81

CHAPTER – IV

DENSITY FUNCTIONAL THEORY STUDY AND

VIBRATIONAL ANALYSIS OF FT-IR AND

FT-RAMAN SPECTRA OF N-HYDROXYPHTHALIMIDE

4.1 INTRODUCTION

Phthalimide and its derivatives are very important compounds.

They are used in the synthesis of antimicrobial activity, antiandrogens and

other agents for treating tumour necrosis factor. Certain phthalimide

derivatives are used as herbicides and for reducing bacterial

contamination. On industrial side, they are acting like bleaching

detergents, anion exchange resins, antidepressants, heat resistant

polymers, flame-retardants, etc.[105]. Consideration of all these factors

led to undertake a detailed infrared and Raman spectral studies and

vibrational assignments of N-hydroxyphthalimide.

The vibrational wavenumbers obtained by quantum chemical

calculations are typically larger than their experimental counterparts[63]

and they have to be scaled by empirical scaling factors ranging from 0.8

to 1.014. These scaling factors are determined from the mean deviation

between the calculated and experimental wavenumbers[106-108]. The

aim of this work is to predict the vibrational spectra of

N-hydroxyphthalimide by applying the density functional theory (DFT)

calculations based on Beck3-Lee-Yang-Parr (B3LYP) level with the use of

the standard 6-31G* basis set. The calculated vibrational wavenumbers

82

were compared with obtained experimental results and simulated and

observed spectra were also analysed in detail.

4.2 EXPERIMENTAL DETAILS

Spectroscopically fine samples of N-hydroxyphthalimide is obtained

from Lancaster Chemical Company, UK, and used as such without further

purification for the spectral measurements. The room temperature

Fourier transform infrared spectra of the title compound is measured in

the region 4000–400 cm-1, at a resolution of ±1cm -1, using BRUCKER IFS

66V vacuum Fourier transform spectrometer, equipped with an MCT

detector, a KBr beam splitter and globar source. Fourier transform Raman

spectra of the title compound is measured in the range of 4000 – 50 cm-1,

using Bruker RFS 100/S FT-Raman spectrometer.

4.2 COMPUTATIONAL DETAILS

Density functional theory calculation was carried out by means of

the 2003 version of the GAUSSIAN suit of program package[73] with

B3LYP level and the standard 6-31G* basis set[71,72] The normal grid

(50, 194) was used for numerical integration. The Cartesian

representation of the theoretical force constants has been computed at

the fully optimized geometry by assuming Cs point group symmetry,

scaling of the force fields were performed by the scaled quantum

mechanical procedure.

83

LYBB

ijji

scaled

ji FccF32

1

)( …(4.1)

Where Ci is the scale factor of coordinate i, F i j B3LYP is the

B3LYP/6-31G* force constant in the local internal coordinates, and F ijscaled

is the scaled force constant. The multiple scaling of the force constants

was performed by the quantum chemical method with selective scaling in

the local symmetry coordinate representation[109] using transferable

scale factors available in the literature[110]. The transformation of force

field from Cartesian to symmetry coordinate, the scaling, the subsequent

normal coordinate analysis, calculations of total energy distribution (TED),

IR and Raman intensities were done on a PC with the version V7.0-G77

of the MOLVIB program written by Sundius[87,111]. To achieve a close

agreement between observed and calculated, the least square fit

refinement algorithm was used to recalculate the normal modes, TED and

the corresponding theoretically expected IR intensities.

The prediction of Raman intensities was carried out by following the

procedure outlined below. The Raman activities (S i) calculated by the

Gaussian–2003 program and adjusted during scaling procedure with

Molvib were converted to relative Raman intensities (I i) using the following

relationship derived from the basic theory of Raman scattering.

)2...(..........)/exp(1

)( 4

kThc

SfI

ii

iioi

Where 0 is the exciting (in cm-1 units), i is the vibrational

wavenumber of the ith normal mode, h, C and k are fundamental

84

constants, and f is a suitably chosen common normalization factor for all

peak intensities.

4.4 RESULTS AND DISCUSSION

4.4.1 Molecular structure and symmetry

The labeling of atoms of the title compounds is shown in Fig.4.1.

The optimized geometrical parameters are presented in Table 4.1. The

global minimum energies obtained by the DFT structure optimization for

the title compound is –588.243143183 Hartrees for B3LYP/6-31G* basis

set. N-hydroxyphthalimide belong to Cs point group symmetry. With 17

atoms composing each structure, each molecule has 45 fundamental

modes of vibrations. For molecules of Cs symmetry, group theory

analysis indicates that the 45 fundamental vibrations will reduce as:

vib = 31A। (in-plane)+ 14A॥ (out-of-plane). From the structural point of

view of the molecules N-hydroxyphthalimide have 18 stretching vibrations,

13 in-plane bending vibrations and 14 out-of-plane bending vibrations.

4.4.2 Assignment of spectra

Detailed description of vibrational modes can be given by means of

normal coordinate analysis. For this purpose, the full set of 66 standard

internal coordinates containing 21 redundancies were defined as give in

Table 4.2. From these, a non-redundant set of local symmetry

coordinates were constructed by suitable linear combinations of internal

coordinates following the recommendations of Pulay et al[112] and they

are presented in Table 4.3. The theoretically calculated density functional

85

theory force fields were transformed to this latter set of vibrational

coordinates and used in all subsequent calculations.

The observed and calculated wavenumbers and normal mode

descriptions for the title compound are reported in Tables 4.4. The

observed and simulated IR spectra of N - hydroxyphthalimide are

presented in Fig. 4.2 and the observed and simulated Raman spectra of

N - hydroxyphthalimide are presented in Fig.4.3. When using

computational methods to predict theoretical normal vibrations for

relatively complex polyatomics, scaling strategies are used to bring

computed wavenumbers into closer agreement with observed

wavenumbers. For the DFT method employed in this work the simplest

limiting scaling strategy was used.

The average difference between unscaled wavenumbers and

observed wavenumbers for N-hydroxyphthalimide was approximately

13.46 cm-1. In order to reproduce the observed wavenumbers, refinement

of scaling factors were applied and optimized via least square refinement

algorithm which resulted an average difference of 6.69 cm-1 between the

experimental and scaled quantum mechanical (SQM) wavenumbers for

6-31G* basis set.

All vibrational assignments are based on the respective point group

symmetry for each molecule. Assignments were made through

visualization of the atomic displacement representations for each

vibration, viewed through GAUSSVIEW[113] and matching the predicted

normal wavenumbers and intensities with experimental data. It is

86

convenient to discuss the vibrational spectra of N-hydroxyphthalimide in

terms of characteristic spectral regions as described below.

4.4.3 C–H Vibrations

Aromatic compounds commonly exhibit multiple weak band in the

region 3100–3000 cm-1 due to aromatic C–H stretching vibrations. The

bands due to C–H in-plane ring bending vibrations, interacting somewhat

with C–C stretching vibrations, are observed as a number of medium and

weak intensity sharp bands in the region 1300–1000 cm-1. The C–H out-

of-plane bending vibrations are strongly coupled vibrations and occur in

the region 900–667 cm-1. Hence, the bands appeared at 3170, 3166,

3156, and 3144 cm-1 in the title compound have been assigned to C–H

stretching vibrations. The in-plane and out-of-plane bending vibrations of

C–H group have also been identif ied for the title compound and they are

presented in Table 4.4.

4.4.4 C=O Vibrations

The carbonyl stretching is very sensitive to the factors that disturb

the nature of the carbonyl group and its precise is characteristic of the

type of the carbonyl compound being studied. Particularly detailed

correlations have been made for the carbonyl bond stretching . The

carbonyl stretching has been most extensively studied by infrared and

Raman spectroscopy. This multiply bounded group is highly polar and

therefore gives rise to an intense infrared absorption band. The carbon-

oxygen double bond is formed by the p –p bonding between carbon and

oxygen. Because of the different electro-negativities of carbon and

oxygen atoms, the bonding electrons are not equally distributed between

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the two atoms. The following two resonance forms contribute to the

bonding of the carbonyl group C=O C+ – O –.

The lone pair of electrons on oxygen also determines the nature of

the carbonyl group. The position of the C=O stretching vibration is very

sensitive to various factors, such as the physical state, electronic effects

by substituents, ring strains, etc.[1] Consideration of these factors

provides further information about the environment of the C=O group.

The carbonyl stretching generally occurs as a strong absorption in the

region from 1730 to 1645 cm -1. This portion of the infrared and Raman

spectrum is most useful because the position of the carbonyl absorption is

quite sensitive to substitution effects and the geometry of the molecule.

In the present investigation, the peaks identified at 1775 cm -1 have been

assigned to C=O stretching vibrations.

4.4.5 C–N Vibrations

The identification of C–N vibrations is a difficult task since the

mixing of vibrations is possible. However, with the help of force field

calculations the C–N vibrations are identified and assigned in this study.

The bands appearing at 1336, 1367 and 1431 cm -1 were designated to

C–N stretching vibrations. The assignments of C–N in-plane and out-of-

plane bending vibrations made in the study were also supported by the

literature[114,115].

4.4.6 C–C vibrations

Benzene has two degenerate modes, e2g (1596 cm-1) and e1u

(1485 cm-1), and two non-generate modes, b2u (1310 cm-1) and a1g

88

(995 cm-1), due to skeleton stretching of C–C bonds. Bands between

1400 and 1650 cm-1 are assigned to these modes. The actual positions

are determined not so much by the nature of the substituents, but by the

form of substitution around the ring. All the wavenumbers except that of

the ring breathing mode (995 cm-1) remain practically unaffected by

substitution. In this study, the bands observed in FT-IR and FT-Raman at

1614, 1516 and 1501 cm-1 are assigned to C=C stretching vibrations[105].

The in-plane and out-of-plane bending vibrations of carbon atoms are

found in the respective characteristic region and they are listed in

Table 4.4.

4.4.7 O–H and N–O Vibrations

Because of greater electro negativity of oxygen than nitrogen the

O–H stretching results in greater change in bond moment. The O–H

stretching vibrations normally occur in the region 3500-3600cm-1 of

infrared spectrum. In the title compound, the infrared bands identified at

3476 cm-1 is designated to O–H stretching vibrations. The bands

identified at 270 and 185 cm-1 in Raman spectra are described to the

wagging vibration of N–O.

4.4.8 Ring Vibrations

The ring stretching, in-plane and out-of-plane bending vibrations

have been identified and presented in Table 4.4. They are also supported

by literature[116].

89

4.5 CONCLUSION

The DFT based SQM approach provides the most reliable

theoretical information on the vibrational properties of medium-size

molecules. Based on that force field obtained by density functional theory

calculations at B3LYP/6-31G* level, the vibrational wavenumbers, infrared

intensities and Raman activities were calculated and a complete

vibrational analysis of the title compound has been carried out.

Refinement of scaling factors applied in this investigation achieved a

weighted rms deviation of 6.69 cm-1 between the experimental and SQM

wavenumbers.

90

Table 4.1 Optimized geometrical parameters of N-hydroxyphthalimide

obtained by B3LYP/6-31G* density functional calculations

Parameters Bond length of

N-HPh (Å) Parameters

Bond angle of

N-HPh (0)

C1–N2 1.4733 C1–N2–C3 115.19

N2–C3 1.4733 N2–C3–C4 102.89

C3-C4 1.5387 C3–C4–C5 109.37

C4-C5 1.3783 C4–C5–C6 121.56

C5–C6 1.3913 C5–C6–C7 117.43

C6–C7 1.4110 C6-C7-C8 121.03

C7–C8 1.4205 C7–C8–C9 121.09

C8–C9 1.4110 N2–C1–O10 122.86

C1–O10 1.2584 C1–N2–O11 121.04

N2-O11 1.3600 C3–N2–O11 123.77

C3–O12 1.2584 N2–C3–O11 126.99

C9–H13 1.0700 C4–C3–O12 130.11

C8–H14 1.0700 C8–C9–H13 121.67

C7–H15 1.0700 C7–C8–H14 119.41

C6–H16 1.0700 C9–C8–H14 119.49

O11–H17 0.9600 C6–C7–H15 119.51

C8–C7–H15 119.46

C5–C6–H16 120.99

C7–CH–H16 121.57

N2–O11–H17 101.47

N-HPh: N-hydroxyphthalimide

91

Table 4. 2

Definition of internal coordinates of N-hydroxyphthalimide

No. Symbol Type Definition

Stretching

1-4 ri C–H C6–H16, C7–H15, C8–H14, C9–H13

5 Ri N–O N2–O11

6-7 pi C–N C1–N2, C3–N2

8-9 qi C=O C3–O12, C1–O10

10-7 Qi C–C C3–C4, C4–C5, C5–C1, C4–C9, C9–C8,

C8–C7, C7–C6, C6–C5

18 i O–H O11–H17

Bending

19-26 i C–C–H C7–C6–H16, C5–C6–H16, C8–C7–H15,

C6–C7–H15, C9–C8–H14, C7–C8–H14,

C4–C9–H13, C8–C9–H13

27-28 i C–C=O C4–C3–O12, C5–C1–O10

29-30 i N–C=O N2–C3–O12, N2–C1–O10

31-32 i C–N=O C1–N2–O11, C3–N2–O11

33-37 i Ring C1–N2–C3, N2–C3–C4, N2–C1–C5,

C3–C4–C5, C4–C5–C1

38-43 i Ring C4–C5–C6, C6–C7–C8, C8–C9–C4,

C5–C6–C7, C7–C8–C9, C9–C4–C5

44 i N–O–H N2–O11–H17

Torsion

45-48 i C–H H16–C6–C7–C5, H15–C7–C8–C6,

H14–C8–C9–C7, H13–C9–C8–C4

49-50 i C=O O12–C3–C4–N2, O10–C1–C5–N2

92

51 i N–O O11–N2–C3–C1

52-56 i Ring C1–C5–C4–C3, C1–N2–C3–C4,

C5–C1–N2–C3, C4–C5–C1–N2,

N2–C3–C4–C5

57-62 I Ring C4–C5–C6–C7, C6–C7–C8–C9,

C8–C9–C4–C5, C5–C6–C7–C8,

C7–C8–C9–C4, C9–C4–C5–C6

63-64 Butterfly C6–C5–C4–C3, C9–C4–C5–C1

65-66 i O–H C1–N2–O11–H17, C3–N2–O11–H17

93

Table 4.3

Definition of local symmetry coordinates used to correct the B3LYP/6-31G*

force field for N-hydroxyphthalimide.

No. Symbol Definition

1-4 CH r1, r2, r3, r4

5 NO R5

6-7 CN p6,p7

8-9 CO q8, q9

10-17 CC Q10, Q11, Q12, Q13, Q14, Q15, Q16, Q17

18 OH 18

19-22 bCH ( 19 – 20)/ 2 , ( 21 – 22)/ 2 ,

( 23 – 24)/ 2 , ( 25 – 26)/ 2

23-24 bCO ( 27 – 29)/ 2 , ( 28 – 30)/ 2

25 bNO ( 31 – 32)/ 2

26 Ring 1 33 + a( 34 + 37) + b ( 35 - 36)

27 Ring 2 (a – b) ( 34 – 37) + (1 – a) ( 35 – 36)

28 Ring 3 ( 38 – 39 + 40 – 41 + 42 – 43 )/ 6

29 Ring 4 (– 38 – 39 + 2 40 – 41 + 42 – 2 43)/ 12

30 Ring 5 ( 38 – 39 + 41 – 42)/2

31 bNOH 44

32-35 CH 45, 46, 47, 48

36-37 CO 49, 50

38 NO 51

94

39 t Ring 1 b ( 52 + 56) + a ( 53 + 55) + 54

40 t Ring 2 (a – b) ( 56 – 52) + (1 – a) ( 55 – 53)

41 t Ring 3 ( 57 – 58 + 59 – 60 + 61 + 62)/ 6

42 t Ring 4 ( 57 – 58 + 60 – 62)/2

43 t Ring 5 (– 57 + 2 58 – 58 – 60 + 2 61 – 62)/ 12

44 Butterfly ( 63 - 64)/ 2

45 tOH 45

A = cos 144o and b = cos 72o.

95

Table 4.4

Assignment of fundamental vibrations of N-hydroxyphthalimide by normal mode analysis based on SQM force field calculations

No. Symmetry Species

Observed

Wavenumber (cm-1)

Calculated

wavenumber (cm-1), B3LYP/6-31G*

force field

IRa Ai

Ramanb Ii

TED (%) among types of internal coordinatesc

IR Raman Unscaled Scaled

1 A' 3476 - 3574 3476 59.431 90.776 OH (100)

2 A' 3190 - 3225 3170 8.995 251.275 CH (99)

3 A' 3158 - 3221 3166 5.083 23.965 CH (99)

4 A' 3148 - 3210 3156 8.319 121.528 CH (99)

5 A' 3140 3142 3198 3144 1.815 63.024 CH (99)

6 A' 1833 - 1859 1837 130.825 91.132 CO (79), bRing A (9), CC (5), CN (5)

7 A' 1782 1779 1797 1775 566.596 24.628 CO (81), bRing A (6) CC (6), CN (5)

8 A' 1623 - 1665 1623 14.401 21.048 CC (63), bCH (20), bRingB (10), bRingA(6)

9 A' 1607 1606 1660 1614 0.347 4.101 CC (66), bCH (24), bRingB (8)

96

10 A' 1569 - 1534 1567 172.835 10.8 bNOH (83), CN (7)

11 A' 1513 - 1510 1516 5.415 5.489 bCH (67), CC(28)

12 A' 1500 - 1504 1501 9.924 0.161 bCH (56). CC(39)

13 A' 1430 - 1435 1431 26.821 44.093 CN (32), NO (28), bCO (14), bRingA (11)

14 A' 1363 - 1400 1367 13.489 3.336 CC (71), bCH (21)

15 A' 1342 - 1319 1336 1.174 0.868 bCH (57), CC (22), bRingA (14)

16 A' 1206 - 1213 1203 4.721 5.146 bCH (57), CC(41)

17 A' 1188 1186 1194 1182 41.025 10.125 CC (43), bCH(22), CN (16), bRingB (9)

18 A' 1172 1170 1190 1175 62.235 58.796 CC (73), bCH (13), NO (5)

19 A' 1136 1137 1142 1139 107.031 1.605 CN (59), bNOH (10), bNO (9), bRingB (8)

20 A' 1080 - 1099 1077 11.154 1.118 bRingB (43), CC (37), bCH (11), CN (6)

21 A' 1018 1014 1044 1024 29.74 20.994 CC (56), bCH (17), NO (14), bCO (7)

22 A" 1008 - 1004 1011 0.011 0.03 CH (84), tRingB (16)

23 A' - 977 992 975 64.773 11.697 CC (48), NO (28), bCO (13), CN (7)

97

24 A" 974 - 968 970 1.157 1.104 CH (92), tRingB (7)

25 A" 911 - 909 915 0.025 3.621 CH (91), tRingB (8)

26 A' 880 - 893 887 48.017 2.517 bCO (37), bRingB(27), CC (16), CN (8)

27 A" 781 - 788 781 36.669 0.965 CH (93)

28 A" 753 - 758 749 1.006 0.18 tRingB (68), CO (16), tRingA (14)

29 A' 711 710 717 709 2.664 0.152 bRingB (53), bCO (26), CC (12)

30 A' 698 - 713 700 5.523 15.392 bRingB (46), CC (34), CN (8)

31 A" 669 - 677 671 6.527 0.163 tRingB (64), CO (22), CH (10)

32 A" 645 - 670 647 49.808 2.943 CO (50), tRingA (35), NO (7)

33 A' 606 602 609 609 0.292 10.602 bRingA (56), bRingB (18), CN (13), CO (5)

34 A' 521 - 525 522 12.96 1.003 bRingA (53), CC (17), bRingB (13), CN (12)

35 A' - 478 470 469 1.185 0.515 tRingB (74), CH (10), tRingA (9), gCO (7)

36 A" 475 - 469 462 1.1331 5.101 CC (32), bRingB (25), NO (14), bRingA(11)

37 A" - 408 409 412 0.237 0.023 tRingB (80), CH (11)

98

38 A' - 347 331 331 14.267 2.653 bCO (56), CC (20), CN (10), bRingB (6)

39 A" - 303 284 302 100.962 6.1 tOH (77), CO (14), tRingA (5)

40 A' - 272 261 270 13.528 1.387 bNO (61) bCO (24), bRingA (8)

41 A' - 235 238 235 0.932 1.22 bRingB (38), CC (32), bCO (16), bRing A(5)

42 A" - 184 203 185 5.374 0.855 NO (56), tOH (16), tRingA (7), CO (7)

43 A" - 154 140 141 0.69 2.037 tRingA (55), tRingB (33), CO (7)

44 A" - 106 119 103 0.454 1.801 tRingA (51)

45 A" - 83 87 85 0.996 0.061 tRingA (51), NO (48)

Abbreviations: : stretching; b: bending; : wagging; t: torsion

a Relative absorption intensities normalized with highest peak absorption.

b Relative Raman intensities calculated by Eq.4.1

c For the notations used see Table 4.3.