Synthesis and anisotropic properties of novel asymmetric diones fused with 1,3-oxazepine and oxazepane rings

Article abstract of DOI:10.1080/15421406.2011.591687

Novel synthesis of heterocyclic liquid crystal compounds containing seven-membered 1,3-oxazepine-4,7-diones, 5,6-dihydro-1,3-oxazepane-4,7-diones, and 5,6-benzo[e] [1, 3]oxazepine-4,7-diones rings at para position has been carried out from the reaction of

Full text of DOI:10.1080/15421406.2011.591687

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Synthesis and Anisotropic Properties of
Novel Asymmetric Diones Fused With
1,3-Oxazepine and Oxazepane Rings
Guan-Yeow Yeap a , Abdulkarim-Talaq Mohammad a & Hasnah Osman
a
a Liquid Crystal Research Laboratory, School of Chemical Sciences ,
Universiti Sains Malaysia , Minden , Penang , Malaysia
Published online: 27 Dec 2011.
To cite this article: Guan-Yeow Yeap , Abdulkarim-Talaq Mohammad & Hasnah Osman (2012) Synthesis
and Anisotropic Properties of Novel Asymmetric Diones Fused With 1,3-Oxazepine and Oxazepane
Rings, Molecular Crystals and Liquid Crystals, 552:1, 177-193, DOI: 10.1080/15421406.2011.591687
To link to this article: http://dx.doi.org/10.1080/15421406.2011.591687
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Mol. Cryst. Liq. Cryst., Vol. 552: pp. 177–193, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.591687
Synthesis and Anisotropic Properties of Novel
Asymmetric Diones Fused With 1,3-Oxazepine
and Oxazepane Rings
GUAN-YEOW YEAP,∗ ABDULKARIM-TALAQ MOHAMMAD,
AND HASNAH OSMAN
Liquid Crystal Research Laboratory, School of Chemical Sciences,
Universiti Sains Malaysia, Minden, Penang, Malaysia
Novel synthesis of heterocyclic liquid crystal compounds containing seven-membered
1,3-oxazepine-4,7-diones, 5,6-dihydro-1,3-oxazepane-4,7-diones, and 5,6-benzo[e]
[1,3]oxazepine-4,7-diones rings at para position has been carried out from the reaction
of maleic, succinic, and phthalic anhydrides with N-(4-(tetradecyloxy)benzylidene)
alkylamine. The various lengths of the even-parity alkyl chains CnH2n+1, in which n
ranges from 6 to 18, were employed in the present study. The molecular structures of
these compounds were substantiated by Fourier transformed infrared and nuclear mag-
netic resonance along with elemental analysis. The correlation between the structures
and the mesomorphic behaviors of N-(4-(tetradecyloxy)benzylidene)alkylamines and
their derivatives was investigated. Present work shows that the formation of mesophases
is strongly dependent on the type of core moiety. Although the imines possessing the alkyl
chain CnH2n+1 (n = 6–14) exhibit smectic A (SmA) phases, the nemactogenic properties
can only be observed in the series of 3,4-dihydrobenzo[e][1,3]oxazepine-1,5-diones.
Keywords 5,6-Benzo[e][1,3]oxazepine-4,7-diones; 5,6-dihydro-1,3-oxazepane-4,7-
diones; liquid crystal; N-(4-(tetradecyloxy)benzylidene)alkylamine; nematic; 1,3-
oxazepine-4,7-diones; smectic A; synthesis
1. Introduction
It has well been claimed that the liquid crystalline behavior of an organic compound is
dependent on its molecular architecture in which a slight change in its molecular geometry
gives rise to a considerable change in its mesomorphic properties [1–5]. In general, the
mesomorphic behavior of an organic compound can be varied by changing the linking,
terminal, and central core systems [6]. In recent years, interest in mesogenic structures
containing heterocyclic rings has increased remarkably owing to their abilities to exhibit
mesogenic behavior either similar to or superior to the linear phenyl analogs [7–15].
The heterocyclic compounds are of great importance as core units in thermotropic
liquid crystals due to their abilities to impart lateral and/or longitudinal dipoles. More-
over, the presence of heteroatoms (O, S, and N) could lead to significant changes in
∗Address correspondence to Guan-Yeow Yeap, Liquid Crystal Research Laboratory, School of
Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia. Fax: 60-4-6574854.
E-mail: gyyeap@usm.my; gyyeap liqcryst usm@yahoo.com
177

178
G.-Y. Yeap et al.
the corresponding liquid crystalline phases and/or in the physical properties of the ob-
served phases. Since most of the heteroatoms thus introduced are claimed to be more
polarizable than carbon, therefore, a large dipole may eventually be introduced into
a liquid crystal structure in comparison with the analogous phenyl-based mesogens
[16–18]. The direction of the dipole moments of the core parts of the liquid crystal
molecules is known to be important especially in determining the molecular alignment
in mesophase [19]. This information propels us to consider the 1,3-oxazepine-diones,
which possess seven-membered heterocyclic ring system. Since the modification of ox-
azepine core as liquid crystalline compounds was not well documented, therefore, we re-
port the novel compounds of 3-alkyl-2-(4-(tetradecyloxy)phenyl)-1,3-oxazepine-4,7-dione,
3-alkyl-2-(4-(tetradecyloxy)phenyl)-5,6-dihydro-1,3-oxazepane-4,7-diones, and 3-alkyl-2-
(4-(tetradecyloxy)phenyl)-5,6-benzo[e][1,3]oxazepine-4,7-diones. The physical properties
of the title compounds were studied by Fourier transformed infrared (FT-IR) and high-
resolution nuclear magnetic resonance (NMR) (1H and 13C NMR). The phase transition
temperatures and enthalpy values of the title compounds were measured by differential
scanning calorimetry (DSC) and the textures of the mesophases were studied by using a
polarizing optical microscope (POM).
2. Experimental
2.1. Synthesis
The synthetic routes toward formation of all the title compounds are depicted in Scheme 1.
The synthesis of each compound in all the series was identical.
2.1.1. Synthesis of 4-(Tetradecyloxy)benzaldehyde. A mixture containing 0.1 mol of
4-hydroxybenzeldehyde, 0.25 mol anhydrous sodium carbonate, and 0.1 mol 1-
bromotetradecane in 50 mL of DMF was allowed to heat for 4 h at 150◦C under continuous
stirring as documented by Catanescu et al. [20]. The resulting mixture was then poured into
an ice water bath (approximately 5◦C) whereupon a precipitate formed. The precipitate
was filtered and washed once with KOH and water, dried, and finally recrystallized from
ethanol.
2.1.2. General Procedure for the Synthesis of N-(4-(Tetradecyloxy)-Benzylidene)
alkylamine (1–7). The imines were synthesized by the same method. The synthetic method
will be described on the basis of compound 1.
A mixture containing equimolar amounts of hexylamine and 4-(tetradecyloxy)
benzaldehyde in absolute ethanol was refluxed for 14 h. The reaction mixture was al-
lowed to cool to 0◦C overnight. It was filtered and washed with 2% HCl and cold water
before being dried at room temperature. The solid thus obtained was recrystallized twice
1
from absolute ethanol. The analytical data, FT-IR, and H and 13C NMR for compounds
1–7 are summarized as follows.
1: Yield 81% m.p. 60◦C–61◦C. Anal.: found for C27H47NO (%): C 80.69, H 11.67,
N 3.58. Calc. (%) C 80.74, H 11.79, N 3.49. IR: υmax(KBr) (cm−1) 3060, 2991, 2960,
1
1638, 1600, 1593, 1250; H NMR δ (CDCl3): 8.02 (s, H7), 7.54 (d, J = 8.8 Hz,
H2 and H6), 6.93 (d, J = 8.6 Hz, H3 and H5), 4.04 (t, C4-OCH2), 3.58 (t, N-CH2),
1.85–1.23 (m, OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 0.91 (t, CH3); 13C NMR
δ (CDCl3): 162.07 (C N), 158.11 (Ar C O), 132.05–116.11 (Ar-C), 71.03 (O CH2),

Synthesis and Anisotropic Properties of Novel Asymmetric Diones
179
Scheme 1. The reaction scheme for intermediates and title compounds with numbering atom.
60.83 (N CH2), 32.88–21.56 (OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 14.93
(CH3).
2: Yield 79% m.p. 64◦C–65◦C. Anal.: found for C29H51NO (%): C 81.08, H 11.84,
N, 3.15. Calc. (%) C 81.05, H 11.96, N 3.26. IR: υmax(KBr) (cm−1): 3044, 2990, 2958,
1
1640, 1598, 1581, 1258; H NMR δ (CDCl3): 8.02 (s, H7), 7.53 (d, J = 8.8 Hz, H2
and H6), 6.94 (d, J = 8.6 Hz, H3 and H5), 4.03 (t, C4 OCH2), 3.60 (t, N CH2),
1.86–1.22 (m, OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 0.90 (t, CH3); 13C NMR

180
G.-Y. Yeap et al.
δ (CDCl3): 162.02 (C N), 158.15 (Ar C O), 132.04–116.13 (Ar C), 71.07 (O CH2),
60.75 (N CH2), 32.85–21.57 (OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 14.92
(CH3).
3: Yield 77% m.p. 68◦C–69◦C. Anal.: found for C31H55NO (%): C 81.29, H 12.07,
N 3.04. Calc. (%) C 81.34, H 12.11, N 3.06. IR: υmax(KBr) (cm−1): 3010, 2986, 2938,
1
1629, 1581, 1510, 1249; H NMR δ (CDCl3): 8.04 (s, H7), 7.55 (d, J = 8.9 Hz, H2
and H6), 6.94 (d, J = 8.7 Hz, H3 and H5), 4.05 (t, C4 OCH2), 3.57 (t, N CH2),
1.86–1.21 (m, OCH2 ((CH2)2-CH2)13) and NCH2 (CH2 CHn), 0.88 (t, CH3); 13C NMR
δ (CDCl3): 161.95 (C N), 158.20 (Ar C O), 132.09–116.15 (Ar C), 71.09 (O CH2),
61.01 (N CH2), 32.86–21.60 (OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 14.93
(CH3).
4: Yield 69% m.p. 74◦C–75◦C. Anal.: found for C33H59NO (%): C 81.69, H 12.17, N
2.81. Calc. (%) C 81.58, H 12.24, N 2.88. IR: υmax(KBr) (cm−1): 3030, 2992, 2951, 1640,
1594, 1522, 1250; 1H NMR δ (ppm) (CDCl3): 8.03 (s, H7), 7.54 (d, J = 8.8 Hz, H2 and
H6), 6.93 (d, J = 8.6 Hz, H3 and H5), 4.04 (t, C4 OCH2), 3.58 (t, N CH2), 1.87–1.23
(m, OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 0.89 (t, CH3); 13C NMR (ppm)
δ (CDCl3): 161.87 (C N), 158.28 (Ar C O), 132.11–116.20 (Ar C), 71.12 (O CH2),
60.92 (N CH2), 32.85–21.58 (OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 14.93
(CH3).
5: Yield 61% m.p. 78◦C–79◦C. Anal.: found for C35H63NO (%): C 81.91, H 12.46, N
2.61. Calc (%) C 81.80, H 12.36, N 2.73. IR: υmax(KBr) (cm−1): 3061, 2988, 2960, 1635,
1
1600, 1582, 1255; HNMR δ (ppm) (CDCl3): 8.06 (s, H7), 7.54 (d, J = 8.8 Hz, H2 and
H6), 6.95 (d, J = 8.6 Hz, H3 and H5), 4.05 (t, C4 OCH2), 3.61 (t, N CH2), 1.88–1.25
(m, OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 0.91 (t, CH3); 13C NMR δ (ppm)
(CDCl3): 161.95 (C N), 158.29 (Ar C O), 132.05–116.14 (Ar C), 71.04 (O CH2),
61.21 (N CH2), 32.86–21.60 (OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 14.95
(CH3).
6: Yield 58% m.p. 77◦C–78◦C. Anal.: found for C37H67NO (%): C 82.03, H 12.48, N
2.60. Calc (%) C 82.00, H 12.46, N 2.58. IR: υmax(KBr) (cm−1): 3056, 2985, 2953, 1631,
1588, 1542, 1248; 1H NMR δ (ppm) (CDCl3): 8.05 (s, H7), 7.52 (d, J = 8.8 Hz, H2 and
H6), 6.94 (d, J = 8.6 Hz, H3 and H5), 4.04 (t, C4 OCH2), 3.60 (t, N CH2), 1.89–1.25
(m, OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 0.90 (t, CH3); 13C NMR δ (ppm)
(CDCl3): 162.11 (C N), 158.28 (Ar C O), 132.04–116.15 (Ar-C), 71.03 (O CH2),
61.16 (N CH2), 32.12–21.60 (OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 14.93
(CH3).
7: Yield 61% m.p. 82◦C–83◦C. Anal.: found for C39H71NO (%): C 82.23, H 12.50, N
2.54. Calc (%) C 82.18, H, 12.56, N 2.46. IR: υmax(KBr) (cm−1): 3017, 2990, 2959, 1638,
1
1591, 1572, 1250. HNMR δ (ppm) (CDCl3): 8.06 (s, H7), 7.55 (d, J = 8.8 Hz, H2 and
H6), 6.95 (d, J = 8.6 Hz, H3 and H5), 4.04 (t, C4 OCH2), 3.61 (t, N CH2), 1.88–1.24
(m, OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 0.91 (t, CH3); 13C NMR δ (ppm)
(CDCl3): 162.05 (C N), 158.29 (Ar C O), 132.05–116.18 (Ar-C), 71.08 (O CH2),
61.76 (N CH2), 31.98–21.59 (OCH2 ((CH2)2 CH2)13) and NCH2 (CH2 CHn), 14.93
(CH3).
2.1.3. Synthesis of Compounds 1a–7a, 1b–7b, and 1c–7c. The title compounds were syn-
thesized by the same method. The synthetic method will be described on the basis of
compound 1a.
A solution containing maleic anhydride (0.01 mol) in dry benzene (10 mL) was added
dropwise to a hot dry benzene solution (20 mL) containing compound 1 (0.01 mol) in a

Synthesis and Anisotropic Properties of Novel Asymmetric Diones
181
round bottom flask equipped with a double-surface condenser fitted with calcium chloride
guard tube. The reaction mixture was refluxed for 4 h. The reaction was monitored by
thin layer chromatography (TLC) and the solvent was distilled off in vacuo. The solid
product thus obtained was filtered and washed with distilled cool water. Resulting solid
1
was recrystallized twice from 1,4-dioxane. The analytical data, FT-IR, and H and 13C
NMR for compounds 1a–7b, 1b–7b, and 1c–7c are summarized as follows.
1a: Yield 61% m.p. 78◦C–79◦C. Anal.: found for C31H49NO4 (%): C 74.61, H 9.85,
N 2.74. Calc. (%) C 74.51, H 9.88, N 2.80. IR: υmax(KBr) (cm−1): 2960, 2928, 2864,
2830, 1730, 1600, 1570, 1246. 1HNMR δ (ppm) [dimethyl sulfoxide (DMSO)]: 9.85 (s,
H7), 7.83 (d, J = 8.1 Hz, H2 and H6), 7.11 (d, J = 8.3 Hz, H3 and H5), 6.41 (d, J = 12.6
Hz, H10), 6.22 (d, J = 12.4 Hz, H9), 4.05 (t, C4 OCH2), 3.15 (t, N CH2), 1.75–1.24
(OCH2 (CH2)2 (CH2)13 and NCH2 (CH2 CHn)+), 0.87 (t, CH3); 13C NMR δ (ppm)
∗
(DMSO): 166.29 (C11), 166.05 (C8), 164.37 (C4), 132.62 (C9), 132.57 (C2 and C6),
130.87 (C10), 115.80 (C3 and C5), 90.06 (C7), 68.89 (O CH2), 39.70 (N CH2), 14.66
(CH3).
2a: Yield 62% m.p. 81◦C–82◦C. Anal.: found for C33H53NO4 (%): C 75.07, H 10.37, N
2.71. Calc. (%) C 75.10, H 10.12, N 2.65. IR: υmax(KBr) (cm−1): 2958, 2924, 2859, 2807,
1728, 1604, 1582, 1244. 1HNMR δ (ppm) (DMSO): 9.85 (s, H7), 7.82 (d, J = 8.1 Hz, H2
and H6), 7.10 (d, J = 8.3 Hz, H3 and H5), 6.40 (d, J = 12.5 Hz, H10), 6.23 (d, J = 12.5,
∗
Hz H9), 4.04 (t, C4 OCH2), 3.15 (t, N CH2), 1.74–1.23 (OCH2 (CH2)2 (CH2)13 and
NCH2 (CH2 CHn)+), 0.86 (t, CH3); 13C NMR δ (ppm) (DMSO): 166.24 (C11), 166.04
(C8), 164.37 (C4), 132.62 (C9), 132.56 (C2 and C6), 130.90 (C10), 115.79 (C3 and C5),
90.12 (C7), 68.90 (O CH2), 39.70 (N CH2), 14.61 (CH3).
3a: Yield 66% m.p. 84◦C–85◦C. Anal.: found for C35H57NO4 (%): C 75.72, H 10.59, N
2.62. Calc. (%) C 75.63, H 10.34, N 2.52. IR: υmax(KBr) (cm−1): 2960, 2935, 2863, 2809,
1698, 1597, 1581, 1250. 1H NMR δ (ppm) (DMSO): 9.87 (s, H7), 7.85 (d, J = 8.2 Hz, H2
and H6), 7.12 (d, J = 8.3 Hz, H3 and H5) 6.40 (d, J = 12.5 Hz, H10), 6.26 (d, J = 12.5
Hz, H9), 4.04 (t, C4 OCH2), 3.16 (t, N CH2), 1.76–1.23 (OCH2 (CH2)2 (CH2)13∗ and
NCH2 (CH2 CHn)+), 0.86 (t, CH3); 13C NMR δ (ppm) (DMSO): 166.22 (C11), 166.06
(C8), 164.50 (C4), 132.64 (C9), 132.59 (C2 and C6), 130.88 (C10), 115.71 (C3 and C5),
90.06 (C7), 68.88 (O-CH2), 39.74 (N-CH2), 14.62 (CH3).
4a: Yield 64% m.p. 90◦C–91◦C. Anal.: found for C37H61NO4 (%): C 76.15, H 10.51,
N, 2.60. Calc. (%) C 76.11, H 10.53, N 2.40. IR: υmax(KBr) (cm−1): 2950, 2919, 2854,
2810, 1685, 1604, 1582, 1252. 1H NMR δ (ppm) (DMSO): 9.85 (s, H7), 7.82 (d, J = 8.1 Hz,
H2 and H6), 7.11 (d, J = 8.3 Hz, H3 and H5), 6.42 (d, J = 12.5 Hz, H10), 6.21 (d, J = 12.4
∗
Hz, H9), 4.03 (t, C4-OCH2), 3.14 (t, N CH2), 1.75–1.22 (OCH2 (CH2)2 (CH2)13 and
NCH2 (CH2 CHn)+), 0.85 (t, CH3); 13C NMR δ (ppm) (DMSO): 166.25 (C11), 166.05
(C8), 164.32 (C4), 132.64 (C9), 132.57 (C2 and C6), 130.89 (C10), 115.90 (C3 and C5),
90.05 (C7), 68.89 (O CH2), 39.73 (N CH2), 14.59 (CH3).
5a: Yield 63% m.p. 98◦C–99◦C. Anal.: found for C39H65NO4 (%): C 76.62, H 10.72, N
2.47. Calc. (%) C 76.55, H 10.71, N 2.29. IR: υmax(KBr) (cm−1): 2958, 2917, 2849, 2798,
1709, 1602, 1583, 1250. 1HNMR δ (ppm) (DMSO): 9.84 (s, H7), 7.81 (d, J = 8.1 Hz, H2
and H6), 7.12 (d, J = 8.4 Hz, H3 and H5), 6.39 (d, J = 12.5 Hz, H10), 6.20 (d, J = 12.3
Hz, H9), 4.04 (t, C4 OCH2), 3.15 (t, N CH2), 1.73–1.22 (OCH2 (CH2)2 (CH2)13∗ and
NCH2 (CH2 CHn)+), 0.86 (t, CH3); 13C NMR δ (ppm) (DMSO): 166.23 (C11), 166.09
(C8), 164.61 (C4), 132.65 (C9), 132.55 (C2 and C6), 130.88 (C10), 116.05 (C3 and C5),
90.00 (C7), 68.90 (O-CH2), 39.73 (N CH2), 14.65 (CH3).
6a: Yield 58% m.p. 114◦C–115◦C. Anal.: found for C41H69NO4 (%): C 76.84, H 10.82,
N 2.13. Calc. (%) C 76.94, H 10.87, N 2.19. IR: υmax(KBr) (cm−1): 2952, 2916, 2860,

182
G.-Y. Yeap et al.
2829, 1710, 1601, 1581, 1254. 1H NMR δ (ppm) (DMSO): 9.85 (s, H7), 7.80 (d, J = 8.1
Hz, H2 and H6), 7.10 (d, J = 8.3 Hz, H3 and H5), 6.40 (d, J = 12.5 Hz, H10), 6.23 (d, J =
∗
12.4 Hz, H9), 4.05 (t, C4-OCH2), 3.15 (t, N-CH2), 1.72–1.22 (OCH2 (CH2)2 (CH2)13
and NCH2 (CH2 CHn)+), 0.85 (t, CH3); 13C NMR δ (ppm) (DMSO): 166.24 (C11),
166.10 (C8), 164.41 (C4), 132.66 (C9), 132.56 (C2 and C6), 130.90 (C10), 116.09 (C3 and
C5), 90.05 (C7), 68.92 (O CH2), 39.74 (N CH2), 14.68 (CH3).
7a: Yield 51% m.p. 119◦C–120◦C. Anal: found for C43H73NO4 (%): C 77.24, H 11.10,
N 2.18. Calc (%) C 77.31, H, 11.01, N 2.10. IR: υmax(KBr) (cm−1): 2956, 2917, 2864, 2831,
1732, 1600, 1582, 1251. 1H NMR δ (ppm) (DMSO): 9.85 (s, H7), 7.85 (d, J = 8.1 Hz, H2
and H6), 7.43 (d, J = 8.5 Hz, H3 and H5), 6.41 (d, J = 12.6 Hz, H10), 6.24 (d, J = 12.5
Hz, H9), 4.05 (t, C4 OCH2), 3.16 (t, N CH2), 1.71–1.21 (OCH2 (CH2)2 (CH2)13∗ and
NCH2 (CH2 CHn)+), 0.85 (t, CH3); 13C NMR δ (ppm) (DMSO): 166.25 (C11), 166.11
(C8), 164.61 (C4), 132.64 (C9), 132.57 (C2 and C6), 130.89 (C10), 115.84 (C3 and C5),
90.06 (C7), 68.90 (O CH2), 39.73 (N CH2), 14.68 (CH3).
1b: Yield 64% m.p. 85◦C–86◦C. Anal.: found for C31H51NO4 (%): C 74.17, H 10.22, N
2.81. Calc. (%) C 74.21, H 10.25, N 2.79. IR: υmax(KBr) (cm−1): 2959, 2914, 2860, 2829,
1718, 1603, 1580, 1249. 1H NMR δ (ppm) (DMSO): 9.85 (s, H7), 7.86 (d, J = 8.6 Hz, H2
and H6), 7.12 (d, J = 8.6 Hz, H3 and H5), 4.06 (t, C4 OCH2), 3.01 (t, N CH2), 2.41
∗
(t, J = 7.1 Hz, H10), 2.27 (t, J = 7.0 Hz, H9), 1.70–1.21 (OCH2 (CH2)2 (CH2)13 and
NCH2 (CH2 CHn)+), 0.86 (t, CH3); 13C NMR δ (ppm) (DMSO): 174.52 (C11), 171.12
(C8), 164.32 (C4), 132.76 (C2 and C6), 115.72 (C3 and C5), 90.10 (C7), 68.88 (O CH2),
39.35 (N CH2), 29.33 (C9), 27.81 (C10), 14.70 (CH3).
2b: Yield 67% m.p. 91◦C–92◦C. Anal.: found for C33H55NO4 (%): C 74.90, H 10.59, N
2.72. Calc. (%) C 74.81, H 10.46, N 2.64. IR: υmax(KBr) (cm−1): 2965, 2925, 2849, 2801,
1720, 1605, 1583, 1250. 1H NMR δ (ppm) (DMSO): 9.86 (s, H7), 7.87 (d, J = 8.6 Hz, H2
and H6), 7.13 (d, J = 8.6 Hz, H3 and H5), 4.07 (t, C4 OCH2), 3.01 (t, N CH2), 2.40
∗
(t, J = 7.1 Hz, H10), 2.27 (t, J = 7.0 Hz, H9), 1.71–1.22 (OCH2 (CH2)2 (CH2)13 and
NCH2 (CH2 CHn)+), 0.87 (t, CH3); 13C NMR δ (ppm) (DMSO): 174.50 (C11), 171.11
(C8), 164.33 (C4), 132.77 (C2 and C6), 115.71 (C3 and C5), 90.11 (C7), 68.89 (O CH2),
39.33 (N CH2), 29.32 (C9), 27.82 (C10), 14.72 (CH3).
3b: Yield 63% m.p. 110◦C–111◦C. Anal.: found for C35H59NO4 (%): C 75.28, H 10.50,
N 2.48. Calc. (%) C 75.36, H 10.66, N 2.51. IR: υmax(KBr) (cm−1): 2979, 2934, 2862, 2830,
1721, 1603, 1580, 1255. 1H NMR δ (ppm) (DMSO): 9.86 (s, H7), 7.86 (d, J = 8.6 Hz, H2
and H6), 7.11 (d, J = 8.6 Hz, H3 and H5), 4.07 (t, C4 OCH2), 3.02 (t, N CH2), 1.71–1.23
(OCH2 (CH2)2 (CH2)13∗ and NCH2 (CH2 CHn)+), 2.40 (t, J = 7.1 Hz, H10), 2.28 (t,
J = 7.0 Hz, H9), 0.86 (t, CH3); 13C NMR δ (ppm) (DMSO): 174.52 (C11), 171.12 (C8),
164.34 (C4), 132.75 (C2 and C6), 115.70 (C3 and C5), 90.10 (C7), 68.90 (O CH2), 39.36
(N CH2), 29.32 (C9), 27.80 (C10), 14.72 (CH3).
4b: Yield 56% m.p. 114◦C–115◦C. Anal.: found for C37H63NO4 (%): C 75.90, H 10.80,
N 2.30. Calc. (%) C 75.85, H 10.84, N 2.39. IR: υmax(KBr) (cm−1): 2959, 2914, 2860, 2829,
1718, 1601, 1587, 1250. 1H NMR δ (ppm) (DMSO): 9.85 (s, H7), 7.88 (d, J = 8.6 Hz, H2
and H6), 7.12 (d, J = 8.6 Hz, H3 and H5), 4.06 (t, C4 OCH2), 3.01 (t, N CH2), 2.41
∗
(t, J = 7.1 Hz, H10), 2.27 (t, J = 7.0 Hz, H9), 1.72–1.22 (OCH2 (CH2)2 (CH2)13 and
NCH2 (CH2 CHn)+), 0.86 (t, CH3); 13C NMR δ (ppm) (DMSO): 174.51 (C11), 171.11
(C8), 164.32 (C4), 115.72 (C3 and C5), 132.77 (C2 and C6), 90.12 (C7), 68.91 (O CH2),
39.33 (N CH2), 29.31 (C9), 27.82 (C10), 14.73 (CH3).
5b: Yield 55% m.p. 120◦C–121◦C. Anal.: found for C39H67NO4 (%): C 76.28, H 11.15,
N 2.19. Calc. (%) C 76.30, H 11.00, N 2.28. IR: υmax(KBr) (cm−1): 2959, 2914, 2860,

Synthesis and Anisotropic Properties of Novel Asymmetric Diones
183
2829, 1725, 1600, 1582, 1252. 1H NMR δ (ppm) (DMSO): 9.84 (s, H7), 7.85 (d, J = 8.6
Hz, H2 and H6), 7.10 (d, J = 8.6 Hz, H3 and H5), 4.06 (t, C4 OCH2), 3.02 (t, N CH2),
∗
2.42 (t, J = 7.1 Hz, H10), 2.26 (t, J = 7.0 Hz, H9), 1.71–1.22 (OCH2 (CH2)2 (CH2)13
and NCH2 (CH2 CHn)+), 0.86 (t, CH3); 13C NMR δ (ppm) (DMSO): 174.50 (C11),
171.13 (C8), 164.33 (C4), 132.76 (C2 and C6), 115.71 (C3 and C5), 90.11 (C7), 68.92
(O CH2), 39.37 (N CH2), 29.33 (C9), 27.82 (C10), 14.75 (CH3).
6b: Yield 55% m.p. 123◦C–124◦C. Anal.: found for C41H71NO4 (%): C 76.66, H 11.19,
N 2.30. Calc. (%) C 76.70, H 11.15, N 2.18. IR: υmax(KBr) (cm−1): 2961, 2922, 2852, 2817,
1730, 1603, 1584, 1252. 1H NMR δ (ppm) (DMSO): 9.85 (s, H7), 7.86 (d, J = 8.6 Hz, H2
and H6), 7.11 (d, J = 8.6 Hz, H3 and H5), 4.05 (t, C4 OCH2), 3.00 (t, N CH2), 2.41
∗
(t, J = 7.1 Hz H10), 2.25 (t, J = 7.0 Hz, H9), 1.72–1.23 (OCH2 (CH2)2 (CH2)13 and
NCH2 (CH2 CHn)+), 0.86 (t, CH3); 13C NMR δ (ppm) (DMSO): 174.52 (C11), 171.12
(C8), 164.34 (C4), 132.76 (C2 and C6), 115.72 (C3 and C5), 90.12 (C7), 68.90 (O CH2),
39.36 (N CH2), 29.33 (C9), 27.80 (C10), 14.78 (CH3).
7b: Yield 48% m.p. 130◦C–131◦C. Anal.: found for C43H75NO4 (%): C 77.36, H 11.07,
N 2.38. Calc. (%) C 77.08, H 11.28, N 2.09. IR: υmax(KBr) (cm−1): 2953, 2915, 2859, 2824,
1719, 1602, 1579, 1254. 1H NMR δ (ppm) (DMSO): 9.86 (s, H7), 7.88 (d, J = 8.6 Hz, H2
and H6), 7.13 (d, J = 8.6 Hz, H3 and H5 4.06 (t, C4 OCH2), 3.01 (t, N CH2), ), 2.41
∗
(t, J = 7.1 Hz, H10), 2.26 (t, J = 7.0 Hz, H9), 1.71–1.22 (OCH2 (CH2)2 (CH2)13 and
NCH2 (CH2 CHn)+), 0.85 (t, CH3); 13C NMR δ (ppm) (DMSO): 174.52 (C11), 171.11
(C8), 164.34 (C4), 132.77 (C2 and C6), 115.72 (C3 and C5), 90.12 (C7), 68.90 (O CH2),
39.36 (N CH2), 29.34 (C9), 27.81 (C10), 14.79 (CH3).
1c: Yield 51% m.p. 85◦C–86◦C. Anal.: found for C35H51NO4 (%): C 76.52, H 9.28, N
2.60. Calc. (%) C 76.46, H 9.35, N, 2.55. IR: υmax(KBr) (cm−1): 2961, 2930, 2853, 2802,
1704, 1607, 1582, 1262. 1H NMR δ (ppm) (DMSO): 9.84 (s, H7), 7.84 (d, J = 7.5 Hz,
H12), 7.74 (d, J = 7.7 Hz, H15), 7.51 (t, J = 7.2 Hz, H13), 7.47 (t, J = 7.4 Hz, H14),
7.35 (d, J = 8.3 Hz, H2 and H6), 7.09 (d, J = 8.2 Hz, H3 and H5), 4.06 (t, C4 OCH2),
3.14 (t, N CH2), 1.74–1.22 (OCH2 (CH2)2 (CH2)13 and NCH2 (CH2 CHn)+), 0.85
∗
(t, CH3); 13C NMR δ (ppm) (DMSO): 168.84 (C11), 167.45 (C8), 164.14 (C4), 135.22
(C14), 129.97 (C12), 128.41 (C13), 125.45 (C2 and C6), 122.35 (C15), 115.00 (C3 and
C5), 89.98 (C7), 68.03 (O CH2), 39.03 (N CH2), 14.56 (CH3).
2c: Yield 50% m.p. 126◦C–127◦C. Anal.: found for C37H55NO4 (%): C 77.98, H 9.48,
N 2.34. Calc. (%) C 77.91, H 9.59, N 2.42. IR: υmax(KBr) (cm−1): 2948, 2924, 2854, 2831,
1700, 1605, 1580, 1261. 1H NMR δ (ppm) (DMSO): 9.85 (s, H7), 7.85 (d, J = 7.5 Hz,
H12), 7.74 (d, J = 7.7 Hz, H15), 7.50 (t, J = 7.2 Hz, H13), 7.48 (t, J = 7.4 Hz, H14),
7.36 (d, J = 8.3 Hz, H2 and H6), 7.10 (d, J = 8.2 Hz, H3 and H5), 4.06 (t, C4 OCH2),
3.15 (t, N CH2), 1.74–1.21 (OCH2 (CH2)2 (CH2)13 and NCH2 (CH2 CHn)+), 0.86
∗
(t, CH3); 13C NMR δ (ppm) (DMSO): 168.85 (C11), 167.44 (C8), 163.12 (C4), 135.23
(C14), 129.97 (C12), 128.40 (C13), 125.44 (C2 and C6), 122.34 (C15), 115.01 (C3 and
C5), 89.97 (C7), 68.05 (O CH2), 39.05 (N CH2), 14.55 (CH3).
3c: Yield 43% m.p. 125◦C–126◦C. Anal.: found for C39H59NO4 (%): C 77.40, H 9.71,
N 2.22. Calc. (%) C 77.31, H 9.82, N 2.31. IR: υmax(KBr) (cm−1): 2950, 2918, 2857, 2821,
1706, 1600, 1577, 1259. 1H NMR δ (ppm) (DMSO): 9.86 (s, H7), 7.86 (d, J = 7.6 Hz,
H12), 7.75 (d, J = 7.7 Hz, H15), 7.52 (t, J = 7.2 Hz, H13), 7.49 (t, J = 7.4 Hz, H14),
7.39 (d, J = 8.3 Hz, H2 and H6), 7.11 (d, J = 8.2 Hz, H3 and H5), 4.07 (t, C4 OCH2),
3.15 (t, N CH2), 1.73–1.23 (OCH2 (CH2)2 (CH2)13 and NCH2 (CH2 CHn)+), 0.85
∗
(t, CH3); 13C NMR δ (ppm) (DMSO): 168.85 (C11), 167.45 (C8), 163.22 (C4), 135.22

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G.-Y. Yeap et al.
(C14), 129.98 (C12), 128.44 (C13), 125.46 (C2 and C6), 122.32 (C15), 115.04 (C3 and
C5), 89.98 (C7), 68.05 (O CH2), 39.04 (N CH2), 14.55 (CH3).
4c: Yield 47% m.p. 132◦C–133◦C. Anal.: found for C41H63NO4 (%): C 77.60, H 10.12,
N 2.30. Calc. (%) C 77.68, H 10.02, N 2.21. IR: υmax(KBr) (cm−1): 2952, 2922, 2864,
2811, 1727, 1601, 1583, 1260. 1H NMR δ (ppm) (DMSO): 9.85 (s, H7), 7.85 (d, J = 7.5
Hz, H12), 7.74 (d, J = 7.7 Hz, H15), 7.52 (t, J = 7.2 Hz, H13), 7.48 (t, J = 7.4 Hz, H14),
7.39 (d, J = 8.3 Hz, H2 and H6), 7.11 (d, J = 8.2 Hz, H3 and H5), 4.08 (t, C4 OCH2),
3.15 (t, N CH2), 1.72–1.22 (OCH2 (CH2)2 (CH2)13 and NCH2 (CH2 CHn)+), 0.87
∗
(t, CH3); 13C NMR δ (ppm) (DMSO): 168.84 (C11), 167.43 (C8), 163.13 (C4), 135.24
(C14), 129.99 (C12), 128.43 (C13), 125.45 (C2 and C6), 122.36 (C15), 115.03 (C3 and
C5), 89.99 (C7), 68.08 (O CH2), 39.04 (N CH2), 14.56 (CH3).
5c: Yield 44% m.p. 128◦C–129◦C. Anal.: found for C43H67NO4 (%): C 78.14, H 10.25,
N 2.08. Calc. (%) C 78.02, H 10.20, N 2.12. IR: υmax(KBr) (cm−1): 2956, 2925, 2848,
2804, 1725, 1604, 1579, 1258. 1H NMR δ (ppm) (DMSO): 9.86 (s, H7), 7.88 (d, J = 7.6
Hz H12), 7.74 (d, J = 7.7 Hz, H15), 7.52 (t, J = 7.2 Hz, H13), 7.49 (t, J = 7.4 Hz, H14),
7.40 (d, J = 8.4 Hz, H2 and H6), 7.14 (d, J = 8.2 Hz, H3 and H5), 4.09 (t, C4 OCH2),
3.17 (t, N CH2), 1.74–1.23 (OCH2 (CH2)2 (CH2)13 and NCH2 (CH2 CHn)+), 0.88
∗
(t, CH3); 13C NMR δ (ppm) (DMSO): 168.84 (C11), 167.44 (C8), 163.12 (C4), 135.23
(C14), 129.98 (C12), 128.44 (C13), 125.44 (C2 and C6), 122.36 (C15), 115.07 (C3 and
C5), 90.08 (C7), 68.08 (O CH2), 39.05 (N CH2), 14.57 (CH3).
6c: Yield 57% m.p. 129◦C–130◦C. Anal.: found for C45H71NO4 (%): C 78.58, H 10.63,
N 2.29. Calc. (%) C 78.33, H 10.37, N 2.03. IR: υmax(KBr) (cm−1): 2957, 2921, 2855,
2813, 1728, 1600, 1581, 1260. 1H NMR δ (ppm) (DMSO): 9.86 (s, H7), 7.86 (d, J = 7.6
Hz, H12), 7.73 (d, J = 7.7 Hz, H15), 7.53 (t, J = 7.2 Hz, H13), 7.48 (t, J = 7.4 Hz, H14),
7.38 (d, J = 8.3 Hz, H2 and H6), 7.11 (d, J = 8.2 Hz, H3 and H5), 4.08 (t, C4 OCH2),
3.16 (t, N CH2), 1.73–1.23 (OCH2 (CH2)2 (CH2)13 and NCH2 (CH2 CHn)+), 0.86
∗
(t, CH3); 13C NMR δ (ppm) (DMSO): 168.95 (C11), 167.45 (C8), 163.11 (C4), 135.22
(C14), 129.98 (C12), 128.45 (C13), 125.46 (C2 and C6), 123.37 (C15), 115.07 (C3 and
C5), 90.08 (C7), 68.06 (O CH2), 39.08 (N CH2), 14.56 (CH3).
7c: Yield 51% m.p. 148◦C–149◦C. Anal.: found for C47H75NO4 (%): C 78.56, H 10.60,
N 1.98. Calc. (%) C 78.61, H 10.53, N 1.95. IR: υmax(KBr) (cm−1): 2961, 2929, 2849,
2816, 1710, 1603, 1580, 1261. 1H NMR δ (ppm) (DMSO): 9.85 (s, H7), 7.87 (d, J = 7.5
Hz, H12), 7.75 (d, J = 7.7 Hz, H15), 7.50 (t, J = 7.2 Hz, H13), 7.49 (t, J = 7.4 Hz, H14),
7.40 (d, J = 8.3 Hz, H2 and H6), 7.15 (d, J = 8.2 Hz, H3 and H5), 4.08 (t, C4 OCH2),
3.16 (t, N CH2), 1.73–1.24 (OCH2 (CH2)2 (CH2)13 and NCH2 (CH2 CHn)+), 0.87
∗
(t, CH3); 13C NMR δ (ppm) (DMSO): 169.16 (C11), 167.44 (C8), 163.12 (C4), 135.24
(C14), 129.97 (C12), 128.45 (C13), 125.45 (C2 and C6), 123.37 (C15), 115.08 (C3 and
C5), 90.07 (C7), 68.07 (O CH2), 39.11 (N CH2), 14.57 (CH3).
2.2. Reagents and Techniques
Hexylamine, octylamine, decylamine, dodecylamine, 4-hydroxybenzeldehyde, and anhy-
drides (maleic, succinic, and phthalic) were obtained from Aldrich. While tetradecylamine,
hexadecylamine, and octadecylamine were purchased from Acros, 1-bromotetradecane was
obtained from Merck. They were used without further purification.
The elemental (CHN) microanalyses were performed using a Perkin Elmer 2400 LS
Series CHNS/O analyzer. Melting points were recorded by Gallenkamp digital melting
point. The measurements were carried out through the scanning at room temperature. FT-
IR measurements on intermediates and title compounds were performed on samples in the

Synthesis and Anisotropic Properties of Novel Asymmetric Diones
185
KBr pellets and the spectra were recorded in the range of 4000–400 cm−1 using a Perkin
Elmer 2000-FT-IR spectrophotometer. The 1H NMR and 13C NMR spectra were recorded
in CDCl3 (for 1–7) and DMSO (for 1a–7b, 1b–7b, and 1c–7c) at 298 K on a Bruker 400
MHz Ultrashied FT-NMR spectrometer equipped with a 5-mm BBI inverse gradient probe.
Chemicals shifts were referenced to internal tetramethylsilane (TMS). The concentration
of solute molecules was 50 mg in 1.0 mL DMSO. Standard Bruker pulse programs [21]
were used throughout the entire experiment.
The phase transition temperatures and enthalpy values were measured by Perkin Elmer
Pyris 1 DSC at heating and cooling rates of 5◦C min−1, respectively.
The textures were observed using a Carl Zeiss Axioskop 40 polarizing microscope
equipped with a Mettler FP5 hot stage and TMS94 temperature controller. The samples
studied by optical microscopy were prepared in thin film sandwiched between glass slide
and cover.
3. Results and Discussion
3.1. Mesomorphic Properties of Intermediates 1–7 and Title Compounds 1a–7a, 1b–7b,
and 1c–7c
The textures illustrated by intermediates 1–7 and title compounds 1a–7a, 1b–7b, and 1c–7c
under POM have been ascertained by comparing them with relevant photomicrograph from
literature [22, 23]. The transition temperatures and associated enthalpies for 1–7, 1a–7a,
1b–7b, and 1c–7c upon heating and cooling are listed in Table 1. It can be inferred from
Table 1 that the imines 1–5 exhibit monotropic behaviors. In addition, the temperatures
with respect to the crystal-isotropic (Cr-Iso) transition upon heating run in these compounds
are found to be higher than the temperature associated with the isotropic-mesophase (Iso-
M) transition in which the compounds undergo supercooling [24]. The observation under
polarized light within the mesomorphic region shows the presence of fan-shaped tex-
ture characteristic of the smectic A (SmA) phase upon cooling from the isotropic liquid
(Fig. 1). The mesomorphic temperature ranges for compounds 1–5 are 9.92◦C, 7.64◦C,
9.24◦C, 7.47◦C, and 7.90◦C, respectively. However, only isotropization and crystallization
are observed upon heating (at 77.14◦C and 82.54◦C, respectively) and cooling (at 42◦C and
61.71◦C, respectively) runs in compounds 6 and 7.
In compounds 1a–7a, it is noteworthy that liquid crystal phases were not observed in
1a, 2a, and 3a, but they exhibit the Cr-Iso transition on heating at 78.32◦C, 81.00◦C, and
84.11◦C, respectively. A reverse process of Iso-Cr was observed on cooling at respective
temperatures of 67.34◦C, 74.45◦C, and 77.27◦C. Moreover, the 4a, 5a, 6a, and 7a are
not mesogenic and inclined to the Cr1-Cr2-Iso transition upon heating run. Moreover, the
Iso-Cr2-Cr1 transition is also observed on cooling run. The texture observed under POM is
indicative of the presence of subphases within the crystal phase (Cr1-Cr2), which resembled
the phenomena reported in literature [2, 25].
For the series of compounds 1b–7b, the DSC and POM analyses reveal that the new
compounds thus synthesized are not mesogenic and exhibit only Cr1-Cr2-Iso and Iso-Cr2-
Cr1 transitions upon heating and cooling runs. This can be substantiated by the DSC, as
shown for compound 6b (Fig. 2). The high values of the enthalpy of the phase transition
obtained from DSC substantiate the crystallization and the Cr1-Cr2 transition. The changes
in crystalline structure for 6a, as observed under polarized light, show a transition from the
texture consisting huge number of slender threads (Cr1) to colored plates (Cr2) when the

186
G.-Y. Yeap et al.
Table 1. Phase transition temperatures (◦C) and the corresponding enthalpies (J g−1) of
intermediates 1–7 and title compounds 1a–7a, 1b–7b, and 1c–7c
Transition temperature (◦C) (corresponding enthalpy
Compounds
changes in KJ mol−1) heating/cooling
1
Cr 60.43 (23.16) I
Cr 43.20 (−19.82) SmA 53.12 (−3.51) I
2
Cr 64.16 (36.05) I
Cr 51.41 (−33.72) SmA 59.05( −2.94) I
Cr 68.31 (47.55) I
3
Cr 53.07 (−64.32) SmA 62.31(−0.91) I
4
Cr 74.11 (29.64) I
Cr 56.95 (−49.23) SmA 64.42 (−8.54) I
Cr 78.00 (26.54) I
5
Cr 60.71 (−19.62) SmA 68.61 (−2.64) I
6
Cr 77.14 (45.31) I
Cr 57.42 (−28.41) I
7
Cr 82.54 (33.89) I
Cr 61.71 (−19.65) I
1a
2a
3a
4a
5a
6a
7a
1b
2b
3b
4b
5b
6b
7b
Cr 78.32 (58.12) I
Cr 67.34 (−38.46) I
Cr 81.00 (64.75) I
Cr 74.45 (−42.87) I
Cr 84.11 (81.23) I
Cr 77.27 (−37.79) I
Cr1 60.19(4.56) Cr2 90.54 (75.70) I
Cr1 48.55(−14.81) Cr2 59.68 (−49.51) I
Cr1 68.31(33.61) Cr2 98.67 (65.31) I
Cr1 52.61(−29.84) Cr2 70.41 (−41.35) I
Cr1 88.28(48.27) Cr2 114.23 (19.75) I
Cr1 48.81(−11.13) Cr2 86.31 (−37.66) I
Cr1 63.49(25.51) Cr2 119.14 (8.26) I
Cr1 40.59(−21.62) Cr2 84.03 (−26.45) I
Cr1 41.35(38.69) Cr2 85.14 (70.31) I
Cr1 37.56(−25.62) Cr2 64.42 (−44.52) I
Cr1 58.47(39.78) Cr2 91.23 (56.29) I
Cr1 43.67(−21.56) Cr2 61.54 (−39.42) I
Cr1 63.45(28.46) Cr2 109.32 (63.26) I
Cr1 38.79(−29.83) Cr2 65.65 (−33.45) I
Cr1 88.28(48.27) Cr2 114.23 (19.75) I
Cr1 48.81(−11.13) Cr2 86.31 (−37.66) I
Cr1 79.32(42.51) Cr2 119.62 (57.81) I
Cr1 68.43(−39.76) Cr2 79.44 (−17.31) I
Cr1 87.51(51.42) Cr2 123 (45.61) I
Cr1 50.43(−28.43) Cr2 91.64 (−42.86) I
Cr1 96.14(18.26) Cr2 129.16 (33.89) I
Cr1 60.59(−21.62) Cr2 84.03 (−26.45) I

Synthesis and Anisotropic Properties of Novel Asymmetric Diones
187
Table 1. Phase transition temperatures (◦C) and the corresponding enthalpies (J g−1) of
intermediates 1–7 and title compounds 1a–7a, 1b–7b, and 1c–7c (Continued)
Transition temperature (◦C) (corresponding enthalpy
Compounds
changes in KJ mol−1) heating/cooling
1c
Cr1 74.39(26.23) Cr2 130.01 (37.87) I
Cr1 58.35(−30.46) Cr2 117.57 (−40.34) N 126.21 (0.72) I
2c
3c
4c
5c
6c
7c
Cr1 77.46(22.67) Cr2 126.61 (28.56) I
Cr1 51.74(−32.89) Cr2 112.92 (−25.22) N 122.45 (0.82) I
Cr1 78.41(18.65) Cr2 125.41 (22.34) I
Cr1 60.26(−37.56) Cr2113.67 (−19.78) N 121.44 (1.53) I
Cr1 76.33(7.57) Cr2 132.92(17.24) I
Cr1 58.57(−39.43) Cr2 117.12 (−3.83) N 125.67 (5.42) I
Cr1 81.41(14.32) Cr2 128.12 (21.31) I
Cr1 69.62(−30.82) Cr2 114.32 (−25.31) N 121.23 (0.91) I
Cr1 82.30(60.83) Cr2 129.36 (15.41) I
Cr1 72.32(−5.95) Cr2 120.45 (−10.64) N 125.36 (1.34) I
Cr1 86.98(13.09) Cr2 148.35 (18.67) I
Cr1 68.35(−18.17) Cr2 132.45 (−53.54) N 142.45 (1.02) I
temperature was increased from 94◦C to 110◦C. This phenomenon can be rationalized by
the minor change of molecular rearrangement within the crystal phase.
All compounds from the series of 1c–7c upon cooling exhibit a nematic (N) phase.
On cooling from the isotropic liquid, the presence of Schlieren texture characteristics of
N phase was observed. The photomicrograph for compound 7c is shown as an example
in Fig. 1. Inspection from the DSC data further suggests that the temperature ranges of
mesophase upon cooling are found to be relatively narrow (8.6◦C, 9.5◦C, 7.8◦C, 8.5◦C,
6.9◦C, 4.9◦C, and 10.0◦C for 1c, 2c, 3c, 4c, 5c, 6c, and 7c, respectively). The narrow ranges
of mesomorphic temperatures indicate that the molecules 1c–7c are not kinetically stable
within this anisotropic region [26]. A thermogram associated with the thermal properties
of compound 7c is shown in Fig. 2.
3.2. Structure–Mesomorphic Property Relationship
From Fig. 3(a), it is apparent that the temperatures associated with the Cr-I and SmA-I
transitions for the intermediates are dependent on the carbon number. These temperatures
increase when the length of the terminal alkyl chain is increased from 6 to 18. A drastic
change is observed when the carbon number varied from 12 to 14 upon the cooling run.
All the compounds 1a–7a and 1b–7b are not mesogenic despite knowing that upon
heating and cooling, the transitions of Cr1-Cr2 and its reverse process occurred within the
crystalline state. Figure 3(b) shows that the isotropization (Cr2-I) temperatures for 4a–7a
ascended from 90.54◦C (4a) to 119.14◦C (7a). The opposite trend was observed when these
compounds were cooled down from isotropic liquid.
The thermal behavior as observed in compounds 1a–7a was not found in 1b–7b (Fig.
3(c)) and this can be explained in terms of the saturation of the seven-membered ring.
Compounds 1a–7a with a C C double bond in the seven-membered ring led to a more
ordered arrangement within the lattice system in comparison to compounds 1b–7b.

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Figure 1. Optical texture of SmA phase at 64.52◦C (top plate) observed in compound 5 and N phase
at 137.23◦C (bottom plate) observed in compound 7c.
A remarkable feature can be inferred from Fig. 3(d) in which the monotropic 1c--7c
upon cooling exhibited well-distinguished transition temperatures associated with I-N, N-
Cr1, and Cr1-Cr2. The transition temperatures for each of the compounds 1c--7c differ in

Synthesis and Anisotropic Properties of Novel Asymmetric Diones
189
Figure 2. DSC thermograms of compounds 6b and 7c.

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G.-Y. Yeap et al.
the following order:
I − N > N − Cr1 > Cr1 − Cr2.
The ability of compounds 1c–7c to exhibit nematogenic properties can probably be
attributed to the presence of the additional aromatic ring fused with the seven-membered
ring resulting in a more rigid core system in comparison to compounds 1a--7a and 1b--7b.
3.3. FT-IR, 1H NMR, and 13C NMR Spectral Studies
The infrared spectra of the title compounds 1a–7a, 1b–7b, and 1c–7c show a strong band at
the range of 1685–1732 cm−1, which can be assigned to the stretching vibration of carbonyl
group C O in the seven-membered rings. The absorption bands observed in the frequency
range of 1244–1262 cm−1 can be assigned to the stretching of the C4 O of the ether linkage
[27]. The presence of the diagnostic bands at the range of 1597–1607 cm−1 and 1570–1587
Figure 3. The dependence of phase transition temperatures T on the number of methylene in the
terminal alkyl chain of (a) compounds 1–7, (b) compounds 4a–7a, (c) compounds 1b–7b, and (d)
compounds 1c–7c.

Synthesis and Anisotropic Properties of Novel Asymmetric Diones
191
Figure 3. (Continued)
cm−1 is attributable to the C C stretching of the aromatic ring [28]. Other major bands
observed at 2914–2979 cm−1 and 2798–2864 cm−1 indicate the presence of carbon chains
in the respective compounds in which the hydrogen atoms are attached to sp3 carbons [29].
1
A complete H NMR assignment for the title compounds can be described on the
basis of respective compounds, as shown in Scheme 1, in which three types of compounds
1
have been differentiated by a, b, and c. The H NMR spectra of title compounds 1a–7a,
1b–7b, and 1c–7c showed a singlet that integrates as one hydrogen at the chemical shift δ =
9.84–9.87 ppm that corresponds to the proton attached to the carbon C7 in heterocyclic
ring. The presence of two doublets in the downfield region of δ = 6.21–6.26 ppm and δ =
6.39–6.41 ppm for compounds 1a–7a can be attributed to H9 and H10 of heterocyclic ring.
However, the 1H NMR spectra of compounds 1b–7b indicate that the H9 and H10 protons
from the heterocyclic ring appear as two triplets at the range of δ = 2.25–2.28 ppm and
δ = 2.40–2.42 ppm, respectively. Moreover, the resonances for the C6H5 appear as two
doublets in downfield region of δ = 7.80–7.85 ppm and δ = 7.10–7.43 ppm corresponding to
the respective phenyl protons H2 (or H6) and H3 (or H5) in compounds 1a–7a. The phenyl
protons H2 (or H6) and H3 (or H5) from compounds 1b–7b appear as doublet at the ranges

192
G.-Y. Yeap et al.
of δ = 7.85–7.88 ppm and 7.10–7.13 ppm, respectively. The 1H NMR data for compounds
1c–7c show diagnostic signals within the range of δ = 7.10–7.88 ppm assignable to the
aromatic protons. As for 1H NMR spectra of compounds 1a–7a, 1b–7b, and 1c–7c, there are
three triplet signals due to the presence of methylene protons, C4 OCH2 of the ether linking
group, methylene protons, and N CH2, and CH3 protons in both chains at the respective
chemical shift ranges of δ = 4.03–4.09 ppm, 3.00–3.17 ppm, and 0.85–0.88 ppm. Two sets
of multiplets at δ = 1.21–1.76 ppm can be assigned to protons OCH2 ((CH2)2 CH2)13
and NCH2 (CH2 CHn).
The structures of the title compounds are further substantiated by the 13C NMR data.
The resonances due to the carbonyl group (C8 and C11) of heterocyclic rings in the title
compounds 1a–7a, 1b–7b, and 1c–7c are located in the downfield (δ = 166.04–166.29 ppm,
171.11–174.52 ppm, and 167.43–168.95 ppm, respectively). The signal that appears within
the range of δ = 89.97–90.12 ppm can be attributed to the C7 in the heterocyclic rings.
The 13C NMR spectra of compounds 1a–7a, 1b–7b, and 1c–7c indicate that the aromatic
carbons give rise to different signals within the frequency range of δ = 115.00–164.61 ppm.
Signals at δ = 132.62–132.66 ppm and δ = 130.87–130.90 ppm indicate the presence of
C9 and C10 in heterocyclic ring in compounds 1a–7a. However, the resonance due to the
C9 and C10 in compounds 1b–7b can be located at the respective chemical shift of δ =
29.31–29.34 ppm and 27.80–27.82 ppm.
The 13C NMR spectra of title compounds confirm that the signal at δ = 68.03–68.92
ppm attributed to the presence of C4O-CH2 group from the ether linkage. Similarly, the
presence of N CH2 can be confirmed by the signal observable at the range of δ =
39.03–39.74 ppm. Signals ascribed to the methylene carbons of the terminal alkyloxy
chain (CH2)2 (CH2)13 and alkyl group NCH2 (CH2 CHn) can be assigned within the
range of δ = 22.90–32.39 ppm. At a high field, a signal at δ = 14.55–14.79 ppm can be
assigned to methyl carbons.
4. Conclusion
Three series of heterocyclic-based liquid crystalline compounds with the heterocyclic ring
at the core position have been synthesized using new methodology and their mesomorphic
properties were analyzed with respect to phase transition temperature and chemical struc-
ture. The intermediate compounds were found to exhibit SmA upon cooling. However, the
types of compounds from a and b series were not mesogenic and only exhibit Cr1-Cr2 upon
cooling and heating. The compounds in c series were found to show monotropic N phase
upon cooling.
Acknowledgments
The authors thank the University Sains Malaysia and the Malaysian Government
for financing this project through USM RU Grants No. 1001/PKIMIA/811127 and
1001/PKIMIA/811159.
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