Synthesis, crystal and DFT studies of N-(carboxyethyl)-2-methylbenzothiazolium bromide

Article abstract of DOI:10.1016/j.molstruc.2019.05.035

The synthesis of benzothiazolium salt, N-(carboxyethyl)-2-methylbenzothiazolium bromide has been carried out by condensation of 2-methylbenzothiazole and 3-bromopropionic acid in solvent free conditions. The desired compound was obtained in excellent yield and its structural characterization was performed by FTIR, ¹H NMR, ¹³C NMR techniques and XRD-analysis. Further the structural properties of the suitable crystal was obtained and analyzed by single crystal X-ray diffraction analysis indicates that the compound crystallizes in the triclinic space group P-1, with Z = 2 and cell parameters a = 8.6554(3) ?, b = 8.9811(3) ?, c = 9.3168(3) ?, α = 61.237(1)°, β = 71.240(1)°, γ = 72.675(1)°. The molecular structure of the corresponding salt was optimized by Density Functional Theory (DFT) method using B3LYP/6-311G++(d,p) level. The molecular geometrical parameters (bond length. bond angle and dihedral angle) were obtained from the optimized structure. In addition, the IR frequencies were calculated using the same level of theory. The comparisons between the experimental and theoretical values of geometrical parameters and FT-IR vibrational spectra have also been discussed.

Full text of DOI:10.1016/j.molstruc.2019.05.035

Accepted Manuscript
Synthesis, crystal and DFT studies of N-(carboxyethyl)-2-methylbenzothiazolium
bromide
Mohamed El Mehdi Mekhzoum, Khadija El Bourakadi, El Mokhtar Essassi, Abou el
kacem Qaiss, Rachid Bouhfid
PII:
S0022-2860(19)30595-2
DOI:
https://doi.org/10.1016/j.molstruc.2019.05.035
MOLSTR 26542
Reference:
To appear in: Journal of Molecular Structure
Received Date: 5 November 2018
Revised Date: 6 May 2019
Accepted Date: 12 May 2019
Please cite this article as: M.E.M. Mekhzoum, K. El Bourakadi, E.M. Essassi, A.e.k. Qaiss, R. Bouhfid,
Synthesis, crystal and DFT studies of N-(carboxyethyl)-2-methylbenzothiazolium bromide, Journal of
Molecular Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.05.035.
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ACCEPTED MANUSCRIPT
Synthesis, Crystal and DFT Studies of N-(carboxyethyl)-2-
methylbenzothiazolium Bromide
a
a,b
a,b
Mohamed El Mehdi Mekhzoum, Khadija El Bourakadi, El Mokhtar Essassi, Abou el kacem
a
a
Qaiss, Rachid Bouhfid
a
Moroccan Foundation for Advanced Science, Innovation and Research (MAScIR), Institute of Nanomaterial
and Nanotechnology (NANOTECH), Rabat Design Center, Rue Mohamed El Jazouli, Madinat El Irfane, 10100
Rabat, Morocco.
b
Mohammed V-Rabat University, Faculty of Science, Laboratoire de Chimie organique et Hétérocyclique,
Rabat, Morocco.
Abstract
The synthesis of benzothiazolium salt, N-(carboxyethyl)-2-methylbenzothiazolium bromide
has been carried out by condensation of 2-methylbenzothiazole and 3-bromopropionic acid in
solvent free conditions. The desired compound was obtained in excellent yield and its
1
13
structural characterization was performed by FTIR, H-NMR, C-NMR techniques and
XRD-analysis. Further the structural properties of the suitable crystal was obtained and
analyzed by single crystal X-ray diffraction analysis indicates that the compound crystallizes
in the triclinic space group P-1, with Z = 2 and cell parameters a = 8.6554(3) Å, b = 8.9811(3)
Å, c = 9.3168(3) Å, α= 61.237(1)°, β = 71.240(1)°, γ= 72.675(1)°. The molecular structure of
the corresponding salt was optimized by Density Functional Theory (DFT) method using
B3LYP/6-311G++(d,p) level. The molecular geometrical parameters (bond length. bond angle
and dihedral angle) were obtained from the optimized structure. In addition, the IR
frequencies were calculated using the same level of theory. The comparisons between the
experimental and theoretical values of geometrical parameters and FT-IR vibrational spectra
have also been discussed.
Keywords: Benzothiazole, Solvent free, Crystal structure, DFT calculation, FT-IR and NMR.

ACCEPTED MANUSCRIPT
Graphical Abstract
Highlights
-
A novel benzothiazolium salt, N-(carboxyethyl)-2-methylbenzothiazolium bromide
has been synthetized under solvent free conditions.
-
-
-
The structure was characterized by both spectroscopic and crystallographic methods
The optimized structure was compared with X-ray diffraction data.
Spectral data were compared with computational ones.

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1
. Introduction
The heterocyclic compounds are versatile products existing in almost all natural and synthetic
organic compounds [1]. Owing to their diverse physical and chemical properties, aromatic
heterocycles have been the subject of great interest to scientists making it a promising
candidate for various applications including biological and pharmaceutical activities. A
considerable attention has been given to the development of novel heteroaromatic
compounds, and several synthetic approaches have been proposed. From chemical point of
view, a heterocyclic compound or ring structure is a cyclic with at least two different kinds of
heteroatoms in the ring. The most common heterocycles are those having five- or six-
membered rings and containing heteroatoms of nitrogen (N), oxygen (O) or sulfur (S). Among
various heterocycles. 1,3-benzothiazole derivatives are an interesting heterocycles class being
studied by many researchers and are reported to possess a wide spectrum of biological
properties [2].
Benzothiazole, also called 1-thia-3-azaindene in organic chemistry, is a heterocyclic
compound containing a ring complex composed of thiazole ring fused with benzene. It is a
weak base and thermally stable molecule [3]. Benzothiazole has electropositive and
electronegative regions which allow for functional modifications. In this heterocyclic
scaffold. the methine carbon between nitrogen and sulphur atoms in the thiazole ring is the
most reactive site for probable substitution [4]. As stated before, benzothiazoles derivatives
are of great importance categories of heterocyclic compounds with a wide range of biological
activities such as antimicrobial [5], antitumor [6], antidiabetic [7], antitubercular [8],
antimalarial [9], anticonvulsant [10], antioxidant [11], anti-inflammatory [12], anti-
mycobacterial [13], anti-cancer [14]. Interestingly, benzothiazoles are present in
bioluminescent luciferin and are used as fluorophores for two photon excitation as well as
absorption processes [15,16]. These compounds have also found application in industry as
anti-oxidants [17], vulcanization accelerators. Various benzothiazoles such as 2-aryl
benzothiazole received much attention due to unique structure and its uses as radioactive
amyloid imagining agents [18]. The importance of benzothiazole derivatives in various fields,
and in particular in chemistry, biology [19] and pharmacology [20] has prompted researchers
to develop numerous synthesis methods for their preparations and to find new fields of
applications. This is confirmed by the presence of benzothiazole nucleus in many traded drugs
and dyes such as riluzole, thioflavin, and thioflavin T [21]. In general, the synthesis of

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benzothiazole derivatives has long attracted the attention of organic chemists to the extent that
these derivatives are found in many biologically active natural products. Numerous methods
are available for the synthesis of N-benzothiazolium derivatives which involve condensation
of benzothiazole with an alkylating agent such as an alkyl iodide, bromide, sulphate or
tosylate, among others. These N-alkyl quaternary ammonium salts bearing 2-
methylbenzothiaole are reported in the literature such as unisolated precursors of cyanine dyes
[
22] as well as potential for selective targeting towards S. cerevisiae infections which are a
major problem in health care [23].
In the recent years, density functional theory (DFT) has been extensively used in theoretical
modeling, drug and functional material design [24,25]. Among DFT calculation, Becke’s
three parameter hybrids functional combined with the Lee–Yang–Parr correlation functional
(B3LYP) is the best predicting results for molecular geometry and vibrational wave numbers
for moderately larger molecule [26,27]. In the view of above significance, the combination of
experimental data with the corresponding DFT/B3LYP calculations has been one of the most
effective approaches used to gather insight into the molecular structure. Although similar
studies on benzothiazolium derivatives have been reported in the literature [28–30]. As a
result, an environmentally benign procedure has been used to synthesize the title compound,
the corresponding salt was obtained and its structure was characterized by various
1
13
spectroscopic methods including IR, H-NMR, C-NMR spectroscopy, single crystal X-ray
diffraction techniques and DFT method at B3LYP/6-311G++(d,p) level. The calculated
molecular geometrical parameters and IR frequencies are compared with experimental ones.
2
. Experimental
.1. Materials and measurements
2
All chemicals used in this work were purchased from Aldrich and were used without further
purification. IR spectra were recorded on an ABB Bomem FTLA 2000–102 FTIR instrument,
-1
(
ATR: SPECAC GOLDEN GATE) in the range 260–4000 cm . Melting point was recorded
1
13
in open capillary on Stuart SMP30 and are uncorrected. H and C NMR spectra were
recorded in DMSO-d using an Avance 300 (Bruker) instrument.
6
2
.2. Experimental procedure for the Synthesis of salt
The general synthetic procedure was employed to prepare the compound N-(carboxyethyl)-2-
methylbenzothiazolium bromide involving the melt reaction of the 3-bromopropionic acid

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with 2-methylbenzothiazole in one step procedure. A mixture of 2-methylbenzothiazole
(
15.75 mmol) and 3-bromopropionic acid (31.50 mmol) was stirred in an oil bath at 150°C for
h. After the desired time, the reaction mixture was slowly cooled and became a thick semi-
solid mass. The solid was recrystallized from methanol to afford the title compound as pale-
4
1
3
brown crystals. Yield: 92 %; m.p. 230-233°C; HNMR (DMSO-d , 300MHz): 2.28(t, J =
6
3
3
7
.2Hz, CH ); 3.25(s, CH ); 4.89(t, J = 7.2 Hz, NCH ); 7.68(dt, J =7.2Hz, H 5); 7.85(dt, J
2 3 2 Ar
1
3
=
7.2Hz, H 4); 8.35(dd, J = 8Hz, H 6); 8.47(dd, J = 8.10 Hz, H 3); CNMR (DMSO-d ,
Ar Ar Ar 6
3
00MHz): 17.7 CH (8); 32.3 CH (10); 45.5 NCH (9); 117.4 CH (3); 125.2 CH (6); 128.5
3 2 2 Ar Ar
CH (5); 129.8 CH (4); 129.4 Cq (7); 141.2 Cq (2); 171.9 Cq (1); 178.6 CO H (11).
Ar
Ar
2
2
.3. X-ray data collections, structure solution and refinement
The crystallographic data for CMTB were collected using a Bruker AXS APEX II single
crystal X-ray diffractometer equipped with graphite-monochromated MoKα radiation (λ =
0
.71073 Å) at room temperature. The solvation of structure determination was carried out by
direct methods using ShelXS [31] and the refinemend with the ShelXL [32] using Least
Squares minimisation. All non-hydrogen atoms were refined anisotropically. Crystal and data
collection parameters are given in Table 1.
Table 1. Crystal data and structure refinement for CMTB
Parameter
Value
Chemical formula
Formula Weight
Temperature
Br. C H NO S
302.18 g/mol
296(2) K
11
12
2
Wavelenght
Crystal System, space group
Unit cell dimensions
0.71073 Å
Triclinic, P-1
a = 8.6554(3) Å α = 61.237(1)°
b = 8.9811(3) Å β = 71.240(1)°
c = 9.3168(3) Å
γ = 72.675(1)°
3
Volume
592.16(3) Å
3
Z , calculated density
F(000)
2, 1.695 g/cm
304
Crystal Size [mm]
Theta range for data collection
Limiting indices
0.30x0.25x0.15
2.5° - 30.6°
-12 ≤ h ≤ 12 ; -12 ≤ k ≤ 12 ; -13 ≤ l ≤ 13
26006
3647 [R(int) = 0.073]
Full-matrix, least-square on F
3647/0/147
0.0297, 0.0687, 0.93
-0.52 and 0.56 e/Å
Reflections collected
Independent method
Refinement method
Data/restraints/parameters
2
2
R, wR , S
3
Min. and Max. Resd. Dens.
2
.4. Computational study

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DFT calculations with Becke’s three-parameter hybrid exchange functional and the
correlation functional of Lee, Yang and Parr (B3LYP) were performed on a personal
computer using Gaussian 09 [33]. Geometry optimization of N-(carboxyethyl)-2-
methylbenzothiazolium bromide (CMTB), was performed by DFT method using B3LYP/6-
3
11G++(d.p) level. Then, in order to access energy and the calculated IR spectra. Frequency
calculation was performed at DFT-B3LYP/6-311G++(d,p) level of DFT method. The normal
modes assignment of the theoretical IR frequencies is visualized and substantiated with the
help of the Gaussview 5.0.9 visualization program. There is no negative frequency in the
calculated IR spectrum which confirms that the optimized geometry of the compound is
located at the minima on the potential energy state. RMS errors were calculated for bond
distance and angle using the following expression.
ꢆ
ꢅ
ꢍꢎꢏ
− ꢈꢉ )ꢐ
ꢊꢋꢌꢊ
ꢀ
ꢁꢂ =ꢃꢄ ꢇ (ꢈ
ꢉ
ꢆ
ꢉ
calc
exp
Where di
respectively.
and di are the theoretical bond distance and experimental bond distance,
3
. Results and Discussion
The title compound, N-(carboxyethyl)-2-methylbenzothiazolium bromide (CMBT) was
prepared as shown in Scheme 1. The benzothiazolium salt was synthesis using an eco-
friendly, one-pot, solvent free reaction, from 2-methylbenzothiazole and the 3-
bromopropionic acid. The reactants were mixed thoroughly for a given period of time. It
should be noted that, by the eco-friendly method presented herein, better yield has been
obtained in comparison to those reported in literature [34,35]. In addition, most of these
classical methods suffer from drawbacks, namely high thermal conditions, long reaction
times, and the use of organic solvents that result in waste streams. In this work, we decide to
move forward and choose the melt reactions that have recently gained popularity because of
cleaner conditions and ease of manipulation. These reaction conditions are within the
framework of green chemistry or solvent-free synthesis [36].

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Scheme 1. Synthesis of N-(carboxyethyl)-2-methylbenzothiazolium bromide
3
.1. NMR spectral analysis
1
13
The H and C NMR spectra were computed to find the nuclear magnetic resonance nature of
the salt. The experimental analysis of the title compound was taken using DMSO as solvent
1
(
see supporting information). In H NMR spectrum, the protons of aromatic ring resonate in
the range 7.68-8.47 ppm. In this respect, a doublet of doublet was observed for H3 and H6 by
having a coupling constant of 8.10, 8 Hz. respectively. A multiple was observed for the
protons H4 and H5 at 7.85 and 7.68 ppm with a coupling constant of J = 7.2 Hz which is
always assigned to the aromatic ring protons. Besides, a singlet with three protons integral at
3
.25 ppm is conveniently assigned to the CH proton of thiazole ring. The signals at 2.28 ppm
3
and 4.89 correspond to a triplet of CH and NCH protons, respectively. The signal attributed
2
2
to the OH proton of carboxylic acid group is absent which may be due to the zwitterionic
1
3
nature of analysed sample. In the CNMR spectrum, the appearance of eleven distinct carbon
signals in the spectrum explicitly confirms the molecular structure of synthesized salt. In our
present investigation, the chemical shifts values of aromatic carbon atoms are observed at
1
17.4, 125.2, 128.5 and 129.8 ppm. The O atom has more electronegative property polarizes
the electron distribution in its bond to adjacent atom and increases the chemical shift value.
Consequently, the higher chemical shift for the carboxylic group carbon C11 was observed at
1
78.6 ppm. Also, the greater deshielding of C1 carbon at 171.9 ppm was caused by the
thiazole ring. The CH carbon C8 resonated at 17.7 ppm. While the signals of CH and NCH
2
3
2
were observed at 32.3 and 45.5 ppm. The signals appeared at 129.4, 141.2 ppm is attributed to
the quaternary carbon (Cq) 2 and 7, respectively.
3
.2. Description of the crystal structure
The most widely used method to obtain information about the properties of organic
compounds is DFT [37,38] and the most widely used function is B3LYP (Becke’s three-

ACCEPTED MANUSCRIPT
parameter hybrid model using the Lee–Yang–Parr correlation functional. Basis sets are also
being used besides these methods and functions for precise calculations [39,40]. In the present
study, the N-(carboxyethyl)-2-methylbenzothiazolium bromide salt was determined by X-ray
analysis and was optimized. The geometry parameters of synthesis compound were examined
using DFT calculation by B3LYP method with 6-311++G(d,p) and compared with the data
obtained from X-ray crystal structure. The calculated optimized geometrical parameters and
the experimental values are depicted in Table 2. The optimized geometric structure of the
compound with the atomic numbering scheme is given in figure 1, along with the ORTEP
drawing of it with the atom-numbering scheme (figure 2).
Figure 1. ORTEP plot (30%) for CMTB.
As seen from the given table 2. There are small differences between theoretical and
experimental values. This slight deviation may come from the environment of the compound.
It is clear that the experimental results belong to solid phase while theoretical calculations
belong to gaseous phase [41]. All theoretical computational values of bond lengths are
slightly higher than experimental ones except for N1-C9, C2-C7, C1-C8 and C7-C6 bonds.
experimental value of C2-C7 (1.396 Å) bond is lower than Calculated value (1.4004 Å). The
bond character of C3-C4 is calculated as 1.3874 Å is slightly deviated with experimental
(1.379 Å) data. The C-C bonds lengths are in the range 1.368-1.516. The bond lengths of C2-
C3 (1.392 Å), C2-C7 (1.396 Å) and C7-C6 (1.394 Å) and these values are greater than that of
C3-C4 (1.379 Å) and C5-C6 (1.368 Å) due to adjacent thiazole ring. In the thiazoline moiety,

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The S1-C7 bond distance is the longest while the N1-C1 is the shortest. The S1-C7 bond
length is calculated to be 1.748 Å, which is close to the typical C-S bond distance for
benzothiazoles [42]. While S1-C1 bond (1.709 Å) is shorter than the average distance for C-S
single bond (1.811 Å) [43]. The bond length between N1-C1 (1.3208 Å) indicates some
double bond character and is conjugated with neighboring bonds. The nitrogen-carbon
distance (N1-C2=1.407 Å) is shorter than the distance characteristics of single C-N bond
length (1.45 Å) but is comparable with the values reported in the analogous structures [44,45].
The bond lengths C10-C9 (1.516 Å), C11-C10 (1.5037 Å) have shown larger values than the
C-C bond lengths which is due to the adjacent C=O and carboxylic groups. Since oxygen is
more electronegative than carbon, the bond length O2-C11 (1.315 Å) decrease as compared to
C-C bond length.
The calculated bond angles are also closer to the XRD values such as C3-C2-
C7=121.24/120.67°, O2-C11-O1=123.35/123.94°, N1-C1-S1=113.37/112.83°, N1-C9-
C10=113.27/112.47°. The deviation of bond angle from 120° shows increase in non-planarity
of the molecule. Both DFT and experimental angles give shortening of angles C5-C6-C7, C4-
C3-C2 involving a common C atom of the two fused rings and increase of angles C6-C7-C2,
C7-C2-C3, C3-C4-C5, C4-C5-C6 from 120° at the benzene ring. These asymmetry of angles
reveals the conjugation with the thiazole ring. These results are similar to those found in the
literature [46]. More distortion in bond parameters is observed in the pentagon ring. The
variation in bond angle depends on the electro negativity of the central atom. If the electro
negativity of the central atom decreases, the bond angle decreases [47]. Therefore, the large
size of the S atom compared with N results in a reduction of the C1—S1—C7 angle (91.11°)
compared with the C1—N1—C2 angle (113.71.2°). This reveals that the S atom might be
using unhybridized p-orbitals for bonding [48]. The presence of higher electronegative group
C=O would be the reason for the lesser bond angle of O1-C11-C10 (123.51°). The angle O2-
C11-C10 (112.12°) which can be assumed as due to the presence of OH group which is
electropositive.
Regarding the dihedral angles, it is also important to note that the experimental dihedral
angles are nearly equal to the calculated values, C9-N1-C1-C8 = 0.66/-0.92, C7-S1-C1-C8 =
1
78.87/176.9º (deviation 1.97°), C9-N1-C1-S1 = 179.94/177.56 (deviation 2.38°), C3-C2-C7-
C6 = 0.92/0.73° (deviation 0.19º) and N1-C2-C3-C4 = -178.77/-179.31°. Planarity of a
molecule can be confirmed from their dihedral angle. Generally, dihedral angle values of 0°,
1
80° or 360° show planarity of the molecule [49]. In the studied molecule, the torsion angles

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N1-C2-C3-C4 (-178.77°), S1-C7-C6-C5 (177.44°), C1-S1-C7-C6 (-177.61°) and C1-N1-C2-
C3 (175.98°) show that C4, C3, C2, C7, C6, C5, C1, N1, S1 are approximately in the same
plane which means that the benzothiazole moiety is somewhat distortion from planarity. Thus,
the geometry of the benzothiazole ring is slightly affected by its substituents. The CH group
3
is planar with respect to the benzothiazole ring, this is supported by the torsion angle values,
C7-S1-C1-C8 = 178.9° and C2-N1-C1-C8 = -178.0° at C8 position. The CH groups at C9
2
and C10 are titled from the benzothiazole ring, as is evident from the angles, C3-C2-N1-C9 =
-2.82°, C8-C1-N1-C9 = 0.66°, S1-C1-N1-C9 = 179.94°, C9-N1-C2-C7 = 179.7°, C2-N1-C9-
C10 = -69.95°, C1-N1-C9-C10 = 111.39°. Likewise, the carboxylic group has the usual cis
conformation; the torsion angle of H1-O1-C11-O2 is 11.72°, while the OH group is located in
the trans position relatively to the ethyl group (the torsion angle C9-C10-C11-O2 = 173.3°).
Figure 2. The theoretical optimized geometric structure of the salt of CMTB.
Table 1. Experimental and optimized geometrical parameters of compound CMTB.
Parameter
Experimental
Theoretical
∆
Bond length (A°)
N1-C2
O2-C11
O1-C11
C2-C3
S1-C7
1.4073
1.3158
1.1989
1.3912
1.7343
1.3952
1.699
1.403
0.0043
0.0047
0.0131
0.0065
0.0137
0.0052
0.0104
0.0166
0.0081
0.0248
1.3205
1.212
1.3977
1.748
C2-C7
S1-C1
1.4004
1.7094
1.3374
1.3874
1.5285
N1-C1
C3-C4
C11-C10
1.3208
1.3793
1.5037

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C4-C5
C7-C6
1.3953
1.3944
1.4035
1.3956
0.0082
0.0012
C5-C6
N1-C9
1.3678
1.4844
1.3872
1.483
0.0194
0.0014
C10-C9
C1-C8
1.516
1.482
0.0127
1.54
0.024
1.4884
0.0064
RMS
Bond Angle (°)
C7-S1-C1
C2-N1-C1
C2-N1-C9
C1-N1-C9
N1-C2-C3
N1-C2-C7
C3-C2-C7
O2-C11-O1
O2-C11-C10
O1-C11-C10
C2-C3-C4
S1-C7-C2
S1-C7-C6
C2-C7-C6
S1-C1-N1
S1-C1-C8
N1-C1-C8
C3-C4-C5
C4-C5-C6
C7-C6-C5
N1-C9-C10
91.12
91.11
0.01
0.4
113.71
121.22
125.06
127.22
111.49
121.24
123.35
112.12
124.51
116.99
110.28
128.73
120.93
113.37
120.9
114.11
121.79
124.01
127.63
111.7
0.57
1.05
0.41
0.21
0.57
0.59
0.83
0.02
0.97
0.08
0.14
0.25
0.54
0.4
120.67
123.94
111.29
124.49
117.96
110.2
128.59
121.18
112.83
121.3
125.72
121.82
121.31
117.68
113.27
0.5279
125.86
121.3
0.14
0.52
0.42
0.32
0.8
120.89
118
112.47
RMS
Dihedral angle (°)
C1-N1-C2-C3
C1-N1-C2-C7
C9-N1-C2-C3
C9-N1-C2-C7
N1-C2-C3-C4
C7-C2-C3-C4
C1-S1-C7-C2
C1-S1-C7-C6
N1-C2-C7-S1
N1-C2-C7-C6
C3-C2-C7-S1
C3-C2-C7-C6
175.98
-1.5
179.88
0.66
3.9
2.16
5.96
3.61
0.54
1.38
2.38
2.32
2.96
0.3
-2.82
3.14
179.7
-178.77
-1.52
176.09
-179.31
-0.14
-0.41
1.97
-177.61
1.12
-179.93
-1.84
178.57
-176.53
0.92
178.87
-179.98
0.73
3.45
0.19

ACCEPTED MANUSCRIPT
C7-S1-C1-N1
C7-S1-C1-C8
C2-N1-C1-S1
C2-N1-C1-C8
C9-N1-C1-S1
C9-N1-C1-C8
C2-C3-C4-C5
O2-C11-C10-C9
O1-C11-C10-C9
C3-C4-C5-C6
S1-C7-C6-C5
C2-C7-C6-C5
C4-C5-C6-C7
C2-N1-C9-C10
C1-N1-C9-C10
C11-C10-C9-N1
RMS
-0.44
-1.65
1.21
1.97
0.3
178.87
1.19
176.9
0.89
-178.08
179.94
0.66
-177.58
177.56
-0.92
0.5
2.38
1.58
1.14
0.79
9.4
0.75
-0.39
173.34
7.86
172.55
-1.54
0.66
0.35
0.31
1.08
1.28
1.52
1.47
0.77
2.09
177.44
0.51
178.52
-0.77
-1.28
0.24
-69.95
111.39
-74.56
2.7962
-71.42
112.16
-72.47
The crystal structure of the molecule CMTB is consolidated by intra and intermolecular
hydrogen bonds involving the bromide anion and carboxylic group. In the crystal structure
cations is bridged by Br atoms. Bromide anions, as an acceptor, connect the molecules with
O2-H2⋅⋅⋅Br1 and C5-H5⋅⋅⋅Br1 hydrogen bonds (table 3).
Table 3. Hydrogen-bond parameters (Å, °).
D-H⋅⋅⋅A
D-H
H⋅⋅⋅A
D⋅⋅⋅A
D-H⋅⋅⋅A
O2-H2⋅⋅⋅Br1
0.821(11)
0.930(2)
0.960(11)
2.361(11)
2.449(2)
2.315(10)
3.1590(12)
3.082(2)
3.119(2)
164.3(16)
125.38(19)
140.9(8)
i
C6-H6⋅⋅⋅O1
C8-H8⋅⋅⋅O1
Symmetry code: (i) 1-x,1-y,1-z
3
.3. FT-IR spectral analysis
In order to give more information on the crystal structure, we have studied the vibrational
properties of our compound using infrared absorption. Vibrational spectroscopy is one of the
most useful tools for characterization of the chemical compounds in terms of both
experimental studies and theoretical calculations. The title molecule under investigation
possesses 28 atoms (N = 28), thus 3N = 84 degrees of freedom. It belongs to the C point
1
group symmetry, and it undergoes 78 normal modes of vibrations when the three translational
(2A' + 1A'') and three rotational (1A' + 2A'') degrees are subtracted. All 78 modes of vibration

ACCEPTED MANUSCRIPT
are distributed as 27 stretching, 26 bending, 21 torsional and 4 out of plan vibration. The
bands that are in the plane of the molecule is represented as A' and out-of-plane as A''. Of the
7
8 normal modes of vibrations, 53 modes of vibrations are in-plane and remaining 25 are out-
of-plane. Therefore the 78 normal modes of vibrations title molecule are distributed as 53A' +
5A''[50]. In agreement with C symmetry all the 78 fundamental vibrations are active in IR
2
1
absorption. The vibrational frequency calculations for normal modes have been performed at
B3LYP level with 6-311G++(d,p) basis set. The detailed assignments of some specific and
important vibrational experimental wavenumbers and their comparisons with theoretically
calculated (scaled) wavenumbers for the normal modes along with their %PED are collected
in Table 3. The observed FTIR spectra of CMTB along with the simulated infrared spectra in
-1
the frequency range 260 to 4000 cm are shown graphically in Figure 3.
Figure 3. Superposition of (a) the experimental and (b) the DFT computed IR spectra of
CMTB
The deviations of the calculated frequencies from the experimental ones are obtained due to
the harmonic approximation of the calculated frequencies as well as due to neglecting of
intermolecular interactions in solid. The calculated vibrational wave numbers are higher than
their experimental values for the majority of the normal modes. Theoretically predicted
wavenumbers are to be scaled down to cope up with the experimental wavenumbers. Scaling
factor used for this title molecule is 0.965 [51,52]. It is also important to note that computed

ACCEPTED MANUSCRIPT
wavenumbers correspond to gaseous phase of isolated molecular state whereas the observed
wavenumbers correspond to the solid-state spectra. In order to investigate the performance
and vibrational frequencies for the title compound root mean square value (RMS) and
correlation coefficient between calculated and observed vibrational frequencies were
2
calculated. The value of correlation coefficient found to be R = 99.88%, showing good
agreement with the calculated wavenumbers with experimental. The correlation graph is
shown in figure 4. The root mean square (RMS) difference between calculated and
-1
experimental frequencies 32.3 cm reveals a better agreement with the experimental data
table 4.
Figure 4. Plots of experimental (exp.) vs. calculated (calcd) IR frequencies
-1
Aromatic compounds commonly exhibit multiple weak bands in the region 3100–3000 cm
due to aromatic C-H stretching vibrations [53,54] and can be distinguished from aliphatic C–
−
1
H stretching bands which usually arise below 3000 cm region [55]. The experimental
spectra show only one very-weak band at 3075 which correspond to C-H stretching of
benzene ring. The calculated IR value which corresponds to the observed IR frequency was
−
1
found as 3076 cm . The C–H stretching vibrational modes in the CH and CH groups are
2
3
–
1
defined by the absorption bands in the 3000–2850 cm range [56]. For methylene group
-1
(
CH ) the observed peak at 2850 cm can be assigned to the symmetric C-H stretching mode
2

ACCEPTED MANUSCRIPT
while the peak at 2990 can be attributed the asymmetric C-H stretching mode. The
asymmetric C-H stretching vibrational mode in the aliphatic CH group is observed at 2936
3
-1
cm . The PED for these modes suggest that these are pure modes. The aromatic C-H in-plane
-1
bending modes of benzene and its derivatives are observed in the region 1300–1000 cm [57].
In the case of benzothiazole vibrations involving the C-H in-plane bending are observed at
-1
1
513, 1444, 1404 and 1194 cm , whereas it was calculated to be found in the range 1461-
-1
-1
1
190 cm . The C-H out-of-plane vibrations are expected below 1000 cm [57] and for the
-1
title compound the theoretical calculations give bands at 965, 922, 830 and 733 cm .
-1
Experimentally these bands are observed at 961, 919, 829 and 721cm in the IR spectrum.
Theoretical values of ring CH, CH and CH stretching and bending vibrations are good
3
2
coherent in experimental values. Other highly characteristic modes are C=C stretching
vibrations for aromatic ring. The spectral assignment was made by Panizzi et al. [58] for
benzothiazole. The carbon–carbon stretching modes of the phenyl group are expected in the
-1
range from 1650 to 1200 cm . In the present case, the carbon-carbon stretching bands of
-1
benzene ring are appeared in the infrared spectrum at 1650, 1579, 1444, 1328 cm and were
matched with the calculated values. The observed vibrational frequencies are generally
intense because of the conjugation between benzene and thiazole rings. These assignments
were supported by the literature [59,60]. In the other hand, the peak at (Exp. 1041, Cal. 1038
-1
cm ) can be attributed to the CCC in-plane bending vibrational modes of benzene ring.
-1
Similarly, the observed IR peaks at 961 and 919 cm can be assigned to the ring torsional
vibrational. These are matched well with theoretical bands. The C=N stretching skeletal bands
−
1
[
61,62] are observed in the range 1672–1566 cm . Kolts and Collier [63] reported a value of
-1
1
517 cm for benzoxazole as νC=N stretching mode. For the title compound, the DFT
-
1
Calculations give νC=N mode at 1513 and experimentally at 1461 cm . The C-S bond is
highly polarisable and hence produces stronger spectral activity. The stretching vibration
-1
assigned to the C-S linkage occurs in the region 700–600 cm [63]. The C-S stretching mode
-1
-1
recorded in FT-IR spectra at 774, 639 cm and calculated at 776, 653 cm , respectively. The
carbonyl stretching frequency has been most extensively studied by infrared spectroscopy
[
63]. This multiply bonded group is highly polar and therefore gives rise to an intense infrared
absorption band in which the position of C=O stretching band depends on the physical state,
electronic and mass effects of neighboring substituents, conjugations and intramolecular and
intermolecular hydrogen bonding [63]. Stretching vibration of C=O group is expected to
-1
appear at 1715–1680 cm [63]. The very strong C=O experimental band observed at 1751
-1
cm . The DFT frequency of C=O stretching vibration is in good agreement with the

ACCEPTED MANUSCRIPT
experimental result. The assignment of the O–H stretching vibrations is pure and
apprehensible. The absorption range for the O-H valence-stretching vibration of hydroxyl
-1
-1
group is usually quoted as being 3400-3448 cm [64] and 3500-3742 cm for carboxylic
-1
groups [65]. In the title compound the O-H stretching vibration observed at 3420 cm
-1
experimentally and 3615 cm in DFT calculation with a pure mode.
-1
Table 4. Major Experimental and calculated vibrational wavenumbers (cm ) of salt at
B3LYP/6-311++G(d, p) level and their assignments.
Mode
No.
Sym.
IR Exp.
frequency (cm )
B3LYP/6-311++G(d,p)
calculated wavenumber
Vibrational assignment (PED%)
-
1
-
1
Unscaled (cm-1)
Scaled (cm )
1
2
3
4
5
6
7
8
9
A'
A'
A'
A'
A'
A'
A'
A'
A'
A'
A'
A'
A'
A'
A'
A''
A''
A''
A'
A''
A''
A'
A''
A'
A''
A'
3494 w
3075 vw,sh
2990 vw,
2963 vw,
2850 m
1715 vs
1650 s
1579 m
1513 m
1444 s
3746
3188
3114
3081
2932
1815
1629
1619
1514
1490
1458
1367
1316
1233
1076
1000
956
859
804
760
677
621
559
499
428
3615
3076
3005
2973
2829
1751
1572
1562
1461
1438
1407
1319
1270
1190
1038
965
922
830
776
733
653
588
539
481
νOH (100)
νCH (60)
νCH2as (89)
νCH3as (88)
νCH2s (88)
νCO (86)
νCC (17/28)
νCC (12/33)
νNC (17) ; βHCH (29)
νCC (10); βHCC (12/24)
βHCH (82)
νCC (15/18/19/22)
νCO (10); βHOC (43)
βHCC (39); βHCN (11)
βCCC (11/12)
τHCCC (10/28/41); τCCCC (11)
τHCCN (25); τHCCC (26/29); τCCCC (10)
τHCCN (25); τHCCC (15/32)
νCC (23); νCO (10) ; νSC (19)
τHCCN (23); τHCCC (25/32)
τHOCC (32); γOCOC (19); νSC (13)
βOCO (40)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
1404 s
1328 m
1263 m
1194 vs
1041 w
961 vw
919 vw
829 m
774 s
721 vw
639 vw
570 vw
529 w
481 vw
435 vw
360 w
τHOCC (12)
βSCN (14)
γNCCC (11)
βOCC (11); βCCN (18); βCNC (29)
413
364
377
ν-stretching; β-in-plane bending; γ-out of plane bending; τ-torsion; vw-very weak; w-weak; m-medium; s-strong; vs-very
strong; sh-shoulder; potential energy distribution (PED ≥ 10%) is given in brackets in the assignment column;; s: symmetric;
as: asymmetric;
4
. Conclusion
In this study, an environmental benign procedure has been proposed to synthesize N-
carboxyethyl)-2-methylbenzothiazolium bromide salt with high yield. The title compound
(
was characterized by elemental analysis, spectroscopic (FT-IR, NMR) and structural (single
crystal X-ray diffraction). The structure of the product was studied using the computational
method of DFT/B3LYP with the 6-311++G (d, p) basis set. After optimizing the molecular
structure, the calculated parameters geometry and vibrational frequencies of the molecule

ACCEPTED MANUSCRIPT
have been compared with the experimental findings. Therefore, it is found a good coincidence
between experimental and computed values.
Supplementary material
The crystallographic information file has been deposited by us in the Cambridge structure
database (CCDC 1883515). These data can be obtained free of charge via
www.ccdc.cam.ac.uk/datarequest/cif, by e-mailing data-request@ccdc.com.ac.uk or by
contacting the Cambridge CB21 EZ, UK; fax: +44 1223 336033.
Acknowledgement
This work was supported by MAScIR; Moroccan Foundation for Advanced Science,
Innovation and Research, MESRSFC and CNRST, Morocco Grant no. 1969/15.
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