Synthesis, spectroscopic characterisation and X-ray analysis of regioisomeric 1,3,5-trisubstituted pyrazoles

Article abstract of DOI:10.1016/j.molstruc.2011.04.014

A new series of regioisomeric 1,3,5-trisubstituted pyrazoles 7-9(a,b) have been synthesized by the reaction of β-diketones (4-6) with methyl hydrazine in ethanol. All the compounds are characterised by the FT-IR, ¹H, ¹³C NMR and mass spectrometry. The crystal structure of compounds 7a, 7b and minor isomer 8b have been determined by X-ray single crystal analysis which showed either of the substituted groups attached to pyrazole ring are essentially non-planar to the central pyrazole ring. Addition of trace amounts of acetic acid during the synthesis of compound 8 resulted in an unexpected compound 10 which is characterised by the X-ray single crystal analysis and is essentially planar. However, crystal structure of 10 is already reported. All structures are further stabilized by the classic and non-classic inter- and intramolecular hydrogen bonding.

Full text of DOI:10.1016/j.molstruc.2011.04.014

Journal of Molecular Structure 995 (2011) 173–180
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic characterisation and X-ray analysis of regioisomeric
1,3,5-trisubstituted pyrazoles
a
b,
Uzma Yunus a, Rukhsana Kauser a, Moazzam H. Bhatti a, , Muhammad Zia-ul-Haq , Wai-Yeung Wong
⇑
⇑
a Department of Chemistry, Allama Iqbal Open University, Islamabad, Pakistan
b Department of Chemistry, Hong Kong Baptist University, Waterloo Road, Kowloon Tong, Hong Kong
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of regioisomeric 1,3,5-trisubstituted pyrazoles 7–9(a,b) have been synthesized by the reac-
tion of b-diketones (4–6) with methyl hydrazine in ethanol. All the compounds are characterised by the
FT-IR, 1H, 13C NMR and mass spectrometry. The crystal structure of compounds 7a, 7b and minor isomer
8b have been determined by X-ray single crystal analysis which showed either of the substituted groups
attached to pyrazole ring are essentially non-planar to the central pyrazole ring. Addition of trace
amounts of acetic acid during the synthesis of compound 8 resulted in an unexpected compound 10
which is characterised by the X-ray single crystal analysis and is essentially planar. However, crystal
structure of 10 is already reported. All structures are further stabilized by the classic and non-classic
inter- and intramolecular hydrogen bonding.
Received 13 December 2010
Received in revised form 18 March 2011
Accepted 10 April 2011
Available online 15 April 2011
Keywords:
Pyrazoles
Methyl hydrazine
b-diketones
X-ray analysis
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
The synthesis of pyrazoles and their derivatives has been well
explored using the so-called [3 + 2] atom fragments, where b-
Pyrazole and its derivatives have wide applications in the phar-
maceutical and agrochemical industries [1]. A number of substi-
tuted pyrazoles exhibit HIV-1 reverse transcriptase and IL-1
synthesis inhibition as well as bacteriostatic, fungicidal, bacterici-
dal, antipyretic and analgesic activity [2–5]. Many heterocyclic
compounds such as pyrazoles, imidazoles and triazoles are known
to possess anti-fertility properties [6]. Some pyrazole derivatives
have been reported to have moderate anti-malarial activities [7]
and are also used as anti-inflammatory [8,9] anti-hyperglycaemic
[10] multidrug resistance modulating (MRD) [11] and analgesic
agents [12].
diketones are used as 3-atom building blocks and hydrazines as
the 2-atom fragment [18]. In view of wide synthetic and biological
applications of the pyrazole compounds, we have synthesized and
structurally characterised six new pyrazole derivatives (Fig. 1).
The X-ray structures of compound 7a, 7b, 8b and 10 are also re-
ported herein.
2. Experimental
2.1. Chemicals and instrumentation
Some pyrazole derivatives have also been used as energetic
compounds because they have high formation enthalpy, good ther-
mal stability and safety characteristics. They are used in energetic
formulations as oxidizers, plasticizer and elastomeric binders [13].
Pyrazole compounds are widely used as an extraction reagent in
the separation of trace metals [14]. Transition metal complexes of
pyrazoles and there derivatives have widely shown herbicidal, fun-
gicidal [15] and anti-amoebic activity [16]. Coordination of pyra-
zole and its derivatives to the metal centre of various biologically
active molecules modifies their activity. Pyrazoles are used as
building blocks in heterocyclic synthesis, as optical brighteners
and UV-stabilizers [17].
All the chemicals used in the synthesis were of analytical grade
and used without further purification. All the solvents were dried
before use by the literature methods [19].
Melting points were determined on a Barnstead Electrothermal
(UK) 9200 and are uncorrected. The infrared spectra were recorded
on FT-IR-8400S shimadzu spectrometer as KBr pellets. The 1H NMR
and 13C NMR were run on Bruker 300 MHz and 75 MHz NMR spec-
trometer respectively in DMSO-d6, using TMS as an internal stan-
dard. Low resolution mass spectra were obtained on Finnigan
MAT 312.
2.2. Synthesis
⇑
Corresponding authors. Tel.: +92 51 9057262; fax: +92 51 9250081 (M.H.
Bhatti). Tel.: +852 3411 7074; fax: +852 3411 7348 (W.Y. Wong).
E-mail addresses: moazzamhussain_b@yahoo.com (M.H. Bhatti), rwywong@hk-
bu.edu.hk (W.-Y. Wong).
The b-diketones 4–6 were prepared by the already reported
procedure [20,21].
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.04.014

174
U. Yunus et al. / Journal of Molecular Structure 995 (2011) 173–180
OH
2
N
2
N
CH3
H3C
1
N
1
N
HO
3
3
5
5
4
4
R
R
R = H, 2-OCH3, 4-OCH3
Fig. 1. General structure and numbering scheme of synthesized regioisomeric pyrazoles.
2.2.1. General procedure for the preparation of 1,3,5-trisubstituted
pyrazoles (7/9 a,b)
37.38; MS m/z (%) 250.4 (M+, 100), 222.3 (23), 207.3 (23), 178
(30), 152 (13), 118.2 (70), 91.1 (10), 77.1 (23), 51 (8).
0.5 mol of b-diketone (4,6) was dissolved in ethanol (130 mL) in
a round bottom flask fitted with a reflux condenser. When all the b-
diketone was dissolved, 0.5 mol of methyl hydrazine was added
drop wise. After the addition of methyl hydrazine, the reaction
mixture was refluxed for 6 h. The major isomer 7/9 was separated
as soon as formed as fine crystals which was filtered and recrystal-
lized from ethanol. The filtrate was concentrated and the crude so-
lid was purified by column chromatography, which gave the minor
isomer 7/9b, which was recrystallized from ethanol.
2.2.1.3. 1-Methyl-5-(20-hydroxyphenyl)-3-(400-methoxyphenyl)pyra-
zole (9a). Yield 54%; m.p. 160–162 °C; Rf value 0.11 (1,2-dichloro-
ethane); FT-IR (KBr cmꢀ1) 3620 (OH), 1640 (C@N), 1607 (C@C),
1365 (CAN), 1250 (OCH3); 1H NMR (DMSO, d ppm) 9.89 (s, 1H,
ArAOH), 7.74–6.69 (m, 8H, ArAH), 6.58 (s, 1H, pyrazole-H4), 3.76
(s, 3H, OCH3), 3.69 (s, 3H, NCH3); 13C NMR (DMSO, d ppm)
158.63, 154.95, 148.67, 141.88, 131.21 (2C), 130.24, 126.29,
126.18, 119.10, 117.48, 115.93, 113.97, 103.02, 54.01, 37.05; MS
m/z (%) 280 (M+, 100), 237 (21), 193.9 (6), 165 (24), 146 (14),
139 (11), 118 (12), 77 (27), 63 (33).
2.2.1.1. 1-Methyl-5-(20-hydroxyphenyl)-3-phenylpyrazole (7a). Yield
53%; m.p. 163–165 °C; Rf value 0.13 (1,2-dichloroethane); FT-IR
(KBr cmꢀ1) 3605 (OH), 1629 (C@N); 1615 (C@C), 1364 (CAN); 1H
NMR (DMSO, d ppm) 9.95 (s, 1H, ArAOH), 7.33–6.91 (m, 9H, ArAH),
6.69 (s, 1H, pyrazole-H4); 3.72 (s, 3H, NCH3): 13C NMR (DMSO, d
ppm) 155.02, 148.78, 142.07, 133.57, 131.28, 130.38, 128.59 (2C),
127.21, 124.93 (2C), 119.16, 117.39, 115.96, 103.66, 37.22; MS
m/z (%) 250.2 (M+, 100), 224 (30), 205 (20), 178 (35), 153 (13),
118 (75), 91 (5), 77 (25), 51 (9).
2.2.1.4. 1-Methyl-3-(20-hydroxyphenyl)-5-(400-methoxyphenyl)pyra-
zole (9b). Yield 7%; m.p. 95–97 °C; Rf value 0.81 (1,2-dichloroeth-
ane); FT-IR (KBr cmꢀ1) 3610 (OH), 1640 (C@N), 1600 (C@C), 1364
(CAN), 1230 (OCH3); 1H NMR (DMSO, d ppm) 10.88 (s, 1H, ArAOH),
7.56–6.86 (m, 8H, ArAH), 6.59 (s, 1H, pyrazole-H4), 3.85 (s, 3H,
OCH3), 3.58 (s, 3H, NCH3); 13C NMR (DMSO, d ppm) 160.10,
155.95, 150.27, 144.46, 130.09 (2C), 128.93, 126.13, 122.19,
119.15, 116.97, 116.64, 114.23 (2C), 102.10, 55.35, 37.32; MS m/z
(%) 280 (M+, 100), 265 (46), 252 (10), 237 (12), 165 (17), 148
(55), 140 (32), 118 (9), 77 (6).
2.2.1.2. 1-Methyl-3-(20-hydroxyphenyl)-5-phenylpyrazole (7b). Yield
17.4%; m.p. 98–100 °C; Rf value 0.69 (1,2-dichloroethane); FT-IR
(KBr cmꢀ1) 3620 (OH), 1630 (C@N), 1610 (C@C), 1370 (CAN); 1H
NMR (DMSO, d ppm) 10.88 (s, 1H, ArAOH), 7.58–6.91 (m, 9H,
ArAH), 6.65 (s, 1H, pyrazole-H4), 3.88 (s, 3H, NCH3): 13C NMR
(DMSO, d ppm) 155.92, 150.31, 144.61, 129.86, 128.98, 128.89,
128.75 (2C), 127.93, 126.14, 119.17, 116.97, 116.53, 102.42,
2.2.2. Preparation of 1,3,5 –trisubstituted pyrazoles (8a,b)
0.5 mol of b-diketone 5 was dissolved in ethanol (130 mL) in a
round bottom flask fitted with a reflux condenser and 3 mL of gla-
cial acetic acid was added. When the whole b-diketone was dis-
Table 1
Crystal data and structure refinements for compounds 7a, 7b, 8b and 10.
Compound 7a
Compound 7b
Compound 8b
Compound 10 [25]
Empirical formula
Formula weight
Crystal shape (colour)
Crystal system
Space group
Unit cell dimension
a (Å)
C
16H14N2O
C16H14N2O
250.29
Block (colourless)
Monoclinic
Pꢁ21/c
C17H16N2O2
280.32
Block (colourless)
Monoclinic
Pꢁ21/n
C16H14N2O2
266.29
Block (yellow)
Orthorhombic
Pꢁ2c–2n
250.29
Block (yellow)
Orthorhombic
Pꢁ21ꢁ21ꢁ21
4.6677(4)
12.3866(10)
21.6888(18)
90.00
90.00
90.00
1253.98(18)
4
1.326
10.3020(8)
6.9323(6)
18.6692(15)
90.00
100.2200(10)
90.00
1312.14(19)
4
1.267
10.4877(7)
12.4162(8)
11.4276(8)
90.00
96.9640(10)
90.00
1477.09(17)
4
1.261
17.5093(16)
10.1881(9)
7.4386(7)
90.00
90.00
90.00
1326.9(2)
4
1.333
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
3
V (Å
)
Z
Dcalc (g cmꢀ3
)
Crystal size (mm)
F(0 0 0)
0.32 ꢂ 0.28 ꢂ 0.25
0.32 ꢂ 0.28 ꢂ 0.24
0.28 ꢂ 0.26 ꢂ 0.24
0.32 ꢂ 0.26 ꢂ 0.25
528
528
592
560
Total reflections
Goodness-of-fit
1812
1.069
3170
0.990
3602
1.026
1735
1.071
h Range for data collection (°)
2.50–28.28
2.72–28.28
2.43–28.33
3.07–28.25

U. Yunus et al. / Journal of Molecular Structure 995 (2011) 173–180
175
solved, 0.5 mol of methyl hydrazine was added drop by drop. After
addition the of methyl hydrazine the reaction mixture was re-
fluxed till the completion of the reaction. The major isomer 8a sep-
arated as soon as formed as fine crystals which was filtered and
recrystallized from ethanol. The filtrate was concentrated and the
crude solid was purified by column chromatography, which gave
the minor isomer 8b, which was recrystallized from ethanol and
an unexpected product 10, which was characterised by X-ray
crystallography.
1H, ArAOH), 7.96–6.89 (m, 8H, ArAH), 6.67 (s, 1H, pyrazole-H4),
3.84 (s, 3H, OCH3), 3.75 (s, 3H, NCH3); 13C NMR (DMSO, d ppm),
156.39, 155.08, 145.73, 141.05, 131.36, 130.32, 128.48, 127.60,
122.12, 120.52, 119.24, 117.68, 116.05, 111.85, 107.72, 55.36,
37.19; MS m/z (%) 280.2 (M+, 100), 248 (35), 165 (12), 118 (20),
77 (6).
2.2.2.2. 1-Methyl-3-(20-hydroxyphenyl)-5-(200-methoxyphenyl)pyra-
zole (8b). Yield 10%; m.p. 77–79 °C; Rf value 0.77 (1, 2-dichloroeth-
ane); FT-IR (KBr cmꢀ1) 2934 (OH), 1630 (C@N), 1600 (C@C), 1362
(CAN), 1248 (OCH3); 1H NMR (DMSO, d ppm) 10.94 (s, 1H, ArAOH),
7.57–6.88 (m, 8H, ArAH), 6.59 (s, 1H, pyrazole-H4), 3.83 (s, 3H,
OCH3), 3.74 (s, 3H, NCH3); 13C NMR (DMSO, d ppm); 156.98,
155.90, 150.14, 141.46, 131.63, 130.95, 128.76, 126.12, 120.74,
2.2.2.1. 1-Methyl-5-(20-hydroxyphenyl)-3-(200-methoxyphenyl)pyra-
zole (8a). Yield 54%; m.p. 214–216 °C; Rf value 0.11 (1, 2-dichloro-
ethane); FT-IR (KBr cmꢀ1) 2939 (OH), 1628 (C@N), 1607 (C@C),
1360 (CAN), 1246 (OCH3); 1H NMR (DMSO-d6, d ppm) 9.97 (s,
COCl
COOH
(i)
R
O
R
(1-3)
OH
O
O
OH
COCl
+
(ii)
R
R
(4-6)
(iii)
CH3
H3C
N
N
OH
OH
N
N
R
R
(7-9b)
(7-9a)
R = H (1,4,7), 2-OCH3 (2,5,8), 4-OCH3 (3,6,9)
Reagents and Conditions, (i) SOCl2, reflux 2 hrs; (ii) NaOH, pyridine, room temperature; (iii)
CH3NHNH2, ethanol, reflux
OCH3
N
OH
HN
(10)
Scheme 1.

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U. Yunus et al. / Journal of Molecular Structure 995 (2011) 173–180
119.09, 118.91, 116.90, 116.85, 111.15, 103.24, 55.49, 37.19; MS
m/z (%) 280.1(M+, 100), 265.1 (13), 248.1 (31), 221.1 (20), 165.1
(9), 160.1 (17), 149.1 (15), 140.1 (14), 131.0 (12), 118.0 (11), 103
(8), 91 (13), 77 (6), 63 (3).
Fig. 2. ORTEP diagram of compounds (a) 7a, (b) 7b and (c) 8b. Thermal ellipsoids have been drawn with 50% probability [27,28].

U. Yunus et al. / Journal of Molecular Structure 995 (2011) 173–180
177
2.3. Single crystal X-ray diffraction studies
1615–1600 and 1370–1360 cmꢀ1. In case of compounds 8 and 9
additional IR bands of
t(OACH3) group appeared at 1250–
Single crystal X-ray diffraction data of compounds 7a, 7b, 8b
and 10 were collected at 173 K using graphite-monochromated
1230 cmꢀ1
.
Mo Ka radiation (k = 0.71073 Å) on a Bruker Smart 1000 CCD dif-
fractrometer. The data were collected using SMART and cell refine-
ment and data reduction were carried out using SAINT [22]. The
structure was solved with direct methods and refined by full ma-
trix least square methods based on F2 using SHELXS97 and SHEL-
XL97 packages [23,24] (see Table 1).
Table 2
Selected bond lengths (Å) and bond angles (°) for compounds 7a, 7b, 8b and 10.
Bond lengths (Å)
Bond angles (°)
Compounds 7a
C5AO1
C7AN1
C9AN2
C10AN1
N1AN2
1.357(2)
1.358(2)
1.340(2)
1.455(2)
1.360(2)
N1AC7AC8
N1AC7AC6
N2AC9AC8
N2AC9AC11
C7AN1AN2
C7AN1AC10
106.26(15)
124.13(17)
110.45(16)
121.72(15)
112.18(15)
128.19(16)
3. Results and discussion
The synthesis of compounds 7–9a,b is illustrated in Scheme 1.
The preparation of the intermediate b-diketones 4–6 by the con-
densation of acid chlorides 1–3 and o-hydroxyacetophenone has
already been reported [20,21]. The reaction of b-diketone with
methyl hydrazine furnished corresponding regioisomeric pyra-
zoles7–9a,b. In the present study, three acids namely, benzoic acid,
ortho-anisic acid and para-anisic acid were converted into their
corresponding acid chlorides and the acid chlorides in each case
were allowed to react with ortho-hydroxyacetophenone which re-
sulted in b-diketones (4–6). Each b-diketone was then treated with
methyl hydrazine in ethanol and refluxed till the completion of
reaction. In case of b-diketones bearing no substituent 4 on phenyl
ring and having a p-methoxy substituent i.e. 6, the reaction oc-
curred smoothly and the major product preferentially crystallized
out from the reaction mixture. However, the other isomer was ob-
tained by column chromatography. In case of b-diketone having an
ortho-methoxy substituent 5 on the phenyl ring, the overall yield
was very low under similar reaction conditions. However, when
ortho-methoxyphenyl substituted b-diketone 5 was reacted under
acidic conditions with methyl hydrazine, the yield was improved
significantly with a marked decrease in reaction time. Moreover,
an unexpected side product was also obtained, which was found
to be 10 by X-ray crystallographic analysis. Probably the acetic acid
used in the reaction had reacted with the methyl hydrazine and
gave hydrazine which on reaction with b-diketone, resulted the
compound 10, however, the crystal structure of 10 is already re-
ported, synthesized by different method [25].
Compound 7b
C1AO1
C7AN1
C9AN2
C10AN2
N1AN2
1.3591(17)
1.3401(15)
1.3582(15)
1.4558(15)
1.3489(13)
O1AC1AC2
O1AC1AC6
N1AC7AC8
N1AC7AC6
N2AC9AC8
N2AC9AC11
C7AN1AN2
N1AN2AC9
N1AN2AC10
C9AN2AC10
117.22(13)
122.53(11)
110.04(10)
120.30(10)
106.58(10)
122.59(10)
105.95(10)
111.73(10)
119.59(10)
128.58(11)
Compound 8b
C1AO1
C7AO1
1.371(2)
1.431(2)
1.348(2)
1.358(2)
1.458(2)
1.3600(19)
1.3570(19)
O1AC1AC2
O1AC1AC6
123.11(15)
116.59(14)
110.05(14)
119.25(14)
106.32(14)
124.66(14)
122.70(14)
117.44(14)
105.57(12)
112.04(13)
118.96(13)
128.98(14)
117.56(14)
C8AN1
N1AC8AC9
N1AC8AC6
N2AC10AC9
N2AC10AC12
O2AC13AC14
O2AC13AC12
C8AN1AN2
N1AN2AC10
N1AN2AC11
C10AN2AC11
C1AO1AC7
C10AN2
C11AN2
C13AO2
N1AN2
Compound 10
C5AO1
C7AN1
1.367(2)
1.343(2)
1.356(2)
1.371(2)
1.433(2)
1.347(2)
N1AC7AC8
N1AC7AC6
N2AC9AC8
N2AC9AC10
O2AC15AC14
O2AC15AC10
C7AN1AN2
C15AO2AC16
110.20(17)
118.73(16)
105.88(16)
123.85(16)
123.25(17)
116.17(16)
105.58(15)
118.02(16)
C9AN2
C15AO2
C16AO2
N1AN2
3.1. Spectroscopic characterisation
The characteristic infrared bands of compounds 7–9,
t(OAH),
t
(C@N), (C@C) and (CAN), are at 3620–3605, 1640–1628,
t
t
Fig. 3. ORTEP diagram of compound 10. Thermal ellipsoids have been drawn with 50% probability [27,28].

178
U. Yunus et al. / Journal of Molecular Structure 995 (2011) 173–180
In 1H NMR spectra of regioisomers 7–9 only one resonance of
3.2. X-ray analysis of 7a, 7b, 8b and 10
pyrazole core are found as sharp singlet in the range 6.69–
6.58 ppm depending on the nature of group attached to pyrazole
core. The OH group signals are also appeared as singlets at 9.95–
10.95 ppm. The other singlet resonances for NACH3 and OACH3
groups are in range of 3.58–3.88 ppm. The assignments of 13C
NMR signals of all regioisomers are straight forward and are as-
signed by comparison with related pyrazole analogues [18].
Methine carbon nuclei C-4 and two quaternary carbon nuclei C-3
and C-5 of pyrazole core fall in the range of 102–107 ppm and
141–151 ppm. The other carbon signals of substituted rings and
NACH3 group are appeared in the expected ranges comparable
to analogous pyrazole derivatives [18].
The crystal structure of compounds 7a, 7b, 8b and 10 are shown
in Figs. 2 and 3. The crystal data and structure refinement details
and selected bond lengths and bond angles are given in Tables 1
and 2 respectively.
In each case one isomer was obtained in large excess as com-
pared to the other isomer. The formation of 7a, 8a & 9a as major
isomer could be understood by the fact that the C@O group adja-
cent to the phenyl or substituted phenyl ring is relatively more
electrophilic as compared to the C@O group next to the phenol
ring. Therefore, nucleophile preferentially attack this C@O group.
On the other hand, in case of substituted hydrazines, the substitu-
ent on Nitrogen of hydrazine reduces the accessibility of substi-
tuted Nitrogen by creating steric hindrance, therefore terminal
All the regioisomers showed the molecular ion peak as base
peak in the mass spectral analysis.
Fig. 4. Intra- and intermolecular hydrogen bonding in (a) 10 and (b) 8b [29].

U. Yunus et al. / Journal of Molecular Structure 995 (2011) 173–180
179
amino group of substituted hydrazine attacks the C@O carbon next
to the substituted phenyl ring. This behaviour is further confirmed
by the X-ray crystallographic studies of regioisomers 7a and 7b.
The torsion angle between pyrazole ring and the hydroxyl substi-
tuted phenyl ring in 7a is 56.51°, whereas the other phenyl ring
is nearly coplanar with the pyrazole ring. In case of 7b the situation
is quite reverse and hydroxyl substituted phenyl ring is almost
coplanar with the pyrazole ring. The other phenyl ring makes a tor-
sion angle of 73.3° with the pyrazole ring. In case of 8b both hydro-
xyl phenyl ring and methoxyphenyl ring are non-planar with the
pyrazole ring as form torsion angle of 25.1° and 120.1° with central
pyrazole ring respectively. The crystal structure of 10 [25] reveals
that whole molecule is essentially planar. The molecule is organ-
ised in the crystal lattice by intra- and intermolecular hydrogen
bonding. Intramolecular hydrogen bonds (O1AH1ꢁ ꢁ ꢁN1 and
N2AH2ꢁ ꢁ ꢁO2) result in pseudo six membered rings as shown in
Fig. 4a. Intermolecular hydrogen bonding, N2AH2ꢁ ꢁ ꢁO1 forms layer
constituted by hydrogen bonded dimer (Fig. 4a). This hydrogen
bond is 2.882(2) Å longer than the intramolecular hydrogen
bonding distances. In case of 8b classic intermolecular hydrogen
bonding O2AH2Bꢁ ꢁ ꢁN1 is present in addition to the non-classic in-
ter- and intramolecular hydrogen bonding involving CAHꢁ ꢁ ꢁO
interactions (Fig. 4b).
The hydrogen bonding pattern is also observed in the com-
pounds 7a and 7b. In 7a intermolecular hydrogen interaction
O1AH1Bꢁ ꢁ ꢁN2 result in hydrogen bonded dimer (Fig. 5a). The
non-classic hydrogen bonding, C10AH10Cꢁ ꢁ ꢁO1, result in intramo-
lecular interaction. In case of 7b only one type of intramolecular
hydrogen bonding (O1AH1Bꢁ ꢁ ꢁN1) is observed which result in
pseudo six membered ring (Fig. 5b). This is interesting to note that
due to presence of methyl group on nitrogen atom adjacent to hy-
droxyl phenyl ring intermolecular hydrogen bonding is observed
between OH group and nitrogen of pyrazole ring of other molecule
in 7a while in 7b methyl group is present on nitrogen atom of
Fig. 5. Intra- and intermolecular hydrogen bonding in (a) 7a and intramolecular hydrogen bonding in (b) 7b [29].

180
U. Yunus et al. / Journal of Molecular Structure 995 (2011) 173–180
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Appendix A. Supplementary data
Supplementary material Crystallographic data for the structural
analysis have been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 699636 for the compound 7a, CCDC No.
708765 for the compound 7b, CCDC No. 708766 for the compound
8b and CCDC No. 699637 for the compound 10. Copies of these
information may be obtained on request from the Director, CCDC,
12 Union Road, Cambridge, CBZ 1EZ, UK (Fax: +44 1223 336033;
email: deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.
ac.uk). Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.
2011.04.014.
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