy (Perkin Elmer
Lambda 35; Waltham, MA, USA).
Figure 1. Structure of oxyma and benzotriazole
derivatives.
and its derivatives,17 ethyl 2-cyano-2-(hydroxyimino)
acetate (Oxyma, 1) has been used as a potential replace-
ment for both HOBt and HOAt (Figure 1).18,19
Recently, N-alkyl-cyanoacetamido oximes 4-7,20–22
N-hydroxybenzimidoyl cyanide
8,
and
N-
hydroxypicolinimidoyl cyanide 9 (Figure 2), were
reported and used for the preparation of sulfonate esters.
The sulfonate esters 10–15 of the oximes shown in Fig-
ure 3 were evaluated for their anti-proliferation effect
on the mouse fibroblast L929. The analysis showed that
these compounds (10–15) have growth inhibition activ-
ity on L929 cells.20
Herein, we report a modified method for the syn-
thesis of the sulfonate esters using dichloromethane-
water (two-phase method) in the presence of sodium
carbonate for the scavenging of the HCl. X-ray crys-
tallography was used to determine the structures of the
three prepared sulfonate esters. Time dependent den-
sity functional theory (TD-DFT) was used to assign
their electronic spectra. The natural bond orbital anal-
ysis was performed to analyze the charge distributions
and to study the different intramolecular charge transfer
within the studied systems.
2.2 General method for the synthesis of oxyma
derivative
The two oximes 8 and 9 were synthesized according to the
previously reported method20 and used for the preparation of
the sulfonate esters 11, 14 and 16.20
2.2a General method for the synthesis of sulfonate
esters: The reported method20 was modified as follows:
To a solution of 5 mmol of oxime 8 (0.73g) or 9 (0.735g)
and Na2CO3 (0.5g, 5 mmol) in 30 mL of dichloromethane
(DCM)-water (1:1), 4-tosyl chloride 18a (0.9g, 5 mmol) or 2-
naphthalene sulfonyl chloride 18b (1.135g, 5 mmol) in 15 mL
of dichloromethane was added dropwise at 0◦C. The reaction
mixture was stirred at 0◦C for 1 h and then at room tempera-
ture for 4 h. After completion of the reaction as monitored by
TLC (ethylacetate-hexane; 4:6), 50 mL of CH2Cl2 was added,
and the organic layer was collected and washed with water
(20 mL) andsaturated aqueous NaCl (20 mL). It was finally
dried over Na2SO4 anhydrous. After removal of the solvent
under reduced pressure, the residue was recrystallized from
2. Experimental
2.1 Materials and methods
Melting points were determined with a Mel-Temp appara- CH2Cl2-hexane to give the sulfonate esters in their crystal-
tus (Chemie GmbH, 82024 Taufkirchen, Germany). Nuclear lized form.
Figure 2. Structure of N-alkyl-cyanoacetamidooximes 4-7, N-hydroxybenzimidoyl
cyanide 8, and N-hydroxypicolinimidoyl cyanide, 9.

Synthesis and DFT studies of Oxyma-sulfonate esters
Figure 3. Structure of 4-tosyl esters 10, 11 and 2-naphthalenesulfonyl esters 12–15.
2.2b N-(tosyloxy)benzimidoylcyanide(11): Theprod- 2.3 Crystal structures determination and refinement
uct was obtained as white crystals, in 84% yield, M.p.: 112◦C;
[Lit2085% yield, M.p.: 110–111◦C]; IR (KBr, /cm−1):
The compounds 11, 14 and 16 were obtained as single crystals
by slow evaporation from its solutions (dichloromethane-
hexane; 2:1) to afford the pure compound at room temper-
ature. Data were collected on a Bruker APEX-II D8 Venture
area diffractometer, equipped with graphite monochromatic
ν
2242 (CN), 1393, 1187 (SO2, sulfonate). 1H NMR (400
MHz, CDCl3) ppm: δ 2.45 (3H, s, CH3), 7.39 (2H, d, Ar-
H, J = 8.8 Hz), 7.46 (3H, t, Ar-H), 7.57 (1H, t, Ar-H,
J = 7.3 Hz), 7.78 (2H, d, Ar-H, J = 8.0 Hz), 7.94 (1H,
d, Ar-H, J = 8.0 Hz).13C NMR (100 MHz, CDCl3) ppm:
δ 21.8, 107.7, 127.3, 127.5, 129.3, 129.4, 130.2, 131.2, 133.5,
139.4, 146.5. Anal. Calcd. for C15H12N2O3S: C, 59.99;
H, 4.03; N, 9.33%. Found: C, 60.16; H, 4.25; N, 9.05%.
α
Mo K radiation, = 0.71073 Å at 293 (2) K. Cell refine-
λ
ment and data reduction were carried out by Bruker SAINT.
SHELXT23,24 wasusedtosolvethestructure. Thefinalrefine-
ment was carried out by full-matrix least-squares techniques
with anisotropic thermal data for non-hydrogen atoms on F.
CCDC 1456403, 1468844 and 1456418 contain the supple-
mentary crystallographic data for this compounds 11,14 and
16, respectively and can be obtained free of charge from the
Cambridge Crystallographic Data Center via www.ccdc.cam.
ac.uk/data_request/cif.
2.2c N-(naphthalen-2-ylsulfonyloxy)benzimidoyl
cyanide (14): The product was obtained as white crystals
in 88%yield, M.p.: 134–135◦C; [Lit20 yield 86%, M.p.:133–
134◦C] IR (KBr, /cm−1): 2234 (CN), 1390, 1186 (SO2,
ν
1
sulfonate). HNMR (400 MHz, CDCl3) ppm: δ 7.44 (2H, t,
Ar-H, J = 8.1 Hz), 7.54 (1H, t, Ar-H, J = 7.3 Hz), 7.65–
7.78 (4H, m, Ar-H), 7.93–8.04 (4H, m, Ar-H), 8.65 (1H, s,
Ar-H). 13CNMR (100 MHz, CDCl3) ppm: δ 107.6, 123.1,
127.1, 127.5, 128.1, 129.3, 129.6, 129.7, 130.0, 131.0, 131.6,
131.9, 133.4, 135.8, 139.5. Anal. Calcd. for C18H12N2O3S:
C, 64.27; H, 3.60; N, 8.33%. Found: C, 64.11; H, 3.35; N,
8.05%.
2.4 Computational details
The quantum chemical calculations were performed at the
DFT/B3LYP level of theory and using the built in 6-31G(d,p)
basis set as in Gaussian 03 software.25 The input structures
were taken from the crystallographic information files (CIFs)
obtained from the X-ray single crystal measurements, which
are reported here for the first time. The optimizations fol-
2.2d N-(tosyloxy)picolinimidoyl cyanide (16): The lowed by frequency calculations at the optimized structures
product was obtained as grey crystals, in 88% yield, M.p.: gave no imaginary frequency modes. In addition, the NMR
◦
129–130 C; IR (KBr, /cm−1): 2247 (CN), 1394, 1173 chemical shifts and the UV-Vis electronic spectral bands were
ν
(SO2, sulfonate). H NMR (400 MHz, CDCl3) ppm: δ 2.46 computed using the GIAO,26,27 and Time Dependent-DFT
1
(3H, s, CH3), 7.39–7.47 (3H, m, Ar-H), 7.78–7.95 (4H, m, (TD-DFT) methods,28–30 respectively. The calculations were
Ar-H), 8.72 (1H, d, Ar-H, J = 4.4 Hz) .13CNMR (100 performed both in the gas phase and in presence of different
MHz, CDCl3) ppm: δ 21.9, 107.4, 121.7, 126.9. 129.3, 130.2, solvents. The effects of solvent on the electronic spectra as
130.9, 137.3, 140.1, 146.8, 146.9, 150.4. Anal. Calcd. for well as the NMR chemical shifts were computed using solvent
C14H11N3O3S: C, 55.80; H, 3.68; N, 13.95%. Found: C, environment of the Polarizable Continuum Model (PCM).
55.96; H, 3.46; N, 14.09%.
Relative chemical shifts are estimated by using corresponding

Saied M Soliman et al.
Scheme 1. Synthesis of oxyma sulfonate esters.
TMS shielding calculated in advance at the same theoretical 140.1(C4), 146.8(C1-SO2), 146.9(C=N, Oxime), and
level as the reference. GaussSum 2.231 was utilized to analyze
the electronic spectra of the studied compounds. Moreover,
theelectronicpropertiesaffectingthenonlinearoptical(NLO)
150.4(C2’).
3.2 X-ray crystallography
properties of the studied systems were computed as obtained
from the frequency calculations.
The natural bond orbital (NBO) calculations were per-
formed using NBO 3.1 program as implemented in the
Figure 4 presents the ORTEP diagrams of the com-
pounds 11, 14 and 16. Displacement ellipsoids are
plotted at the 40% probability level for non-H atoms.
The crystallographic data and refinement information
are summarized in Table 1. The asymmetric units con-
tain one independent molecule as shown in Figure 4. All
the bond lengths and angles are within normal ranges.34
Gaussian 03W package at the DFT/B3LYP level in order
to understand various intramolecular charge transfer interac-
tions between the filled orbitals of one subsystem and vacant
orbitals of another subsystem, which is a measure of the inter-
molecular delocalization or hyper-conjugation.32,33
3.3 DFT studies
3. Results and Discussion
3.3a Structure and electronic properties: The cal-
culated geometries using B3LYP method drawn using
Chemcraft software35 are shown in Figure 5. The over-
lay of the calculated and experimental X-ray structures
indicated that the optimized molecular structures agreed
well with the experimental results. Based on the calcu-
lated correlation coefficients (R2) shown in Table S1
(Supplementary Information), the bond distances and
angles obtained from the present calculations showed
good correlations with the experimental data. The R2
values for the bond distances and angles are in the range
of 0.9886–0.9969 (Table S1, Supplementary Informa-
tion).
3.1 Synthesis of oxyma sulfonate
The two oxyma 8 and 9 were prepared from their
aryl nitrile derivatives 17a, b following the reported
method,19 and then reacted with the sulphonyl chloride
derivatives 18a, b using the modified two-phase method
(DCM-H2O) to afford the sulfonate esters 11, 14 and 16
(Scheme 1) in excellent yields and purities as observed
from their spectral data.
The charge distribution has a direct relation to the
polarity of the compound since the compounds have
almost similar structure patterns. The natural bond
orbital (NBO) calculations were used to predict the nat-
The 1H NMR of N-(tosyloxy)picolinimidoyl cyanide ural atomic charges (QNAC) at different atomic sites.
16 as a prototype showed a singlet peak at δ 2.46 The results of the natural atomic charges are given in
related to CH3group, multiplet peak at δ 7.39–7.47 cor- Table 2. For all compounds, the three sulfonate O-atoms
responding to the three protons (H3,H5,H5’), multiplet have the highest negative charge where the two free O-
peak at δ 7.78–7.95 corresponding to the four protons atoms are more negative than the third one. It is the
(H3’,H4’,H2 and H6), and doublet peak at δ 8.72 corre- least negative in case of the pyridine derivative. The Sul-
sponding to the H6’. 13C NMR of 16 showed carbon sig- fur atom is electropositive in all the studied compounds
nal peaks at δ 21.9(CH3), 107.4 (CN), 121.7(C3’), 126.9 where the QNAC is in the range 2.3910–2.3941e. The H-
(C5’), 129.3 (C2’), 130.2(C6), 130.9(C3,5), 137.3(C4’), atoms are also electropositive. In contrast, all C-atoms

Synthesis and DFT studies of Oxyma-sulfonate esters
Figure 4. ORTEP diagrams of the 11, 14 and 16. Displacement ellipsoids are plotted at the 50% probability
level for non-H atoms.
are electronegative except those attached to higher elec- favored over the others due to chelate effect. Dark blue
tronegative atoms such as nitrogen. The nitrile group regions around the S-atom of the sulfonate reveal the
(C ≡ N) nitrogen is richer in electrons than that for the electron poor character of this atomic site in all com-
C=N. In 16, the most electronegative N-atom is the pyri- pounds.
dine ring N-site. In this regard, a comparison between
thecalculateddipolemomentsofthestudiedcompounds
revealed that the dipole moment values were calculated
to be 7.7231, 7.5512, and 8.7468 Debye for 11, 14 and
16, respectively. It is clear that the presence of one more
heteroatom (N) in the case of 16 leads to more polar
structure than the others.
3.3b Frontiermolecularorbitals: Thefrontiermolec-
ular orbitals HOMO and LUMO refer to the highest
occupied and lowest unoccupied molecular orbitals,
respectively. Their energies are important as they reflect
the ability of the compound to give or take electrons
(Table 3). The order of compounds according to HOMO
energy is 14 > 11 > 16. Hence, compound 14 is con-
sidered the most reactive compound towards electron
donation. In contrast, 16 has the lowest energy LUMO
orbital, and as a result is considered the best electron
acceptor. In presence of solvent, all the HOMO levels
are destabilized. The maximum destabilization occurred
for 11. On the other hand, all the LUMO levels are sta-
bilized where the maximum stabilization occur for 16.
The difference in energy between HOMO and LUMO is
the lowest amount of energy required for the electronic
transition. Theoretically, the lowest transition energy is
calculated to be 4.5294, 4.1451 and 4.6866 eV, for com-
pounds 11, 14 and 16, respectively in the gas phase. In
presence of acetonitrile as solvent, the electronic tran-
sitions become easier and require a lower amount of
energy. Among all the studied compounds, 14 has the
lowest transition energy either in the gas phase or solu-
tion, in agreement with the fact that the presence of more
Map of the electron densities over the molecular elec-
trostatic potential is a useful picture for predicting the
electrophilic and nucleophilic region in the molecular
systems. In these maps, the red regions are usually char-
acterized by high electron densities and susceptible to
be attacked by an electrophile. The dark blue regions
are the most favored sites to be attacked by nucleophile
as it is considered as electron poor regions. The maps of
the molecular electrostatic potential (MEP) were drawn
using GaussView software and shown in Figure 6. For
all the studied system, the N and O-atom of the nitrile
and sulfonate groups, respectively, are the most reactive
to the attack of electrophile. It is clear that 16 has an
electron-rich region around the N-atoms of the nitrile
and pyridine rings. As a result, we could predict that
this compound could act as good ligand in coordination
chemistry than the others. The coordination of the metal
ion as electrophile to these atomic sites of 16 is more

Saied M Soliman et al.
Table 1. Crystal data for 11, 14 and 16.
11
14
16
Crystal data
Chemical formula
Mr
Crystal system, space
group
C15H12N2O3S C18H12N2O3S C14H11N3O3S
300.33 336.36 301.32
Triclinic, P-1 Triclinic, P-1 Triclinic, P-1
Temperature (K)
100
100
100
a, b, c (Å)
5.4641 (3),
8.1232 (5),
15.8195 (9)
100.840 (2),
98.332 (2),
97.180 (2)
673.93 (7)
2
7.4962 (9),
7.4973 (9),
14.0427 (16) 16.426 (2)
87.459 (4),
77.948 (4),
80.483 (4)
761.16 (16)
2
5.2075 (6),
8.0975 (10),
◦
γ
, β, ( )
α
90.911 (5),
98.825 (5),
97.860 (5)
677.52 (14)
2
V (Å3)
Z
α
α
α
Mo K
0.25
Radiation type
Mo K
0.25
Mo K
0.23
μ (mm−1
)
Crystal size (mm)
0.48 × 0.27 × 0.36 × 0.21 × 0.37 × 0.19 ×
0.14
0.15
0.06
Data collection
Tmin, Tmax
No. of measured,
independent and
0.889, 0.965
12941, 3096, 9292, 3280,
2639
0.921, 0.966
0.913, 0.984
7960, 3082,
2076
2487
σ
observed [I > 2 (I)]
reflections
Rint
0.045
0.050
0.082
Refinement
R[F2 >
0.038, 0.095, 0.046, 0.116, 0.059, 0.143,
2
2
σ
2 (F )], wR(F ), S
No. of reflections
No. of parameters
No. of restraints
1.04
3096
191
1.03
3280
217
1.01
3082
191
0
0
0
ꢀ
max, ꢀ
(eÅ−3
)
0.43, −0.42
0.44, −0.42
0.47, −0.44
ρ
ρ
min
CCDC No.
1456403
1468844
1456418
π
conjugated -systeminthecompoundlowerstheenergy observed transition bands and the calculated
val-
λmax
ues together with their oscillator strengths (fosc) based
on the TD-DFT calculations are given in Table 4.
gap between the HOMO and LUMO levels.
The assignment of these electronic transition bands
is given in the molecular orbital diagram shown in Fig-
ures 7 and S5–6 (Supplementary Information). For 14,
these two absorption bands are observed at 231 and 281
nm. The TD-DFT calculations predicted these bands at
235.6 nm (fosc = 0.029) and 279.9 nm (fosc = 0.051),
respectively in the gas phase. In presence of acetoni-
3.4 UV-Vis electronic absorption spectra
TheexperimentallymeasuredUV-Viselectronicabsorp-
tion spectra of the studied compounds in different
solvents are shown in Figure S4 (Supplementary Infor-
mation). All the studied compounds have two common
transition bands. We noted a significant hyperchromic
effect by changing the solvent from ACN to methanol to
DCM to DMF. In contrast, changing the solvent showed
trile as solvent, the
of the longer wavelength band
λmax
showed almost no variation but some decrease in its
absorption intensity is noted. In contrast, hypsochromic
shift and increase in the absorption intensity occurred
very little effect on the
values indicating that the
λmax
solvent change exerts a very little effect on the energies
of the molecular orbitals included in these transitions.
From this point of view, we decided to perform TD-
DFT calculations on one of these solvents to assign
the obtained electronic transition bands. The maximum
for the shorter
band with increasing solvent polar-
λmax
ity from the gas phase to acetonitrile. The assignments
of the electronic spectra shown in these figures revealed
the higher energy transitions observed for compound 16
absorption wavelengths (
λmax
) of the experimentally
where the two bands were observed at shorter
than
λmax

Synthesis and DFT studies of Oxyma-sulfonate esters
Figure 5. The optimized molecular structures of the studied compounds (left) and structure overlay
between the calculated and X-ray single crystal structure (right).
the others, both experimentally and theoretically. These correlation coefficients are given in the same table.
two bands were assigned to be mainly among molec- For compound 14, the correlation is moderate in the
ular orbital with higher energy differences than those gas phase (0.7712–0.7669) and generally improved
occurred in 14.
(0.8114–0.8861) when solvent effects were considered.
For the rest of the compounds, the correlation coeffi-
cients are high indicating the good correlations between
the calculated and experimental data. It is worth noting
that the presented calculation gave better correlations
with the experimental data for protons than carbon.
Usually, the opposite of this was common in litera-
ture.
3.5 NMR spectra
The nuclear magnetic resonance (NMR) chemical shifts
werecalculatedusingGIAOmethodinthegasphaseand
in the solution in order to match the results with those
obtained experimentally. The calculated and experi-
mental chemical shifts of the studied compounds are
given in Table S2 (Supplementary Information). Cor- 3.5a Nonlinearoptical(NLO)properties: Non-linear
relations between the experimental and calculated 1 H- optical (NLO) effects occur when an intense beam of
and 13C-NMR chemical shifts were performed and the light such as laser interact nonlinearly with a material

Saied M Soliman et al.
α
Table 2. The calculated natural charges of the
studied compounds.
NLO materials. The components of polarizability ( )
and hyperpolarizability (β) were used to calculate the
α
total polarizability ( tot) and hyperpolarizability (βtot)
11
14
16
using equations 1 and 2, respectively.
Atom QNAC Atom QNAC Atom QNAC
ꢀ
ꢁ
1
3
αtot
αxx
α
α
zz
=
+
+
(1)
S1 2.3937 S1 2.3941 S1 2.3910
yy
O2 −0.8967 O2 −0.8950 O2 −0.8974
O3 −0.9002 O3 −0.9014 O3 −0.8965
O4 −0.5659 O4 −0.5658 O4 −0.5582
N5 −0.0935 N5 −0.0949 N5 −0.0905
N6 −0.2554 N6 −0.2549 N6 −0.2454
C7 −0.1994 C7 −0.1698 N7 −0.4358
ꢀ
ꢁ
ꢀ
ꢁ
2
2
βtot = βxxx + βxyy + βxzz + βyyy + βyxx + βyzz
ꢀ
ꢁ
2
+ βzzz + βzxx + βzyy
(2)
α
The high values of polarizability ( ) and the first hyper-
polarizability (β) of the investigated molecules clearly
reveal that they have nonlinear optical (NLO) behavior
α
H8
0.2727 H8
0.2713 C8 −0.1985
C9 −0.2288 C9 −0.0582 H9
H10 0.2482 C10 −0.1994 C10 −0.2280
C11 0.0013 H11 0.2466 H11 0.2488
0.0019
0.2733
(Table 5). In comparison to urea (
= 25.8793 A.U
tot
and βtot = 43.1140 A.U), compounds 14, 16 and 11 have
αtot
C12 −0.2302 C12 −0.2310 C12
values higher by 9.05, 7.44 and 7.63 times and βtot
values higher by 7.71, 2.66 and 5.83 times. The values
H13 0.2469 H13 0.2480 C13 −0.2304
C14 −0.1983 C14 −0.2200 H14 0.2469
H15 0.2721 H15 0.2470 C15 −0.1996
C16 −0.3573 C16 −0.2118 H16 0.2714
C17 −0.7051 H17 0.2434 C17 −0.3578
H18 0.2495 C18 −0.0429 C18 −0.7053
H19 0.2567 C19 −0.2003 H19 0.2482
H20 0.2483 H20 0.2477 H20 0.2501
α
of the total polarizability ( tot) and hyper-polarizability
(βtot) shown in Table 5 indicated that 14 could be the best
candidate for nonlinear optical applications as it has the
α
tot
highest
and βtot values compared to the others. The
higher conjugation occurred in 14 due to the presence
of naphthyl group could be the reason for such NLO
enhancement.
C21
C22
0.2378 C21 −0.2206 H21 0.2570
0.1236 H22 0.2725 C22
0.2451
0.1119
0.1678
C23 −0.0885 C23 −0.3480 C23
C24 −0.1985 C24
H25 0.2603 C25
0.1246 C24
0.2378 C25 −0.2377
3.5b Second order perturbation energy analyses: The
analysis of the interaction energies between the filled
natural bond orbitals (NBOs) and the empty ones shed
light on the ease of electron delocalization among
electron pairs in the studied systems. The interaction
energies deduced from the NBO analyses were shown
in Table S3 (Supplementary Information). The most
important interactions occurred in the studied systems
C26 −0.2320 C26 −0.0886 H26 0.2662
H27 0.2469 C27 −0.2079 C27 −0.2007
C28 −0.2173 H28 0.2558 H28 0.2519
H29 0.2455 C29 −0.2318 C29 −0.2632
C30 −0.2319 H30 0.2483 H30 0.2512
H31 0.2482 C31 −0.2170 C31
0.0268
C32 −0.2083 H32 0.2456 H32 0.2356
H33 0.2557 C33 −0.2319
H34 0.2470
π
π∗
π∗
σ∗
intramolec-
are
ular charge transfer (ICT). Because all the studied
π∗
→
, n →
and n →
C35 −0.1982
H36 0.2599
π
π
molecules have conjugated -system, so many
→
ICT interactions were occurred. For 14, the strongest
π
π∗
→
ICT interaction has 20.40 kcal/mol for the
to produce new fields, altered in its propagation char- BD(2)C33-C35 → BD∗(2)C29-C31 charge transfer
π
acteristics like frequency or amplitude, compared to the which is related to the phenyl ring -system. Another
incident fields.36 NLO is a hot topic in chemistry and ICT also have high stabilization energy (20.08 kcal/mol)
π
physics researches and it has many applications related takes place between one of the phenyl ring -system as
to optical and electronic devices.37–40 Organic systems the donor (BD(2)C26-C27) and the BD*(2)N5-C24 as
π
π
π∗
having donor–acceptor -conjugation are of interest in acceptor. In the case of 16, the highest energy
→
the field of nonlinear optical (NLO) properties. The ICT interaction (28.14 kcal/mol) occurred among the
∗
π
nature of substituent and steric hindrance affects the pyridine ring -bonds (BD(2)C25-C27 → BD (2)N7-
π
degree of -conjugation of the substances and hence C24) while the second highest one (26.47 kcal/mol)
its hyperpolarizability will be affected. As a result, the is BD(2)C12-C13 → BD∗(2)C15-C17 for the p-tolyl
NLO of compound could be improved by the proper group. The latter occurred in 11 with almost the same
selection of substituent.41
ICT interaction energy (26.81 kcal/mol). For all com-
π∗
Quantum chemical calculations can play an impor- pounds, there is only one significant n →
ICT
tant role in the understanding of the structure–property delocalization occurred from the second lone pair of O4
π∗
relationship, which could be assisted in designing novel (LP(2)O4) to the -empty NBO of the adjacent N5=C

Synthesis and DFT studies of Oxyma-sulfonate esters
Figure 6. MEP maps of the studied compounds.
Table 3. The energies of the frontier molecular orbitals in the gas phase
and in presence of acetonitrile as solvent.
11
14
16
gas
ACN
gas
ACN
gas
ACN
HOMO −6.9411 −6.8908 −6.5683 −6.3275 −7.1950 −7.1441
LUMO −2.4118 −2.5154 −2.4232 −2.5258 −2.5084 −2.6384
Gap
4.5294
4.3754
4.1451
3.8017
4.6867
4.5057

Saied M Soliman et al.
Table 4. The calculated and experimental (nm) and their oscillator strengths.
λ
max
(
max)exp.
(
max)calc
λ
fosc
Assignment
λ
11
227
282
14
229.6
258.7
0.344
0.071
H-5 → L (15%), H-1 → L+1 (61%)
H-4 → L (79%), H → L+2 (13%)
231
281
16
219
277
233.8
279.4
0.919
0.013
H-2 → L+1 (27%), H-1 → L+2 (13%), H → L+2 (28%)
H-2 → L+1 (36%), H-1 → L+1 (15%), H → L+2 (41%)
223.7
258.7
0.152
0.071
H-5 → L (36%), H-1 → L+1 (17%), H → L+2 (11%)
H-4 → L (79%), H → L+2 (13%)
compounds having the p-tolyl group, this ICT interac-
tion has almost the same strength. Two factors could
lead to such variations: (1) the O4 atom has more devi-
ation by 1◦ from the C=N5 bond in 11 and 16 compared
to 14 which will slightly weaken LP(2)O4 → C = N;
(2) the electronic factor where the naphthyl ring con-
π
jugated -system could be a better electron donor to
the sulphonate moiety than the p-tolyl group, this will
make the O4-atom more e-rich and more ICT to the
neighboring C=N bond will take place for 14 than the
others. All the studied compounds have common fea-
σ∗
tures of n →
ICT interactions, all have 10 of these
σ∗
interactions except 16 has one more n → ICT from
LP(1)N7 → BD∗(1)C24-C25 (10.28 kcal/mol) due to
the replacement of the phenyl by pyridyl one. The high-
est of these interactions occurred from LP(3)O2 and
σ∗
LP(3)O3 filled NBOs to the empty
NBOs of the
S1-O4 bond. These interactions stabilized the system
upto 38.96, 38.21 and 38.16 kcal/mol for 14, 16 and 11,
respectively.
3.5c Reactivitydescriptors: Severalreactivitydescrip-
tors such as ionization potential (I), electron affinity (A),
η
chemical potential (μ), hardness ( ) as well as elec-
ω
trophilicity index ( ) were proposed for understanding
various aspects of reactivity associated with chemi-
cal reactions.42–47 The definition of these parameters is
given by Equations 1–5.
These chemical reactivity descriptors could be used
for describing the different pharmacological and bio-
logical reactivity of compounds. Based on the molecular
orbital calculations of the synthesized compounds, these
reactivity descriptors are summarized and listed in
Table 6. The results showed the order of the studied
molecules according to chemical hardness is 16 > 11 >
14. Compound16hasthehighestchemicalhardnessasit
Figure 7. The origin of the most important spectral bands
of 11.
bond. The stabilization energies of these ICT interac- hasonemoreelectronegativeatominitsstructure. More-
tions are 14.94, 18.43 and 15.62 kcal/mol for 11, 14 and over, all compounds have negative chemical potential so
16, respectively. It is the maximum for 14. In the two are considered stable compounds. It is well-known that

Synthesis and DFT studies of Oxyma-sulfonate esters
Table 5. The polarizability and hyperpolarizability components and their total values
(A.U) of the studied compounds.
Parameter
11
14
16
11
14
16
αxx
αxy
αyy
αxz
αyz
αzz
233.6056 285.5122 225.5522 βxxx 119.5136
94.6122 −81.4442
−15.2611 −3.9882 −13.3882 βxxy −166.5150 233.0252 −26.0682
197.1262 222.3290 190.7274 βxyy
3.6825 −25.3824
47.1599 −62.4914 −38.3951
97.9542 −55.7361
5.2904 βyyy −11.1243
−26.5293
27.5889 −23.8767 βxxz 143.3713 116.2308
85.6555
161.8942 194.8585 161.1696 βxyz −106.4500 −125.3100 −93.1212
βyyz −41.5483 10.6334 −58.7575
βxzz
βyzz
βzzz
0.6574 −1.9668
35.2847 −27.8183
13.2321
47.2213
6.4433 −3.4542
19.9696
αtot
197.5420 234.2332 192.4831 βtot 251.1929 332.5459 114.5019
Table 6. The quantum chemical reactivity
parameters of compounds 12, 14 and 16.
to polarity is 16 > 11 > 14. Analyses of the elec-
tronic spectra were made using the TD-DFT method
and the molecular orbitals involved in these electronic
transitions were discussed. NBO method was used to
calculate the natural atomic charges and investigate the
intramolecular charge transfer interactions occurred in
the studied systems. Chemical reactivity studies showed
that the most electrophilic compound is 16 and the order
of the studied molecules according to chemical hardness
is 16 > 11 > 14. According to the total polarizability
Parameter
11
14
16
I = −EHOMO
A = −ELUMO
6.9411
2.4118
2.2647
6.5683
2.4232
2.0726
7.1950
2.5084
2.3433
η
= (I − A)/2
μ = −(I + A)/2 −4.6764 −4.4958 −4.8517
2
ω
= μ /2η
4.8283
4.8760
5.0225
α
(
tot) and hyperpolarizability (βtot), 14 could be the best
candidate for nonlinear optical applications.
the flow of electrons could take place from the molecule
with the highest chemical potential. From this point of
view, the ability of the studied compounds to electron
flow from it will be the highest for 14. Moreover, the
electrophilicity index of the studied compounds is in
the order 16 > 14 > 11. As a result, 16 has the high-
est electrophilicity index so it has higher electrophilic
behavior compared to the others,48 in agreement with
Supplementary Information (SI)
NMR and UV-Vis absorption spectra, Tables S1–S3 and Fig-
ures S1–S7 are given as supplementary information. For
details see www.ias.ac.in/chemsci.
Acknowledgements
a large number of strong electronegative atoms in this The authors extend their appreciation to the Deanship of Sci-
entificResearchatKingSaudUniversityforfundingthis work
through research Group No. (RGP-234, Saudi Arabia).
compound compared to the others.
4. Conclusions
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