CHAPTER IV SPECTROSCOPIC AND MOLECULAR STRUCTURE...

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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109

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.


110

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.


Figure 4.1. Pathway of the synthesis of 4M3NPBS.

NO2

NH

NO2

NH2

+SO2Cl

CH3

SO2

H3C

︵C2H5 ︶N3ACETONE


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


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].


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)


111

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-


112

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,


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


Figure 4.3 Molecular Packing Diagram of 4M3NPBS

Figure 4.4 Plot of Calculated Versus Experimental bond lengths


113

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.


114

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


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


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.


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


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


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,


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


117

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


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


Figure 4.6(a). The 1H NMR spectrum of 4M3NPBS.


Figure 5b The 13C NMR of the title compound.


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,


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


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.


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.


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


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


Figure 4.7 Mulliken Charge distribution of 4M3NPBS


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


-.075 .077

Figure 4.8. Molecular Electrostatic Potential (MEP) of 4M3NPBS.


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.


Figure 4. 9 UV-VIS absorption Spectrum of 4M3NPBS


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


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


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.


126

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CHAPTER IV SPECTROSCOPIC AND MOLECULAR STRUCTURE...

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