Structural, vibrational and DFT studies on 2-chloro-1H-isoindole-1,3(2H)-dione and 2-methyl-1H-isoindole-1,3(2H)-dione

Article abstract of DOI:10.1016/j.saa.2009.07.012

The Fourier transform infrared (FTIR) and FT-Raman spectra of 2-chloro-1H-isoindole-1,3(2H)-dione and 2-methyl-1H-isoindole-1,3(2H)-dione have been measured in the range of 4000-400 and 4000-100 cm^-1, respectively. Complete vibrational assignment and analysis of the fundamental modes of the compounds were performed using the observed FTIR and FT-Raman data. The geometry was optimised without any symmetry constraints using the DFT/B3LYP method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The vibrational frequencies determined experimentally are compared with those obtained theoretically from DFT gradient calculations employing the B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p) methods for the optimised geometry of the compounds. The structural parameters and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The force fields obtained from DFT method were utilised and the potential energy distributions of all the fundamental vibrations of the compounds were calculated.

Full text of DOI:10.1016/j.saa.2009.07.012

Spectrochimica Acta Part A 74 (2009) 642–649
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Structural, vibrational and DFT studies on 2-chloro-1H-isoindole-1,3(2H)-dione
and 2-methyl-1H-isoindole-1,3(2H)-dione
V. Arjunana,∗, I. Saravananb, P. Ravindranb, S. Mohanb
a Department of Chemistry, Kanchi Mamunivar Centre for Post-Graduate Studies, Puducherry 605008, India
b Centre for Research and Development, PRIST University, Vallam, Thanjavur 613 403, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The Fourier transform infrared (FTIR) and FT-Raman spectra of 2-chloro-1H-isoindole-1,3(2H)-dione
and 2-methyl-1H-isoindole-1,3(2H)-dione have been measured in the range of 4000–400 and
4000–100 cm−1, respectively. Complete vibrational assignment and analysis of the fundamental modes of
the compounds were performed using the observed FTIR and FT-Raman data. The geometry was optimised
without any symmetry constraints using the DFT/B3LYP method with 6–31G(d,p) and 6–311++G(d,p) basis
sets. The vibrational frequencies determined experimentally are compared with those obtained theoreti-
cally from DFT gradient calculations employing the B3LYP/6–31G(d,p) and B3LYP/6–311++G(d,p) methods
for the optimised geometry of the compounds. The structural parameters and normal modes of vibration
obtained from DFT method are in good agreement with the experimental data. The force fields obtained
from DFT method were utilised and the potential energy distributions of all the fundamental vibrations
of the compounds were calculated.
Received 11 February 2009
Received in revised form 2 July 2009
Accepted 7 July 2009
Keywords:
2-Chloro-1H-isoindole-1,3(2H)-dione
2-Methyl-1H-isoindole-1,3(2H)-dione
DFT
FTIR
FT-Raman
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
acetic acid is proposed for direct titrations of a variety of simple
and complex reductants [6]. The potassium phthalimide is used
1H-isoindole-1,3(2H)-dione (phthalimide) is used in plastics,
in chemical synthesis and in research. 2-Chloro-1H-isoindole-
1,3(2H)-dione (2CIDO) and 2-methyl-1H-isoindole-1,3(2H)-dione
(2MIDO) are commonly known as N-chlorophthalimide and N-
methylphthalimide, respectively. N-Halophthalimides have been
used in organic synthetic methodology especially in the oxidation
and halogenation of reactions [1]. In most cases these reagents
are converted to phthalimide in the end of reactions, as nontoxic
chemicals. N-Bromophthalimide has been found to be an efficient
and selective reagent for the mild oxidative cleavage of oximes to
yield the corresponding carbonyl compounds in good to excellent
yields [2]. The photoinitiated free radical chlorination of hydrocar-
bons with N-chlorophthalimide has been reported [3]. 2CIDO was
successfully used in the ring expansion of peniciline-V sulfoxide
p-nitrobenzyl ester to 3-exomethylene cephalosporin-V sulfoxide
p-nitrobenzyl ester [4]. 2CIDO is mainly used as an intermediate for
the production of medicine, pharmacy, dyes, pesticides, fire retar-
dant and photo copying chemicals. 2CIDO is also used as a biocidal
compound containing chlorine that can be made into a device con-
taining the chlorine biocide that can be released in an effective
amount into the environment of use and that releases its chlo-
rine for its biocidal activity [5]. N-Chlorophthalimide in anhydrous
in the Gabriel synthesis of amines. The selective electro reduction
of N-methylphthalimide to 3-hydroxy-2-methyl-isoindolin-1-one
has been performed in ionic liquids using phenol as a proton
donor under silent and ultrasonic conditions [7]. The structural
geometries of hydrogen-bonded clusters involving aminophthal-
imide molecules have been determined by infrared spectroscopy in
both the ground and excited electronic states [8]. The photophysical
and photochemical properties of N-phthaloylvaline methyl ester in
comparison with N-methylphthalimide and N-propylphthalimide
were studied by nanosecond laser flash photolysis [9]. The funda-
mental vibrational modes of a series of halophthalonitriles have
been studied using Raman and infrared spectroscopy [10]. Den-
sity functional study and the FTIR spectra of phthalimide and
N-bromophthalimide have been studied [11]. The vibrational stud-
ies on phthalimide and its N-substituted derivatives were carried
out [10–13] and show better agreement with the experimental
values of structural characteristics than with the calculations con-
taining the gradient corrected exchange functional [14].
Density functional theory (DFT) in recent years has proved
to be superior to conventional ab initio Hartee–Fock methods in
computing quantitative vibrational properties in a cost-effective
fashion. The theoretical DFT studies give information regarding
the structural parameters, the functional groups, orbital interac-
tions and vibrational frequencies. The introduction of one or more
substituents in the five membered ring of 1H-isoindole-1,3(2H)-
dione leads to the variation of charge distribution in the molecule,
∗
Corresponding author. Tel.: +91 413 2211111; fax: +91 413 2251613.
E-mail address: varjunftir@yahoo.com (V. Arjunan).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.07.012

V. Arjunan et al. / Spectrochimica Acta Part A 74 (2009) 642–649
643
and consequently, this greatly affects the structural, electronic and
vibrational parameters. The structural characteristics and vibra-
tional spectroscopic analysis of the compound under investigation,
2-chloro-1H-isoindole-1,3(2H)-dione (2CIDO) and 2-methyl-1H-
isoindole-1,3(2H)-dione (2MIDO) have not been studied. Thus,
owing to the industrial and biological importance of the com-
pounds, extensive spectroscopic studies on 2CIDO and 2MIDO were
carried out by analysing the FTIR and FT-Raman spectra, in an
effort to provide possible explanations for our observations and
to understand the effect of chloro and methyl groups on the char-
acteristic frequencies of the 1H-isoindole-1,3(2H)-dione moiety.
The density functional theory (DFT) is a popular post-HF approach
for the calculation of molecular structures, vibrational frequencies,
polarizabilities and energies of the molecules [15]. The DFT cal-
culations with the hybrid exchange correlation functional B3LYP
(Becke’s three parameter (B3) exchange in conjunction with the
Lee–Yang–Parr’s (LYP) correlation function) which are especially
important in systems containing extensive electron conjugation
and/or electron lone pairs [16–19].
Fig. 1. Molecular structure and atom numbering scheme of 2-chloro- and 2-methyl-
1H-isoindole-1,3(2H)-dione (X = Cl and –CH3).
4. Results and discussion
4.1. Molecular geometry
Themolecularstructureandtheschemeofnumberingtheatoms
of 2CIDO and 2MIDO are represented in Fig. 1. The 2CIDO is a
planar molecule with C2V symmetry that has 42 normal modes
of vibrations distributed into the irreducible representation as
ꢀ vib = 15a1 + 6a2 + 7b1 + 14b2. Therefore, in the C2V point group, all
of the fundamental vibrations are Raman active and all but the a2
vibrations are infrared active. The vibrations of the a1 and b2 species
are the in-plane modes and those of a2 and b1 species the out of
plane vibrations.
The isoindoline ring system in 2MIDO is essentially planar [18]
and the geometry of 2MIDO is considered by possessing CS point
group symmetry. Thus, the 51 fundamental modes of vibrations of
the compound are distributed into the irreducible representations
under CS symmetry as 33 in-plane vibrations of Aꢀ species and 18
out of plane vibrations of Aꢀꢀ species, i.e., ꢀ vib = 33Aꢀ + 18Aꢀꢀ. All the
vibrations are active in both infrared and Raman.
2. Experimental
The synthesis of 2-methyl-1H-isoindole-1,3(2H)-dione was per-
formed by mixing phthalic anhydride, a methanamine solution
and triethylamine in toluene using the procedure of Liang et al.
[20]. The purity of the sample was confirmed by determining the
melting point (m.p. 130–131 ◦C) and by performing the elemental
analysis. The 2-chloro-1H-isoindole-1,3(2H)-dione was purchased
from Shandong Tianyu Fine Chemicals Ltd., China and used as such
to record the FTIR and FT-Raman spectra. The FTIR spectra were
recorded by KBr pellet method, on a Bruker IFS 66V spectrome-
ter equipped with a Globar source, KBr beam splitter, and a MCT
detector in the range of 4000–400 cm−1. The spectral resolution
was 2 cm−1. The FT-Raman spectra were also recorded in the range
of 4000–100 cm−1 using the same instrument with FRA 106 Raman
module equipped with Nd:YAG laser source operating at 1.064 ␮m
with 200 mW power. The frequencies of all sharp bands are accurate
4.2. Structural properties
to 2 cm−1
.
The interaction of chloro and methyl substituent on the ring is
of great importance in determining its structural and vibrational
properties. The optimised structural parameters bond lengths and
the bond angles for the thermodynamically preferred geometry
of 2CIDO and 2MIDO at B3LYP level of theory with 6–31G(d,p)
and 6–311++G(d,p) basis sets are presented in Table 1 in accor-
dance with the atom numbering scheme of the molecules shown in
Fig. 1. It is observed that replacing the imide hydrogen by chlorine
and bulky methyl group caused significant geometric perturbation
in the five-membered heterocyclic ring and the carbonyl groups,
which are closest to the substituents. It is seen that the geom-
etry of the benzene ring is relatively unperturbed. It is observed
that the influence of the substituent on the molecular parameters,
particularly in the C–C bond distance of ring carbon atoms seems
to be negligibly small except N8–C7 and N8–C9, where the sub-
stituents exert direct field effect. N–C bond distances are shorter
in the case of 2MIDO (1.404 Å) than that of 2CIDO (1.418 Å). The
substituent effects are pronounced well in the bond angle of the
heterocyclic ring of the compounds. The bond lengths and angles
of the compounds 2CIDO and 2MIDO determined at the DFT level
of theory are in good agreement with the structural parameters of
1H-isoindole-1,3(2H)-dione [29,30]. The thermodynamic parame-
ters of the compound have also been computed at B3LYP method
with 6–31G(d,p) and 6–311++G(d,p) basis sets and are presented in
Table 2. The reported SCF energy of 1H-isoindole-1,3(2H)-dione is
−513.876 a.u. [11] and the experimental dipole moment value mea-
sured in dioxane at 30◦ is 2.91 Debye [31,32]. The calculated SCF
energy and entropy of the compounds clearly indicate that 2CIDO
3. Computational details
The gradient corrected density functional theory (DFT) [21] with
the three-parameter hybrid functional Becke3 (B3) [17] for the
exchange part and the Lee–Yang–Parr (LYP) correlation function
[18], level of calculations have been carried out in the present
investigation, using 6–31G(d,p) and 6–311++G(d,p) basis sets with
Gaussian-03 [22] program package, invoking gradient geometry
optimisation [23] on a Pentium-IV/1.6 GHz processor. Following
geometry optimisations with B3LYP method using 6–31G(d,p) and
6–311++G(d,p) basis sets, the optimised structural parameters were
used in the vibrational frequency calculations to characterise all
stationary points as minima. Then vibrationally averaged nuclear
positions of the compounds 2CIDO and 2MIDO were used for
harmonic vibrational frequency calculations resulting in IR and
Raman frequencies together with intensities and Raman depolar-
ization ratios. The dipole moment derivatives and polarizability
derivatives were computed analytically. The Raman intensities
were computed in the double harmonic approximation [24], ignor-
ing cubic and higher force constants and omitting second and
higher polarizability derivatives. Owing to the complexity of the
molecule, the potential energy distributions of the vibrational
modes of the compounds are also calculated through normal
coordinate analysis [25–27] using the force constants obtained
from the DFT method utilising the program of Fuhrer et al.
[28].

644
V. Arjunan et al. / Spectrochimica Acta Part A 74 (2009) 642–649
Table 1
Structural parameters calculated for 2-chloro-1H-isoindole-1,3(2H)-dione and 2-methyl-1H-isoindole-1,3(2H)-dione employing B3LYP/6–31G(d,p) and B3LYP/6–311++G(d,p)
methods.
Structural parameters
2-Chloro-1H-isoindole-1,3(2H)-dione
2-Methyl-1H-isoindole-1,3(2H)-dione
1H-isoindole-1,3(2H)-dionea
B3LYP/6–31G(d,p)
B3LYP/6–311++G(d,p)
B3LYP/6–31G(d,p)
B3LYP/6–311++G(d,p)
Internuclear distance (Å)
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C6–C1
C5–C7
C7–N8
N8–C9
C9–C6
C7–O10
C9–O11
N8–Cl12
N8–C12
1.401
1.400
1.401
1.387
1.398
1.387
1.493
1.418
1.418
1.493
1.207
1.207
1.701
1.399
1.398
1.399
1.385
1.395
1.385
1.493
1.418
1.418
1.493
1.201
1.201
1.701
1.401
1.400
1.401
1.387
1.396
1.387
1.494
1.403
1.405
1.494
1.215
1.215
1.399
1.398
1.399
1.385
1.394
1.385
1.494
1.402
1.404
1.494
1.209
1.209
1.385
1.377
1.382
1.373
1.389
1.374
1.485
1.388
1.376
1.478
1.202
1.218
1.451
1.086
1.092
1.454
1.084
1.091
C–H (aromatic)
1.086
1.084
C–H (methyl)b
Bond angle (◦)
C2–C1–C6
C2–C1–H13
C6–C1–H13
C3–C2–C1
C3–C2–H14
C1–C2–H14
C2–C3–C4
C2–C3–H15
C4–C3–H15
C3–C4–C5
C3–C4–H16
C5–C4–H16
C4–C5–C6
C4–C5–C7
C6–C5–C7
117.353
121.795
120.852
121.115
119.364
119.521
121.115
119.363
119.522
117.352
121.795
120.853
121.534
129.253
109.213
121.532
109.218
129.250
103.746
130.056
126.198
114.075
122.958
122.967
117.393
121.664
120.944
121.094
119.376
119.530
121.094
119.376
119.530
117.393
121.664
120.944
121.513
129.289
109.197
121.514
109.197
129.289
103.835
130.086
126.079
113.935
123.033
123.032
117.377
121.743
120.880
121.077
119.341
119.582
121.083
119.338
119.579
117.386
121.736
120.878
121.527
130.256
108.217
121.550
108.314
130.137
105.603
129.298
125.099
112.369
117.404
121.623
120.973
121.066
119.348
119.586
121.069
119.346
119.585
117.411
121.616
120.973
121.516
130.288
108.195
121.534
108.302
130.164
105.687
129.221
125.093
112.257
117.1
121.4
121.5
117.2
121.4
130.5
108.0
121.3
107.8
130.8
105.3
129.4
125.2
112.8
C5–C6–C1
C5–C6–C9
C1–C6–C9
C5–C7–N8
C5–C7–O10
N8–C7–O10
C7–N8–C9
C7–N8–Cl12
C9–N8–Cl12
C7–N8–C12
C9–N8–C12
C6–C9–N8
C6–C9–O11
N8–C9–O11
N–C–H (methyl)a
H–C–H (methyl)a
123.624
124.007
105.498
129.020
125.482
109.472
109.473
123.584
124.159
105.559
128.971
125.470
107.463
109.842
103.747
130.062
126.191
103.835
130.087
126.078
106.1
128.6
125.3
a
Values taken from Ref. [29].
Mean value.
b
is more stable than 2MIDO and 1H-isoindole-1,3(2H)-dione. The
higher dipole moment of 2CIDO than that of 1H-isoindole-1,3(2H)-
dione and 2MIDO is due to the electronic effect of chlorine and more
resonance stabilisation.
4.3.1. Carbon vibrations
The carbon–carbon stretching modes of the benzene ring are
expected in the range from 1650 to 1200 cm−1. Benzene has two
degenerate modes at 1596 cm−1 (e2g) and 1485 cm−1 (e1u). Simi-
larly the frequency of two non-degenerate modes are observed at
1310 cm−1 (b2u) and 995 cm−1 (a1g) in benzene. The 1H-isoindole-
4.3. Vibrational analysis
1,3(2H)-dione vibrational modes are well known [33–35]. The C
C
stretching of 2CIDO is observed at 1688, 1607 and 1466 cm−1 while
the C–C stretching is assigned to the wavenumbers 1371, 1356, 1340
and 1173 cm−1. The CNC symmetric stretching of 2CIDO under a1
species is assigned to the wavenumber 1293 and 1304 in infrared
and Raman, respectively. In 2MIDO, the skeletal carbon–carbon
stretching modes are observed in the expected region. The CNC
symmetric stretching of 2MIDO is observed at 1386 cm−1. The CNC
stretching of 2MIDO is observed at higher wavenumber due to the
electron releasing field effect of methyl group. All other in-plane
The observed vibrational assignments and analysis of 2CIDO
and 2MIDO are discussed in terms of fundamental bands, over-
tones and combination bands. The FTIR and FT-Raman spectra
of 2CIDO and 2MIDO together with the simulated spectrum are
shown in Figs. 2–5. The observed and calculated frequencies
using B3LYP/6–31G(d,p) and B3LYP/6–311++G(d,p) force field along
with their relative intensities, probable assignments and potential
energy distribution (PED) of 2CIDO and 2MIDO are summarised in
Tables 3 and 4, respectively.

V. Arjunan et al. / Spectrochimica Acta Part A 74 (2009) 642–649
645
Table 2
The calculated thermodynamic parameters of 2-chloro-1H-isoindole-1,3(2H)-dione and 2-methyl-1H-isoindole-1,3(2H)-dione employing B3LYP/6–31G(d,p) and
B3LYP/6–311++G(d,p) methods.
Thermodynamic parameters (298 K)
2-Chloro-1H-isoindole-1,3(2H)-dione
2-Methyl-1H-isoindole-1,3(2H)-dione
B3LYP/6–31G(d,p)
B3LYP/6–311++G(d,p)
B3LYP/6–31G(d,p)
B3LYP/6–311++G(d,p)
SCF energy (a.u.)
−973
72.12
34.59
95.58
70.35
66.34
−973
−552
96.49
36.39
97.70
94.72
90.41
−553
Total energy (thermal), Etotal (kcal mol−1
)
71.76
95.97
Heat capacity at const. volume, Cv (cal mol−1 K−1
)
34.65
95.72
69.98
65.96
36.47
98.81
94.20
89.84
Entropy, S (cal mol−1 K−1
)
Vibrational energy, Evib (kcal mol−1
)
Zero-point vibrational energy, E0 (kcal mol−1
)
Rotational constants (GHz)
A
B
C
1.72
0.64
0.46
1.73
0.64
0.47
1.72
0.86
0.58
1.73
0.86
0.58
Dipole moment (Debye)
ꢁx
ꢁy
ꢁz
ꢁtotal
4.33
−0.00
0.00
4.45
0.00
2.30
0.04
0.20
2.31
2.41
0.04
−0.00
−0.00
4.33
4.45
2.41
Fig. 2. FTIR spectrum of 2-chloro-1H-isoindole-1,3(2H)-dione. (a) Observed and (b)
calculated.
Fig. 4. FTIR spectrum of 2-methyl-1H-isoindole-1,3(2H)-dione. (a) Observed and (b)
calculated.
Fig. 3. FT-Raman spectrum of 2-chloro-1H-isoindole-1,3(2H)-dione. (a) Observed
and (b) calculated.
Fig. 5. FT-Raman spectrum of 2-methyl-1H-isoindole-1,3(2H)-dione. (a) Observed
and (b) calculated.

Table 3
The observed FTIR, FT-Raman and calculated frequencies using B3LYP/6–31G(d,p) and B3LYP/6–311++G(d,p) force field along with their relative intensities, probable assignments and potential energy distribution (PED) of
2-chloro-1H-isoindole-1,3(2H)-dione.a.
Species
Observed wavenumber B3LYP/6–31G(d,p) calculated wavenumber
B3LYP/6–311++G(d,p) calculated wavenumber
Depolarization ratio
Assignment
%PED
(cm−1
FTIR
)
FTR
Unscaled (cm−1
)
Scaled (cm−1
)
IR intensity
Raman activity
Unscaled (cm−1
)
Scaled (cm−1
)
IR intensity
3432 sh
3215 sh
1726 × 2
1607 × 2
␯C–H
␯C–H
␯C–H
a1
b2
a1
b2
b2
a1
b2
a1
a1
b2
a1
a1
a1
b2
b2
a1
a1
b2
b2
a2
b1
a2
b2
a1
b1
a2
b2
b1
a1
a2
a1
a1
a2
b1
b2
a1
b2
b1
b2
a2
b1
b1
3223
3220
3208
3195
1872
1834
1661
1659
1507
1505
1402
1311
1305
1201
1190
1178
1113
1081
1038
1011
976
911
877
864
794
780
708
701
691
675
587
525
466
413
387
326
248
3094
3091
3080
3067
1797
1761
1595
1593
1447
1445
1346
1259
1253
1153
1142
1131
1068
1038
996
971
937
875
842
829
762
749
680
673
8.18
2.76
7.02
252.99
25.20
137.48
65.19
90.25
16.08
30.21
4.13
3203
3200
3189
3176
1845
1802
1644
1643
1496
1494
1384
1309
1290
1194
1186
1174
1109
1069
1033
1011
984
909
873
858
794
788
709
707
691
674
587
525
464
411
386
328
251
3107
3104
3093
3081
1790
1748
1595
1594
1451
1449
1342
1270
1251
1158
1150
1139
1076
1037
1002
981
954
882
847
832
770
764
688
686
670
654
569
509
450
399
374
318
7.05
1.44
4.42
0.12
0.75
0.50
0.75
0.13
0.75
0.75
0.73
0.75
0.19
0.15
0.66
0.24
0.35
0.75
0.12
0.75
0.75
0.13
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.11
0.75
0.13
0.75
0.75
0.74
0.36
0.15
0.75
0.75
0.75
0.75
0.75
0.75
92␯
CH
3094 w
3101 w
3086 m
3063 m
1783 vs
1736 w
90␯
CH
94␯
CH
3066 w
1787 m
1726 vs
1688 w
1607 m
1466 m
1371 m
1.78
1.50
␯C–H
91␯
CH
20.74
584.24
10.80
2.28
8.32
1.36
30.44
1.07
192.37
0.84
0.62
5.95
33.27
96.91
0.22
0.00
0.96
0.00
22.27
49.98
15.82
0.00
2.84
66.26
24.07
0.00
1.39
33.26
746.88
13.53
2.95
7.98
1.16
32.27
0.42
201.32
0.51
0.38
4.95
24.79
136.14
0.53
0.00
1.49
0.00
31.33
50.45
22.37
0.00
3.99
76.68
24.27
0.00
1.74
␯C
␯C
␯C
␯C
␯C
O
O
C
C
C
95␯
C
O
94␯
93␯
92␯
90␯
94␯
93␯
95␯
91␯
90␯
C
O
CC
CC
CC
CC
CC
CC
1613 w
1468 w
3.69
0.31
␯C–C
␯C–C
␯C–C
␯sCNC
␯C–C
␤C–H
␤C–H
␤C–H
␯aCNC
␤C–H
␥C–H
␥C–H
␥C–H
␤CCC
␯N–Cl
␥C–H
␶CNC
␤CCC
␻CNC
␤CCC
␥CCC
␤CNC
␤CCC
␥CCC
␥CCC
␤CCN
1356 m
4.09
0.00
21.54
35.51
6.57
23.04
1.45
7.88
25.72
0.03
1.22
3.94
4.17
7.76
0.50
0.01
0.04
3.37
20.44
0.43
8.52
0.25
0.68
0.00
12.17
0.64
2.97
1340 m
1293 vs
1171 w
1152 vw
1110 w
1096 s
1304 m
1173 vs
1163 m
1109 w
1086 m
CNC
CC
82␤CH + 15␤CCC
80␤CH + 16␤CCC
78␤CH + 18␤CCC
1078 s
91␯
CNC
1009 s
886 vw
853 vw
78␤CH + 16␤CCC
76␥CH + 12␥CCC
75␥CH + 16␥CCC
72␥CH + 20␥CCC
80␤CCC + 12␤CH
864 s
799 m
703 vs
798 vw
90␯
N-Cl
74␥CH + 14␥CCC
71␶CNC + 18␥C
O
67␤CCC + 19␤CH
69␻CNC + 20␥C
70␤CCC + 15␤CH
68␥CCC + 19␥CH
67␤CNC + 21␤C
69␤CCC + 19␤CH
65␥CCC + 20␥CH
61␥CCC + 24␥CH
64␤CCN + 19␤C
694 m
679 m
O
O
685 vs
587 m
663
648
564
504
447
396
372
313
238
205
526 m
10.70
0.00
0.07
0.83
7.79
0.91
1.16
0.11
0.00
2.49
13.20
0.00
0.36
0.69
7.47
0.95
0.37
0.22
0.00
3.16
381 m
O
␤C
␤C
O
O
75␤C O + 12␤CCN
72␤C O + 15␤CCN
64␥CCN + 21␥C
252 m
211 w
169 m
116 s
243
207
183
133
123
84
214
190
141
132
4.01
213
189
137
127
␥CCN
␤N–Cl
O
182
135
127
86
0.84
2.43
0.00
0.90
70␤N-Cl + 19␤C
O
␥C
␥C
O
O
69␥C O + 18␥CCN
67␥C O + 22␥CCN
64␥N–Cl + 16␥CNC
101 s
86
1.82
84
2.11
␥N–Cl
+ 15␥C
O
␯: stretching; ␤: in-plane bending; ␦: deformation; ␳: rocking; ␥: out of plane bending; ␻: wagging; and ␶: twisting/torsion, wavenumbers (cm−1); IR intensities (km/mol) and Raman scattering activities (Å)4/(a.m.u).
a

Table 4
The observed FTIR, FT-Raman and calculated frequencies using B3LYP/6–31G(d,p) and B3LYP/6–311++G(d,p) force field along with their relative intensities, probable assignments and potential energy distribution (PED) of
2-methyl-1H-isoindole-1,3(2H)-dione.a.
Species
Observed wavenumber
B3LYP/6–31G(d,p) calculated wavenumber
B3LYP/6–311++G(d,p) calculated wavenumber
Depolarization ratio
Assignment
%PED
(cm−1
FTIR
)
FTR
Unscaled (cm−1
)
Scaled (cm−1
)
IR intensity
Raman activity
Unscaled (cm−1
)
Scaled (cm−1
)
IR intensity
3454 w
1721 × 2
␯C−H
Aꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀꢀ
Aꢀ
Aꢀ
3220
3216
3204
3191
3172
3130
3064
3091
3087
3076
3063
3045
3005
2941
9.93
5.30
8.43
1.88
0.86
259.52
24.38
125.96
63.52
43.07
86.25
177.19
3201
3197
3186
3173
3149
3110
3049
3105
3101
3090
3078
3055
3017
2958
8.62
3.19
5.47
1.55
0.65
0.12
0.74
0.54
0.75
0.75
0.75
0.05
95␯
CH
3084 w
␯C−H
92␯
CH
␯C−H
94␯
CH
3065 m
3038 w
␯C−H
90␯
CH
␯aCH3
93␯
CH
3022 vw
2951 w
1823 w
1770 m
1760 s
1721 vs
1612 w
1534 vw
1468 s
15.08
36.21
13.97
33.93
␯aCH3
␯sCH3
94␯
CH
2949 w
91␯
CH
1438 × 2
1090 + 610
Aꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀ
Aꢀꢀ
Aꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀ
Aꢀ
Aꢀꢀ
Aꢀ
Aꢀ
Aꢀ
Aꢀꢀ
Aꢀꢀ
1761 vs
1720 w
1612 m
1511 w
1853
1804
1664
1660
1523
1507
1505
1502
1467
1416
1399
1314
1277
1221
1194
1184
1157
1102
1041
1024
1008
988
974
911
873
799
786
721
720
708
680
610
536
480
1779
1732
1597
1594
1462
1447
1445
1442
1408
1359
1343
1261
1226
1172
1146
1137
1111
1058
999
983
968
948
935
875
838
767
755
62.93
575.47
11.97
2.71
10.88
5.94
91.21
12.23
28.03
5.31
19.46
3.65
2.28
19.67
9.26
45.22
0.88
0.32
8.16
58.42
5.95
8.73
2.58
0.34
19.27
1.78
0.05
3.81
1.23
4.11
4.24
0.21
0.02
3.91
16.57
0.23
0,47
8.65
1.08
5.71
0.68
1823
1769
1647
1645
1511
1496
1493
1489
1460
1401
1382
1311
1268
1211
1189
1181
1149
1099
1035
1012
1009
982
977
908
872
801
798
727
719
709
680
610
537
478
1768
1716
1598
1596
1466
1451
1448
1444
1416
1359
1341
1272
1230
1175
1153
1146
1115
1066
1004
982
979
953
948
881
846
777
774
705
697
688
660
592
521
464
451
87.84
754.64
17.03
2.47
12.13
5.49
0.13
0.75
0.75
0.73
0.70
0.75
0.27
0.75
0.20
0.33
0.73
0.70
0.68
0.24
0.75
0.24
0.75
0.75
0.13
0.65
0.75
0.22
0.75
0.75
0.72
0.75
0.75
0.75
0.14
0.65
0.75
0,12
0.75
0.30
0.75
␯C
␯C
␯C
␯C
O
O
C
C
92␯
C
O
91␯
C
O
94␯
90␯
CC
C
C
1465 vw
␦aCH3
82␦CH3 + 12␤CNC
89␯
␯C
␯C
C
C
C
C
0.15
8.14
0.11
91␯
CC
85␦CH3 + 12␤CNC
87␦CH3 + 10␤CNC
10.68
100.82
254.35
15.08
2.44
47.17
21.90
5.04
5.11
0.26
6.90
0.21
117.74
0.00
1.44
16.73
0.00
6.56
12.23
0.02
83.78
1.09
1.33
0.00
␦aCH3
␦sCH3
␯sCNC
1438 vs
1386 vs
1343 vw
1293 m
1253 m
1188 m
1167 m
1435 vw
1385 w
1344 vw
126.94
237.21
17.28
5.17
41.35
20.78
3.53
5.53
0.31
6.38
0.09
88.40
0.00
13.74
0.91
0.00
5.29
10.35
0.04
65.64
0.91
0.98
0.01
92␯
CNC
␯C
␯C
C
C
89␯
CC
91␯
CC
1254 vw
1191 s
1169 s
␯aCNC
␯CC
89␯
CNC
92␯
CC
␤C
␤C
H
H
79␤CH + 15␤CCC
75␤CH + 18␤CCC
82␳CH3 + 10␤CNC
78␤CH + 15␤CCC
80␤CH + 12␤CCC
79␻CH3 + 16␥CNC
76␥CH + 15␥CCC
71␥CH + 18␥CCC
1090 m
1072 w
␳CH3
␤C
␤C
H
H
1011 s
970 w
1015 s
968 vw
␻CH3
␥C
␥C
H
H
␯N C(H3)
␥C
␤CCC
76␯N–C + 16␤C
O
H
69␥CH + 19␥CCC
74␤CCC + 15␤CH
69␥CH + 15␥CCC
70␥CCC + 14␥CH
68␥CCC + 16␥CH
67␤CCC + 19␤CH
72␤CCC + 14␤CH
70␥CCC + 16␥CH
850 m
794 m
859 vw
796 vw
␥C H
␥CCC
␥CCC
␤CCC
␤CCC
␥CCC
␤CNC
␤CCN
␤CCC
␥CCC
718 vs
697 w
711 s
692
691
680
653
586
515
461
450
682 vw
610 m
533 s
477 vw
611 s
530 vw
474 w
3.68
9.64
13.00
0.00
4.19
67␤CNC + 19␤C
O
11.86
13.18
0.00
68␤CCN + 20␤C
O
65␤CCC + 21␤CH
69␥CCC + 14␥CH
469
465

648
V. Arjunan et al. / Spectrochimica Acta Part A 74 (2009) 642–649
and out of plane CCC, CNC and CCN vibrations are presented in
Tables 3 and 4. The PED contribution of these modes shows that
the CCC fundamentals are mixed with the C–H vibration, while CNC
and CCN modes are significantly overlapped with C O vibration.
4.3.2. C–H vibrations
The aromatic C−H stretching vibrations are normally found
between 3100 and 3000 cm−1. The Raman depolarization data
make it reliable to assign the high-frequency ring stretching mode
of a1 species of 2CIDO. The strong polarized lines at 3107 cm−1 cal-
culated by B3LYP method and 3086 cm−1 in Raman are assigned to
the a1 modes, whereas the weak and medium depolarized lines at
3094 and 3066 cm−1 in the infrared and the corresponding Raman
lines 3101 and 3063 cm−1 are the b2 C–H stretching fundamentals
of 2CIDO. In 2MIDO the C–H stretching frequencies are overlapped
together and observed at 3084 and 3065 cm−1 in the said region.
The C−H in-plane bending modes are normally observed in the
region of 1300–1000 cm−1. These modes are observed in 2CIDO
at 1340, 1163, 1110 and 1096 cm−1 and the corresponding fre-
quencies in 2MIDO are attributed to the wavenumbers 1167 and
1072 cm−1. All these assignments are in good agreement with the
literatures [13,36,37]. The C–H out of plane bending modes of the
compounds are observed in the region of 1000–600 cm−1. The nor-
mal co-ordinate analysis reveals that the aromatic C–H in-plane and
out of plane bending vibrations have substantial overlapping with
the ring CCC in-plane and out of plane bending modes, respectively.
4.3.3. C O vibrations
The C O stretching modes are the most characteristic ones for
molecules which have the O C–X–C O system. It is well known
that in general the in-phase mode is higher in frequency than the
out-of-phase mode. An out-of-phase C O stretching mode is low-
ered in frequency by the electronic effects arising from resonance
stabilisation. The in-phase and out-of-phase C O stretching modes
of 1H-isoindole-1,3(2H)-dione, show a frequency separation that
has been explained by mechanical coupling, hydrogen bonding and
resonance stabilisation [38]. In this investigation, the characteristic
band separations of C O stretching modes of the compounds dis-
cussed in terms of electronic effects by resonance stabilisation were
considered to be more effective, using the resonance structures: (i)
O
C–X+ C–O−; (ii) O−–C X+–C O. Moreover, combination bands
enhanced by Fermi resonance with strong fundamentals contribute
likely to the absorption pattern in this region.
For cyclic imides, two carbonyl stretching modes are normally
expected, one lying in the region 1970–1735 cm−1 and the other
in the region 1750–1680 cm−1. The position of C O stretching
depends upon conjugation, hydrogen bonding and the size of the
ring to which it is attached. Unsaturation results in an increase in
wavenumber of about 15 cm−1. In the vibrational spectra of 2CIDO,
the most intense band corresponds to the stretching vibration of
the carbonyl groups observed at 1787 and 1726 cm−1 in infrared
while in Raman the corresponding wavenumbers are obtained at
1783 and 1736 cm−1. The C O stretching of a1 species falls at higher
wavenumber than that of b2 symmetry. The corresponding bands in
2MIDO are assigned to the modes observed at 1760 and 1721 cm−1
in IR and at 1761, 1720 cm−1 in Raman spectra. The electron attract-
ing chlorine attached to nitrogen in 2CIDO increases the frequency
of C O absorption since it effectively competes with the carbonyl
oxygen for the electrons of nitrogen, thus increasing the force con-
stant of the C O bond. These assignments are in good agreement
with the literatures [12,36,38].
4.3.4. N–Cl vibrations
Strong characteristic absorption due to N–X stretching vibration
isobservedinthelowfrequencyregion. TheN–Clstretchingabsorp-
tion is observed in 2CIDO at 703 cm−1. The observed vibrational

V. Arjunan et al. / Spectrochimica Acta Part A 74 (2009) 642–649
649
mode at 169 cm−1 is attributed to the in-plane bending vibration
and the out of plane bending mode of N–Cl is assigned to the line
at 101 cm−1 in Raman.
basis set. The basis sets 6–31G(d,p) and 6–311++G(d,p), are equally
reliable for the determination of the electronic structure by quan-
tum chemical investigations of organic compounds.
4.3.5. Methyl group vibrations
References
The –CH3 group frequencies, make a significant contribution to
2MIDO. Under CS symmetry, the asymmetric stretching and asym-
metric deformation modes of the –CH3 group would be expected to
be depolarized under Aꢀꢀ symmetry species. The symmetric methyl
stretching, ꢂs(CH3) mode is established at 2951 and 2949 cm−1
in the infrared and Raman, respectively. The asymmetric methyl
stretching, ꢂa(CH3) vibrations under Aꢀꢀ and Aꢀ species of 2MIDO are
observed at 3038 and 3022 cm−1. The asymmetrical methyl defor-
mation mode, ıa(CH3) is observed at 1468 cm−1 under Aꢀꢀ species.
The symmetrical methyl deformation mode, ıs(CH3), is seen at
1438 cm−1 in IR and at 1435 cm−1 in Raman. The methyl defor-
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in Table 4. All assignments were based on the visualization of nor-
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