Synthesis, spectral, X-ray diffraction and DFT studies on 1-(2-methyl-2-propenyl)-3-(2,3,4,5,6-pentamethylbenzyl)benzimidazolium chloride hydrate

Article abstract of DOI:10.1080/15421406.2018.1446692

A new benzimidazole based N-heterocyclic carbene (NHC) salt (1) was synthesized by the reaction of benzimidazole precursor with alkyl halide. The structure of 1 was determined by elemental analysis, FT-IR, ¹H NMR and ¹³C NMR spectroscopy tecniques and X-ray crystallography. The compound crystallized in the triclinic space group P-1 with two molecules in the unit cell. The optimization of 1 was firstly performed at B3LYP/6-311G++(d,p) level, then the theoretical spectral studies performed and compared with the experimental values. Besides the frontier molecular orbital energies and chemical reactivity analysis of 1, together with the electrostatic potential and molecular electrostatic potential analyses were performed at the same level of theory.

Full text of DOI:10.1080/15421406.2018.1446692

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis, spectral, X-ray diffraction and DFT
studies on 1-(2-methyl-2-propenyl)-3-(2,3,4,5,6-
pentamethylbenzyl)benzimidazolium chloride
hydrate
Neslihan Şahin, Işın Kılıç-Cıkla, Namık Özdemir, Nevin Gürbüz & İsmail
Özdemir
To cite this article: Neslihan Şahin, Işın Kılıç-Cıkla, Namık Özdemir, Nevin Gürbüz & İsmail
Özdemir (2018) Synthesis, spectral, X-ray diffraction and DFT studies on 1-(2-methyl-2-
propenyl)-3-(2,3,4,5,6-pentamethylbenzyl)benzimidazolium chloride hydrate, Molecular Crystals
and Liquid Crystals, 664:1, 109-123, DOI: 10.1080/15421406.2018.1446692
To link to this article: https://doi.org/10.1080/15421406.2018.1446692
Published online: 21 Jun 2018.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gmcl20

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
https://doi.org/./..
Synthesis, spectral, X-ray diffraction and DFT studies on
-(-methyl--propenyl)--(,,,,-pentamethylbenzyl)
benzimidazolium chloride hydrate
Neslihan S¸ahina,b,c, Is¸ın Kılıç-Cıklad, Namık Özdemire, Nevin Gürbüzb,c
and Ismail Özdemir
,
b,c
˙
aDepartment of Basic Education, Faculty of Education, Cumhuriyet University, Sivas, Turkey; bDepartment of
c
˙
Chemistry, Faculty of Science and Art, Inönü University, Malatya, Turkey; Catalysis Research and Application
Center, Inönü University, Malatya, Turkey; dDepartment of General Secretary, Ondokuz Mayıs University,
Samsun, Turkey; eDepartment of Mathematics and Science Education, Faculty of Education, Ondokuz Mayıs
University, Samsun, Turkey
ABSTRACT
KEYWORDS
DFT calculations;
A new benzimidazole based N-heterocyclic carbene (NHC) salt (1) was
synthesized by the reaction of benzimidazole precursor with alkyl
halide. The structure of 1 was determined by elemental analysis, FT-IR,
1H NMR and 13C NMR spectroscopy tecniques and X-ray crystallogra-
phy. The compound crystallized in the triclinic space group P-1 with two
molecules in the unit cell. The optimization of 1 was firstly performed
at B3LYP/6-311G++(d,p) level, then the theoretical spectral studies per-
formedandcomparedwiththeexperimentalvalues. Besidesthefrontier
molecular orbital energies and chemical reactivity analysis of 1, together
with the electrostatic potential and molecular electrostatic potential
analyses were performed at the same level of theory.
N-Heterocyclic carbene; X-ray
diffraction; H and C NMR
1. Introduction
N-Heterocyclic carbene (NHC) is a cyclic carbene species with two neighboring nitrogen
atoms. NHCs were first searched out in 1968 by Ofele, Wanzlick and Schonherr [1, 2]. In the
1970’s, Lappert submitted a series of complexes via cleavage of the electronically rich olefin
[3]. In 1991, the first isolated NHC was reported by Arduengo [4]. The synthetic process is
deprotonation of precursor azolium salt with sodium or potassium hydride in the presence
of KOtBu in DMSO [5–7]. Another developed method is based on deprotonation of the cor-
responding salts in liquid ammonia [8, 9]. Reaction of imidazol-2-thiones with potassium
metal [10], thermal elimination of methanol from adducts to form triazol-2-ylidene [11], and
elimination of phenoxides is other synthesis methods.
Recently, N-heterocyclic carbenes have been increasingly used as ligands in coordination
chemistry due to their strong electron-donating property. Moreover, NHCs have excellent
air and moisture stability [12]. N-Heterocyclic carbenes have been used in metal com-
plex catalysts for many important organic synthesis reactions such as hydrogenation [13],
hydroformylation [14, 15], C-C coupling [16, 17], olefin metathesis [18, 19], hydrosilylation
CONTACT Is¸ınKılıç-Cıkla
Turkey.
ikilic@omu.edu.tr
DepartmentofGeneralSecretary,OndokuzMayısUniversity,Samsun,
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor and Francis Group, LLC

110
N. S¸AHIN ET AL.
Scheme . Synthesis of 1.
[20, 21] and etc. in pharmaceutical sciences [22, 23]. Also, recent studies have employed the
use of NHC ligands in order to reduce carbon dioxide into either methanol or formic acid
[24–27].
We herein report preparation, detailed X-ray structural analysis, spectroscopic charac-
terization and some theoretical properties of newly synthesized 1-(2-methyl-2-propenyl)-3-
(2,3,4,5,6-pentamethylbenzyl) benzimidazolium chloride hydrate molecule.
2. Materials and measurements
2.1. Synthesis
Benzimidazole (10 mol) was added to a solution of NaH (10 mol) in dry THF (30 mL), and
the mixture was stirred for 1 h at room temperature. 3-Chloro-2-methyl-1-propene (10.1 mol)
was added dropwise upon to obtained solution and heated for 24 h at 60°C. Then, the THF
was removed under the vacuum. Dichloromethane (50 mL) was added upon the solid. The
mixture was filtered and the obtained clear solution was concentrated under vacuum. Then
the solution was distillated. The obtained 1-(2-methyl-2-propenil)benzimidazole (1 mmol)
and 2,3,4,5,6-pentamethylbenzyl chloride (1 mmol) were stirred in DMF (5 mL) for 24 h at
80°C. White products were collapsed. Following the completion of the process, the solution
was filtered, and rinsed out with diethylether and dried under vacuum. Crude product was
recrystallized from dichloromethane/diethylether mixture (Scheme 1).
2.2. Experimental details
The synthesis of 1 was carried out under argon in flame-dried glassware using standard
Schlenk line techniques. Chemicals and solvents were purchased from Sigma Aldrich Co.
(Dorset, UK). The solvents used were dried by distillation over the drying agents and were
transferred under Argon. Elemental analyses were performed by the Turkish Research
Council (Ankara, Turkey) Microlab. Melting point was determined using Electrothermal
9100 melting point detection apparatus.1H NMR and 13C NMR spectra were recorded
using a Varian As 400 Mercury spectrometer operating at 400 MHz (1H), 100 MHz (13C) in
CDCl3 with tetramethylsilane as the internal reference. Yield: 84%, mp 201–202°C, ν(CN):
1
1556 cm−1. H NMR (399.9 MHz, CDCl3) δ (ppm): 1.75 (s, 3H, NCH2C(CH3)CH2), 2.29,
2.27 and 2.24 (s, 15H, CH2C6(CH3)5-2,3,4,5,6), 2.49 (border s, 2H, H2O), 4.85 (s, 1H,
NCH2C(CH3)CH2), 5.06 (s, 1H, NCH2C(CH3)CH2), 5.36 (s, 2H, NCH2C(CH3)CH2), 5.87
(s, 2H, CH2C6(CH3)5-2,3,4,5,6), 7.33–7.29 (m, 2H, NC6H4N), 7.57–7.47 (m, 1H,

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
111
Table . Crystallographic data of 1.
CCDC deposition number 
Crystal data
Data collection
STOE IPDS
Chemical formula
Color/ shape
CHN.Cl.HO
Colorless/ Prism
.
. × . × .
MoKα, λ = .

Diffractometer
Reflections collected
Independent/observed refl.
Absorption correction
Tmin, Tmax
F
Rint
θ range (°)

Formula weight
Crystal size (mm)
/
integration
., .

.
. ࣘ θ ࣘ .
˚
Wavelength (A)
Temperature (K)
Crystal system
Space group
Triclinic
P -
Unit cell parameters
Index ranges
− ࣘ h ࣘ , − ࣘ k ࣘ ,
˚
a, b, c (A)
.(), .(),
.()
.(), .(),
.()
.()

.
.
− ࣘ l ࣘ 
Refinement
α, β, γ (°)
Data/restraints/parameters
//
.
., .
., -.
Goodness of fit on F

˚
Volume (A )
Final R indices [I > σ(I)]
ꢀρmax, ꢀρmin (e/A )

˚
Z
Density (Mgm−
)
μ (mm−
)
NC6H4N), 7.84 (d, 1H, NC6H4N, J = 7.6 Hz), 11.04 (s, 1H, NCHN).13C NMR
(100.5 MHz, CDCl3) δ (ppm): 17.1 (CH2C6(CH3)5-2,3,4,5,6), 19.7 NCH2C(CH3)CH2),
48.4 (CH2C6(CH3)5-2,3,4,5,6), 53.5 (NCH2C(CH3)CH2), 113.7 (NCH2C(CH3)CH2),
115.3 (NCH2C(CH3)CH2), 124.9, 127.0, 127.1, 131.5, 131.8, 133.6, 134.0, 137.4
and 137.8 (NC6H4N and CH2C6(CH3)5-2,3,4,5,6), 143.8 (NCHN). % Anal. Calcd. for
C23H29N2Cl.H2O: C, 71.39; H, 8.08; N: 7.24. Found: C, 71.41; H, 8.10; N, 7.26.
2.3. X-ray crystallography
Crystallographic measurements were carried out on STOE IPDS II diffractometer using
˚
MoKα radiation (λ = 0.71073 A). The structure was solved by direct methods using
SHELXT-2016 [28] and refined by a full matrix least squares procedure using SHELXL-2017
[29]. All H atoms were placed in geometrically idealized positions and constrained to ride
˚
–
on their parent atoms with C H distances in the range 0.93–0.97 A. The DFIX restraints of
˚
˚
O—H = 0.82 A and H—H = 1.35 A were applied for OH2 distances. The final period of
refinement process results in R1 = 0.0695 and wR2 = 0.1796 for the observed reflections.
A summary of the crystal data and refinement parameters of the compound are listed in
Table 1. Molecular figures were generated using PLATON [30] and ORTEP-3 [31].
2.4. Computational details
In the present work, all theoretical calculations were performed using the Gaussian09W pro-
gram [32]. The first-hand geometry of the compound was taken from the X-ray diffraction
results. Geometry optimization was firstly performed using the density functional theory
with B3LYP. The 6–311++(d,p) basis set was assigned to all atoms. Vibrational wavenum-
bers were computed at same DFT level and no imaginary wavenumber modes were obtained.
A scaling factor of 0.9679 [33] was applied to obtain a better agreement between the opti-
mized and experimental wavenumbers. The 1H and 13C NMR chemical shifts were calculated
within the GIAO approach [34] and converted to the TMS scale. The default solvation model

112
N. S¸AHIN ET AL.
Figure . (a) The molecular structure of 1 with thermal ellipsoids at % probability. Dashed lines show the
intermolecularO˗H···Clhydrogenbond. (b)TheoptimizedgeometryofthecompoundobtainedatBLYP/-
G++(d,p) level.
IEF˗PCM [35] was preferred to include the effect of solvent on the theoretical NMR param-
eters using chloroform. Since experimental 1H NMR chemical shift values are not available
for individual hydrogen atoms of CH2 and CH3 groups, we have presented the average of
the computed values for these hydrogen atoms. In order to investigate the reactive sides of 1,
electrostatic potential (ESP) and molecular electrostatic potential (MEP) analyses were per-
formed by B3LYP/6–311G++(d,p) method. We also calculated the HOMO-LUMO energies
and chemical reactivity parameters of the compound at the same level of theory.
3. Results and discussion
3.1. Molecular geometry of NHC salt 1
From the single crystal X-ray diffraction analysis, it can be inferred that NHC salt 1 crystallizes
with a water molecule in the asymmetric unit. The experimental and optimized molecular
geometries of the title compound are shown in Fig. 1 and selected geometric parameters are
given in Table 2.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
113
Table . Comparison of some important geometric parameters of 1 with the experimental data.
Parameters
˚
Bond lengths(A)
XRD
DFT –G++(d,p)
Related experimental data
N-C
N-C
N-C
N-C
N-C
N-C
C-C
C-C
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.
.
.
.
.
.
.
.
.
.
.()a, .()b, .()c, .()d
.()a, .()b, .()c, .()d
.()a, ,()b .()c, .()d
.()a, .()b, .()c, .()d
.()d
.()d
C-C
C-C
Bond angles (o)
N-C-N
.()
.()
.()
.()
.()
.()
.()
.
.
.
.
.
.
.
.()a, .()b, .()d
.()d
C-N-C
C-N-C
C-N-C
.()d
C-N-C
N-C-C
N-C-C
Torsion angles(o)
C-N-C-N
N-C-C-C
N-C-C-C
C-N-C-C
C-N-C-C
N-C-C-C
N-C-C-C
.()
.()
− .()
− .()
.()
.()
− .()
− .
.
− .
− .
.
.
− .
a,b,c,d: Taken from Ref. [], [], [], [], respectivily.
According to X-ray diffraction data, NHC salt 1 crystallized in triclinic space group
P -1 with two molecules in the unit cell. The benzimidazole ring system is nearly planar
˚
with the maximum deviation of 0.022 A (C2) from mean plane. The N1—C1, N2—C1,
˚
N1—C2 and N2—C7 bond distances [1.323(4), 1.323(4), 1.390(3) and 1.389(3) A, respec-
tively] and C1—N2—C7, C1—N1—C2 and N1—C1—N2 bond angles [107.9(2), 107.9(2) and
111.1(2)°, respectively] are similar to those found in related benzimidazole compounds [36–
39]. The pentamethylbenzyl ring plane is almost perpendicular to this plane with an angle of
87.69°. This angle has changed to 79.37° in the optimized geometry. The orientation of the
compound changed noticeably with the optimization. In around 2-methyl-2-propenyl chain,
while the N2—C8—C9—C10/C11 torsion angles were experimentally observed at 145.0(4)°/-
34.6(5)°, computed at 124.17°/-60.01° for B3LYP. The orientation of pentamethylbenzyl ring
was defined by torsion angles N1—C12—C13—C14 [101.2(3)°] and C2—N1—C12—C13
[154.1(3)°], but these torsion angles in the optimized structure have been calculated at 91.19°
and 160.29°, respectively.
In the molecular structure of 1-(2-methyl-2-propenyl)-3-(2,3,4,5,6-pentamethylbenzyl)
benzimidazolium chloride hydrate, the atom O of water molecule acts as hydrogen-bond
˚
donor to atom chlorine with the parameters H···Cl = 2.329(12) A and O-H···Cl = 169°. The
˚
intermolecular bond has been calculated more strongly with H···Cl = 2.210 A and O-H···
Cl = 175°. The intermolecular hydrogen bond which formed between the atom C12 in main
molecule and the atom O1 in the molecule at (x, 1+y, z) supports the crystal packing of the
structure, as seen in Fig. 2. The geometric parameters of these interactions are listed in Table 3.
There are also π···π stacking interactions between the benzimidazole ring systems in the

114
N. S¸AHIN ET AL.
˚
Table . Hydrogen bonding geometry of 1 (A,°)
D-H···A
D-H
H···A
D···A
D-H···A
O˗HA···Cl
.()
.
.()
.
.()
.()


C˗HBOi
D: donor; A: acceptor. Symmetry codes: (i) x, +y, z
molecules at (x, y, z) and (1-x, 2-y, -z) with the corresponding ring-centroid separations being
˚
3.5334 and 3.5879 A (Fig. 3).
3.2. Spectroscopic data of NHC salt 1
The 13C and 1H NMR spectra of NHC salt 1 in CDCl3 are shown in Figs. 4–5 and chemical
shifts are listed in Table 4 together with the calculated values. 1H peaks are labeled as singlet
(s), doublet (d) and multiplet (m). Chemical shifts and coupling constants are reported in
ppm and in Hz, respectively. The isotropic shielding values were used to calculate the isotropic
chemical shifts (δ) with respect to TMS [δiso(X) = σTMS(X) – σiso(X)]. The calculated 1H and
Figure . A partial view of the packing of 1, showing hydrogen bond interactions as red dashed lines
(H atoms in hydrogen bonds have only been showed in main molecule).
Figure . A view of the packing of 1 from c face. Green lines show the π–π interactions between the centres
of rings. H atoms have been omitted for clarity.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
115
Figure . C NMR chemical shifts of 1 in CDCl.

Figure . H NMR chemical shifts of 1 in CDCl.
13C chemical shielding of TMS at B3LYP/6-311G++(d,p) level in CDCl3 are 31.97 ppm and
184.66 ppm, respectively.
The unknown chemical properties of the complicated compounds can be clarified by the
isotropic chemical shifts of the elements. The benzimidazolium salt has an acidic NCHN pro-
ton which came to at 11.04 ppm as a singlet in the 1H NMR spectrum. And the chemical shift
of the corresponding carbene carbon was appeared at 143.8 ppm in the 13C NMR spectrum.
These chemical shifts have duly been calculated at 12.66 ppm and 154.0 ppm in B3LYP. In
aromatic rings, the chemical shifts corresponding to carbon and hydrogen atoms are usually
observed in the region of 100–160 ppm and 6–8 ppm, respectively [40, 41]. In the present
work, aromatic protons on the benzimidazolium ring were appeared at 7.33–7.29, 7.77–7.47
and 7.84 ppm, respectively. Aromatic carbons at the benzimidazolium ring and pentamethyl-
benzyl were monitored 124.9, 127.0, 127.1, 131.5, 131.8, 133.6, 134.0, 137.4 and 137.8 ppm,
respectively. Methyl substituted benzylic proton and carbon were detected at 5.87 ppm as a
singlet and 48.4 ppm and calculated 5.51 ppm and 52.1 ppm, respectively. Methyl protons
on the benzylic group signaled three different singlet that are 2.24, 2.27 and 2.29 ppm. And
carbons of these methyl groups came to 17.0, 17.1 and 17.3 ppm at the 13C NMR spectrum.

116
N. S¸AHIN ET AL.
Table . Experimental and calculated H and C NMR chemical shifts δ(ppm) from TMS.
Atom
Experimental
Calculated
Atom
Experimental
Calculated
H(HO)
H
H
H
H
. s
. s
. d, J = .Hz
.–. m
.–. m
.–. m
.a
.
.
.
.
.
C
.
.
.
.
.
.
.
.
.
.
.
.
C
C
C
C
C
H
H(CH)
H(CH)
H(CH)
H(CH)
H(CH)
H(CH)
H(CH)
H(CH)
H(CH)
. s
. s, . s
. s
. s
. s
. s
. s
. s
. s
.a
.a
.a
.a
.a
.a
.a
.a
.a
C
C
C
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
C
C
C
C
C
C
C
C
C
C
C
C
C
C
.
.
.
.
.
.
a: average (the atom numbering according to Fig.  used in the assignment of chemical shifts.)
Theoretical 1H and 13C chemical shifts of methyl groups on the benzylic group were calcu-
lated in the range of 2.21–2.69 ppm and 19.0–20.2 ppm, respectively. In the calculated spec-
trum, –CCH3 protons belonging to 2-methyl-2-propenyl which detected at 1.75 ppm shifted
to higher field, and NCH2 protons shifted to higher frequencies. Terminal –CH2 on the 2-
methyl-2-propenyl came to 4.85 and 5.06 ppm as two different singlets. Carbons of 2-methyl-
2-propenyl were detected at 53.5, 115.3, 113.7 and 19.7 ppm and calculated at 59.1, 154.8 122.6
and 19.9 ppm, respectively. The recorded chemical shifts of NHC salt 1 are mostly compatible
with the calculated values and the previously reported results [42]. Also, protons of water on
the NHC salt 1 gave a border singlet at 2.49 ppm.
The experimental and theoretical IR spectra of NHC salt 1 are shown in Fig. 6 and some
characteristic vibrations were given in Table 5. The experimental spectrum of the com-
=
–
pound contains some characteristic bands of the stretching vibrations of the C N, C H and
=
=
C C groups. Evident of formation of the benzimidazolium salt 1 was ν(C N) bound which
showed a peak at 1557 cm−1 and calculated at 1522 cm−1. While the−s1tretching vibrations
–
=
of C H bonds have three or four peaks in the region 3000–3100cm , the C C stretch-
ing vibrations usually occur in the region 1400–1625cm−1 in the literature [43]. Vibra-
−1
–
tions belonging to the C H aromatic stretching were observed 3069, 3096 and 3111 cm−1.
–
Aliphatic C H stretching vibrations of methyl group were viewed at 2941 and 2914 cm .
Peaks at 1609 and 1662 cm−1 are C C stretching vibration modes. These peaks were cal-
=
culated with strong intensity at 1588 and 1652 cm−1. It is known that the OH vibrations of
nonhydrogen-bonded or a free hydroxyl group occur strongly in the 3550–3700 cm−1 region.
If an intramolecular hydrogen bonding presents, the O–H stretching band would reduce to
3200–3550 cm−1 region, due to the sensitivity of the OH group vibrations to the environment
[44]. While the nonhydrogen-bonded O1–H1B stretching vibration occurs at 3756cm−1 in the
calculated spectrum of NHC salt 1, there is a strong peak at 3407 cm−1 corresponding to O1–
H1A stretching vibration.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
117
Figure . FT-IR spectra belong to experimental (red) and optimized (blue) structures.
3.3. HOMO-LUMO and chemical reactivity analyses
Frontier molecular orbitals which called as HOMO (highest occupied molecular orbital) and
LUMO (lowest unoccupied molecular orbital) have an important role in molecular interac-
tions. While the HOMO energy symbolizes the ability of giving an electron, LUMO energy
represents the ability of getting an electron. Since the energy gap between these orbitals is
closely related to electron conductivity, it is a critical parameter to define the molecular elec-
trical transport [45]. The energy gaps are also liable for the chemical and spectroscopic prop-
erties of organic molecules. In order to explain the energetic and chemical reactivity of NHC
Table . Some experimental and calculated vibrational frequencies (cm−) of 1.
Assignmentsa
KBr
BLYP/–G++(d,p)
–
ν (O H)
,




ν (C H) as
–
–
ν (C H) s
ν (Caromatic H) s
–
–
–
ν (Caromatic H) as
–
ν (C H) as


–
–







–
ν (C H) s
ν (C H) as
–
–
–
ν (C H) as
ν (C H) s
ν (C H) as
–
ν (C H) s
–
ν (C H) s
–
–
ν (C H)
=
ν (C C)
,

,


=
ν (C N)
–
α (O H)
–
α (C H)







–
γ (C H)
ω (C H)
–
–
ω (O H)
a; ν: stretching, γ : rocking, α: scissoring ω: wagging.
s: symmetric, as: asymmetric.

118
N. S¸AHIN ET AL.
Table . Calculated HOMO-LUMO energies and chemical reactivity
descriptors of the compound.
Molecular properties (eV)
Calculated values
HOMO energy, EHOMO
LUMO energy, ELUMO
Energy gap, ꢀE
Ionization potential, IP
Electron Affinity, EA
Electronegativity, χ
Chemical hardness, η
Chemical potential, µ
Electrophilicity Index, ω
Global softness, S (eV)−
− .
− .
.
.
.
.
.
− .
.
.
salt 1, some characteristics such as hardness (η), chemical potential (μ), softness (S), elec-
tronegativity (χ) and electrophilicity index (ω) were calculated using HOMO and LUMO
energies. The calculated results are listed in Table 6.
The hardness and softness are decisive criterions to define chemical reactivity or kinetic
stability of a molecule. While the soft molecules have small energy gaps, the hard ones have
large energy gaps [46]. So it can be said that the hard molecules are more stable than the soft
ones. Electronegativity states the ability of an atom or a functional group to pull electrons or
electron density towards itself. The energy lowering due to maximal electron flow between
HOMO and LUMO orbitals can be evaluated using a factor called as electrophilicity index
[47].
The energy and compositions of some selected molecular orbitals are given in Table 7 and
the pictorial representations of molecular orbital distributions are shown in Fig. 7. In LUMO,
the charge density is mainly localized over the benzimidazole ring with contributions of 97%.
Whereas HOMO is fully characterized by a charge distribution on atom chlorine (94%). The
calculated energy gap for NHC salt 1 is the medium energy gap which value of 3.62 eV and
shows the high electrical activity of the compound.
Table . Energy and compositions of some selected molecular orbitals.
‘% of composition
MO
E(eV)
Cl
HO
Benzimidazole
CHC(CH)
CHC(CH)CH
LUMO+
LUMO+
LUMO+
LUMO+
LUMO+
LUMO
− .
− .
− .
− .
− .
− .







































































HOMO
− .
− .
− .
− .
− .
− .
− .
− .
− .
− .
− .










HOMO-
HOMO-
HOMO-
HOMO-
HOMO-
HOMO-
HOMO-
HOMO-
HOMO-
HOMO-





MOLECULAR CRYSTALS AND LIQUID CRYSTALS
119
Figure . Contour plots of some molecular orbitals of 1.
3.4. Mulliken and natural population analyses
Mulliken analysis that calculates the effective atomic charges is the most common popula-
tion analysis. Mulliken charges are used to understand the charge distribution on the chem-
ical bonding [48]. Atomic charges affect the electronic structure, dipole moment, molecular
polarizability and more a lot of behavior of a molecular system. Atomic charges obtained by
Mulliken population analysis and natural charges obtained by natural bond analysis for the
title compound are listed in Table 8. The absolute values of the natural charges of all hydrogen
atoms on the basis of NPA are normally positive. The absolute value of the natural charges
is negative at all the heteroatoms in the molecule. The carbon atoms of pentamethylbenzyl
are more negative when compare with the other aromatic carbons. This is in agreement with
electrostatic potential lines (Fig. 8).
Figure . (a) Molecular electrostatic potential (MEP) of 1. (b) Electrostatic potential (ESP) of 1.

120
N. S¸AHIN ET AL.
Table . Calculated net charges by Mulliken population method and natural population analysis.
–G++(d,p)
–G++(d,p)
–G++(d,p)
–G++(d,p)
Atom
Mulliken charges
Natural charges
Atom
Mulliken charges
Natural charges
Cl
O
HA
HB
N
N
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
− .
− .
.
.
.
− .
− .
.
H
H
H
H
H
HA
HB
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
− .
.
.
.
.
.
− .
− .
.
.
− .
.
.
HA
HB
HA
HB
HC
HA
HB
HA
HB
HC
HA
HB
HC
HA
HB
HC
HA
HB
HC
HA
HB
HC
− .
− .
− .
− .
.
− .
− .
− .
− .
.
− .
− .
− .
− .
− .
− .
− .
− .
− .
− .
− .
− .
− .
− .
.
.
− .
− .
− .
.
.
.
.
− .
.
.
.
.
.
.
.
.
− .
− .
− .
− .
− .
.
.
.
− .
− .
3.5. Electrostatic potential (ESP) and molecular electrostatic potential (MEP) analyses
ESP and MEP analyses of NHC salt 1 were performed by B3LYP/6-311G++(d,p) method
at the 0.02 isovalues. Figure 8a,b shows the molecular electrostatic potential and contour of
electrostatic potential for the title compound. The colour code of MEP map is in the range
between the -7.352 a.u. (darkest red) and 7.352 a.u. (darkest blue), and potential increases in
the order red < orange < yellow < green < blue.
The MEP mapped surfaces shows the charge distributions of molecules in three-
dimensional and helps to determine the relative polarity of molecules and nucleophilic and
electrophilic reactions [49, 50]. The contour maps are drawn in the molecular plain two
dimensionally and used to show lines of constant density or brightness. The electron rich
lines around oxygen and chlorine are theoretically potential active sides of the molecule and
justify the intermolecular hydrogen bonding of NHC salt 1 as shown in the packing diagram.
–
–
The green region shows the close to zero ESP value and characterize the C C and C N bonds.
4. Conclusion
Firstly, to obtain benzimidazole precursor, benzimidazole and 3-chloro-2-methyl-1-propene
were reacted. Then, 1 was prepared and fully characterized by elemental analysis, X-ray crys-
1
tallography, FT-IR, H and 13C NMR spectroscopy techniques. In addition, the molecular
1
geometry, vibrational frequencies and H and 13C NMR chemical shift values of the com-
pound have been calculated using DFT/B3LYP method. In the1H NMR spectrum of 1, the sig-
nal for the acidic carbene proton at the 2-position in the benzimidazolium ring was observed

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
121
in the expected range. In the FT-IR spectrum, the characteristic bands assigned to the
–
–
ν(O H) and ν(C H) vibrations of the compound were recorded in agreement with the pre-
viously reported results.
Although the discrepancies between the experimental and optimized geometric parame-
ters, theoretical calculations support the solid state structure of 1. This can mainly attributed
to the solid state interactions in the crystal structure which are absent in the quantum mechan-
ical modeling of the compound. The most negative potential areas in MEP are on oxygen and
chlorine atoms and the X-ray analysis showed that these atoms act as acceptor in intra and
intermolecular hydrogen bonding of compound. The electron rich lines around oxygen and
chlorine in EPS are theoretically potential active sides of the molecule and verify the MEP
map. Although the N atoms have high electronegativity, these atoms are concealed by high
positive atoms in the region. The net charge distribution of title compound was calculated
by the Mulliken and natural population methods. MEP, Mulliken population analysis, NPA
results are consistent with each other related to chemically reactivity of molecule. The results
of HOMO-LUMO and chemical reactivity analyses support the high electrical activity of the
compound. The energy and compositions of some selected molecular orbitals were also cal-
culated. The low energy unoccupied orbitals of the compound, from LUMO to LUMO+2,
have π∗ character and are concentrated on benzimidazole ring. The high energy occupied
orbitals (HOMO—HOMO-2) of the compound have π character on Cl (p) orbitals. It would
be heplful in next studies to understand the nature of electronic transitions in the compound.
Acknowledgements
The authors acknowledge the Scientific and Technological Research of Turkey (TÜBITAK-BIDEB), the
National Research Fellow-ship Programme for grants to N. S¸., Amasya University, Turkey, for the use
of the Gaussian09W program and Ondokuz Mayıs University, Turkey, for the use of the STOE IPDS 2
diffractometer (purchased under grant F.279 of the University Research Fund).
Supplementary data
Crystallographic data for the structural analysis have been deposited with the Cambridge
Crystallographic Data Center, CCDC reference number: 1582192. Copies of this infor-
mation may be obtained free of the charge from the Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (Fax: +44-1223-336033; E-mail: deposit@ ccdc.cam.ac.uk or
http://www.ccd.cam.ac.uk).
References
[1] Wanzlick, H. W. & Schönherr, H. J. (1968). Angew. Chem. Int. Ed., 7(2), 141.
[2] Öfele, K. (1968). J. Organomet. Chem., 12(3), 42.
´
[3] Cardin, D. J., Çetinkaya, B., Lappert, M. F., Manojlovic-Muir, L. & Muir, K. W. (1971). J. Chem.
Soc. D, 8, 400.
[4] Arduengo III, A. J., Harlow, R. L. & Kline, M. (1991). J. Am. Chem. Soc., 113(1), 361.
[5] Wanzlick, H. W. (1970). Chem. Ber., 103(4), 1037.
[6] Wanzlick, H. W. & Schonherr, H. J. (1970). Liebigs Ann. Chem., 731, 176.
[7] Walentowski, R. & Wanzlick, H. W. (1970). Z. Naturforsch. B: Chem. Sci., 25(12), 1421.
[8] Herrmann, W. A., Elison, M., Fischer, J., Köcher, C. & Artus, G. R. (1996). Chem. Eur. J., 2(7), 772.
[9] Herrmann, W. A., Köcher, C., Gooßen, L. & Artus, G. R. (1996). Chem. Eur. J., 2(12), 1627.
[10] Kuhn, N. & Kratz, T. (1993) Synthesis, 1993(06), 561.

122
N. S¸AHIN ET AL.
[11] Enders, D., Breuer, K., Raabe, G., Runsink, J., Teles, J. H., Melder, J. P., Ebel K. & Brode, S. (1995).
Angew. Chem. Int. Ed., 34(9), 1021.
˙
[12] S¸ahin, N., Demir, S. & Özdemir, I. (2015). Arkivoc, 20.
[13] Ortega, N., Tang, D. T. D., Urban, S., Zhao, D. & Glorius, F. (2013). Angew. Chem. Int. Ed., 52(36),
9500.
[14] Bortenschlager, M., Schütz, J., von Preysing, D., Nuyken, O., Herrmann, W. A. & Weberskirch, R.
(2005). J. Organomet. Chem., 690(24), 6233.
[15] Van Rensburg, H., Tooze, R. P., Foster, D. F. & Slawin, A. M. (2004). Inorg. Chem., 43(8),
2468.
˙
[16] Gürbüz, N., Karaca, E. Ö., Özdemir, I. & Çetinkaya, B. (2015). Turk. J. Chem., 39(6), 1115.
[17] Godoy, F., Segarra, C., Poyatos, M. & Peris, E. (2011). Organometallics, 30(4), 684.
[18] Paradiso, V., Bertolasi, V. & Grisi, F. (2014). Organometallics, 33(21), 5932.
[19] Monsaert, S., De Canck, E., Drozdzak, R., Van Der Voort, P., Verpoort, F., Martins, J. C. & Hen-
drickx, P. (2009). Eur. J. Org. Chem., 2009(5), 655.
[20] Munz, D., Allolio, C., Meyer, D., Micksch, M., Roessner, L. & Strassner, T. (2015). J. Organomet.
Chem., 794, 330.
[21] Duan, W. L., Shi, M. & Rong, G. B. (2003). Chem. Commun., (23), 2916.
[22] Sakamoto, R., Morozumi, S., Yanagawa, Y., Toyama, M., Takayama, A., Kasuga, N. C. & Nomiya,
K. (2016). J. Inorg. Biochem., 163, 110.
[23] Bertrand, B., Citta, A., Franken, I. L., Picquet, M., Folda, A., Scalcon, V., Rigobello, M. P., Gendre,
P. L., Casini, A. & Bodio, E. (2015). J. Biol. Inorg. Chem., 20(6), 1005.
[24] Schmeier, T. J., Dobereiner, G. E., Crabtree, R. H. & Hazari, N. (2011). J. Am. Chem. Soc., 133(24),
9274.
[25] Riduan, S. N., Zhang, Y. & Ying, J. Y. (2009). Angew. Chem. Int. Ed., 121(18), 3372.
´
[26] Sanz, S., Benitez, M. & Peris, E. (2009). Organometallics, 29(1), 275.
[27] Lee, C. H., Laitar, D. S., Mueller, P. & Sadighi, J. P. (2007). J. Am. Chem. Soc., 129(45),
13802.
[28] Sheldrick, G.M. (2015). Acta Crystallogr. Sect. A, 71, 3.
[29] Sheldrick, G.M. (2015). Acta Crystallogr. Sect. C, 71, 3.
[30] Spek, A. L. (2009). Acta Crystallogr. Sect. D, 65, 148.
[31] Farrugia, L. J. (1999). J. Appl. Crystallogr., 32, 837.
[32] Frisch, M. J. et. al. (2009). Gaussian 09, Revision E.01, Gaussian Inc.: Wallingford, CT.
[33] Andersson, M. P. & Uvdal, P. (2005). J. Phys. Chem. A, 109, 2937.
[34] Wolinski, K., Hinton, J. F. & Pulay, P. (1990). J. Am. Chem. Soc., 112, 8251.
[35] Cance‘s, E., Mennucci, B. & Tomasi, J. (1997). J. Chem. Phys., 107, 3032.
[36] Liu, Q. X., Yin, L. N., Cheng, F. J., Guoa, J. H. & Songb, H. B. (2006). Acta Crystallogr. Sect. E, 62,
3604.
[37] Korotkikh, N. I., Raenko, G. F., Pekhtereva, T. M., Shvaika, O. P., Cowley, A. H. & Jones, J. N.
(2006). Russ. J. Org. Chem., 42(12), 1822.
˘
[38] Özdemir, N., Dayan, O., Tercan Yava¸soglu, M. & Çetinkaya, B. (2014). Spectrochim. Acta, Part A,
131, 145.
˙
˙
[39] Akkoç, S., Kayser, V., Ilhan, I. Ö., Hibbs, D. E., Gök, Y., Williams, P. A., Hawkins, B. & Lai, F.
(2017). J. Organomet. Chem., 839, 98.
[40] Durga, R., Anand, S., Rajkumar, K., Ramalingam, S. & Sundararajan, R. S. (2016). J. Appl. Phys.,
8, 01.
[41] Bingöl Alpaslan, Y., Gökçe, H., Macit, M., Alpaslan, G. & Özdemir, N. (2015). J. Mol. Struct., 1096,
43.
˙
ˇ
[42] Dogan, Ö., Demir, S., Özdemir, I. & Cetinkaya, B. (2011). Appl. Organomet. Chem., 25(3),
163.
[43] Eazhilarasi, G., Nagalakshmi, R. & Krishnakumar, V. (2008). Spectrochim. Acta, Part A, 71,
502.
[44] Tanak, H., Alaman Agar, A. & Büyükgüngör, O. (2012). Spectrochim. Acta, Part A, 87, 15.
[45] Demircioglu, Z., Albayrak Ka¸sta¸s, Ç. & Büyükgüngör, O. (2015). Spectrochim. Acta, Part A, 139,
˘
539.
˘
[46] Temel, E., Ala¸salvar, C., Eserci, H. & Agar, E. (2017). J. Mol. Struct., 1128, 5.
[47] Xavier, R. J. & Dinesh, P. (2014). Spectrochim. Acta, Part A, 118, 999.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
123
[48] Arshad, M. N., Asiri, A. M., Alamry, K. A., Mahmood, T., Gilani, M. A., Ayub, K. & Biriniji, A. S.
(2015). Spectrochim. Acta, Part A, 142, 364.
[49] Saka, E. T., Uzun, S. & Çaglar, Y. (2016). J. Organomet. Chem., 810, 25.
[50] Dani, R. K., Bharty, M. K., Kushawaha, S. K., Prakash, O., Singh, R. K. & Singh, N. K. (2013).
Polyhedron, 65, 31.