Synthesis and crystal structures of N-substituted pyrazolines

Article abstract of DOI:10.3390/molecules18022386

Four pyrazole compounds, 3-(4-fluorophenyl)-5-phenyl-4,5-dihydro- 1Hpyrazole- 1-carbaldehyde (1), 5-(4-bromophenyl)-3-(4-fluorophenyl)-4,5- dihydro-1H-pyrazole- 1-carbaldehyde (2), 1-[5-(4-chlorophenyl)-3-(4- fluorophenyl)-4,5-dihydro-1H-pyrazol-1- yl]ethanone (3) and 1-[3-(4- fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl]propan- 1-one (4), have been prepared by condensing chalcones with hydrazine hydrate in the presence of aliphatic acids, namely formic acid, acetic acid and propionic acid. The structures were characterized by X-ray single crystal structure determination. The dihedral angles formed between the pyrazole and the fluoro-substituted rings are 4.64(7)° in 1, 5.3(4)° in 2 and 4.89(6)° in 3. In 4, the corresponding angles for molecules A and molecules B are 10.53(10)° and 9.78(10)°, respectively.

Full text of DOI:10.3390/molecules18022386

Molecules 2013, 18, 2386-2396; doi:10.3390/molecules18022386
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Crystal Structures of N-Substituted Pyrazolines
Wan-Sin Loh 1, Ching Kheng Quah 1, Tze Shyang Chia 1, Hoong-Kun Fun 1,2,*,
Majal Sapnakumari 3, Badiadka Narayana 3 and Balladka Kunhanna Sarojini 4
1
X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia,
Penang 11800 USM, Malaysia
2
Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University,
Riyadh 11451, Saudi Arabia
3
Department of Studies in Chemistry, Mangalore University, Mangalagangotri-574 199, India
4
Department of Chemistry, P.A. College of Engineering, Nadupadavu, Mangalore-574 153, India
* Author to whom correspondence should be addressed; E-Mail: hfun.c@ksu.edu.sa;
Tel.: +966-1467-7335; Fax: +966-1467-6220.
Received: 12 December 2012; in revised form: 2 February 2013 / Accepted: 7 February 2013 /
Published: 20 February 2013
Abstract: Four pyrazole compounds, 3-(4-fluorophenyl)-5-phenyl-4,5-dihydro-1H-
pyrazole-1-carbaldehyde (1), 5-(4-bromophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazole-
1-carbaldehyde (2), 1-[5-(4-chlorophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazol-1-
yl]ethanone (3) and 1-[3-(4-fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl]propan-
1-one (4), have been prepared by condensing chalcones with hydrazine hydrate in the
presence of aliphatic acids, namely formic acid, acetic acid and propionic acid. The
structures were characterized by X-ray single crystal structure determination. The dihedral
angles formed between the pyrazole and the fluoro-substituted rings are 4.64(7)° in 1,
5.3(4)° in 2 and 4.89(6)° in 3. In 4, the corresponding angles for molecules A and
molecules B are 10.53(10)° and 9.78(10)°, respectively.
Keywords: synthesis; X-ray diffraction; pyrazole; crystal structure
1. Introduction
The reaction of chalcones with hydrazine derivatives is one of the most extensively applied
reactions in organic synthesis. Investigations revealed that in most cases the products formed are

Molecules 2013, 18
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pyrazoline derivatives [1–4]. However, the reactions may also produce pyrazole derivatives [5] and
Schiff base hydrazones [6]. These reactions are usually carried out in an acidic medium.
Pyrazoline derivatives display various biological activities such as antitumor, antifungal,
antiviral, antiparasitic, anti-inflammatory and analgesic, antimycobacterial, anticancer, antibacterial,
insecticidal, antinociceptive, hypotensive, antidepressant, photoluminiscence, anti-tubercular,
antiamoebic, MAO-inhibitory, amine oxidase inhibitory and antioxidant properties [7–9]. Several
1,3,5-triaryl-2-pyrazoline derivatives were also used as scintillation solutes [10]. Pyrazoline derivatives
with a phenyl group at the 5-position have been shown to possess good film-forming properties and
exhibit excellent characteristics of blue photoluminescence, fluorescence and electroluminescence [11].
In view of importance of pyrazolines and in continuation of our work on the synthesis and structure
determination of various pyrazoline derivatives [12–15], we report the synthesis and crystal structures of
four novel N-substituted pyrazolines.
2. Results and Discussion
One of the most convenient methods for the synthesis of pyrazolines is the reaction of
α,β-unsaturated ketones with hydrazine hydrate and its derivatives. New N-substituted pyrazolines, 1–4
have been synthesized by the reaction of respective chalcone with hydrazine hydrate in the presence of
different aliphatic acids as shown in Scheme 1. The crystallographic data for the four compounds are
listed in Table 1.
Scheme 1. Preparation of N-substituted pyrazoline compounds.
2.1. Crystal Structure Description of Compound 1
The molecular structure of 1 is depicted in Figure 1a. The pyrazole ring (N1/N2/C7–C9) is almost
planar with a r.m.s deviation of 0.0457Å. This ring forms a dihedral angle of 4.64(7)° with the
fluoro-substituted benzene ring (C1–C6) and is almost perpendicular with the benzene ring (C10–C15),
with a dihedral angle of 84.83(7)°. Bond lengths and angles are within the normal ranges [16]. In the
crystal structure of 1, the molecules are linked into planes parallel to the ab-plane by intermolecular
C–H•••O hydrogen bonds as shown in Figure 2a (Table 2). These planes are further linked into a three-
dimensional network by intermolecular C–H•••F hydrogen bonds (Figure 2b; Table 2).

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Table 1. Crystal data and parameters for structure refinement of 1, 2, 3 and 4.
2388
Compound
1
2
895316
C16H12BrFN2O
347.19
3
4
CCDC deposition numbers
895315
C16H13FN2O
268.28
895317
895318
Molecular formula
C17H14ClFN2O
316.75
C18H17FN2O
296.34
Molecular weight
Crystal system
Monoclinic
Cc
Monoclinic
Cc
Monoclinic
P21 /c
Triclinic
Space group
P1
a/Å
b/Å
c/Å
α /°
β/°
11.9069(7)
6.2516(4)
17.3103(10)
90
6.2375(14)
12.191(3)
18.703(4)
90
6.1087(4)
12.3725(9)
19.6142(14)
90
9.3334(2)
13.2760(3)
13.2857(3)
107.052(1)
95.124(1)
96.629(1)
1550.14(6)
4
98.737(1)
90
93.239(5)
90
97.769(1)
90
γ/°
V/ Å3
Z
1273.58(13)
4
1419.9(6)
4
1468.83(18)
4
D
calc (g cm−3)
1.399
1.624
1.432
1.270
Crystal Dimensions (mm) 0.19 × 0.32 × 0.46 0.13 × 0.29 × 0.41 0.17 × 0.17 × 0.29 0.11 × 0.17 × 0.29
μ/mm−1
Radiation λ (Å)
Tmin/Tmax
0.10
0.71073
2.906
0.71073
0.274
0.71073
0.088
0.71073
0.9559/0.9810
7119
0.3792/0.7074
9227
0.9238/0.9549
16261
0.9753/0.9907
33624
Reflections measured
−16, 16; −8, 8;
−22, 24
−8, 7; −15, 15;
−24, 24
−8, 8; −16, 17;
−22, 27
−13, 11; −18, 18;
−18, 18
Ranges/indices (h, k, l)
θ limit (°)
Unique reflections
Observed reflections
(I > 2σ(I))
2.4–30.1
1866
2.2–27.5
2748
2.0–30.2
4340
1.6–30.1
9058
1847
2600
3706
5096
Parameters
181
1.07
172
1.131
200
1.047
399
1.043
Goodness of fit on F2
R1, wR2 [I ≥ 2σ(I)]
0.0267, 0.0748
0.0672, 0.1814
0.0341, 0.1010
0.0628, 0.1538
Figure 1. (a)–(d) ORTEP diagrams of 1–4 drawn at 50% ellipsoids for non-hydrogen atoms.
(a)

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Figure 1. Cont.
(b)
(c)
(d)

Molecules 2013, 18
Figure 2. (a)–(b) Crystal structure of compound 1 with intermolecular hydrogen bonding
2390
patterns shown as dashed lines. H atoms not involved in the crystal structure have been
omitted for clarity.
Table 2. Hydrogen bond geometries for compounds (1), (2), (3) and (4).
D–H···A
(1)
d(D–H) (Å) d(H···A) (Å) d(D···A) (Å) Angle (D–H···A) (°)
C2–H2A···O1 i
C8–H8B···O1 ii
C13–H13A···F1 iii
C15–H15A···O1 iv
(2)
0.95
0.99
0.95
0.95
2.36
2.60
2.53
2.36
3.2950(16)
3.5011(16)
3.1809(17)
3.2691(17)
166
151
126
161
C2–H2A···O1v
C12–H12A···F1vi
C15–H15A···O1vii
0.95
0.95
0.95
2.37
2.48
2.37
3.305(10)
3.322(10)
3.257(10)
167
148
155

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Table 2. Cont.
D–H···A
d(D–H) (Å) d(H···A) (Å) d(D···A) (Å) Angle (D–H···A) (°)
(3)
C2–H2A···O1viii
C14–H14A···F1ix
C15–H15A···O1 x
(4)
0.93
0.93
0.93
2.43
2.49
2.52
3.2492(14)
3.3462(14)
3.4282(14)
147
154
166
C1A–H1AA···O1B xi
C1B–H1BA···O1A xii
C9B–H9BA···O1A xiii
0.95
0.95
1.00
0.95
2.43
2.43
2.56
2.48
3.324(2)
3.223(2)
3.345(2)
156
141
135
151
C15B–H15B···O1A iv
3.349(2)
i
ii
iii
iv
v
1/2 + x, 3/2 + y, z; 1/2 + x, 1/2 + y, z; −1/2 + x, 3/2 − y, 1/2 + z; x, 1 + y, z; −3/2 + x, −1/2 + y, z;
vi
vii
viii
ix
x
3/2 + x, 3/2 − y, 1/2 + z; −1 + x, y, z; 1 − x, −1/2 + y, 3/2 − z; 2 − x, 1/2 + y, 3/2 − z; 1 + x, y, z;
xi 1 − x,1 − y, 1 − z; xii 1 − x, −y, −z.
2.2. Crystal Structure Description of Compound 2
Figure 1b shows the molecular structure of 2. The pyrazole ring (N1/N2/C7–C9) with r.m.s
deviation of 0.0434Å is almost coplanar with the fluoro-substituted benzene ring (C1–C6) with a
dihedral angle of 5.3(4)° and it is almost perpendicular with the bromo-substituted benzene ring (C10–C15)
with a dihedral angle of 85.1(4)° which is identical to that of compound 1. Bond lengths and angles are
within the normal ranges [16]. The crystal structure of 2 is shown in Figure 3. Intermolecular C–H•••O
hydrogen bonds (Table 2) link the molecules to form planes parallel to the ab-plane as shown in
Figure 3a. These planes are further inter-connected into a three-dimensional network via C–H•••F
hydrogen bonds (Table 2; Figure 3b).
Figure 3. (a)–(b) Crystal structure of compound 2 with intermolecular hydrogen bonding
patterns shown as dashed lines. H atoms not involved in the crystal structure have been
omitted for clarity.

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Figure 3. Cont.
2.3. Crystal Structure Description of Compound 3
The molecular structure of 3 is given in Figure 1c. The pyrazole ring (N1/N2/C7–C9) with r.m.s
deviation of 0.0259Å, forms dihedral angles of 4.89(6) and 85.76(6)°, respectively, with the fluoro-
and chloro-substituted benzene rings (C1–C6 & C10–C15). Bond lengths and angles are within the
normal ranges [16]. Figure 4 shows the crystal structure of 3. The molecules are linked together via
two C–H•••O and one C–H•••F hydrogen bonds (Table 2), generating R23 (9) ring motifs [17] and form
planes parallel to the ab-plane.
Figure 4. (a)–(b) Crystal structure of compound 3 with intermolecular hydrogen bonding
patterns shown as dashed lines. H atoms not involved in the crystal structure have been
omitted for clarity.

Molecules 2013, 18
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Figure 4. Cont.
2.4. Crystal Structure Description of Compound 4
Figure 1d shows the molecular structure of 4, which contains two crystallographically independent
molecules, namely molecules A and B. The pyrazole rings (N1/N2/C7–C9) in both molecules are
almost planar with r.m.s. deviations of 0.0425Å for A and 0.0333Å for B. In molecule A, the pyrazole
ring forms dihedral angles of 10.53(10)° with the fluoro-substituted benzene ring (C1A–C6A) and
80.63(10)° with the benzene ring (C10A–C15A). In molecule B, the corresponding dihedral angles are
9.78(10) and 79.78(10)°. Bond lengths and angles are within the normal ranges [16]. In the
crystal structure of 4 (Figure 5a), molecules A and B are interlinked via C9B–H9BA•••O1A and
C15B–H15B•••O1A hydrogen bonds (Table 2) to form R12 (6) ring motifs [17] which play a role in
_ _
stabilizing the crystal structure. These sets of ring motifs are then linked into chains along the [011] as
shown in Figure 5b via intermolecular C1A–H1AA•••O1B and C1B–H1BA•••O1A hydrogen bonds
(Table 2).
Figure 5. (a)–(b) Crystal structure of compound 4 with intermolecular hydrogen bonding
patterns shown as dashed lines. H atoms not involved in the crystal structure have been
omitted for clarity.

Molecules 2013, 18
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Figure 5. Cont.
3. Experimental
3.1. Materials and Method
X-ray diffraction studies were carried out using the Bruker SMART Apex II and Apex II Duo CCD
diffractometers. Melting points were taken in open capillary tubes and were uncorrected. The purity of the
compounds was confirmed by thin layer chromatography using Merck silica gel 60 F254 coated
aluminium plates. Elemental analyses were carried out by using VARIO EL-III (Elementar
Analysensysteme GmBH, Hanau, Germany).
3.2. General Procedure for the Synthesis of N-Substituted Pyrazolines
A mixture of substituted chalcone (0.01 mol) and hydrazine hydrate (0.5 mL, 0.01 mol) in 25 mL
formic or acetic or propionic acid was refluxed for 8 h. The reaction mixture was cooled and poured
into 50 mL ice-cold water. The precipitate was collected by filtration and purified by recrystallization
from ethanol. The crystals were grown by the slow evaporation method.
3-(4-Fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazole-1-carbaldehyde (1). Solvent for recrystallization:
acetone; Yield: 87%; m.p. 154–157 °C; Analytical data: Found (Cald): C%: 71.60 (71.63); H%: 4.91
(4.88); N%: 10.41 (10.44).

Molecules 2013, 18
2395
5-(4-Bromophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazole-1-carbaldehyde (2). Solvent for
recrystallization: toluene; Yield: 78%; m.p. 99–101 °C; Analytical data: Found (Cald): C%: 55.32
(55.35); H%: 3.50 (3.48); N%: 8.03 (8.07).
1-[5-(4-Chlorophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazol-1-yl]ethanone (3). Solvent for
recrystallization: ethanol; Yield: 72%; m.p. 110–112 °C; Analytical data: Found (Cald): C%: 64.42
(64.46); H%: 4.49 (4.45); N%: 8.80 (8.84).
1-[3-(4-Fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl]propan-1-one (4). Solvent for recrystallization:
acetone; Yield: 67%; m.p. 113–115 °C; Analytical data: Found (Cald): C%: 72.95, (72.97); H%: 5.78,
(5.81); N%: 9.45 (9.40).
3.3. X-ray Crystallographic Analysis
Selected crystals were mounted on glass fibers and intensity data were collected using either Bruker
SMART Apex II or Apex II Duo CCD diffractometer. The data for these compounds were processed
with SAINT and corrected for absorption using SADABS. The structures of the compounds were
solved by direct method using the program SHELXTL [18], and were refined by full-matrix least
squares technique on F2 using anisotropic displacement parameters. The non-hydrogen atoms were
refined anisotropically. All the H atoms in these compounds were calculated geometrically with
isotropic displacement parameters set to 1.2 (1.5 for methyl groups) times the equivalent isotropic U
values of the parent carbon atoms. A rotating group model was applied to the methyl groups.
Hydrogen bonding interactions are shown in Table 2. CCDC 895315 for (1), 895316 for (2), 895317
for (3) and 895318 for (4) contain the supplementary crystallographic data for this paper. These data
can be obtained free of charge at http://www.ccdccam.ac.uk/const/retrieving.html or from the
Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk.
4. Conclusions
The crystal and molecular structures of 3-(4-fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazole-1-
carbaldehyde (1), 5-(4-bromophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazole-1-carbaldehyde (2),
1-[5-(4-chlorophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazol-1-yl]ethanone (3) and 1-[3-(4-
fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl]propan-1-one (4) are reported. These data represent
the confirmation of the structures of the four newly reported N-substituted pyrazoline compounds.
Acknowledgments
The authors extend their appreciation to The Deanship of Scientific Research at King Saud
University for the funding the work through the research group project No. RGP-VPP-207.
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