Molecular, spectroscopic and thermal studies on catechol, 4,5-dibromocatechol, resorcinol, hydroquinone and 4-4′-dihydroxybiphenyl derivatives armed with benzothiazole moieties

Article abstract of DOI:10.1016/j.molstruc.2013.01.042

A new series of catechol, 4,5-dibromocatechol, resorcinol, hydroquinone and 4-4′-dihydroxybiphenyl derivatives possessing two benzothiazole moieties at respective positions of 1,2, 1,3, 1,4 and/or 4,4′ has successfully been synthesized. The molecular structures were fully elucidated by spectroscopic techniques (¹H NMR, ¹³C NMR and two dimensional COSY, HMBC, HMQC, DEPT-135 and DEPT-90). The connectivity study between the cause of using different core systems in the target compounds and the anisotropic behavior as inferred from phase transition temperature and relevant morphology studies has led to some unique features arising from this series. Compounds with ortho substituent exhibit enantiotropic N and SmA phases. The analogues containing resorcinol and 4,4′-disubstituentbiphenyl show enanotiotropic nematic behavior while the hydroquinone derivative induces the formation of monotropic nematogen. An extensive study to further substantiate the relationship between the stability of the nematic phase and associated transition temperatures due to different core systems is also reported.

Full text of DOI:10.1016/j.molstruc.2013.01.042

Journal of Molecular Structure 1039 (2013) 189–196
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Molecular, spectroscopic and thermal studies on catechol,
4,5-dibromocatechol, resorcinol, hydroquinone and 4-40-dihydroxybiphenyl
derivatives armed with benzothiazole moieties
a
b
Arwa Alshargabi a, Guan-Yeow Yeap a, , Wan Ahmad Kamil Mahmood , Rakesh Samikannu
⇑
a Liquid Crystal Research Laboratory, School of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia
b Department of Chemistry, Anna University, Chennai, Tamil Nadu 600 025, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
Benzothiazole based liquid crystals
synthesized.
RO
OR
The structural evaluation by 1HA1H
COSY, 1HA13C HMBC and 1HA13C
HMQC.
OR
"
RO
OR
OR
"
All compound exhibited nematic
phase.
N
S
N
N
O
R =
O
10
Br
Br
RO
OR
RO
OR
a r t i c l e i n f o
a b s t r a c t
A new series of catechol, 4,5-dibromocatechol, resorcinol, hydroquinone and 4-40-dihydroxybiphenyl
derivatives possessing two benzothiazole moieties at respective positions of 1,2, 1,3, 1,4 and/or 4,40
has successfully been synthesized. The molecular structures were fully elucidated by spectroscopic tech-
niques (1H NMR, 13C NMR and two dimensional COSY, HMBC, HMQC, DEPT-135 and DEPT-90). The con-
nectivity study between the cause of using different core systems in the target compounds and the
anisotropic behavior as inferred from phase transition temperature and relevant morphology studies
has led to some unique features arising from this series. Compounds with ortho substituent exhibit enan-
tiotropic N and SmA phases. The analogues containing resorcinol and 4,40-disubstituentbiphenyl show
enanotiotropic nematic behavior while the hydroquinone derivative induces the formation of monotropic
nematogen. An extensive study to further substantiate the relationship between the stability of the
nematic phase and associated transition temperatures due to different core systems is also reported.
Ó 2013 Elsevier B.V. All rights reserved.
Article history:
Received 14 October 2012
Received in revised form 14 January 2013
Accepted 17 January 2013
Available online 13 February 2013
Keywords:
Catechol
Resorcinol
Hydroquinone
Liquid crystal dimers
2D NMR spectroscopy
Thermal behavior
1. Introduction
associated with the versatility and workability of liquid crystals
[1–4]. Among these liquid crystals, the supramolecular assemblies
An enormous type of liquid crystals has been disclosed in the
past wherein a wide variety of physical properties ranging from
the dielectric, electro-optical, thermal conductivity to ferroelectric,
fast switching ability and selectivity in reflecting light has been
composed of oligomeric liquid crystals (LCs) and the liquid crystal
compounds with obtuse and acute angled configurations have con-
tributed tremendously toward the design of new liquid crystalline-
based devices [5–7].
Recently the LCs particularly the liquid crystal dimers have re-
ceived overwhelming attention owing to their ability to exhibit dif-
ferent phases and functionality as useful models for the semi-
⇑
Corresponding author. Fax: +60 4 6574854.
E-mail address: gyyeap@usm.my (G.-Y. Yeap).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.01.042

190
A. Alshargabi et al. / Journal of Molecular Structure 1039 (2013) 189–196
flexible and/or main-chain liquid crystal polymers such as liquid
crystal oligomers containing semi-rigid mesogenic units connected
via flexible spacers [8–14]. The salient feature of liquid crystal olig-
omers can be exemplified by the pronounced odd–even effect
when the length of the spacer was varied [15,16].
critical applications within a wide temperature range of function-
ality [4].
In view of this, we are prompted to employ catechol, 4,5-dib-
romocatechol, resorcinol, hydroquinone and 4-40-dihydroxybi-
phenyl as core systems attached by the benzothiazole units. The
thermal and optical behavior were investigated extensively with
the aim of tapping the unique mesomorphic behavior among this
series.
In 1907, Vorländer has proposed a rule stating that ‘the liquid
crystalline state is obtained for the most linear molecules’, but de-
tails of their molecular structure and micro-segregation have later
attracted much attention for producing novel and self-assemblies
compounds [17]. Later in 1929, Vorländer has reported the liquid
crystalline properties of some compounds such as bis[4-(4-meth-
oxy-phenylazo)phenyl]isophthalate and 1,2-phenylene bis-[4-(4-
ethoxyphen ylazoxy)benzoate] of which the molecules were pre-
sumed to possess obtuse and acute angled configurations, respec-
tively [18–20]. Subsequently, Goring et al. had described tuning-
fork-shaped molecules that showed undulated smectic structures
[21] and Attard et al. reported Y-shaped molecules wherein three
mesogenic groups were symmetrically connected to a phenyl ring
[22]. Besides, the U-shaped LCs had also been investigated by sev-
eral research groups [23–26]. Attard and Douglass had studied the
structure-properties correlation of dimeric compounds derived
from phthalic acid which had provided important insight on
U-shaped LC systems [21]. The attempt by Jackson et al. to investi-
gate the cyanobiphenyl-based LC dimers containing catechol as a
linking group had also disclosed the odd–even effect as resulted
from varying the parity of the spacer wherein the even derivatives
possessed higher melting and clearing points [25,27].
2. Experimental details
2.1. Materials
2-Amino-6-ethoxybenzothiazole and 1,10-dibromodecane
were purchased from Acros Organics (New Jersey, USA). Whist so-
dium nitrite and phenol were obtained from M&R and Sigma, the
catechol, resorcinol, hydroquinone and 4,40-dihydroxybipheneyl-
ene were purchased from Aldrich. All solvents and reagents were
used without further purification. 4,5-dibromocatechol was syn-
thesized according to the reported method [30]. The synthetic
route to prepare all the intermediates and target compounds with
atomic numbering scheme are shown in Scheme 1.
2.2. Characterization
2.2.1. Physical measurements
Melting points were recorded by Gallenkamp digital melting
point apparatus. The CHN microanalyses were carried out on Per-
kin–Elmer 2400 LS Series CHNS/O analyzer.
Todate, the majority of work on bent, banana, – V- and
U-shaped liquid crystals have been reported [28,29]. These types
of molecular topology and their abilities to form mesophases
have geared towards the investigation of molecular assembly
as these molecular architectures are found to be important in
2.2.2. FTIR measurement
Infrared spectra for all intermediates and title compounds were
obtained from Perkin–Elmer 2000 FT-IR spectrophotometer in
N
N
N
i
NH2
S
HO
N
OC2H5
S
C2H5O
1
5
6
N
S
4
11
15
12
14
16
18
20
22
24
ii
N
Br
2
7
1
8
N
O
3
O
19
23
10
25
17
OH
OH
21
13
9
2
HO
HO
HO
HO
Br
Br
iii
iii
iii
iii
iii
HO
OH
HO
OH
OR
26
27
27
27
RO
26
RO
26
RO
26
28
Br
27
28
28
29
28
29
27
28
31
30
RO
OR
29
Br
31
26
31
29
30
RO
31
RO
31
30
OR
30
3a
30
29
OR
3b
3e
3c
3d
N
N
Where R =
S
N
O(CH2)10
C2H5O
Scheme 1. Synthetic rote for the target compounds 3a–3e. Reagent: (i) NaNO2, H2SO4, Phenol, NaOH; (ii) Br(CH2)10Br, K2CO3, KI, Acetone; (iii) K2CO3, KI, DMF.

A. Alshargabi et al. / Journal of Molecular Structure 1039 (2013) 189–196
191
Table 1
the temperature of the sample was controlled by an accuracy of
0.1°.
Phase transition temperatures and enthalpy changes for 3a–3e.
Compound
Phase transition temperature, °C heating cooling
(associated enthalpy change, kJ molꢀ1
)
2.3. Synthesis
3a
Cr 69.0 (11.6) Cr1 75.8 (1.9) SmA123.0 (2.1) N 152.7
(1.0) I
2.3.1. 4-((5-Ethoxybenzothiazol-2-yl)diazenyl)phenol (1)
This compound was obtained from our earlier reported method
[32].
I 151.5 (1.4) N 122.1 (1.9) SmAa
Cr 108.4 (15.1) SmA135.4 (1.6) N 145.4 (0.3) I
I 144.9 (0.5) N 134.5 (1.9) SmAa
Cr 122.7 (55.4) N 151.6 (2.0) I
I 151.1 (2.1) N 125.4 (59.5) Cr
Cr 189.0 (116.1) I
I 183.1 (7.5) N 176.4 (79.3) Cr
Cr 179.8 (29.6) N 226.0 (3.6) I
I 221.1 (4.5) N 167.6 (31.2) Cr
3b
3c
3d
3e
2.3.2. Synthesis of 4-((6-ethoxybenzothiazol-2-
yl)diazenyl)bromodecanoxyphenyl (2)
A solution consisting of compound 1 (8.33 mmol) in 150 ml of
dry acetone, potassium carbonate (62 mmol), a catalytic amount
of potassium iodide (100 mg) and a fivefold excess of 1,10-dibro-
modecane (41.6 mmol) was refluxed for 24 h. K2CO3 was removed
from hot solution by filtration and the acetone was removed under
reduced pressure. The product was recrystallized three times from
ethanol whereupon the pure compound was isolated.
Cr, crystal; N, nematic; I, isotropic.
a
The formation of SmA was observed until room temperature.
which the samples were mixed with KBr in the range of 4000–
400 cmꢀ1
.
2.3.3. Synthesis of 3a–3e
A mixture of compound 2 (100 mmol) and the desired dihydr-
oxyl compounds (i.e. catechol, resorcinol, hydroquinone, 4,40-dihy-
droxybiphenyl) (220 mmol) were dissolved in 30 ml dry DMF in
the presence of K2CO3 (500 mmol) and catalytic amount of KI
(100 mg). The mixture was heated on the oil bath at 80 °C with
continuous stirring for 48 h for 3a, 3b and 3c whilst 24 h for 3d
and 3e. The resulting solution was then cooled and poured in ice
water to remove the inorganic materials and the precipitate thus
formed was filtered and washed several times by water. The prod-
uct was purified by column chromatography using CHCl3 as eluent
and finally recrystallized from DMF to yield the pure desired
compounds.
2.2.3. NMR measurement
The 1H- and 13C NMR spectra were obtained using Bruker
Avance 500 and ultrashield spectrometers equipped with ultra-
shield magnets. Standard Bruker pulse programs were used
throughout the entire experiment [31]. The 1H- and 13C NMR data
for target compounds were further substantiated with the aids of
2D 1HA1H correlation spectroscopy (COSY), 1HA13C heteronuclear
multiple quantum correlation (HMQC) and 1HA13C heteronuclear
multiple bond correlation (HMBC) by using deuterated chloroform
(CDCl3), dimethysulphoxide (DMSO-d6) as solvents and tetrameth-
ylsilane (TMS) as internal standard.
2.2.4. Phase transition temperature and enthalpy values
The phase-transition temperature and associated enthalpy val-
ues were determined by using a differential scanning calorimeter
Seiko DSC6200R operated at a scanning rate of 5 °C minꢀ1 both
on heating and cooling cycles.
3. Results and discussion
The analytical data for intermediate 2 and final compounds 3a–
3e are shown in Table 1. The yields are found to be more than 65%
while the purity for each compound is also in agreement with
respective empirical formula.
2.2.5. Texture observation
Texture observation of the mesophase was carried out by using
Carl Zeiss Axioskop 40 polarizing microscope equipped with a Lin-
kam LTS350 hot stage and TMS94 temperature controller. The
samples studied by optical microscope were prepared in thin film
sandwiched between glass slide and cover.
3.1. Anisotropic behavior
The phase sequences and related transition temperatures upon
heating and cooling for 3a–3e are listed in Table 1. All the textures
observed under the polarized light have been identified through
comparison with those reported in the literatures [33,34].
2.2.6. X-ray diffraction study
The texture observation reveals that the compounds 3a and 3b
are enantiotropic N and SmA phase. Upon cooling 3a from isotropic
liquid, the nematic droplets appear and coalesce to form the clas-
sical schlieren texture with two-brush and four-brush defects
(Fig. 1a). Further cooling has led to the appearance of fan shaped
texture indicating the SmA phase which remains unchanged until
The X-ray diffraction measurement on 3a was carried out using
a Bruker D8 Discover and GADDS system. The homeotropic align-
ment of the samples was obtained by slow cooling of a drop of
the isotropic liquid below the clearing temperature. The X-ray
beam was directed almost parallel to the substrate surface and
Fig. 1. Photomicrographs showing the (a) classical schlieren texture with two-brush and four-brush defects, (b) SmA texture for compound 3a, (c) nematic schlireren texture
for compound 3e.

192
A. Alshargabi et al. / Journal of Molecular Structure 1039 (2013) 189–196
Fig. 2. DSC thermogram of compound 3a upon heating and cooling.
room temperature (Fig. 1b). However, compounds 3c and 3e show
enantiotropic N phase while compound 3d is a monotropic nema-
togen (Fig. 1c).
From the DSC thermogram for 3a, there are two endotherms ob-
servable at 69.0 °C and 75.8 °C with enthalpies
D
H = 11.6 kJ molꢀ1
and 1.9 kJ molꢀ1 during the heating run and these can be assigned
to CrACr1 and Cr1ASmA transitions, respectively. Subsequently,
the third transition at 123.0 °C corresponds to SmAAN with
D
H = 2.1 kJ molꢀ1 followed by the transition of NAI at 152.7 °C in
which the
D
H = 1.0 kJ molꢀ1. However, upon cooling two peaks
are observed at 151.5 °C and 122.1 °C with respective enthalpy val-
ues of 1.4 kJ molꢀ1 and 1.9 kJ molꢀ1 assignable to IAN and NASmA
transitions. There is no other peak which indicates the presence of
SmAACr transition. Another interesting feature is that no sign of
crystallization even the compound was left for 2 days at room tem-
perature. However, a mechanical disturbance induces crystalliza-
tion process (see Fig. 2).
Fig. 3. The correlation between the transition temperatures and the target
compounds possessing benzothiazole units at different positions.
3.2. Mesogenic properties and chemical constitution relationship
ties between 3a and 3b reveals that both compounds 3a and 3b ex-
hibit N and SmA phases. The thermal stability of SmA phase for 3a
is higher than 3b by DSmA = 20.2 °C upon heating run. This phe-
nomenon indicates that the bromine (Br) atoms are considered lar-
ger than the H atom and hence is more polarizable because the
valence electrons are located far apart from the nucleus [35]. How-
ever, 3a possesses higher nematic mesophase and thermal stability
An extensive study upon the changes of mesomorphic proper-
ties resulted from the attachment of two identical mesogenic
groups to different cores (i.e. catechcol, 4,5-dibromocatechol, res-
orcinol, hydroquinone and 4,40-dihydroxybiphenyl), wherein the
alkyl spacer of CnH2n with n = 10 remains intact, has been carried
out.
(D
TN = 29 °C and
DT = 126 °C) in comparison to 3b (DTN = 10 °C
Fig. 3 indicates that the phase transition temperatures are
dependent on catechol, disubstituted catechol, resorcinol, hydro-
quinone and dihydroxybiphenyl. Whilst the present compounds
3a and 3b exhibit the phase sequence IANASmAACr, compounds
3c, 3d and 3e are inclined to IANACr. Moreover, by increasing
the linearity there is a gradual increase in the clearing point from
152.1 °C (3a) to 226.5 °C (3e).
It can also be inferred from Fig. 3 that the thermal stability of
SmA phase for compounds 3a and 3b are considered high wherein
the temperature ranges upon heating are 97 °C and 109 °C, respec-
tively. These values were obtained from the point where the com-
pounds (3a and 3b) show the SmA phase which persists until room
temperature (25 °C). A comparison on the liquid crystalline proper-
and T = 119 °C). This observation indicates that the lateral bro-
D
mine substituent in 3b has not only increased the breadth of the
molecule but also the distorted planarity in the system due to ste-
ric interaction. These factors would decrease the nematic meso-
phase range and thermal stability for 3b as compared with 3a [36].
The linking position between mesogenic group and spacer var-
ies from the ortho in 3a to meta in 3c until para in 3d. Due to this
molecular configuration characteristic, the compound 3a is found
to be more effective in enchancing the formation of the enantio-
tropic N and SmA phases. However, 3c was found to exhibit enan-
tropic N phase and compound 3d shows monotropic N phase only.
Furthermore, there is a clear crystallization except for 3a and 3b.
Compounds 3a and 3b were found to show the phase sequence

A. Alshargabi et al. / Journal of Molecular Structure 1039 (2013) 189–196
193
3.4. Spectroscopic technique
From the FT-IR spectra (Table 2), a sharp peak at 2978–
2852 cmꢀ1 indicates the presence of CH aliphatic bonds. The
absorption band at 3069 cmꢀ1 is due to aromatic CH and the strong
absorption band at 1598 cmꢀ1 corresponds to olefinic double bond
(C@C). The absorption with a strong intensity at 1496–1470 cmꢀ1
can be assigned to aryl–alkyl ether linkage which substantiates
the incorporation of the methylene spacer (CH2). The band at
1578 cmꢀ1 due to C@N from benzothiazol while the sharp peak
at 1259 cmꢀ1 representing CAO stretching.
1H NMR spectral data of the compounds 3a–3e are summarized
in Table 3. The 1H NMR data show that the chemical shifts of 3a–3e
resonate as a triplet at d = 4.10–4.16 ppm and these can be as-
signed to methylene proton H2 whilst the resonances recorded
within the range of d = 4.01–4.1 ppm and d = 3.92–3.99 ppm are
attributed to methylene protons H16 and H25, respectively. The
multiplet at d = 1.74–1.87 ppm corresponds to H17 and H24. The
remaining methylene protons appear at d = 1.33–1.51 ppm with
the triplet appears at d = 1.44–1.50 ppm can be assigned to the ter-
minal methyl H1 proton. The aromatic protons for H11 and H15
were observed as doublet at d = 6.99–7.11 ppm and the protons
for H12 and H14 which appear as doublet at d = 7.99–8.08 ppm.
A singlet observed at d = 7.97–8.10 ppm can be attributed to aro-
matic proton H5. For the proton H9, it resonates as a singlet at
d = 7.18–7.32 ppm. The H4 signal appears as doublet–doublet in
the region of d = 7.01–7.13 ppm.
Fig. 4. XRD pattern for compound 3a.
of IANASmA and compound (4,40 benzene derivative) 3e shows
the highest TIAN transition.
The difference in the molecular geometry between compounds
3d and 3e lies in the number of phenyl rings. The presence of an
additional phenyl ring in compound 3e increases the molecular
length and the overall polarizability of the molecule leading to
stronger cohesive force at centre. Hence, it increases the aspect ra-
tio for this compound and this can be exemplified by the greater
nematic phase length and higher thermal stability of 3e in compar-
ison to compounds 3a, 3b and 3c [37].
In 3a, a remarkable upfield shift for the singlet at d = 6.88 ppm
represents H27AH30. However, in 3b, the downfield shift of the
singlet at d = 7.07 ppm is assigned to protons H27 and H30. 1H
NMR spectrum of 3c exhibit a doublet at d = 6.45 ppm, a singlet
at d = 6.48 ppm and a triplet at d = 7.14 ppm which can be ascribed
to protons H27, H29 with H31 and H28, respectively.
3.3. XRD study on compound 3a
In order to ascertain the nature of the smectic A phase formed
by the symmetrical dimers, X-ray powder diffraction studies were
carried out on 3a. The X-ray pattern (Fig. 4) associated with the N
and SmA phases for 3a is shown in Fig. 4. The diffraction pattern
shows a sharp reflection in the small angle region with d (molecu-
lar length) value of 32.7 Å corresponding to a typical signals for
smectic phase with Bragg reflection. In the wide angle region a dif-
fuse reflection is seen with a spacing of 4.5 Å corresponding to the
intermolecular separation within the smectic layer due to the li-
quid-like positional correlation [38]. The calculated molecular
length of the molecule 3a, measured with Chem3D molecular mod-
el in which the calculated result derived from the MM2 is 32.5 Å
(Fig. 5). Obviously the value 32.7 Å corresponds to the length of
the molecule and the value d/l ratio is one. Thus, it is proven that
the present dimer 3a exhibits a monolayer SmA phase over a wide
thermal range which includes the room temperature [39].
For 3d, 1H NMR showed a singlet at d = 6.84 ppm which can be
assigned to protons H27AH31. For 3e, the doublet at d = 6.95 ppm
and 7.44 ppm is caused by protons H28, H30 and H 27, H31,
respectively.
1HA1H COSY results of compounds 3a–3e are listed in Table 3.
The correlation of the 1HA1H COSY experiment of compound 2 is
employed to assign the aromatic and aliphatic protons (Table 3).
Inspection from Fig. 6 for compound 2 suggests the correlation be-
tween H2 with the respective protons H1 and H3. A similar phe-
nomenon can also be found on H4 which has correlated with H5.
The correlation by COSY also reveals that the H11 and H15 protons
from the aromatic ring are correlated with respective H12 and H14.
The proton H4 or H5 is correlated with proton H6 or H7 and a sim-
Fig. 5. The molecular shape of 3a (energy-minimized model derived from CS ChemDraw Ultra 9.0).

194
A. Alshargabi et al. / Journal of Molecular Structure 1039 (2013) 189–196
Table 2
H1, can be correlated with H17. In the same way, a correlation can
also be observed in compounds 3a–3e with more correlations for
aromatic protons attached to C25 in compound 2 by substitution
reaction.
Vibrational frequencies (cmꢀ1) and their assignments for compounds 2 and 3a–3e.
Compound
m
CphAH
mCH3
m
CH2
@
@
mC N
@
dCH
mCAO
mC
C
@
2
3077
3063
3070
3066
3069
3069
2981 2851 1598
2978 2851 1598
2978 2852 1598
2977 2826 1598
2979 2852 1598
2978 2853 1598
1578
1557
1578
1580
1576
1581
1498–1971 1262
1498–1471 1256
1497–1471 1260
1497–1474 1254
1496–1472 1258
1498–1474 1246
Table 4 summarizes the 13C NMR spectroscopic results of com-
pounds 3a–3e. The 13C NMR spectroscopy data for 3a shows the
peaks at d = 64.15 ppm and 68.60 ppm which can be attributed to
the C2 and C16. While a singlet at d = 69.30 ppm represents the
carbon C25 which has substantiated the formation of the ether
bond with catechol. The C1 is observed at d = 14.78 ppm whereas
the remaining alkyl carbons are located at d = 25.29–29.54 ppm.
The resonance due to aromatic carbons C4, C5, C9, C11 or C15
and C12 or C14 are observed at d = 116.52 ppm, 125.44 ppm,
105.08 ppm, 115.08 ppm and 126.14 ppm, respectively. The reso-
nances recorded at d = 114.26 ppm and 121.07 ppm can be attrib-
uted to C28 or C29 and C27 or C30. On the other hand, the
signals due to the quaternary aromatic carbons C3, C6, C7, C8,
C10 and C13 are observed at d = 158.68 ppm, 147.33 ppm,
173.94 ppm, 136.10 ppm, 146.12 ppm and 163.62 ppm, respec-
tively. While the singlet at the low field (d = 149.29 ppm) is due
to C26 or C31.
3a
3b
3c
3d
3e
m
= Stretching; d = bending.
Table 3
1H NMR chemical shifts (d/ppm) of compounds 3a–3e.
Atom no.
Chemical shift (ppm)
3a
3b
3c
3d
3e
H1
H2
H4
H5
1.47
4.12
7.01
8.01
7.26
7.07
7.99
4.03
1.78, 1.82
1.34–1.49
3.99
6.88
6.88
1.44
4.10
7.08
7.99
7.26
6.99
7.97
4.01
1.76, 1.82
1.32–1.45
3.92
7.06
–
1.48
4.13
7.08
8.01
7.28
7.02
7.99
4.05
1.78, 1.82
1.33–1.48
3.93
6.48
7.14
1.50
4.16
7.13
8.04
7.32
7.11
8.02
4.10
1.77, 1.85
1.36–1.51
3.92
6.84
6.84
1.50
4.16
7.13
8.10
7.18
7.10
8.08
4.15
1.79, 1.87
1.38–1.51
3.99
7.45
6.95
H9
The 1HA13C HMQC spectra of compounds 2 and 3a–3e provide
the information on the interaction between the protons and the
carbon atoms which are directly attached to each other (Tables 4
and 5, ESI ). As a representative, the discussion will be based on
the spectrum of 3e (Fig. 7). It can be deduced from Fig. 4 that the
aromatic protons for H11 (magnetically equivalent to H15), H12
(magnetically equivalent to H14), H5, H4 and H9 in aromatic rings
are correlated with C11 (magnetically equivalent to C15), C12
(magnetically equivalent to C14), C5, C4 and C9, respectively. A
similar phenomenon can also be found on H27 (magnetically
equivalent to H31, H34, H36) and H28 (magnetically equivalent
to H30, H33, H37) in biphenyl ring which have correlated with
C27 (magnetically equivalent to C31, C34, C36) and C28 (magnet-
ically equivalent to C30, C33, C37), respectively. Moreover, the al-
kyl carbon atoms of C1, C2, C16, C17 or C24 and C25 show a cross
peak with proton H1, H2, H16, H17 or H24 and H25, respectively.
The aromatic quaternary carbons for all compounds 2 and 3a–
3e were confirmed via the connectivities between the carbon and
H11,15
H12,H14
H16
H17, H24
H18AH23
H25
H27
H28
H29
H30
6.88
–
6.48
–
–
6.88
–
7.06
–
–
6.45
6.84
6.84
6.95
7.45
H31
ilar phenomenon can also be found on H8 or H9 which has estab-
lished connectivities with H10 or H11. Fig. 3 also shows that the
ether group of proton H25 is correlated with the respective proton
H24 and a similar phenomenon can also be found on H16 which
has correlation with H17. The correlation inferred from COSY spec-
tra has also shown that the H18, which has overlapped with proton
Fig. 6. 1HA1H COSY spectrum of compound 2.

A. Alshargabi et al. / Journal of Molecular Structure 1039 (2013) 189–196
195
Table 4
13C NMR chemical shift for compounds 3a–3e.
Carbon no.
Chemical shift (ppm)
3a
3b
3c
3d
3e
C1
14.78
14.78
14.79
14.77
14.79
C2
64.15
64.13
64.17
64.16
64.27
C3
C4
C5
C6
C7
C8
C9
C10
158.68
116.52
125.44
147.33
173.94
136.10
105.08
146.12
115.08
126.41
163.62
68.60
158.67
116.51
125.42
147.30
173.91
136.10
105.05
146.11
115.06
126.39
163.59
68.57
158.70
116.53
125.46
147.36
173.96
136.12
105.12
146.15
115.11
126.42
163.65
68.62
158.69
116.52
125.43
147.32
173.95
136.10
105.11
146.13
115.10
126.41
163.65
68.68
158.81
116.56
125.52
147.53
174.04
136.24
105.36
146.33
115.22
126.44
163.74
68.71
C11, C15
C12, C14
C13
C16
C17
29.54
29.49
29.47
29.45
29.48
C18, C23
C19AC22
C24
25.99, 26.05
29.13–29.50
29.54
25.92, 25.98
29.48–29.07
29.49
25.97, 26.06
29.11–29.36
29.47
25.80, 25.95
28.51–29.40
29.45
26.01, 26.11
29.17–29.39
29.48
C25
69.30
69.63
67.99
68.61
68.24
C26
C27
C28
C29
C30
C31
C32
C33, C37
C34, C36
C35
149.29
121.07
114.26
114.26
121.07
149.29
–
–
–
–
149.09
118.17
114.74
114.74
118.17
149.09
–
–
–
–
160.41
106.68
129.76
106.68
160.41
101.55
–
–
–
–
153.24
115.58
115.58
153.24
115.58
115.58
–
–
–
–
158.39
127.69
114.95
133.51
114.95
127.69
133.51
114.95
114.95
158.39
Fig. 7. 1HA13C HMQC spectrum of compound 3e.
its neighboring proton by HMBC correlation spectra. The aliphatic
protons for all title compounds exhibit correlation with the at-
tached aromatic ring carbon. However, the HMBC spectra of 3c
(Fig. 8) has shown that the H25, C16 and C2 are correlated with
the carbons C26 or 30, and, C13 and C3 with 2J. A similar phenom-
enon can also be found on H27 (magnetically equivalent to H29)
which is correlated with C31 with 2J. The quaternary carbons C10
and C13 are assigned based on correlations with H11 or H15 with
1J and 2J, respectively. In addition, H12 or H14 is correlated with
C13 and C10 with 1J and 2J, respectively. In the same way, H28 is
also correlated with carbons C26 and C30 with 2J. The H5 from
the phenyl ring adjacent to nitrogen atom in thiazole ring is corre-
lated with carbons C6 with 1J, C8 and C3 with 2J. In addition to the
quaternary carbons, CH, CH2, CH3 carbons are also used to establish
the assignment with the aids of DEPT-90, DEPT-135 and DEPT-45
experiments.

196
A. Alshargabi et al. / Journal of Molecular Structure 1039 (2013) 189–196
Fig. 8. 1HA13C HMBC spectrum of compound 3c.
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A new series of dimeric compounds in which two mesogenic
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Acknowledgments
The authors would like to thank Universiti Sains Malaysia for
funding the project through FRGS Grant (Account No. 203/PKI-
MIA/6711192). Authors also thank Ms Anna Zep and her supervisor
Prof E. Gorecka for the powder X-ray diffraction measurement.
Appendix A. Supplementary material
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