Synthesis, experimental and theoretical investigations of some new 4,4′-bis(3-substituted-4,5-dihydro-1H-1,2,4-triazol-5-one-4-yl)diphenylmethane derivatives

Article abstract of DOI:10.1016/j.molstruc.2008.09.002

The 4,4′-bis(3-substituted-4,5-dihydro-1H-1,2,4-triazol-5-one-4-yl)diphenylmethane derivatives 3 were synthesized in the cyclization reaction of semicarbazide derivatives 2 in alkaline solution. The synthesized compounds were characterized by elemental an

Full text of DOI:10.1016/j.molstruc.2008.09.002

Journal of Molecular Structure 919 (2009) 170–177
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Journal of Molecular Structure
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Synthesis, experimental and theoretical investigations of some new
4,40-bis(3-substituted-4,5-dihydro-1H-1,2,4-triazol-5-one-4-yl)diphenylmethane
derivatives
b
c
d
Monika Pitucha a, , Piotr Borowski , Zbigniew Karczmarzyk , Andrzej Fruzinski
*
´
a Department of Organic Chemistry, Faculty of Pharmacy, Medical University of Lublin, Staszica 6, 20-081 Lublin, Poland
b Faculty of Chemistry, Maria Curie-Skłodowska University, pl. M. Curie-Skłodowskiej 3, 20-031 Lublin, Poland
c Department of Chemistry, University of Podlasie, 3-Maja 54, 08-110 Siedlce, Poland
d
_
´
Institute of General and Ecological Chemistry, Technical University, Zwirki 36, 90-924 Łódz, Poland
a r t i c l e i n f o
a b s t r a c t
The 4,40-bis(3-substituted-4,5-dihydro-1H-1,2,4-triazol-5-one-4-yl)diphenylmethane derivatives 3 were
synthesized in the cyclization reaction of semicarbazide derivatives 2 in alkaline solution. The synthe-
sized compounds were characterized by elemental analyses, IR, 1H and 13C NMR, as well as MS. Molecular
structure of compound 3a was determined by the X-ray analysis. Theoretical calculations (DFT/B3LYP/6-
311G**) of molecular structures were carried out for all final (cyclic) compounds. In addition vibrational
spectrum of 3a was reproduced by means of the single-parameter and SQM scaling approaches and the
assignment of bands was proposed. Investigated new compounds exhibit antinociceptive properties.
Ó 2008 Elsevier B.V. All rights reserved.
Article history:
Received 8 August 2008
Received in revised form 28 August 2008
Accepted 8 September 2008
Available online 14 September 2008
Keywords:
1,2,4-Triazol-5-one
Semicarbazide derivative
Cyclization
Crystal and molecular structure
Theoretical calculations
1. Introduction
azide derivatives 2 (cf. Scheme 1). Some behavioral tests (e.g.
‘‘writhing syndrome” test) were also performed in order to check
The chemistry and structure of heterocyclic compounds has been
an interesting field of study for a long time. The synthesis of 1,2,4-
triazoles and investigation of their chemical and biological behavior
have gained more importance in recent decades for biological,
medicinal and agricultural reasons. 1,2,4-Triazole and 1,2,4-tria-
zol-5-one are reported to exhibit a broad spectrum of biological
activities such as antifungal, antimicrobial, hypoglycemic, antihy-
pertensive, analgesic, antiparasitic, antiviral, anti-inflammatory,
antitumor and anti-HIV properties [1–7]. Several compounds con-
taining 1,2,4-triazole ring, for example fluconazole and itraconazole
[8,9], are well-known drugs. Triazoles are obtained in the ring clo-
sure processes. This methodology has been known for years. For
example 1,2,4-triazol-5-one derivatives can be synthesized from
(i) semicarbazides, either in the dehydratation reaction in basic
medium [10,11] or their reaction with ethyl formate [12], (ii) amid-
razones (in the reaction with phosgene) [13], (iii) semicarbazones
(in the oxidation reaction) [14] and from other compounds.
the influence of compounds 3a and 3b on the central nervous sys-
tem (CNS) of mice. For example, preliminary pharmacological
studies clearly revealed that investigated derivatives show antino-
ciceptive activity in a wide range of doses. Further studies to deter-
mine their mechanism of action are in progress. Therefore,
investigations of title compounds to establish their structures were
undertaken. They are considered to be potentially useful for future
work aimed at understanding their biological activity. It is always
desirable to confirm the experimentally obtained structures as well
as some of the physicochemical properties of investigated systems
by theoretical calculations. In this work we report theoretical
structures (DFT/B3LYP/6-311G**) of all final compounds, energetic
effects of the reactions 1a?2a and 2a?3a, as well as detailed
assignment of bands on the vibrational spectrum of 3a.
2. Experimental
In this paper, new 4,40-bis(3-substituted-4,5-dihydro-1H-1,2,
4-triazol-5-one-4-yl)diphenylmethane derivatives 3 were synthe-
sized in the cyclization reaction of the corresponding bis-semicarb-
Melting points were determined in a Fisher–Johns block and
were not corrected. Elemental analysis was made on Perkin-Elmer
2400 CHN Analyzer. IR spectra were recorded in KBr disc using a
Specord IR-75 spectrophotometer. 1H and 13C NMR spectra were
recorded on a Bruker AC 200F instrument (300 MHz) in DMSO-d6
with TMS as an internal standard. The mass spectra were obtained
* Corresponding author. Tel.: +48 81 535 73 73.
E-mail address: monika.pitucha@am.lublin.pl (M. Pitucha).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.09.002

M. Pitucha et al. / Journal of Molecular Structure 919 (2009) 170–177
171
NH2
NH
O
OCN
NH
NH
O
R
R
HN
O
ether
+
NH2
R
NH
OCN
R
O
1
HN
O
NH
NH
O
2
NaOH
HCl
O
NH
N
N
1, 2, 3
R
a
b
Me
R
CH2
N
O
CH3
N
N
N
c
CH2
N
HN
R
3
d
PhCH2
N
Scheme 1.
with an AMD-604 mass spectrometer using a 70 eV electron beam.
Chemicals were purchased from Merck Co. or Fluka Ltd. and used
without further purification. The purity of obtained compounds
was checked by TLC on aluminium oxide 60 F254 plates (Merck)
in a CHCl3/C2H5OH (10:1 and 10:2) solvent system with UV or
iodine visualization.
The starting carboxylic acid hydrazides were prepared from the
reactions of corresponding ester carboxylic acid with hydrazine
hydrate by the method described earlier [15,16].
20.13%. IR (KBr): 3278 (NH); 3102 (CHar); 2913, 1434 (CHal); 1689
(C@O). 1H NMR (DMSO-d6) d: 3.47 (s, 4H, 2CH2); 3.54 (s, 6H, 2CH3);
3.74 (s, 2H, CH2); 5.83–5.89 (m, 4H, 4CHar); 6.60–6.62 (m, 2H,
2CHar); 7.02–7.39 (m, 8H, 8CHar); 7.99, 8.61, 9.76 (3s, 6H, 6NH).
2.1.3. 4,40-Bis[1-(1,2,4-triazol-1-yl)methyl-semicarbazide]diph-
enylmethane (2c)
Yield 3.88 g (73%), m.p.: 149–151 °C. Found: C, 51.89%; H,
4.52%; N, 31.59%; Calculated for C23H24N12O4 532.5: C, 51.87%; H,
4.54%; N, 31.57%. IR (KBr): 3303 (NH); 3028 (CHar); 2853, 1402
(CHal); 1658 (C@O). 1H NMR (DMSO-d6) d: 3.86 (s, 2H, CH2); 4.83
(s, 4H, 2CH2); 7.08–7.60 (m, 8H, 8CHar); 7.95 (s, 2H, 2CHar); 8.49
(s, 2H, 2CHar); 8.76, 9.43, 10.15 (3s, 6H, 6NH).
2.1. General procedure for the synthesis of 4,40-bis(1-substituted-
semicarbazide)diphenylmethane (2a–2d)
A mixture of hydrazide (0.02 mol) 1 and 4,40-diphenylmethane
diisocyanate (2.5 g, 0.01 mol) in 10 mL of anhydrous diethyl ether
was kept at room temperature for 24 h. Then the formed product
was filtered off, washed with diethyl ether and crystallized from
ethanol.
2.1.4. 4,40-Bis(1-phenylacetyl-semicarbazide)diphenylmethane (2d)
Yield 3.40 g (74%), m.p.: 255–256 °C. Found: C, 62.05%; H,
4.77%; N, 18.90%. Calculated for C24H23N6O4 459.5: C, 62.73%; H,
5.04%; N, 18.87%. IR (KBr): 3294 (NH); 3030 (CHar); 2917, 1454
(CHal); 1661 (C@O). 1H NMR (DMSO-d6) d: 3.39 (s, 4H, 2CH2);
3.85 (s, 2H, CH2); 7.06–7.39 (m, 18H, 18CHar); 8.01, 8.62, 9.90
(3s, 6H, 6NH).
2.1.1. 4,40-Bis(1-acetyl-semicarbazide)diphenylmethane (2a)
Yield 3.17 g (80%), m.p.: 320–321 °C. Found: C, 57.29%; H, 5.60%;
N, 21.18%. Calculated for C19H22N6O4 398.4: C, 57.27%, H, 5.57%, N,
21.10%. IR (KBr): 3213 (NH); 3071 (CHar); 2983, 1428 (CHal); 1702
(C@O). 1H NMR (DMSO-d6) d: 1.75 (s, 6H, 2CH3); 3.79 (s, 2H,
2CH2); 7.06–7.38 (m, 8H, 8CHar); 7.90, 8.61, 9.59 (3s, 6H, 6NH).
2.2. General method for the synthesis of 4,40-bis(3-substituted-4,5-
dihydro-1H-1,2,4-triazol-5-one-4-yl)diphenylmethane (3)
A mixture of semicarbazide 2 (0.01 mol) and 2% aqueous solu-
tion of sodium hydroxide (30 mL) was refluxed for 15 h. After
cooling, the solution was neutralized with dilute hydrochloric
acid. The precipitate was filtered off and then crystallized from
ethanol.
2.1.2. 4,40-Bis [1-(1-methylpyrrole-2-yl)acetyl-semicarbazide]diph-
enylmethane (2b)
Yield 4.56 g (82%), m.p. 211–213 °C. Found: C, 62.61%; H, 5.67%;
N, 20.20%. Calculated for C29H32N8O4 556.6: C, 62.57%; H, 5.80%; N,

172
M. Pitucha et al. / Journal of Molecular Structure 919 (2009) 170–177
2.2.1. 4,40-Bis(3-methyl-4,5-dihydro-1H-1,2,4-triazol-5-one-4-
yl)diphenylmethane (3a)
Table 1
Crystal data and structure refinement for 3a
Yield 3.00 g (83%), m.p.: 308–310 °C. Found: C, 62.93%; H,
5.05%; N, 23.14%. Calculated for C19H18N6O2 362.4: C, 62.97%; H,
5.01%; N, 23.19%. IR (KBr): 3186 (NH); 3068 (CHar); 2929, 1451
(CHal); 1712 (C@O). 1H NMR (DMSO-d6) d: 2.04 (s, 6H, 2CH3);
4.07 (s, 4H, CH2); 7.32–7.44 (m, 8H, 8CH); 11.57 (s, 2H, 2NH). 13C
NMR (DMSO-d6) d: 12.3 (2 ꢀ CH3); 40.01 (CH2); 127.2, 129.6,
131.1, 141.2, 143.8 (14 ꢀ CH); 154.3 (2 ꢀ C@O). MS, m/z (%): 362
(M+, 38), 165 (100), 132 (62), 56 (50), 40 (70).
Empirical formula
Formula weight
Crystal system
Space group
Unit cell parameters
C19H18N6O2
362.39
monoclinic
C2/c
a = 30.499(4) Å
b = 9.318(1) Å
c = 27.257(3) Å
b = 103.97(1)o
7517.0(15) Å3
16
Volume, V
Molecular multiplicity, Z
Density (calculated)
Radiation
Wavelength
Cell parameters from
h range for lattice parameters
Absorption coefficient,
Absorption correction
Tmin/Tmax
h range for data collection
Index ranges h, k, l
No. of measured reflections
No. of independent reflections
No. of observed reflections
1.281 g/cm3
2.2.2. 4,40-Bis[(3-(1-methylpyrrole-2-yl)methyl-4,5-dihydro-1H-1,2,4-
triazol-5-one-4-yl)diphenylmethane (3b)
MoK
a
k = 0.71073 Å
131 reflections
2.67–15.26o
Yield 4.21 g (81%), m.p.: 225–227 °C. Found: C, 66.88%; H,
5.46%; N, 21.50%. Calculated for C28H28N8O2 520.3: C, 66.91%;
H, 5.42%; N, 21.53%. IR (KBr): 3158 (NH); 3060 (CHar); 2984,
1426 (CHal); 1702 (C@O). 1H NMR (DMSO-d6) d: 3.31 (s, 6H,
2CH3); 3.82 (s, 4H, 2CH2); 4.06 (s, 2H, CH2); 5.43–5.78 (m,
4H, 4CH); 6.51–6.58 (m, 2H, 2CH); 7.12–7.37 (m, 8H, 8CH);
11.78 (s, 2H, 2NH). 13C NMR (DMSO-d6) d: 23.6 (2 ꢀ CH2);
33.2 (CH3); 40.0 (CH2); 106.2, 107.5, 114.1, 121.9, 125.9,
127.3, 129.2, 129.5, 130.9, 141.4, 145.2 (24 ꢀ Car); 154.4
(C@O). MS, m/z (%): 520 (M+, 19), 119 (32), 94 (100), 93 (16),
80 (18).
l
0.088 mmꢁ1
Multiscan [42]
1.54–27.91o
0.6687
ꢁ40/39, ꢁ12/12, ꢁ34/34
62062
8718 (Rint = 0.1298)
3269 with I > 2r(I)
Refinement
Refinement method
Full-matrix least-squares on F2
0.0720, 0.1686
0.957
Final R indices: R, wR(F2)
Goodness-of-fit on F2, S
Data/restraints/parameters
Extinction coefficient
Largest diff. peak and hole
8718/0/501
2.2.3. 4,40-Bis[3-(1,2,4-triazol-1-yl)methyl]-4,5-dihydro-1H-1,2,4-
triazol-5-one-4-yl) diphenylmethane (3c)
0.0013(2)
+0.474/ꢁ0.200 eÅꢁ3
0.000
Yield 3.52 g (71%), m.p.: 215–217 °C. Found: C, 55.59%; H,
4.09%; N, 33.84%. Calculated for C23H20N12O2 496.5: C, 55.54%;
H, 4.06%; N, 33.86%. IR (KBr): 3213 (NH); 3071 (CHar); 2989,
1458 (CHal), 1702 (C@O). 1H NMR (DMSO-d6) d: 4.04 (s, 2H,
CH2); 5.35 (s, 4H, 2CH2); 7.18–7.37 (m, 10H, 10CHar); 7.90 (s,
2H, 2CHar); 8.10 (s, 2H, 2CHar); 12.09 (s, 2H, 2NH). 13C NMR
(DMSO-d6) d: 39.9 (CH2); 44.4 (2 ꢀ CH2); 127.0, 129.7, 144.7,
151.6 (16 ꢀ Car); 154.2 (C@O). MS, m/z (%): 496 (M+, 5), 69
(100), 42 (40).
(D/r)
max
2.4. Computational details
Theoretical calculations of the molecular structure involved
geometry optimization of 3a–d at DFT/B3LYP level [23–25] with
6-311G** basis set [26]. Calculation of harmonic frequencies at
the same level of theory was also carried out in order to establish
the type of stationary point on the potential energy hypersurface.
All frequencies turned out to be real indicating that the local min-
ima were found. The energetic effects of reactions 1a?2a and
2a?3a were also found. In order to accomplish this task, structures
of 1a, 2a, as well as that of 4,40-diphenylmethane diisocyanate and
water molecules were also optimized, and harmonic frequencies
were calculated (DFT/B3LYP/6-311G**). Harmonic frequencies were
then used in order to correct energies for the so-called zero-point
energy (ZPE), which is not negligible in the case of processes
accompanied by a change of the number of vibrational degrees of
freedom. This part of a research was carried out with the parallel
version of the PQS quantum chemistry package [27,28]. The vibra-
tional spectrum of 3a was then reproduced by using two scaling
methods: single-parameter frequency scaling and the so-called
Scaled Quantum Mechanical (SQM) [29,30] methods. A number
of well-resolved bands in the range of 400ꢁ4000 cmꢁ1 of the
experimental IR spectrum apart from
2.2.4. 4,40-Bis(3-benzyl-4,5-dihydro-1H-1,2,4-triazol-5-one-4-yl)diph-
enylmethane (3d)
Yield 2.92 g (69%), m.p.: 220–221 °C. Found: C, 68.11%; H,
4.46%; N, 19.81%. Calculated for C24H19N6O2 423.4: C, 68.07%;
H, 4.52%; N, 19.85%. IR (KBr): 3164 (NH); 3034 (CHar); 2824,
1455 (CHal), 1704 (C@O). 1H NMR (DMSO-d6) d: 3.80 (s, 4H,
2CH2); 4.01 (s, 2H, CH2); 6.84–7.27(m, 18H, 18CHar); 11.72 (s,
2H, 2NH).
2.3. X-ray analysis
Colorless prismatic crystals of 3a suitable for X-ray diffraction
analysis were grown by slow evaporation of an ethanol solution.
X-ray data were collected on the Bruker SMART APEX II CCD dif-
fractometer at room temperature; crystal sizes 0.12 ꢀ 0.11
ꢀ 0.07 mm,
x scans. The structure was solved by direct methods
using SIR92 [17] and refined by full-matrix least-squares with
1. the broad, irregular band at 670–700 cmꢁ1 (due to the presence
of a number of minima and inflection points it is difficult to
decide upon its origin),
SHELXL97 [18]. The N-bound H atoms involved in intermolecular
hydrogen bonds were located from
Dq map and refined freely
[NAH = 0.88(5)–1.02(6) Å]. The remaining H atoms were posi-
tioned geometrically and treated as riding on their parent C
atoms with CAH distances of 0.93 (aromatic), 0.96 (CH3) and
0.97 (CH2). All H atoms were refined with isotropic displacement
parameters taken as 1.5 times those of the respective parent
atoms. Crystal and experimental data are listed in Table 1.
Molecular graphic was prepared using ORTEP3 for Windows
[19]. PARST [20] and PLATON [21] were used for geometrical cal-
culations. All calculations were performed using WINGX version
1.64.05 package [22].
2. the band at 1261 cmꢁ1 (there is no theoretical mode reasonably
close to that band, so it is likely that it corresponds to some
overtone),
3. the high-energy band at 3186 cmꢁ1, corresponding to the NꢁH
stretching mode of hydrogen-bonded group (inclusion of that
band in the SQM calculations results in the factor for NꢁH
stretching of approximately 0.75, which is much lower than its
typical value close to 0.92 for isolated NH groups [30]. However,
the assignment of this band is unambiguous without
calculations),

M. Pitucha et al. / Journal of Molecular Structure 919 (2009) 170–177
173
were assigned to non-scaled vibrational modes. In addition three
shoulder bands (denoted Sh) were added. With this selection the
set of bands considered here consisted of 37 items. It should be
realized at this point that the theoretical vibrational spectrum of
a compound built from two identical fragments, like in the case
of molecule 3a, has a specific shape – many frequencies are
‘‘(nearly) doubled” since they describe the vibrations analogous
in both fragments (or appropriate linear combinations of these).
However, they have often different intensities. The band in the
experimental spectrum is likely to be their superposition. We
decided to assign a given band to the mode with higher theoretical
intensity. The single frequency scaling parameter calculated for the
selected set of bands is 0.9746. The standard implementation of
the SQM program [30,31] was used in order to carry out the SQM
calculations. Nine scaling factors, i.e. factors for
4,5-dihydro-1H-1,2,4-triazol-4-yl)methyl]-4,5-dihydro-1H-1,2,4-
triazol-5-one [35], octane-1,8-diylbis(3-ethyl-1H-1,2,4-triazol-
5(4H)-one) [36] and 1,4-bis(3-ethyl-5-oxo-4,5-dihydro-1H-1,2,4-
triazol-4-yl)butane [37]. The 1,2,4-triazole and phenyl rings are
planar to within 0.009(5) and 0.006(5) Å for A, 0.004(5) and
0.015(6) Å for B, 0.001(6) and 0.012(7) Å for C and 0.010(5) and
0.009(4) Å for D. In the crystal structure, molecules are linked into
chains parallel to Z crystallographic axis via pairs of the intermo-
lecular NAH...O hydrogen bonds: N1AAH1A...O5D(i) [N1AAH1A =
0.88(6) Å, H1A...O5D = 1.96(6) Å, N1A...O5D = 2.822(6) Å, N1AA
H1A...O5D = 166(5)o and (i) = ꢁx + 1, ꢁy, ꢁz + 1], N1BAH1B...
O5C(ii) [N1BAH1B = 1.02(5) Å, H1B...O5C = 1.79(5) Å, N1B...O5C =
2.795(5) Å, N1BAH1B...O5C = 170(5)o and (ii) = ꢁx + 1/2, ꢁy ꢁ 1/2,
ꢁz],
N1CAH1C...O5B(iii)
[N1CAH1C = 1.03(5) Å,
H1C...O5B =
1.81(5) Å, N1C...O5B = 2.8092(5) Å, N1CAH1C...O5B = 165(4)o and
(iii) ꢁx + 1/2, ꢁy ꢁ 1/2, ꢁz] and N1DAH1D...O5A(iv) [N1DAH1D =
0.98(6) Å, H1D...O5A = 1.85(6) Å, N1D...O5AD = 2.799(6) Å, N1DA
H1D...O5A = 163(4)o and (iv) = ꢁx + 1, ꢁy, ꢁz + 1].
1. XAX stretching,
2. C@O stretching,
3. CAH stretching,
4. XAXAX in-plane deformation,
5. XAXAH in-plane deformation,
6. HAXAH in-plane deformation,
7. XAXAXAX torsion,
8. XAXAXAH torsion,
9. HAXAXAH torsion,
3.3. Theoretical investigations
The calculated geometrical parameters of 3a–d are reported in
Table 2, next to crystallographic data for 3a. In the following, the
results obtained in the case of compounds of type a will be dis-
cussed first. The geometry optimization (DFT/B3LYP/6-311G**)
was carried out for both AB and CD structures of 3a (cf. Section
3.2), with the experimental geometries taken as starting points. Fi-
nal (optimal) structures turned out to be energetically equivalent –
the energy difference is about 0.2 kcal/mol. Both AB and CD mole-
cules have basically the same theoretical bond lengths and valence
angles. They reproduce the experimental values with reasonable
accuracy. We want to emphasize, that the theoretical geometry
will be compared to the solid-phase geometry, in which the two
molecules form molecular dimer. Justification of that procedure
can be found elsewhere [38]. The largest observed difference is
0.03 Å for bond lengths and 2° for valence angles. The discrepan-
cies between calculated and experimental values are somewhat
larger than typical DFT/B3LYP error limits for geometrical parame-
ters ( 1%). However, it should be noted that the reported in Table
2 values concern the molecular fragment which in solid-state is in-
volved in hydrogen bonding (not taken into account in calculations
on isolated molecules). For example C@O bond lengths (O5AC5)
should be elongated when the hydrogen bond to N1AH is formed
in the crystal structure – the experimental value is therefore larger
than calculated. Similar effects are expected in the case of com-
pounds 3b–d. However, significant discrepancies, up to more than
20°, are observed in the case of torsion angles. This is not a surprise
since molecular torsions, in particular these describing the relative
orientation of two adjacent, connected by a single bond fragments
(rings) of a molecule, cause minor change of total energy. It is
therefore possible that the crystal formation may introduce their
significant strain due to intermolecular interactions. With our
computer facilities we could in fact carry out full DFT geometry
optimization on the molecular dimer (90 atoms). It did not seem
to be reasonable to us since the accuracy of intermolecular param-
eters is not expected to be high enough due to the dispersive type
of intermolecular interactions in the dimer. On the other hand the
MP2 calculations, which account for this type of interactions, are
not yet practical on such large systems and for that reason they
were not carried out. One can, in fact, simplify calculations on
the basis of molecular symmetry [38]. We cannot take advantage
of that in this case – the AB and CD molecules are not symmetry
related. The discrepancies in torsion angles should not constitute
a problem in calculating both the relative energy of 2a?3a
reaction and vibrational spectrum of 3a. Note that in the first case
the reaction is carried out in the liquid phase, in which monomers
where X denotes a general non-hydrogen atom, were opti-
mized. The optimized factors in the above order are: 0.9172,
0.8331, 0.9254, 1.1035, 0.9781, 0.9709, 0.9452, 0.9654 and 0.9950.
3. Results and discussion
3.1. Synthesis
The 4,40-bis(3-substituted-4,5-dihydro-1H-1,2,4-triazol-5-one-
4-yl)diphenylmethane derivatives 3 were synthesized in the cycli-
zation reaction of semicarbazide derivatives 2 in alkaline medium.
The starting materials for synthesis of these compounds were:
hydrazides of acetic acid 1a and its derivatives 1b–d, in which
one of the hydrogen atoms of the methyl group is substituted by
an appropriate group (cf. Scheme 1). Newly synthesized com-
pounds were then characterized by elemental analyses, IR, 1H
and 13C NMR, as well as MS and X-ray for 3a (cf. Section 2).
3.2. X-ray investigation
A search of the Cambridge Structural Database (CSD version
2008; [32,33]) provided 48 organic structures with 1,2,4-triazol-
5-one system and did not reveal any crystal structures of com-
pounds containing their keto-enol tautomeric form. The X-ray
structure analysis of 3a revealed, that the asymmetric part of the
unit cell of 3a contains two independent molecules AB and CD,
as shown in Fig. 1. Both molecules exist in the keto tautomeric
form with the C5mAO5m bond lengths of 1.233(5), 1.227(5),
1.231(5) and 1.233(5) Å for m = A, B, C and D, respectively, typical
for a carbonyl group and with H atoms connected to the N1m
atoms of triazole rings. The conformations of the two molecules
described by the torsion angles C3mAN4mAC11mAC12m and
C13mAC14mAC17nAC14m, where m = A or B and n = A and
m = C or D and n = C (Table 2) differ significantly by a rotation of
phenyl rings around C17nAC14m bonds by about 30o (Fig. 2a) or
by a rotation of triazole rings around N4mAC11m bonds by nearly
180o (Fig. 2b). The bond distances and angles in 3a are in normal
ranges [34] and are comparable to the corresponding values ob-
served in related structures e.g. 4-ethyl-3-[(3-methyl-5-thioxo-

174
M. Pitucha et al. / Journal of Molecular Structure 919 (2009) 170–177
Fig. 1. ORTEP drawing of 3a with numbering of non-H atoms.
Table 2
Selected geometrical parameters (Å, °) of 3a–d
3a
3b
3c
3d
A
B
C
D
Bond distances
O5AC5
N1AC5
N1AN2
N2AC3
N4AC3
N4AC5
1.233(5)/1.212
1.345(6)/1.372
1.384(5)/1.377
1.297(5)/1.297
1.377(5)/1.391
1.389(6)/1.418
1.227(5)/1.212
1.351(5)/1.373
1.380(5)/1.377
1.294(5)/1.297
1.379(5)/1.391
1.369(5)/1.418
1.231(5)/1.212
1.346(6)/1.372
1.383(6)/1.377
1.294(6)/1.297
1.362(6)/1.392
1.382(6)/1.418
1.233(5)/1.212
1.342(5)/1.373
1.390(5)/1.377
1.294(6)/1.297
1.372(5)/1.391
1.384(6)/1.418
1.217/1.212
1.370/1.374
1.377/1.377
1.297/1.297
1.390/1.392
1.411/1.415
1.208/1.210
1.379/1.374
1.370/1.373
1.298/1.293
1.386/1.387
1.418/1.421
1.212/1.212
1.372/1.373
1.376/1.376
1.295/1.295
1.393/1.393
1.418/1.418
Valence angles
C5AN1AN2
C3AN2AN1
C3AN4AC5
C3AN4AC11
C5AN4AC11
N2AC3AN4
N2AC3AC6
N4AC3AC6
O5AC5AN1
O5AC5AN4
N1AC5AN4
112.8(4)/114.2
104.5(4)/104.8
107.4(4)/107.8
128.5(4)/128.7
123.7(4)/123.5
111.6(4)/111.6
123.8(4)/123.3
124.6(4)/125.1
129.6(5)/130.1
126.6(4)/128.4
103.7(4)/101.5
112.2(4)/114.2
104.8(4)/104.8
107.7(4)/107.9
126.1(4)/128.6
125.9(4)/123.5
111.3(4)/111.6
125.1(4)/123.4
123.7(4)/125.0
128.1(4)/130.1
127.7(4)/128.4
104.2(4)/101.5
112.1(4)/114.2
104.4(4)/104.8
107.4(4)/107.8
128.2(4)/128.7
124.3(4)/123.5
112.0(5)/111.6
124.9(5)/123.2
123.1(5)/125.1
128.6(4)/130.0
127.4(4)/128.5
104.0(4)/101.5
112.9(4)/114.2
104.0(4)/104.8
107.6(4)/107.9
128.1(4)/128.6
124.2(4)/123.5
111.9(4)/111.6
124.7(4)/123.2
123.4(4)/125.1
129.2(5)/130.0
127.2(4)/128.5
103.6(4)/101.5
114.1/114.2
104.6/104.8
107.9/108.0
129.2/128.1
123.0/123.9
111.7/111.5
123.5/123.0
124.8/125.5
129.7/130.1
128.6/128.5
101.8/101.5
114.2/114.2
104.6/104.6
107.7/107.5
128.7/128.9
123.6/123.6
112.0/112.2
122.0/123.6
125.9/124.2
130.0/130.2
128.6/128.4
101.4/101.5
114.3/114.3
104.8/104.8
107.8/107.8
128.9/128.8
123.3/123.4
111.6/111.6
124.5/124.7
123.9/123.7
130.1/130.1
128.4/128.4
101.5/101.4
Torsion angles
C3AAN4AAC11AAC12A
C3BAN4BAC11BAC12B
C3CAN4CAC11CAC12C
C3DAN4DAC11DAC12D
C13AAC14AAC17AAC14B
C13CAC14CAC17CAC14D
C14AAC17AAC14BAC13B
C14CAC17CAC14DAC13D
52.6(7)/52.4
111.3(5)/127.1
67.2(8)/51.7
105.7(5)/127.8
147.9(5)/122.1
ꢁ45.0(6)/ꢁ56.7
ꢁ79.3(6)/ꢁ63.0
116.8(5)/116.4
Experimental/theoretical parameters of 3a and theoretical values for both sides of molecules 3b–d are given.
exist. In the latter case differences in theoretical wavenumbers for
both AB and CD structures in the region of 400ꢁ4000 cmꢁ1 are in
most cases lower than 1 cmꢁ1. Somewhat larger differences (up
to 9 cmꢁ1) are observed for modes below 400 cmꢁ1, i.e. in the re-
gion usually not reported in standard IR spectra, in which such tor-
sional motions are likely to occur.
In addition, the calculations of structure and energy of enol tau-
tomeric form for 3a was carried out. The total energy turned out to
be by approximately 35 kcal/mol higher than for the corresponding
keto form. Thus, it is not supposed to be present in the solid-phase.
This is in accord with crystallographic data.
rected for ZPE), is observed. Indeed, this reaction has been carried
out at room temperature. Note that the above energy drop refers
to the overall energetic effect. However, no transition states were
searched for. Most probably some activation energy to overstep
some transition state is needed for the 1a?2a reaction to proceed,
as the period of 24 h is required for obtaining the reasonable yield
of 2a of 80%. In addition, slow energy release (no significant thermal
effect has been observed) seems to confirm this supposition. On the
other hand an increase of the energy by somewhat less than 9 kcal/
mol (ZPE corrected value) is observed for the reaction 2a?3a. This is
in accord with the necessity of refluxing the reactants for the period
of 15 h for this reaction to proceed with 83% yield.
The energetic effects of reactions 1a?2a and 2a?3a are depicted
on Fig. 3. As it can be seen the substantial energy drop for the first of
these processes, approximately equal to 26 kcal/mol (the value cor-
Since the IR spectra of the compounds 3a–d have not yet been
reported, a more detailed than in Section 2 assignment of bands

M. Pitucha et al. / Journal of Molecular Structure 919 (2009) 170–177
175
The 9-parameter SQM method provides high quality results. This
time the RMS value is less than 7 cmꢁ1, confirming our assignment
of bands. Such good agreement is partially due to the separate
treatment of the C@O stretching mode. Still a few of the calculated
frequencies exhibit deviations from the experimental values that
are larger than 10 cmꢁ1
.
The above mentioned band corresponding to C@O stretching
mode is one of the most important on the IR spectrum. As known,
the position of this band varies depending on substituents in the
direct vicinity of the carbonyl group. Actually IR spectra of com-
pounds related to these considered in the present work, were re-
ported before [40]. The main difference is the presence of two
instead of one carbonyl groups in the triazole ring. The reported
resonance structures clearly reveal that they are not equivalent –
in one of them the order of C@O bond, and consequently its vibra-
tional frequency, is lower. In addition some of the substituents also
possess carbonyl group, and so two or three bands in the region of
1650–1850 cmꢁ1 are observed on their IR spectra. Apparently, the
bond of the reduced order is responsible for the appearance of the
band somewhat above 1700 cmꢁ1; the other bond gives band close
to 1800 cmꢁ1. Compounds synthesized in the present work also
show a band in the region 1700–1715 cmꢁ1. This time, however,
the reduction of the C@O stretching frequency is due to the hydro-
gen bond formation that weakens the C@O bond. This is fully con-
sistent with the crystallographic data that prove its elongation. In
addition the SQM scaling factor reported in Section 2.4 is 0.8331,
which is significantly lower than the value of approximately 0.92
obtained recently by one of the co-authors [yet unpublished re-
sults] for isolated carbonyl group.
Fig. 2. The overlays of two crystallographic independent molecules of 3a by least-
squares fitting of the atoms of the central alkyl spacer: C14A, C17A, C14B and C14D,
C17C, C14C, respectively (a) and C14A, C17A, C14B and C14C, C17C, C14D,
respectively (b) [RMS = 0.008 Å for (a) and 0.009 Å for (b)].
We also carried out the calculations of the vibrational frequen-
cies using recently proposed ESFF scaling procedure [41]. This
method, that uses effective scaling factors obtained as PED-
weighted combinations of local scaling factors, turned out to be
more efficient that the SQM method, at least in the case of applica-
tions done already. The detailed discussion of the ESFF results is
beyond the scope of this paper. It will be reported in the forthcom-
ing paper in which, in addition to 3a, other molecules investigated
here will be considered. At this point we only mention that the re-
sults obtained with 8-parameter ESFF approach are of not worse
quality to these of obtained in this work with 9-parameter SQM
approach.
The selected bond lengths and valence angles of the remaining
molecules, 3b–d, are also listed in Table 2. This time no experimen-
tal data are available. The theoretical geometrical parameters of
the triazole ring of 3b–d reported in Table 2 are very similar to
these of 3a. Different substituents R apparently do not affect this
part of a molecule. Note, that in spite of their totally different char-
acter, they are all bound to the triazole ring via the CH2 group. No
significant changes in the triazole ring are therefore expected. On
the other hand we do not report theoretical torsion angles. The
starting geometries of each of the three molecules were chosen
by inspection and for that reason the converged geometry is one
of many local, close in energy minima, differing by torsions of
one of the rings of the molecule with respect to another.
Fig. 3. Energetic effects of reactions 1a?2a and 2a?3a (MDI denotes 4,40-
diphenylmethane diisocyanate). Dashed lines refer to the energy levels obtained
from electronic (DFT/B3LYP/6-311G**) energies, solid lines – to ZPE corrected values.
for at least one system is desired. Again we decided to consider the
simplest case 3a. The experimental wavenumbers for bands and
the corresponding theoretical non-scaled, single-parameter scaled
and SQM-scaled frequencies are given in Table 3. Our assignment,
based on calculated PED (potential energy distribution) coefficients
[39], is reported in the last column. The RMS value for all 37 non-
scaled frequencies is close to 40 cmꢁ1, which is typical for the har-
monic approximation the Wilson–Decius–Cross approach is based
on. Scaling by using single-parameter provides substantial
(although not sufficient) improvement – the RMS value dropped
down to nearly 20 cmꢁ1. It is still five times higher than the reso-
lution of the present experiment. However, this calculation re-
4. Conclusions
In this paper we report some properties of newly synthe-
sized 4,40-bis(3-substituted-4,5-dihydro-1H-1,2,4-triazol-5-one-4-
yl)diphenylmethane derivatives 3a–d. The methodology adopted
involves a wide variety of physicochemical techniques, including
X-ray analysis, IR, NMR and MS spectrometry, as well as theoretical
calculations.
vealed one important feature
–
the difference between
experimental and scaled frequency for C@O stretching mode is
up to a few times higher than for all other X–X stretching modes.
For that reason we decided, against the original recommendation
[30], to treat this mode separately in subsequent SQM calculations.
It is shown that in the case of the simplest of the systems con-
sidered in this work, i.e. 4,40-bis(3-methyl-4,5-dihydro-1H-1,2,4-

176
M. Pitucha et al. / Journal of Molecular Structure 919 (2009) 170–177
Table 3
Experimental (m m m m
(expt.)), non-scaled ( (calc.)), single-parameter scaled ( (1-par.)) and SQM-scaled ( (SQM-9)) vibrational frequencies (in cmꢁ1), as well as the proposed assignment
(contributions higher than 15% are listed) for 3a
No.
m(expt.)
m(calc)
D
m
m(1-par)
D
m
m(SQM-9)
D
m
Assignment
32
33
34
35
36
37
39
44
45
48
49
50
51
55
56
58
61
63
66
67
74
75
77
79
84
86
91
93
95
505.67
519.98
595.69
598.71
611.77
623.52
646.03
716.40
744.33
517.34
526.99
592.22
596.90
614.20
629.43
650.58
734.47
755.88
802.98
810.73
820.06
836.95
877.54
931.31
965.33
1001.53
1023.86
1046.22
1055.15
1144.06
1197.38
1210.60
1224.17
1319.13
1340.61
1409.52
1438.23
1452.36
1480.00
1489.33
1547.67
1618.38
1643.14
1825.65
3041.63
3191.76
11.67
7.01
ꢁ3.47
ꢁ1.81
2.43
5.91
4.55
18.07
11.55
9.61
504.19
513.60
ꢁ1.48
ꢁ6.38
ꢁ18.51
ꢁ16.98
ꢁ13.18
ꢁ10.08
ꢁ11.98
ꢁ0.59
512.42
521.52
602.20
604.56
617.20
629.30
645.48
719.05
739.47
796.11
809.71
820.11
823.55
865.64
916.03
952.84
987.54
1014.85
1027.22
1039.85
1125.27
1173.68
1186.79
1194.45
1297.18
1315.47
1386.67
1414.78
1433.09
1457.31
1466.56
1518.27
1575.60
1603.16
1711.47
2925.96
3070.50
6.75
1.54
6.51
5.85
5.43
5.78
31% Ar asym. tor. + 24% Ar-TAZ wag. + 16% Ar-CH2 wag.
32% Ar asym. tor. + 24% Ar-TAZ wag. + 16% Ar-CH2 wag.
21% NAH wag.
24% C@O rock.
26% Ar asym. def.
34% TAZ def.
42% Ar asym. def. + 29% TAZ tor.
67% Ar puck.
31% Ar puck. + 26% C@O wag.
32% TAZ def. + 24% Ar-H wag.
52% TAZ def.
29% TAZ def.
77% Ar-H wag.
52% Ar-H wag.
53% CH2 rock. + 21% Ar-H wag.
71% Ar-H wag. + 17% Ar puck.
42% CH3 rock.
54% Ar trig. def.
35% Ar str.
577.18
581.73
598.59
613.44
634.05
715.81
736.68
782.58
790.13
799.22
815.69
855.24
907.65
ꢁ0.55
2.65
ꢁ7.65
ꢁ10.79
ꢁ10.64
ꢁ8.22
ꢁ4.61
ꢁ8.71
ꢁ11.75
ꢁ11.77
ꢁ16.92
ꢁ13.23
ꢁ12.31
ꢁ32.73
5.08
ꢁ13.23
ꢁ12.10
ꢁ15.22
ꢁ12.57
ꢁ5.97
ꢁ6.92
ꢁ14.90
ꢁ17.87
ꢁ9.01
ꢁ4.86
2.74
8.94
12.67
3.25
1.69
793.37
800.77
9.96
(Sh)807.44
820.30
12.62
16.65
13.59
11.91
12.76
8.53
863.95
919.40
952.57
993.00
ꢁ3.37
940.80
976.08
0.27
ꢁ5.46
3.77
1011.08
1031.95
1061.07
1109.91
1180.18
1191.94
1208.29
1298.18
1312.52
1380.63
1416.58
(Sh)1433.33
(Sh)1451.41
1474.80
1515.98
1580.78
1593.60
1711.80
2929.27
3067.62
12.78
14.27
ꢁ5.92
34.15
17.20
18.66
15.88
20.95
28.09
28.89
21.65
19.03
28.59
14.53
31.69
37.60
49.54
113.85
112.36
124.14
997.85
1019.64
1028.34
1114.99
1166.95
1179.84
1193.07
1285.61
1306.55
1373.71
1401.68
1415.46
1442.40
1451.49
1508.34
1577.26
1601.39
1779.27
2964.35
3110.66
ꢁ4.73
ꢁ21.22
15.36
ꢁ6.50
ꢁ5.15
ꢁ13.84
ꢁ1.00
2.95
37% CAN str.
59% Ar-H rock. + 32% Ar str.
56% CH2 twist. + 25% Ar str.
75% Ar-H rock. + 18% Ar str.
40% Ar-CH3 str. + 23% Ar str.
23% Ar-H rock. + 15% Ar str.
35% Ar str. + 24% Ar-H rock.
32% CH3 sym. def. + 27% CAN str. + 18% Ar-TAZ str.
45% CH3 sym. def.
32% Ar str. + 28% Ar-H rock.
85% CH3 asym. def.
75% CH3 asym. def.
50% Ar-H rock. + 34% Ar str.
67% Ar str.
54% C@N str.
6.04
ꢁ1.80
ꢁ0.24
5.90
98
100
102
105
106
111
114
124
ꢁ23.31
ꢁ7.64
ꢁ3.52
7.79
67.47
35.08
ꢁ8.24
2.29
ꢁ5.18
9.56
ꢁ0.33
ꢁ3.31
2.88
71% C@O str.
100% CH3 str.
99% Ar-H str.
43.04
RMS
38.26
18.93
6.97
D
m
denotes the difference between theoretical and experimental frequency. The abbreviation TAZ refers to the triazole ring. The integer value in the first column referees to
the number of theoretical frequency that follows from calculations. Root mean square (RMS) deviations for theoretical frequencies are given in the last row.
triazol-5-one-4-yl)diphenylmethane, 3a, the asymmetric part of
the unit cell contains two independent molecules, both existing
in the keto tautomeric form. The higher stability of keto form
was confirmed by theoretical calculations – the total energy of
the enol form turned out to be significantly higher. Theoretically
calculated geometrical parameters confirm the structure found
experimentally. Good agreement was obtained for theoretical
and experimental bond lengths and valence angles. Some differ-
ences are attributed to hydrogen bonding present in the crystal
structure, which is not accounted for in the calculations on isolated
molecules. Theoretical torsion angles, in particular these describ-
ing relative orientation of two subunits (rings) of the molecule, dif-
fer significantly from experimental ones on account of strain that
the molecule may undergo during crystal formation. Theoretically
calculated geometries of the remaining compounds, 3b–d, are ex-
pected to account for the experimental structures with similar
accuracy.
compounds, as well as for intermediates they were obtained from
(i.e. 4,40-bis(1-substituted-semicarbazide)diphenylmethanes). IR
spectrum of 3a was also calculated using two different scaling ap-
proaches. Detailed assignment of bands on the IR spectrum is also
reported.
Appendix A
A.1. Supplementary materials
CCDC-680033 for 3a contains supplementary crystallographic
data for this paper. The data can be obtained free of charge at
http://www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre (CCDC), 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 (0) 1223 336 033; email:
deposit@ccdc.cam.ac.uk].
The calculated energetic effects of the reactions leading to the
final (cyclic) compound 3a seem to confirm, at least qualitatively,
the conditions under which the reactions were carried out. How-
ever, no reaction path for the cyclization reaction has been pro-
posed. Some preliminary calculations have already been carried
out, but it is definitely to early to arrive at reliable conclusions. This
problem will be dealt with in the forthcoming paper.
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