Mesomorphic properties of 4-benzoylaminobenzonitrile derivatives having an electron-withdrawing group with hydrogen bonding ability

Article abstract of DOI:10.1246/cl.2003.114

4-Benzoylaminobenzonitrile derivatives having an electronwithdrawing group with hydrogen bonding ability such as a formyl or a nitro group at the C-3 position of the benzonitrile moiety were synthesized. They had the higher transition temperatures than the parent compound. It is explained by the intramolecular hydrogen bonding between the lateral group at C-3 and the amide proton to prohibit the free rotation around the N-benzonitrile bond, which made molecules flat to increase transition temperatures.

Full text of DOI:10.1246/cl.2003.114

114
Chemistry Letters Vol.32, No.2 (2003)
Mesomorphic Properties of 4-Benzoylaminobenzonitrile Derivatives Having an Electron-
withdrawing Group with Hydrogen Bonding Ability
Masashi Hashimoto, Seiji Ujiie,y and Akira MoriÃyy
Graduate School of Engineering Sciences, 39, Kyushu University, Kasuga-koen, Kasuga, Fukuoka 816-8580
yDepartment of Material Science, Interdisciplinary Faculty of Science and Engineering, Shimane University, Matsue 690-8504
yyInstitute of Advanced Material Study, 86, Kyushu University, Kasuga-koen, Kasuga, Fukuoka 816-8580
(Received October 17, 2002; CL-020884)
4-Benzoylaminobenzonitrile derivatives having an electron-
withdrawing group with hydrogen bonding ability such as a
X
N
CN
formyl or a nitro group at the C-3 position of the benzonitrile
moiety were synthesized. They had the higher transition
temperatures than the parent compound. It is explained by the
intramolecular hydrogen bonding between the lateral group at C-
3 and the amide proton to prohibit the free rotation around the N-
benzonitrile bond, which made molecules flat to increase
transition temperatures.
H11C5O
4a: X=H, Cr • 64 • N • 97 • Iso
4b: X=OH, Cr • 80 • SmA • 81 • N • 124 • Iso
5a: X=H
5b: X=Br
NC
NH2
5c: X=CHO
5d: X=NO2
X
Aldehyde 3b was prepared from 4-cyanoaniline (5a);
bromination of 5a with N-bromosuccinic amide (NBS) gave 2-
bromo-4-cyanoaniline (5b), which was reacted with 4-alkoxy-
benzoyl chloride in pyridine in the presence of DMAP to give N-
(2-bromo-4-cyanophenyl)-4-alkoxybenzamide (3d).6 Conse-
quently, compound 5b was reacted with n-BuLi and with DMF
at À78 ꢀC to give 2-formyl-4-cyanoaniline (5c), which gave
aldehyde 3b6 by the reaction with 4-alkoxybenzoyl chloride.
Compound 3c6 with a nitro group was prepared by benzoylation
of 4-cyano-2-nitroaniline (5d) with 4-alkoxybenzoyl chloride. In
the 1H NMR spectrum of aldehyde 3b, the amide proton [ꢀ 12.17
(1H, br s)] and the aromatic proton [9.12 (1H, d, J ¼ 8:9 Hz)] at
C-5 appeared at the lower field than parent 3a [8.22 (1H, br s) and
7.79 (1H, d, J ¼ 8:0 Hz)]. Chemical shifts [ꢀ 11.46 (1H, br s) and
9.22 (1H, d, J ¼ 8:9 Hz)] of the corresponding protons of
compound 3c are close to those of aldehyde 3b whereas those
[8.58 (1H, br s) and 8.76 (1H, d, J ¼ 8:9 Hz)] of compound 3d are
close to parent 3a. These low field shifts of the amide proton and
the ring proton at C-5 of compounds 3b and 3c must be due to an
intramolecular hydrogen bonding and the anisotropy effect of the
benzoyl carbonyl group, respectively. These resulted that they are
flat.
We have previously reported the mesomorphic properties of
2-(4-alkoxybenzoylamino)- (1) and 2-(4-alkoxybenzoyloxy)-5-
cyanotropones (2).1 The transition temperatures of amide 1 are
higher than those of ester 2 because the single crystallographic
analysis of an amide derivative showed that the core structure is
almost flat2 through anintramolecular hydrogenbonding between
the tropone carbonyl and the NH group while the core part of an
ester derivative is twisted.3 Furthermore, troponoid amide 1 has
higher transition temperatures than the corresponding benzenoid
amide 3a. It must be due to the free rotation around N-benzonitrile
bond of benzenoid amide 3a, which reduces an intermolecular
overlap between neighboring molecules. It has been already
known that an introduction of a hydroxy group into compound 4a4
enhanced the transition temperatures, by forming an intramole-
cular hydrogen bonding in compound 4b.5 Similar results were
observed in 5-alkyl-2-(4-alkoxyphenyl)pyridines.5 In this paper,
based on the results obtained in troponoid amide 1, we introduce a
lateral group such as a formyl or a nitro group with hydrogen
bonding ability at C-3 of the benzonitrile ring of amide 3a to
report the mesomorphic properties.
The transition temperatures of 3 are summarized in Table 1.
Polarizing microscopic observations showed that aldehyde 3b
(n ¼ 8) had schlieren textures at 159.6 ꢀC and focal-conic and
homeotropic textures at 152.6 ꢀC, which indicated that they were
nematic and smectic A phases, respectively. The X-ray diffrac-
tion studies of aldehyde 3b (n ¼ 16) and bromide 3d (n ¼ 16)
derivatives showed that the ratio of the layer spacing (d) and the
calculated molecular length (l) by MM2 is 1.3 for 3b and 1.3 for
3d, which concluded that they had an interdigitated bilayer
structure.
When a formyl group was introduced at the C-3 of the
benzonitrile ring, the transition temperatures were increased.
Although the melting points were increased by 22 ꢀC as the
maximum temperature, the clearing points were increased by 43–
61 ꢀC, which are close to those of troponoid amide 1.1 It is
explained by the prohibition of the free rotation between the N-
O
N
O
O
O
NC
NC
H
2
1
O
OCnH2n+1
OCnH2n+1
O
N
5
3a: X=H
OCnH2n+1
3b: X=CHO
3c: X=NO2
3d: X=Br
NC
H
3
X
Copyright Ó 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.2 (2003)
Table 1. Transition temperatures of 4-benzoylaminobenzonitrilesa
115
n
Transition temp./ꢀC
n
Transition temp./ꢀC
3a
4
8
12
14
16
4
Crꢁ161.7ꢁIso
3c
4
8
12
14
16
Crꢁ113.0ꢁIso
Crꢁ123.8ꢁIso
Crꢁ98.0ꢁSmAꢁ101.4ꢁIso
Crꢁ97.6ꢁSmAꢁ119.6ꢁIso
Crꢁ103.7ꢁSmAꢁ124.5ꢁIso
Crꢁ101.5ꢁSmAꢁ126.1ꢁIso
Crꢁ122.4ꢁ(SmAꢁ107.5ꢁ)Iso
Crꢁ131.0ꢁ(SmAꢁ118.4ꢁ)Iso
Crꢁ126.4ꢁ(SmAꢁ123.7ꢁ)Iso
Crꢁ155.7ꢁNꢁ165.0ꢁIso
3b
8
Crꢁ145.5ꢁSmAꢁ156.7ꢁNꢁ160.0ꢁIso
Crꢁ135.9ꢁSmAꢁ168.6ꢁIso
Crꢁ131.8ꢁSmAꢁ166.8ꢁIso
Crꢁ131.6ꢁSmAꢁ166.8ꢁIso
3d
8
Crꢁ95.7ꢁ(Nꢁ82.0ꢁ)Iso
12
14
16
12
14
16
Crꢁ97.7ꢁ(SmAꢁ85.8ꢁNꢁ86.8ꢁ)Iso
Crꢁ96.8ꢁ(SmAꢁ92.3ꢁ)Iso
Crꢁ99.3ꢁ(SmAꢁ95.6ꢁ)Iso
aCr: crystals, SmA: smectic A phase, N: nematic phase, Iso: isotropic liquid. ( ) means monotropic transition.
benzonitrile ring. An intramolecular hydrogen bonding between
the formyl group and the amide proton made the core part flat,
which increased the thermal stability of the smectic A phase.
Although the intramolecular hydrogen bonding played a role to
prohibit intermolecular hydrogen bonding, the tight overlapping
between flat molecules increased the melting points as well as the
clearing points. When the length of the alkoxy side chain of 3b is
short, an nematic phase appears.
By introducing an electron-withdrawing group with intra-
molecualr hydrogen bonding ability, the transition temperatures
were increased. The lateral group at C-3 took part in prohibiting
the free rotation around the N-benzonitrile moiety through
intramolecular hydrogen bonding to induce mesogenic proper-
ties.
References and Notes
Next, a nitro group was introduced at the C-3 position. The
transition temperatures of nitro compound 3c were reduced when
compared with those of aldehyde 3b. This should be due to the
repulsive force of ionic nitro groups, which made intermolecular
interactions weaker to reduce the transition temperatures
although the core part of nitro compound 3c is flat. When
compared the transition temperatures of compounds 3b and 3c
with parent 3a, the melting points of 3c were reduced while those
of 3b and their clearing points of compounds 3b and 3c were
increased.
1
2
M. Hashimoto, S. Ujiie, and A. Mori, Chem. Lett., 2000, 758.
A. Mori, K. Hirayama, N. Kato, H. Takeshita, and S. Ujiie,
Chem. Lett., 1997, 509.
A. Mori, N. Kato, H. Takeshita, R. Nimura, M. Isobe, C. Jin,
and S. Ujiie, Liq. Cryst., 28, 1425 (2001).
3
4
5
R. T. Klingbiel, D. J. Genova, T. R. Criswell, and J. P.
Van Meter, J. Am. Chem. Soc., 96, 7651 (1974).
V. Vill, ‘‘4.2-LiqCryst Database of Liquid Crystalline
Compounds,’’ Fujitsu Kyushu System Engineering, Fukuoka
(2002).
Finally, we introduced a bromine atom at the C-3 position.
Both melting and clearing points were decreased to induce an
nematic phase as observed in 3d (n ¼ 8). These results are
consistent with the views that the lateral substituent has a large
effect on melting point and the thermal stability of the smectic
phases and has a less pronounced effect on the nematic clearing
point.7
6
All new compounds gave satisfactory spectral data. The
selected elemental analysis data are shown: 3b (n ¼ 12):
Found: C, 74.62; H, 7.89; N, 6.45%. Calcd for C27H34N2O3:
C, 74.62; H, 7.86; N, 6.40%. 3c (n ¼ 12): Found: C, 69.33; H,
7.36; N, 9.41%. Calcd for C26H33N3O4: C, 69.16; H, 7.37; N,
9.31%. 3d (n ¼ 12): Found: C, 64.37; H, 6.81; N, 5.80%.
Calcd for C26H33BrN2O2: C, 64.33; H, 6.85; N, 5.77%.
L. K. M. Chan, G. W. Gray, and D. Lacey, Mol. Cryst. Liq.
Cryst., 123, 185 (1985); R. A. Lewthwaite, J. W. Goodby, and
K. J. Toyne, Liq. Cryst., 16, 299 (1994); A. Mori, S.
Yamamoto, M. Takemoto, and S. Ujiie, Chem. Lett., 2002,
186.
The molecular breadths of 3 were calculated by MM2 as
7
ꢀ
ꢀ
ꢀ
ꢀ
follows; 3a; 6.6 A, 3b; 8.0 A, 3c; 8.5 A, and 3d; 8.1 A. Although
compound 3c with the widest molecular breadth is less favorable
to exhibit mesogenic properties, they had higher transition
temperatures than bromide 3d. This should be attributable to
the intramolecular hydrogen bonding ability of the nitro group.