Post on 29-Jul-2020
CHAPTER IV
SPECTROSCOPIC AND MOLECULAR STRUCTURE
INVESTIGATION OF 4-METHYL-N-(3-
NITROPHENYL)BENZENE SULFONAMIDE WITH
EXPERIMENTAL AND THEORETICAL APPROACHES
4.1 INTRODUCTION
Aniline is an aromatic amine and its derivatives are widely used in
pharmaceutical manufacturing, electro-optical, dye stuff and other commercial and
industrial applications. The material meta-nitroaniline whose chemical formula is
C6H6N2O2 is one of the organic material revealing NLO property to find
application in telecommunications and possibilities for optical information storage,
frequency conversion, optical processing, high speed electro-optic modulator and
deflector, optical bistability and computing [1-3]. The relative second harmonic
intensity of meta-nitroaniline crystal is 100 times larger than ADP [4].
Meta-nitroaniline has been the subject of much study because of its
relatively simple molecular structure, and a large electro-optic [5,6] and nonlinear
optic effects [7-18]. Ryu et al [19] studied Seeded supercooled melt growth and
polar morphology of organic nonlinear optical crystal, meta-nitroaniline.
Szostak et al [20] contributed the molecular mechanism of optical nonlinearity and
electrical conductivity of 3-nitroaniline single crystals by dielectric, electric and
quantum chemical studies. Adhyapak et al [21] studied synthesis, characterization
studies and single mode waveguide properties of m-NA doped Au/PVA nano-
composites:
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Valluvan et al [22] studied the growth of organic nonlinear materials of
meta-nitroaniline single crystals by slow evaporation method and its
characterization. Adhyapak et al [23] studied preparation, characterization and non-
linear optical properties of pristine m-nitroaniline and its recycled polystyrene (Re-
PS) coated single crystals.
The spectroscopic studies were performed in the frame of search for a
relationship between vibrational spectra and optically nonlinear (NLO) properties
of the mna crystal [24–28]. Metanitro aniline crystallizes in the
non centrosymmetric, orthorhombic, mm2 space group [29,30] what lies also at the
origin of its pyroelectricity [31], piezoelectricity [32], ferroelectrical features [33],
and recently detected terahertz emission [34,35].In this work, 4-methyl-N-(3-
nitrophenyl)benzene sulfonamide (4M3NPBS) are prepared from the reaction of a
paratoluene sulfonyl chloride with meta nitroaniline.
Literature survey shows that neither spectroscopic characterizations nor
computational studies have been done so far on the 4M3NPBS compound. As a
part of our ongoing studies on sulfonamide, in this chapter, synthesis, crystal
structure, characterization studies, NBO and NLO properties, HOMO-LUMO
analysis and molecular electrostatic potential of 4M3NPBS are studied. The X-ray
crystallographic structure of 4M3NPBS has been reported in literature [36]. We
collected data independently from the crystal grown by us to carry out a
comparative study between the experimental data and the optimized geometry
performed using DFT method.
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4.2 SYNTHESIS
Meta Nitroaniline (7.15 gm), Triethylamine (4 ml) were dissolved in
acetone (8 ml). To this solution, Para toluene sulfonyl chloride (9.53 gm) in
acetone (12.5 ml) was added in drops with continuous stirring for two hours. The
resulting solution was allowed to evaporate. The residue was washed several times
with water and then with petroleum ether solution (In the synthesis of the
4M3NPBS reported earlier [36], pyridine was used as a catalyst and reactions
subjected to heating and cooling). The crude product of the title compound was
recrystallized from ethanol. After one week pale yellow crystals suitable for x-ray
diffraction studies were obtained. The scheme of the synthesis is shown in
Figure 4.1.
4.3 SINGLE CRYSTAL X-RAY DIFFRACTION ANALYSIS
4.3.1 Crystal Structure Determination
A crystal with dimensions of 0.30 x 0.20 x 0.20 mm was used for collection
of intensity data on a “Bruker Apex II CCD” area detector diffractometer with
graphite monochromatic MoKα radiation (0.71073) ω scan technique. The
programs used to solve and refine the structure were SHELXS-97, SHELXL97 and
PLATON [37, 38]. The refinement was carried out by using the Full matrix least
square on F2. All non hydrogen atoms were refined anisotropically. All hydrogen
atoms have been geometrically fixed and refined with isotropic thermal
parameters. Crystallographic details are shown in Table 4.1, whereas the selected
bond lengths and bond angles are given in Table 4.2.
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Figure 4.1. Pathway of the synthesis of 4M3NPBS.
NO2
NH
NO2
NH2
+SO2Cl
CH3
SO2
H3C
︵C2H5 ︶N3ACETONE
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Table 4.1
Crystal data and structure refinement
Empirical formula C13H12N2O4S
Formula weight 292.31
Temperature 293(2) K
Wavelength 0.71073 A
Crystal system, space group Monoclinic, P21/n
Unit cell dimensions a = 12.753(3) Å alpha = 90 °.
b = 7.7239(6) Å beta = 101.771(3) °.
c = 13.5485(9) Å gamma = 90 °.
Volume 1306.5(3) Å3
Z, Calculated density 4, 1.486 Mg/m3
Absorption coefficient 0.263 mm-1
F(000) 608
Crystal size (0.30 x 0.20 x 0.20) mm3
Theta range for data collection 2.00 to 31.33 °.
Limiting indices -18<=h<=18, -11<=k<=11, -19<=l<=18
Reflections collected / unique 17318 / 4273 [R(int) = 0.0227]
Completeness to theta = 31.33 99.7 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.952 and 0.910
Refinement method Full-matrix least-squares on F2
Data / restraints / parameters 4273 / 1 / 187
Goodness-of-fit on F^2 1.027
Final R indices [I>2sigma(I)] R1 = 0.0391, wR2 = 0.1104
R indices (all data) R1 = 0.0528, wR2 = 0.1213
Extinction coefficient 0.0019(5)
Largest diff. peak and hole 0.327 and -0.315 e.Å-3
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Table 4.2
Selected bondlengths and bondangles
Parameter Experiment a Experiment B3LYP
Bond Lengths(Å) C1-C6 1.379(2) - 1.3954 C1-C2 1.3848(19) - 1.3979 C1-S1 1.7561(13) 1.7628(17) 1.7909 C2-C3 1.381(2) - 1.3913 C8-C13 1.3855(16) - 1.3981 C8-C9 1.3899(19) - 1.3917 C12-N2 1.4686(16) 1.468(2) 1.4736 C8-N1 1.4130(17) 1.416(2) 1.4166 O1-S1 1.4275(10) 1.4341(14) 1.4616 O2-S1 1.4247(11) 1.4277(14) 1.4622 N1-S1 1.6256(13) 1.6316(16) 1.71 N2-O3 1.2117(8) 1.213(2) 1.2299 N2-O4 1.2211(16) 1.227(2) 1.2311 Bond angles(°) C5-C4-C7 120.40(15) - 121.13 C1-S1-O1 109.17(6) 109.24(8) 108.31 C1-S1-O2 107.83(7) 107.87(9) 107.87 C1-S1-N1 106.89(7) 106.61(8) 106.57 O1-S1-O2 119.43(7) 119.37(9) 122.89 O1-S1-N1 104.12(7) 104.23(9) 103.44 O2-S1-N1 108.73(7) 108.83(8) 106.65 O3-N2-O4 122.89(12) 122.59(16) 124.68 Dihedral angles(°) C6-C1-C2-C3 -0.5 - -.4731 C1-C2-C3-C4 -0.2 - -.1150 C2-C3-C4-C7 -179 - -179.96 C7-C4-C5-C6 179.5 - 179.21 C9-C8-C13-C12 179.8 - 179.35 C11-C12-N2-O3 -173 - -176.22 C13-C12-N2-O3 6.56 - .4 C11-C12-N2-O4 6.6 - 179.45 N2-C12-C13-C8 179.81 - 179.49 C13-C12-N2-O4 -173.5 - -179.81 C13-C8-C9-C10 0.2 - .597
a XRD taken from Reference[ 14].
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Figure 4.2(a) An ORTEP drawing of 4M3NPBS, with the atom numbering Scheme.
Displacement ellipsoids are drawn at the 30% Probability level
Figure 4.2(b) Optimised structure of 4MN3NPBS with atom numbering obtained by
DFT/B3LYP 6-31G(d,p)
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4.3.2 Crystal Structure Analysis
The ORTEP [39] diagram of the title molecule showing 30% Probability
displacement ellipsoids is shown in Fig.4.2. In the crystal structure of the title
compound C13H12N2O4S, the mean plane distance between the dihedral angles
(C6-C1-C2-C3) and (C13- C8-C9-C10) of the tolyl and nitrophenyl ring is
92.19(4)⁰. This shows their non coplanar conformation. This is in Contrast with the
near coplanar conformation reported for the crystal structure of 4-[(2-hydroxy-
benzylidene)-amino]-N-(5-methyl-isoxazol-3-yl)-benzenesulfonamide[40]. All the
Caro-Caro and C-C bond lengths are comparable to the reported mean values of
Caro-Caro =1.380Å and C-C =1.530Å [41]. The atoms around the sulfonamide
“S” atom in the title compound are arranged in a slightly distorted tetrahedral
configuration. The largest deviation is in the angle O (2)-S (1)-O (1) of 119.43(7)°,
but it conforms to the non-tetrahedral arrangement commonly observed in
sulfonamides [42,43]. The bond angle N1–S1–C1 of 107.70(14)° is
correspondingly smaller than the tetrahedral value of 109° [44]. The S1-C1
distance of 1.7561(13) Å is normal single bond values and agrees well with those
observed in other sulfonamides [45]. The torsion angle τ(C-S-N-C) defining the
conformation of the sulfonamide group is reported to lie in the range 60-90⁰ [46].
In the present crystal structure, the torsion angle τ(C8-N1-S1-C1) is 67.35(14)°.
The position of the methyl group C7 is defined by the torsion angles τ1(C7-C4-C5-
C6) and τ2(C2-C3-C4-C7) are 179.56(14)° and -179.23(16)° respectively. The
molecules in the unit cell are related to each other by inversion. In each molecule
the tolyl ring and phenyl rings are orthogonal to each other. In fact the phenyl ring
is deviated from the planar configuration by 0.1-0.5º, see Table 4.2. The nitro
group is found out of plane by 0.2-7.0º, see Table 4.2. The amide groups are found
to be out-of-plane indicated from the torsional angles τ1(C8-N1-S1-O2), τ2(C6-C1-
S1-N1), τ3(C2-C1-S1-N1), τ4(C6-C1-S1-O2), τ5(C2-C1-S1-O2) and τ6(C8-N1S1-
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C1) are -48.81, 44.33, -138.83, 161.09, -22.07 and 67.35° respectively. The bond
angles C11-C12-C13 and C13-C8-C9 of phenyl ring are 124.31(12) and
119.48(12)° slightly deviating from hexagonal structure due to the substitution of
nitro and amide groups.
4.3.3. Hydrogen Bonding Geometry
The crystal packing is stabilized by weak intermolecular N-H…O
interaction. An N-H-O bond links the molecules into infinite chains running along
the diagonal of the ac plane of the crystal is shown in Figure 4.3. The amino
nitrogen N1-H is involved in intermolecular interaction with nitro oxygen. The
amino nitrogen N1-H acts as donor with nitro oxygen O4 of symmetry related x, y,
z molecule. The weak inter and intramolecular interactions (N1-H1-O4), (C6-H6-
O3), (C7-H7-O3), (C9-H9-O1) and (C13-H13-O2) of the title compound obtained
by XRD are shown in the Table 4.3.
4.3.4 Geometrical Structure
The molecular structure of 4M3NPBS obtained by B3LYP 6-31G(d,p) is
shown in Figure 4.2 (b). In the tolyl ring, all the carbon-carbon bond lengths are
calculated in the range of 1.395–1.401 Å for B3LYP and observed in the range of
1.378 –1.386 Å for XRD data. Loughery et al [47] reported the bond lengths,
S31–O32 = 1.4337, S31–O33 = 1.4256, S31–N34 = 1.6051, S31–C28 = 1.7737
and C21–N20 = 1.4212 Å, whereas the corresponding values for the title
compound are, 1.4616, 1.4622, 1.71, 1.79 and 1.416Å. The above said bond
lengths, S1–O1, S1–O2, S1–N1, and S1–C1 and C8–N1 are in agreement with the
experimental values (1.427, 1.424, 1.625, 1.756 and 1.413 Å). Panicker et al [48]
reported the molecular structure and conformations of benzene sulfonamide by gas
electron diffraction and quantum chemical calculations. According to their results,
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Table 4.3
Hydrogen bond geometry(Å)
iC6-H6…O3 0.93(3) 2.54 3.391(2) 152 iiC13-H13…O2 0.93(3) 2.36 2.768(18) 126 iiiC7-H7...O3 0.96(3) 2.60 3.449(2) 148 iiC9-H9...O1 0.93(3) 2.52 3.223(2) 132
Note: D: Donor, A: Acceptor
Symmetry transformations used to generate equivalent atoms:
i, x-1/2,-y-1/2,z-1/2
ii, -X+1/2, Y-1/2, -Z+1/2
iii, -X-1/2,Y-1/2,-Z+1/2
D-H-A D-H H-A D…A (DHA) °
iN1-H1…O4 0.853(3) 2.23 3.061(19) 173.7
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Figure 4.3 Molecular Packing Diagram of 4M3NPBS
Figure 4.4 Plot of Calculated Versus Experimental bond lengths
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the bond lengths, CS, SN and SO vary in the range of 1.7756–1.7930, 1.6630–
1.6925 and 1.4284–1.4450 Å respectively. The bond angles, CSN, CSO and NSO
vary in the range of 103.9°, 107.1°, 107.6°, 109.8°, 105.5° and 107.7° respectively.
These values are in agreement with the corresponding values for the title
compound. At C8 position, the bond angles C9–C8–N1, C13–C8–C9 and C13–
C8–N1 are117.51°, 119.48° and 122.97° respectively. This asymmetry in angles
reveals the interaction between N-H group and phenyl ring. The torsion angle
τ(C6–C1–S1–N1) is calculated as 97.37° for B3LYP, which falls within the
expected range (70–120°). The torsion angles τ1(C7–C4–C5–C6) and τ2(C2–C3–
C4–C7) are 179.96° and -179.85° respectively for B3LYP. These torsion angles
are in agreement with the XRD data. Further, the results of our calculations
showed that S1–O1 and S1–O2 bonds show typical double bond characteristics
and all other bond lengths fall within the expected range. The experimental bond
lengths are slightly shorter than that of theoretical values. Theoretical bond lengths
vary ± .085 Å where comparing with the XRD data and these differences are
probably due to intramolecular interactions in the solid state. Graphic correlation
between experimental versus theoretical bond lengths is shown in Figure 4.4. The
values of correlation coefficient provide good linearity between calculated and
experimental bond lengths (correlation coefficient R2 of .9857). From the
theoretical values, we can find that most of the optimized bond angles are slightly
larger than the experimental values, due to the theoretical calculations belong to
the isolated molecules in gaseous phase and the experimental results belong to the
molecules in solid phase. The bond angle (O1-S-O2) varies 2.09° and (O3-N2-O4)
deviates 3.54° from XRD data. In spite of the differences, calculated geometric
parameters represent a good approximation and they are the bases for calculating
other parameters such as vibrational frequencies and thermodynamic properties.
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4.4 VIBRATIONAL ASSIGNMENTS
The vibrational frequency and approximate description of each normal
mode obtained using DFT/B3LYP method with 6-31G(d,p) basis set [49-53] are
given for this compound in Table 4.4. The experimental FTIR spectrum and
FT-Raman are shown in Figure 4.5(a) and Figure 4.5(b). As it is seen from
Table 4.4, the predicted harmonic vibration frequencies and the experimental data
are very similar to each other. Vibrational assignments have been carried out using
VEDA programme combined with Gauss view software [54-55]. Vibrational
frequencies calculated at B3LYP/6-31G(d,p) level were scaled by 0.96 [56].
4.4.1 N-H Vibrations
As it is seen in Table 4.4, the N–H stretching mode, calculated as
3387 cm-1 is observed at 3274cm-1 in the FTIR spectrum, 3275 cm-1 in the FT-
Raman spectrum. This difference between experimental and calculated N–H
stretching vibration (113 cm-1) can be due to N–H–O strong intermolecular
hydrogen bond which has not been taken into consideration in the calculation. In
the literature, some N-H stretching modes observed experimentally for the
different substituent sulfonamide are 3273, 3343 and 3284 cm-1 [57]. Theoretical
value for the N–H stretching vibration was reported as 3466 cm-1 theoretically
[58]. The N-H in-plane bending vibration is expected near 1400 cm-1. This
vibration is usually masked by the strong intense band of CH3 asymmetric bending
or SO2 asymmetric stretching. In the present case, 1409 cm-1 in the FTIR spectrum,
1447, 1362 and 1206 cm-1 theoretically are due to N-H in-plane bending vibration.
The modes 65, 68 and 69 having wavenumbers 538, 478 and 437 cm-1 are
calculated to N-H out of plane bending vibration.
4.4.2 C-H vibrations
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Table 4.4 Vibrational wavenumbers obtained for 4M3NPBSat B3LYP/6-31G(d,p) [(harmonic frequency cm−1), IR intensities (K mmol−1),Raman intensities (arb. units)].
Mode nos
Experimental (cm−1) FT-IR
FT-raman
DFT Calculated (cm−1) (scaled)
IbIR Ic
Raman Vibrational assignments PED (%)
1 3274 3275 3432 15.9 34.3 νNH(100) 2 3118 3105 3125 1.1 36.5 νCH(97) ring 2 3 3090 3076 3108 0.5 41.4 νCH(97) ring 2 4 3101 1.8 18.4 νCH(99) ring 2 5 3095 0.5 30.9 νCH(95) ring 1 6 3089 0.4 29.1 νCH(94) ring 1 7 3077 2.2 31.7 νCH(93) ring 2 8 3063 3.5 37.0 νCH(95) ring 1 9 3060 3.1 37.5 νCH(94) ring 1 10 2924 2935 3009 4.2 25.1 νCH(90) methyl 11 2979 4.1 44.1 νCH(100) methyl 12 2875 2924 6.5 100.0 νCH(100) methyl 13 1614 6.4 7.1 νON(22)+νCC(35)ring 2 14 1610 1602 1588 7.0 32.2 νCC(43) ring 1 15 1592 1575 28.6 19.9 νON(11)+νCC(38) 16 1523 1527 1563 50.6 10.2 νON(36)+νCC(10) 17 1562 14.5 8.2 νCC(39)ring 1 18 1475 2.1 0.5 βHCC(64) ring 1 + βCCC(10)ring 1 19 1466 22.1 1.0 βHCC(55)ring 2 20 1409 1447 14.1 7.2 νCC(13)+βHNC(15)+βHCC(11)ring 2 21 1446 4.1 7.7 βHCH(58)methyl 22 1438 1.9 8.5 βHCH(45) methyl 23 1384 3.0 0.6 νCC(35)+βHCC(22)ring 1 24 1371 0.1 17.0 βHCH(90)methyl 25 1362 32.0 1.8 νCC(25)+βHNC(40)ring 2 26 1343 100 80.3 νON(39)+νON(40)+βONO(11) 27 1309 11.0 3.1 νCC(33)ring 2 28 1299 1.5 1.3 νCC(52)ring 1 29 1283 3.6 0.5 βHCC(59) ring 1 30 1338 1353 1280 23.4 1.2 νSO(12)+βHCC(10) 31 1260 1286 1260 32.4 17.6 νNC(19)+νSO(34)+βHCC(10) 32 1224 1248 1206 23.1 23.0 νCC(13)+νNC(21)+βHNC(13)+βHCC(23) 33 1186 1.2 5.9 νCC(49)+βCCC(13)ring 1 34 1164 1.3 1.6 νCC(21)+βHCC(41)ring 2 35 1154 1.1 2.1 νCC(14)+βHCC(74)ring 1 36 1155 1169 1101 21.4 5.2 νCC(11)+νSO(13)+βHCC(32) 37 1093 37.1 11.8 νCC(13)+νSO(32)+βHCC(13) 38 1072 6.1 5.8 νCC(14)+νNC(14)+βHCC(24) 39 1089 1104 1071 6.4 0.9 νCC(23)+βHCC(37)ring 2 40 1046 26.7 3.2 νCC(31)+νSO(60) 41 1023 1.7 0.0 βHCH(24) methyl +�HCCC(55) 42 991 1015 992 2.5 0.5 βCCC(69)ring1 43 974 0.8 17.5 βCCC(67)ring1
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44 972 1.1 0.6 τHCCC(48) ring 1 45 954 948 0.1 0.3 τHCCC(72)ring1 46 946 0.4 0.1 τHCCS(84) 47 930 0.1 0.5 τHCCC(40)+ τHCCS(42) 48 925 19.2 1.7 νNC(29)+βCCC(17)ring 2 49 888 0.5 0.3 τHCCN(22)+ τHCCC(67)ring2 50 860 3.3 0.7 τHCCN(63)+ τHCCC(10) 51 821 0.2 1.5 τHCCS(43)+ τHCCC(42)ring2 52 811 1.1 3.0 νSN(22)+βONO(29) 53 818 815 796 4.0 1.7 βONO(16)+βCCC(11)ring 2 54 791 5.3 0.6 τHCCC(41)+ τHCCS(33)ring 1 55 780 2.1 6.1 τHCCC(26) ring 2 56 771 18.0 11.4 τHCCC(11)ring 2 57 722 718 13.1 1.1 τHCCC(12)+ τOCON(62) 58 685 4.4 0.7 τCCCC(61)ring 1 59 695 638 673 3.5 1.7 βONO(17)+βCCC(15) 60 655 3.0 0.2 τHCCC(17)+ τCCCC(58)ring 2 61 665 623 22.3 0.9 νCC(14)+νSC(14)+βCCC(24)+ τONOS(13) 62 621 1.5 2.7 βCCC(66)ring 1 63 613 612 8.9 2.5 νSN(11)+βCCC(25)ring 2 64 557 541 26.3 1.5 βONC(18)+βOSO(14)+βCSN(11) 65 538 8.2 0.5 τHNCC(28)+ τONOS(10)+ τNCCC(12) 66 532 514 8.4 0.4 βONC(28)+βNCC(10)+βOSO(12) 67 508 20.0 0.6 βONC(11)+ τONOS(30) 68 478 12.6 0.3 τHNCC(27)+ τCCCC(13)+ τCSCC(16) 69 437 6.0 1.3 τHNCC(31)+ τCCCC(11)ring 2 70 420 0.2 0.1 τHCCC(32)+ τCCCC(21)+ τNCCC(20) 71 407 0.1 0.5 βCCC(32)ring 1 72 398 0.1 0.1 τCCCS(58) ring 1 73 351 392 0.6 0.4 νNC(36)+βONO(12)+βCCC(15)ring 2 74 340 0.5 2.6 βOSO(13) 75 331 0.9 0.2 βCCC(30)+ τCCCS(10)+ τONCS(12) 76 315 303 0.6 0.8 βCCC(19)+βCSN(10) 77 273 0.0 1.8 βOSN(41) 78 266 0.9 1.9 νSC(31)+βNCC(11)+βOSN(19) 79 233 1.4 1.2 τCCCC(12)+ τCSCC(14) 80 209 0.0 0.3 βSNC(13)+ τCCCC(21)ring 1 81 178 161 0.4 0.5 βCCC(28)+ τONCS(11)+ τNCCC(21) 82 156 0.3 0.7 βCCC(18)+ τCCCC(11)+�NCCC(18) 83 131 0.3 0.7 βCCC(11)+βCSN(22) 84 99 1.1 0.6 βNCC(16)+βSNC(43) 85 84 0.2 0.8 τCCCS(36)+ τCSNC(15) 86 51 0.1 0.3 τONCC(80) 87 31 0.1 0.0 τHCCC(90)ring 1 88 28 0.0 2.8 τCCSN(42)+ τCCCS(10)+ τCSNC(29) 89 20 0.1 3.4 τCCSN(46)+ τCSNC(40) 90 7 0.2 1.7 τSNCC(84) ν, stretching; β, in plane bending; τ, out of plane bending; ring 1: tolyl ring ; ring 2 : nitrophenyl ring a Scaling factor: 0.961 for DFT (B3LYP)/6-31G(d,p) b Relative absorption intensities normalized with highest peak absorption equal to 100. c Relative Raman intensities normalized to 100.
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4000 3500 3000 2500 2000 1500 1000 500
B3LYP
Tran
smis
sion
(arb
.uni
ts)
wavenumber (cm-1)
Experimental
Figure 4.5(a) Experimental and Theoretical FTIR Spectra of 4M3NPBS
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3500 3000 2500 2000 1500 1000 500
Ram
an in
tens
ity (a
.u)
Wavenumber cm-1
Experimental
B3LYP
Figure 4.5(b). Experimental and Theoretical FT-Raman spectra of the 4M3NPBS
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115
The aromatic structures show the presence of C–H stretching vibrations in
the region 3100–3000 cm-1 which is the characteristic region for the ready
identification of C–H stretching vibrations. In this region, the bands are not
affected appreciably by the nature of substituents [59-60]. The modes (2-9) are due
to C–H stretching of hydrogen bonded carbon atoms of phenyl rings. These modes
are pure C–H stretching vibrations with a PED contribution nearly 90%. The
aromatic C–H in-plane bending modes of benzene and its derivatives are observed
in the region 1300–1000 cm-1 with a weak intensity in the vibrational spectra
[61-62]. The C–H out-of-plane bending vibrations occur in the range
1000-750 cm-1 in the aromatic compounds [61-62]. The computations suggest that
the expected other bands of C-H in-plane or out-of plane bending vibrations are
masked by other strong vibrational modes. The same trend is observed in the
4M3NPBS compound. The C-H asymmetric stretching vibrations of the CH3 group
are seen between 3060 cm-1 and 2984 cm-1. The symmetric alkyl C-H stretching
band of the CH3 group is observed at 2924, 2875 cm-1 in the IR spectrum, 2935
cm-1 in the Raman spectrum 3009, 2979 and 2924 cm-1 theoretically. The other
fundamental CH3 group vibrations which are CH3 bending, CH3 rocking appear in
the wavenumber region of 1461-792 cm-1. The wavenumbers 1446, 1438 and 1371
cm-1 of the modes 21, 22 and 24 are due to in plane bending vibration of methyl
group. The wavenumbers 1023, 972 and 31 cm-1 of the modes 41, 44 and 87 are
due to methyl torsion.
4.4.3 C-C vibrations
The aromatic carbon–carbon stretching vibration occurs in the region
1589-1301 cm-1. In the present work, the wavenumbers observed at 1610,
1592 cm-1 in the IR spectrum, 1602 cm-1 in the Raman spectrum and 1588, 1562,
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116
1447, 1384, 1309 and 1299 cm-1 theoretically are due to aromatic C-C stretching
vibrations.
4.4.4 Heavy Atoms Fundamentals Vibrations
The asymmetric and symmetric stretching modes of SO2 group appear in
the region1360-1310 cm-1 and 1165-1135 cm-1 [66]. Chohan et al. [63] reported the
SO2 stretching vibrations at 1345, 1110 cm-1 for sulfonamide derivatives.
Hangen et al [64] reported SO2 modes at 1314, 1308, 1274, 1157, 1147, 1133 cm-1
for sulfonamide derivatives. The observed bands at 1338, 1155cm-1 in the IR
spectrum, 1353, 1169 in the FT-Raman spectrum and 1280, 1260, 1101 and 1093
cm-1 theoretically are assigned as SO2 stretching modes. The SO2 scissoring and
wagging vibrations occur in the range 570± 60 cm-1 and 520±40cm-1 [66]. The
corresponding bands are observed for 4M3NPBS compound at 557 cm-1 and 532
cm-1 in the FT-IR spectrum, calculated as 541 and 514 cm-1 respectively.
Aromatic nitro compounds showed strong absorption due to the
asymmetric and symmetric stretching at 1570-1485 cm-1 and 1370-1320 cm-1
respectively [65]. The asymmetric stretching was observed at 1523 cm-1 in the
FTIR spectrum, 1527 cm-1 in the FT-Raman spectrum and 1575 and 1563 cm-1
theoretically. The calculated value of 1343 cm-1 with a PED contribution 79% was
assigned to symmetric stretching mode. The deformation vibrations of NO2 group
(scissoring, wagging, rocking and twisting) were observed in the low frequency
region [66]. A strong band at 818 cm-1 was assigned to NO2 scissoring mode [66].
In the present case, 818 cm-1 in the FTIR spectrum, 815 cm-1 in the FT-Raman
spectrum and 796 and 695 cm-1 theoretically.
The S-N stretching vibration is expected [67] in the region 905 ± 30 cm-1.
The C-S stretching vibration is expected at the wavenumber 666 cm-1
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experimentally and at the wave number 672 cm-1 theoretically [67]. In the present
case, modes of 811 and 612cm-1 are due to S-N stretching vibration.
Panicker et al [68] reported the CN stretching modes at 1219, 1237 cm-1 and at
1292, 1234 and 1200 cm-1 theoretically. The C-N stretching modes are observed at
1224 and 1089 cm-1 in the IR spectrum, 1286 in the Raman spectrum, and at 1260,
1206 and 1065 cm-1 theoretically. The above conclusions are in good agreement
with the similar sulfonamide compounds [69].
4.5 FTNMR SPECTRAL ANALYSIS
The FTNMR spectra are presented in Figures 4.6 (a) and 4.6(b)
respectively and the chemical shifts are tabulated with the assignments in Table
4.5. As it is seen in Figure 4.6 (a), this compound shows thirteen different Carbon
atoms, which is consistent with the structure on the basis of molecular symmetry. 1H NMR spectrum Figure 4.6(b) of the title compound is investigated, it can be
seen that total number of protons are in agreement with the integration values
presented in this spectrum.
Chemical shifts were reported in ppm relative to TMS for 1H NMR and 13C NMR spectrum provides information about the number of different types of
protons and also the nature of immediate environment of each of them. 13C NMR
spectrum also provides the structural information with regard to different carbon
atoms present in the molecules. The chemical shifts of aromatic protons and
aromatic carbons of substituted sulfonamides are shown by Gowda et al [70]. In
the 1H NMR spectrum, a singlet at 2.3 ppm indicates the three protons of methyl
group. The above said methyl group protons are calculated in the range of
1.7 ppm - 2.09 ppm for B3LYP. The eleven aromatic protons of nitrophenyl and
tosyl group are appeared as multiplet in the range of 7-8 ppm and are calculated in
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Table 4.5
The chemical shift in 1H NMR and 13CNMR spectrum of 4M3NPBS crystal
Spectrum Experimental (CDCl3) signal
at δ(PPM)
B3LYP Calculated
Chemical shift at δ(PPM)
Group Identification
1H NMR 2.41(singlet)
1.768 1.765 2.095
3 protons of the Methyl carbon(C7)
7.97 7.95 7.93 7.63 7.51 7.49 7.45 7.29
8.96 8.01 7.92 7.76 7.75 7.73 7.46 7.19
Proton of (C6) Proton of (C2) Proton of (C11) Proton of (C13) Proton of (C5) Proton of (C3) Proton of (C10) Proton of (C9)
7.29 5.8 N-H Proton 13C NMR 21.59 10.79 C7 methyl group carbon 148.77 139.20 C 12 (NO2 attached carbon) 144.78 135.53 C4 (methyl group attached
carbon) 138.03 127.31 C8 (N-H attached carbon) 135.45 126.51 C1(SO2 attached carbon) 130.27 122.46 C9 130.24 117.47 C10 127.30 115.30, 115.20 Meta carbons of tolyl ring 126.23 114.09, 112.95 Ortho carbons of tolyl ring 119.64 110.04 C11 115.13 105.61 C13 76.77-77.28 79.86 Carbon of the solvent CDCl3
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Figure 4.6(a). The 1H NMR spectrum of 4M3NPBS.
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Figure 5b The 13C NMR of the title compound.
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118
the range of 7.19-8.96 ppm for B3LYP. The N1H group of the nitrophenyl is
responsible for the appearance of broad singlet at 7.25 ppm and calculated as
5.8ppm for B3LYP. In general, highly shielded protons appear downfield and vice
versa. The protons associated with the carbons C6 and C2 are appeared at higher
chemical shift of 8 ppm, 8.96 ppm theoretically. The protons associated with C5
and C3 are appeared at upfield chemical shift of 7.51 and 7.49 ppm, calculated as
7.75 and 7.73 ppm because of shielding by the hyperconjugative effect of methyl
group. The protons associated with C13 and C11 are appeared at high chemical
shift of 7.93 and 7.63 ppm, calculated as 7.92 and 7.76 ppm due to the
electronegative effect of nitro group. The proton associated with C10 carbon is
appeared at 7.45 ppm in the proton NMR spectrum, calculated as 7.46 ppm. In the
13C NMR spectrum, the methyl carbon of the tolyl group give signal at 21.59
ppm, calculated as 10.79 ppm. The sixteen aromatic carbons of the nitrophenyl and
tolyl group are appeared as multiplet in the range of 115.13–148.77 ppm and are
found to be in the range of 105.61–139.20 ppm for B3LYP. The C12 carbon of the
phenyl ring appears 148.77 ppm, due to neighbouring nitro group, calculated as
139.20 ppm. The signal at 144.78ppm is assigned to the C4 carbon of the tosyl ring
which is bonded with methyl group, calculated as 135.53ppm. The signal at
138.03 ppm is assigned to the C8 carbon of the phenyl ring which is bonded with
N-H group, calculated as 127.31 ppm. The signal at 135.45 ppm is assigned to the
C1 carbon of the tolyl ring which is bonded with sulfonyl group, calculated as
126.51 ppm. The Meta carbons (C3,C5) of the tosyl ring are responsible for the
signal at 127.30 ppm, calculated as 115.30 ppm. The ortho carbons (C2,C6) of the
tosyl ring are responsible for the signal at 126.23 ppm, calculated as 114.09 ppm
and 112.67 ppm. The signals at 130.27 ppm, 130.24 ppm, 119.64 ppm, 105.13 ppm
are assigned to the (C9, C10, C11 and C13) carbons of the nitrophenyl ring. The
above said carbons of the nitrophenyl ring are calculated as, 122.46 ppm,
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119
122.46 ppm, 110.04 ppm and 105.61 ppm for B3LYP. (See ortep diagram for
numbering of atoms). A Signal at 76 –78 ppm indicates the carbon atom of the
CDCl3 (solvent), calculated as 79 ppm. As it is seen from the Table 4.5, calculated 1H and 13C chemical shifts values of the title compound are generally agreement
with the experimental 1H and 13C chemical shifts data.
4.6 NBO ANALYSIS
NBO analysis provides a possible, “natural Lewis structure” picture of ø,
because all orbital details are mathematically chosen to include the highest
possible percentage of the electron density. A useful aspect of the NBO method is
that it gives information about interactions in both filled and virtual orbital spaces
that could enhance the analysis of intra-and intermolecular interactions. The
second order Fock matrix was carried out to evaluate the donor–acceptor
interactions in the NBO analysis [69-71]. The interactions result is a loss of
occupancy from the localized NBO of the idealized Lewis structure into an empty
non-Lewis orbital. For each donor (i) and acceptor (j), the stabilization energy E(2)
associated with the delocalization i→j is estimated as
E(2) = ∆Eij = qi ⎟⎟⎠
⎞⎜⎜⎝
⎛
− )(),( 2
ij
jiFεε
(4.1)
Where qi is the donor orbital occupancy, are εi and εj diagonal elements
and F(i,j) is the off diagonal NBO Fock matrix element. Natural bond orbital
analysis provides an efficient method for studying intra and intermolecular
bonding and interaction among bonds, and also provides a convenient basis for
investigating charge transfer or conjugative interaction in molecular systems. Some
electron donor orbital, acceptor orbital and the interacting stabilization energy
resulted from the second-order micro-disturbance theory are reported [72]. The
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120
larger the E(2)value, the more intensive is the interaction between electron donors
and electron acceptors, i.e. the more donating tendency from electron donors to
electron acceptors and the greater the extent of conjugation of the whole system.
Delocalization of electron density between occupied Lewis type (bond or lone
pair) NBO orbitals and formally unoccupied (antibond or Rydgberg) non- Lewis
NBO orbitals correspond to a stabilizing donor–acceptor interaction. NBO analysis
has been performed on the molecule at the DFT/B3LYP/6-31G(d,p) level in order
to elucidate the conjugation, hyperconjugation and delocalization of electron
density within the molecule. The intra molecular interaction are formed by the
orbital overlap between (σ and π (C–C, C-H and CN) and σ*and π *(C-C, C-H and
C-N)) bond orbital which results intra molecular charge transfer (ICT) causing
stabilization of the system. These interactions are observed as increase in electron
density (ED) in C–C anti bonding orbital that weakens the respective bonds [73].
The electron density of conjugated double as well as single bond of the aromatic
ring (~1.9e) clearly demonstrates strong delocalization inside the molecule. The
strong intramolecular hyperconjugation interaction of the σ (C –C) to the π*(C–C)
bond in the ring leads to stabilization of some part of the ring as evident from
Table 4.6. For example, the intramolecular hyper conjugative interaction of
σ (C1–C6) distribute to σ * (C1–C2) leading to stabilization of ~6.0 kJ/mol. This
enhanced further conjugate with anti-bonding orbital of π*(C2–C3) and (C4–C5),
leads to strong delocalization of 24.76 and 15.64 kJ/mol respectively. The
magnitude of charges transferred from (LP(2)O9)→(C16-H29) shows weak
intramolecular interaction which is shown in the hydrogen bonding interactions of
XRD result. The magnitude of charges transferred from (LP(2)O9)→(C1-S7) and
(LP(1)N10)→(C11-C12) show that stabilization energy of about ~18.17 KJ/mol
and ~ 49 KJ/mol respectively. The delocalization of electron π*(C2-C3) to
π*(C4-C5) with enormous stabilization energy of about ~ 335.75 KJ/mol.
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Table 4.6
Second order perturbation theory analysis of Fock matrix in NBO basis
Donor (i) Type ED(e)
AcceptorType ED(e)
E(2)a (KJ/mol)
E(j)-E(i)b(a.u)
F(i,j)c
(a.u)
C1-C2 σ 1.9691 C1-C6 σ* 0.0281 7.16 1.41 0.09
C2-C3 σ* 0.023 5.5 1.43 0.079
C1-C6 σ 1.9696 C1-C2 σ* 0.0304 7.56 1.4 0.092
σ C5-C6 σ* 0.0205 4.74 1.42 0.074
C1-C6 π 1.9696 C2-C3 π* 0.3069 24.76 0.33 0.081
C4-C5 π* 0.3236 15.64 0.34 0.065
C2-C3 π 1.6643 C1-C6 π* 0.3881 19.58 0.3 0.069
C4-C5 π* 0.3236 24.9 0.32 0.081
C4-C5 π 1.9677 C1-C6 π* 0.3881 29.54 0.29 0.083
C2-C3 π* 0.3069 19.79 0.31 0.071
C1-S7 σ 1.9609 C2-C3 σ* 0.3023 3.03 1.37 0.058
C5-C6 σ* 0.0205 2.59 1.36 0.053
S7- O8 σ* 0.1188 2.57 1 0.046
S7- O9 σ* 0.1477 3.43 1 0.054
S7- N10 σ* 0.2763 2.56 0.81 0.043
N10-H25 σ* 0.0227 0.68 1.01 0.024
N17-O18 σ 1.9948 C13-C14 σ* 0.4254 6.19 0.53 0.057
N17-O19 σ 1.9931 C13-C14 σ* 0.0295 2.97 1.55 0.051
LP(2)O9 σ 1.81254 C16-H29 σ* 0.0481 0.83 0.73 0.023
LP(2)O9 σ 1.82125 C1-S7 σ* 0.20187 18.17 0.43 0.08
LP(1)N10 π 1.76109 C11-C12 π* 0.37596 49.05 0.34 0.119
C1-C6 π* 1.6943 C2-C3 π* 0.30699 251.37 0.01 0.089
C1-C6 π* 1.6943 C4-C5 π* 0.32365 165.94 0.02 0.095
C2-C3 π* 1.66043 C4-C5 π* 0.32365 335.75 0.01 0.094 a E(2) means energy of hyper conjugative interaction (stabilization energy). b Energy difference between donor and acceptor i and j NBO orbitals. c F(i,j) is the fork matrix element between i and j NBO orbitals.
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121
4.7 NONLINEAR OPTICAL EFFECTS
Hyperpolarizabilities are very sensitive to the basis sets and levels of
theoretical approach employed [74-76], that the electron correlation can change the
value of hyperpolarizability. Urea is one of the prototypical molecules used in the
study of the Non Linear Optical (NLO) properties of molecular systems. Therefore
it has been used frequently as a threshold value for comparative purposes. The
calculations of the total molecular dipole moment (μ), linear polarizability (α) and
first-order hyperpolarizability (β) from the Gaussian output have been explained in
detail previously and DFT has been extensively used as an effective method to
investigate the organic NLO materials [74-76]. The polar properties of the title
compound were calculated at the DFT (B3LYP)/6-31G(d,p) level using Gaussian
03W program package. Urea is one of the prototypical molecules used in the study
of the NLO properties of the molecular systems. Therefore it was used frequently
as a threshold value for comparative purposes. The calculated values of β for the
title compound is 56.02x10-31esu shown in Table 4.7, which are 9.23 times greater
than those of urea (β of urea is 6.0690×10−31 esu obtained by DFT (B3LYP)/6-
31G(d,p) method). Since the values of the first hyperpolarizability tensors of the
output file of Gaussian 03W are reported in atomic units (a.u.), the calculated
values were converted into electrostatic units (1 a.u. = 8.6393×10−33 esu. The
4M3NPBS with greater dipole moment and hyperpolarizability value than urea
shows that the molecule has large NLO optical property.
4.8 MULLIKEN ATOMIC CHARGES
Mulliken atomic charge calculation plays an important role in the
application of quantum mechanical calculations to molecular systems. The
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Table 4.7
The first hyperpolarizability of 4M3NPBS
B3LYP
6-31G(d,p)
a.u (esux10-33)
Βxxx 15.21 131.4038
Βxxy -78.42 -677.494
Βxyy -174.153 -1504.56
Βyyy -465.443 -4021.1
Βxxz -68.449 -591.351
Βxyz 2.898 25.03669
Βyyz 64.767 559.5415
Βxzz -22.675 -195.896
Βyzz -64.242 -555.006
Βzzz 136.893 1182.66
Βtotal 648.476 5602.379
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Figure 4.7 Mulliken Charge distribution of 4M3NPBS
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122
calculated Mulliken charge values of 4MNBS are listed in Table 4.8. The charge
distribution is shown in Fig 4.6. The Mulliken atomic charge analysis of 4MNBS
shows that the presence of two oxygen atoms in the sulphonamide moiety (O8
=−0.0731); (O9=−0.1872) imposes positive charge on the sulfur atom
S7 = 0.6780. However, the carbon atoms C1, C3, C5, C12, C13 and C15 posses
small negative charges, whereas carbon atoms C2, C4, C6 C11, C14 and C16
posses positive charge due to large negative charge (-0.3133 and -0.3085) of N10
and N17. Moreover, there is no difference in charge distribution observed on all
hydrogen atoms except the H25 and methyl group hydrogens (H30, H31 and H32).
The large positive charges on H25 (0.3511) and H31 (0.1687) is due to large
negative charge accumulated on the N10 atom and C20 (methyl carbon) atom
respectively.
4.9 MOLECULAR ELECTROSTATIC POTENTIAL
Molecular Electrostatic potential at the B3LYP/6-31G(d,p) optimized
geometry wascalculated. The molecular electrostatic potential (MEP) is related to
the electronic density and a very useful descriptor for determining sites for
electrophilic attack and nucleophilic reactions as well as hydrogen–bonding
interactions [77]. As it is seen in Figure4.9, the red region is localized on the
oxygen atoms of nitro group and sulfonyl group has value of -0.075 a.u. and the
maximum blue region localized on the N1–H1 bond has value of +0.077 a.u,
indicating the possible sites for electrophilic attack and nucleophilic reaction
respectively. These sites give the information about the region, from where the
compound can have intermolecular interactions. Hence, the molecular electrostatic
potential map confirms the existence of intermolecular N–H-O interactions.
4.10 ELECTRONIC ABSORPTION SPECTRUM
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-.075 .077
Figure 4.8. Molecular Electrostatic Potential (MEP) of 4M3NPBS.
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123
The UV–vis electronic spectrum of compound in ethanol solution was
recorded within 200–800 nm range is shown in Fig.4.10. To support experimental
observations, the theoretical electronic excitation energies, absorption wavelength
and oscillator strength were calculated by the TDDFT/PCM within GAUSSIAN03
program. This calculation was performed assuming the title compound was in the
gas phase and without solvent effects. The comparison between the measured and
computed UV-Vis data at 221 nm and 322 nm (experimental) show good
agreement with computed TD-DFT data at 207.7 nm and 309.27 nm by
TD-B3LYP/6-31G(d,p) method. These excitations correspond to π-π* and n to π*
and electronic transitions. The analysis of the wave function indicates that the
electron absorption corresponds to the transition from the ground to the first
excited state.
It is mainly described by one-electron excitation from the highest occupied
molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO).
The HOMO energy characterizes the ability of electron giving, LUMO
characterizes the ability of electron accepting, and the gap between HOMO and
LUMO characterizes the molecular chemical stability [78]. The HOMO is located
over the entire rings except methyl group of the tolyl ring and nitro group of the
phenyl ring. LUMO is delocalized on the nitrophenyl moiety. The HOMO to
LUMO transition implies an electron density transfer to the nitrophenyl ring from
tolyl moiety. The HOMO and LUMO surfaces are sketched in Figure 4.10.
According to the B3LYP/6-31G(d,p) calculation, the energy gap between
(ΔE) transition from HOMO (-2.48 eV) to LUMO (-1.36 eV) of the molecule is
about -1.12 eV. The lower value of HOMO and LUMO energy gap explains the
eventual charge transfer interactions taking place within the molecule.
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Figure 4. 9 UV-VIS absorption Spectrum of 4M3NPBS
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Figure 4. 10 HOMO‐LUMO surfaces of 4M3NPBS
LUMO plot
ELUMO=‐2.48 eV
Energy Band Gap=‐1.12 eV
EHOMO = ‐2.48 eV
HOMO Plot
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124
The quantum chemical reactivity descriptors of molecules such as hardness,
chemical potential, softness, electronegativity and electrophilicity index as well as
local reactivity have been calculated. The computed quantum chemical descriptors
based upon DFT calculations are presented in Table 4.9.
4.11 THERMAL ANALYSIS
Thermal analysis of 4M3NPBS was carried out using a Perkin Elmer
model, simultaneous thermo gravimetric/differential thermal (TG/DT) analyser.
The sample was scanned in the temperature range 100-1000 ⁰C at a rate of 10 ⁰C
for 1 sec. The TG/DT curve is shown in Fig. 4.11. The first endothermic peak
observed at 142.9oC is attributed to the melting point of the 4M3NPBS crystal. At
the melting point, no weight loss was observed in the TG curve. The weight loss
starts around 293oC and the major weight loss (64%) takes place over a large
temperature range (293-450oC). Almost all the compounds decomposed as gaseous
products over a temperature range (450-1000oC). The 4M3NPBS is chemically
stable up to 293oC, above which temperature the sample gradually decomposes.
No exothermic or endothermic peak was observed below the melting point
endotherm, indicating the absence of any isomorphic phase transition in the
sample.
4.12 CONCLUSION
4-methyl-N-(3-nitrophenyl)benzene sulfonamide has been synthesized and
characterized by FTIR, NMR and X-ray single-crystal diffraction. Theoretical
(B3LYP) structural parameters and scaled vibrational frequencies are in agreement
with the experimental values. Any discrepancy noted between the observed and the
calculated values may be due to the fact that the calculations were actually done on
a single molecule in the gaseous phase contrary to the experimental values
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125
recorded in the solid state where the presence of intermolecular Coulombic
interactions. The considerable differences between experimental and calculated
results of FTIR and FT-Raman can be attributed to the existence of N-H-O type
intermolecular hydrogen bonds in the crystal structure. Theoretical 1H and 13C
chemical shift values (with respect to TMS) were reported and compared with
experimental data, showing good agreement for both 1H and 13C. NBO result
reflects the charge transfer mainly due to C–C group. The 4M3NPBS exhibited
good NLO activity. Moreover, frontier molecular orbitals and molecular
electrostatic potential were visualized. Electronic transition and energy band gap of
the title molecule were investigated and interpreted. The lower energy gap
-1.12 eV illustrates the high reactivity of the title compound and the most
prominent transition corresponds to π-π* electronic transition. The title compound
is chemically stable up to 293°C.
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126
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