Structure and spectroscopic characteristics of 4-tert-butylphenoxyacetylhydrazones of arylaldehydes

Article abstract of DOI:10.1016/j.saa.2006.02.049

By reaction of 4-tert-butylphenoxyacetylhydrazide with aromatic aldehydes and acetone a new series of 4-tert-butylphenoxyacetylhydrazones was synthesized. The structural peculiarities of the investigated molecules have been determined by means of X-ray analysis and IR spectroscopy. The diagnostically important IR spectral criteria required for the conformational analysis of acethylhydrazones have been considered. It was established that the 4-tert-butylphenoxyacetylhydrazide in condensed phase exists only as a Z_N-C(O)-conformer. Its derivatives exist as E_N-C(O) and Z_N-C(O)-forms. As a rule, the prevalence of Z_N-C(O)-form has been observed in CCl₄ solutions. The structure of investigated compounds is also determined by a system of inter- and intramolecular hydrogen bonds. The energy of hydrogen bonds was estimated.

Full text of DOI:10.1016/j.saa.2006.02.049

Spectrochimica Acta Part A 66 (2007) 250–261
Structure and spectroscopic characteristics of
4-tert-butylphenoxyacetylhydrazones of arylaldehydes
a,∗
a
a
a
b
a
S.N. Podyachev , I.A. Litvinov , R.R. Shagidullin , B.I. Buzykin , I. Bauer , D.V. Osyanina ,
a
a
b
a
L.V. Avvakumova , S.N. Sudakova , W.D. Habicher , A.I. Konovalov
A.E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of Russian Academy of Sciences, Arbuzov str. 8, 420088 Kazan, Russia
a
b
Dresden University of Technology, Institute of Organic Chemistry, Mommsenstraße 13, D-01062 Dresden, Germany
Received 15 December 2005; received in revised form 22 February 2006; accepted 22 February 2006
Abstract
By reaction of 4-tert-butylphenoxyacetylhydrazide with aromatic aldehydes and acetone a new series of 4-tert-butylphenoxyacetylhydrazones
was synthesized. The structural peculiarities of the investigated molecules have been determined by means of X-ray analysis and IR spectroscopy.
The diagnostically important IR spectral criteria required for the conformational analysis of acethylhydrazones have been considered. It was
established that the 4-tert-butylphenoxyacetylhydrazide in condensed phase exists only as a ZN–C(O)-conformer. Its derivatives exist as EN–C(O) and
Z
N–C(O)-forms. As a rule, the prevalence of ZN–C(O)-form has been observed in CCl
determined by a system of inter- and intramolecular hydrogen bonds. The energy of hydrogen bonds was estimated.
2006 Elsevier B.V. All rights reserved.
4
solutions. The structure of investigated compounds is also
©
Keywords: 4-tert-Butylphenoxyacetylhydrazide; 4-tert-Butylphenoxyacetylhydrazones; Conformation; Hydrogen bonds; IR spectroscopy; X-ray crystallography
1
. Introduction
conformers and the formation of additional hydrogen bonds.
These compounds are also of interest as structural blocks of
calix[4]arene derivatives [7,8].
Hydrazides and acylhydrazones are nowadays of consider-
able technical and commercial importance [1]. This is con-
nected with their wide using as drugs, complexones, photo-
thermochromic compounds and precursors for organic synthesis
In this paper we show IR spectroscopy data of 4-tert-butyl-
phenoxyacetylhydrazide and 4-tert-butylphenoxyacetylhydra-
zones of arylaldehydes in solid state and in non-polar solvent
(CCl4) along with the results of the single crystal X-ray diffrac-
tion study.
[
2–4]. In case of acylhydrazones the presence of the carbonyl
oxygen atom promotes the formation of a chelate binding cen-
ter [3]. It also leads to the formation of EN–C(O)/ZN–C(O) amide
conformers (Scheme 1) due to the hindered rotation around the
N C( O) bond [5,6].
2. Experimental
The influence of functional groups in acetylhydrazone frag-
ment of molecules and the character of hydrogen bonds on the
configuration equilibrium in hydrazones is insufficiently inves-
tigated. Taking this fact into consideration, we investigated the
structure of 4-tert-butylphenoxyacetylhydrazyde and its con-
densation products with carbonyl compounds (Scheme 2). The
peculiarity of these compounds is the presence of an ether oxy-
gen atom and conformationally labile C C and C O bonds. This
increases the probability of the realization of a large number of
2.1. Materials
All reagents were used as commercially received without
further purification. K CO (p.a.) was annealed prior to use.
2
3
The general synthetic methods and the structure formulae
of the investigated compounds are presented in Scheme 2.
The ethyl ester of 4-tert-butylphenoxyacetic acid (1) and
4-tert-butylphenoxyacetylhydrazide (2) used in this work
were obtained according to literature methods [9,10]. The
composition and the structure of the obtained compounds have
1
been confirmed by means of elemental analysis, H NMR
∗
(Table 1), IR spectroscopy and X-ray analysis. The purity of
the compounds was monitored by TLC.
Corresponding author. Tel.: +7 843 2727394; fax: +7 843 2732253.
E-mail address: spodyachev@iopc.knc.ru (S.N. Podyachev).
1
386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.02.049

S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
251
cipitate was formed. The solvent was removed from the reaction
mixture by distillation and the solid remainder was washed with
hexane and recrystallized from CCl4.
2
.1.2.1. 4-tert-Butylphenoxyacetylhydrazone of benzaldehyde
◦
(4). 4 (0.84 g, 90%) was obtainedas a white powder(mp 172 C;
Scheme 1.
elemental analysis for C19H22N2O2, calculated: C, 73.52; H,
.14; N, 9.03%; found: C, 73.38; H, 8.07; N, 9.51%).
7
2
4
.1.1. Preparation of the
-tert-butylphenoxyacetylhydrazone of acetone (3)
A solution of (3 mmol) 4-tert-butylphenoxyacetylhydrazide
2.1.2.2. 4-tert-Butylphenoxyacetylhydrazone of 4-bromobe-
nzaldehyde (5). 5 (1.1 g, 93%) was obtained as a white pow-
◦
(2) in 5 ml water and 10 ml acetone was refluxed for 3 h. The
der (mp 155–157 C; elemental analysis for C H Br N O ,
19 21 1 2 2
precipitate was filtered off and washed several times with dis-
calculated: C, 58.62; H, 5.44; N, 7.20; Br, 20.53%; found: C,
58.63; H, 5.77; N, 7.27; Br, 21.13%).
tilled water. 3 (0.65 g, 82%) was obtained as a white powder
◦
(
mp 70–72 C; elemental analysis for C H22N2O2, calculated:
15
C, 68.67; H, 8.45; N, 10.68%; found: C, 68.70; H, 8.67; N,
2
.1.2.3. 4-tert-Butylphenoxyacetylhydrazone of 4-nitroben-
1
0.98%).
zaldehyde (6). 6 (0.63 g, 59%) was obtained as a yellowish
powder (mp 184 C; elemental analysis for C19H21N3O4, cal-
◦
culated: C, 64.21; H, 5.96; N, 11.82%; found: C, 64.52; H, 5.74;
N, 12.18%).
2
4
.1.2. General procedure for the synthesis of
-tert-butylphenoxyacetylhydrazones of aromatic
aldehydes (4–9)
To a boiling solution of (3 mmol) 4-tert-butylphenoxyacety-
lhydrazide (2) in 4 ml EtOH under stirring were added 3 mmol
of the corresponding aldehyde (4-bromobenzaldehyde and 4-
nitrobenzaldehyde were initially dissolved in 3 ml hot EtOH).
The reaction mixture was refluxed for 1 h. In the case of com-
pounds 4–7 the precipitate was filtered off, washed several times
with a mixture of water/EtOH (1:1), and recrystallized from
EtOH. As a result of the synthesis of compounds 8 and 9 no pre-
2.1.2.4. 4-tert-Butylphenoxyacetylhydrazone of salicylalde-
hyde (7). 7 (0.92 g, 90%) was obtained as a white powder (mp
165–167 C; elemental analysis for C19H22N2O3, calculated: C,
◦
69.92; H, 6.79; N, 8.58%; found: C, 69.97; H, 7.80; N, 9.13%).
2.1.2.5. 4-tert-Butylphenoxyacetylhydrazone of pyridine-4-
carbaldehyde (8). 8 (0.72 g, 77%) was obtained as a white
◦
powder (mp 93 C; elemental analysis for C18H21N3O2, cal-
Scheme 2.
Table 1
1
a
H chemical shifts (ppm) of ZN–C(O) (EN–C(O))-conformers 3–9 in CDCl3
Compound
H-1
H-2b
H-3b
H-4
H-5
9.10 (8.39)
9.55 (10.08)
9.99 (9.55)
9.75 (10.35)
10.91 (9.90)
9.75 (10.35)
9.68 (9.29)
R1
R2
3
4
5
6
7
8
9
1.29 (1.28)
1.32 (1.30)
1.31 (1.30)
1.31 (1.26)
1.30 (1.27)
1.31 (1.28)
1.31 (1.29)
7.34 (7.29)
7.36 (7.32)
7.36 (7.32)
7.36 (7.32)
7.34 (7.23)
7.36 (7.32)
7.35 (7.29)
6.87 (6.90)
6.92 (6.96)
6.91 (6.94)
6.91 (6.94)
6.89 (6.92)
6.91 (6.94)
6.91 (6.94)
4.61 (4.98)
4.67 (5.16)
4.67 (5.14)
4.68 (5.17)
4.64 (4.98)
4.68 (5.16)
4.69 (5.15)
2.12 (2.02)
8.25 (7.86)
8.21 (7.79)
8.44 (7.97)
8.43 (7.97)
8.35 (7.83)
8.28 (7.96)
1.89 (1.84)
7.38–7.77c
7.54–7.64
7.79–8.26c
6.99–7.20 ; 9.52 (9.97 )
7.49–8.68
7.28–8.16c
c
c
d
d
c
a
Numbering follows from Scheme 2.
b
c
d
3
Doublet ( J ≈ 8.6 Hz).
Chemical shifts for conformers are not assigned due to signals overlapping.
OH proton.

2
52
S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
culated: C, 69.43; H, 6.80; N, 13.49%; found: C, 67.96; H, 7.00;
N, 13.88%).
the plain P2, which includes the hydrazide fragment and OCH2-
bridge, are practically coplanar (Table 3).
The hydrogen atom of the amide group in hydrazide 2, addi-
tionally to its involvement in the intramolecular hydrogen bond,
at the same time takes part in the formation of an intermolec-
ular hydrogen bond with the C O group of the neighbouring
molecule (see Fig. 2, 2). One of the hydrogen atoms of the termi-
nal amino group of hydrazide 2 is also involved in the formation
of intermolecular H-bonds with the carbonyl oxygen of another
molecule (1/2 + x, 3/2 − y, z), which leads to a non-equivalence
of the protons of the primary amino group.
2
.1.2.6. 4-tert-Butylphenoxyacetylhydrazone of pyridine-2-
carbaldehyde (9). 9 (0.74 g, 79%) was obtained as a white
powder (mp 119–121 C; elemental analysis for C18H21N3O2,
calculated: C, 69.43; H, 6.80; N, 13.49%; found: C, 70.41; H,
7
◦
.56; N, 14.10%).
2
.2. Spectroscopy
The parameters of the H-bonds are the following: intra-
molecular—N(1)–H(1) O(2), N(1)–H(1) 1.15 A, H(1) O(2)
Microanalyses of C, H, N were carried out with a CHN-
S analyser (Carlo Erba). H NMR spectra were recorded on
a Bruker MSL-400 instrument with a working frequency of
.
. .
. . .
˚
1
.
. .
. . .
˚ ˚
1
1
−
.89 A, N(1) O(2) 2.607(4) A, angle N(1)–H(1) O(2)
◦
. . .
ꢀ
17 ; intermolecular—N(1)–H(1) O(1 ) [3/2 − x, −1/2 + y,
4
00.13 MHz. Chemical shifts in δ have been determined in
.
. .
ꢀ ꢀ
˚ ˚
O(1 ) 2.26 A, N(1) O(1 ) 3.219(4) A, angle
. . .
z], H(1)
CDCl3 with Me4Si as an internal standard at a temperature of
.
. .
ꢀ
◦
˚
. . .
ꢀꢀ
N(1)–H(1) O(1 ) 140 ; N(2)–H(201) O(1 ) [1/2 + x, 3/2 − y,
◦
3
0 C. The signals for conformers were assigned in accordance
.
. .
ꢀꢀ
. . .
ꢀꢀ
˚
z], N(2)–H(201) 1.20 A, H(201) O(1 ) 1.89 A, N(2) O(1 )
with [5,6]. IR absorption spectra of Nujol emulsions and CCl4
.
. .
ꢀꢀ ◦
˚
.078(3) A, angle N(2)–H(201) O(1 ) 170 . The system of
3
−
2
−5
solutions (10 to 10 M) of compounds were recorded on a
Vector-22 Bruker FT-IR spectrophotometer with a resolution of
hydrogen bonds in the crystal of hydrazide 2 represents a
flattened two-dimensional network parallel to the plain XOZ
Fig. 2, 2).
−1
4
cm
.
(
In the crystal of hydrazone 4 the asymmetric part of the unit
2
.3. Crystal structure determination
cell contains two independent molecules (4A and 4B), wherein
the tert-butyl group of molecule 4B is disordered. The main
geometric parameters (bond lengths and bond angles) in the two
independent molecules are the same within the limits of exper-
imental error (excluding the disordered tert-butyl group, for
which the geometric parameters have been determined with low
accuracy). The non-hydrogen atoms of the carbonylhydrazone
and the oxymethyl groups are practically in one plain P2 (see
The X-ray diffraction data were collected on a CAD-4 Enraf-
Noniusautomaticdiffractometerusinggraphitemonochromated
Cu K␣ (λ = 1.54184 A) radiation. The details of crystal data, data
˚
collection and the refinement are given in Table 2. The stabil-
ity of crystals and experimental conditions were being checked
every 2 h using three control reflections, while the orientation
was being monitored every 200 reflections by centering two
standards. No significant decay was observed. Corrections for
Lorentz and polarization effects were applied. Absorption cor-
rection was not applied. The structures 2, 7 were solved by
direct methods using MolEN package [11], and structures 4,
◦
Table 3). This plane has a dihedral angle only of 8.1 (molecule
◦
4
A) and 10.2 (molecule 4B) with the phenyl ring (plain P3)
of the benzylidene fragment. In contrast to hydrazide 2, in this
case the Z-conformer takes place relative to the bond C(1)–C(2),
however, the tert-butylphenoxy moiety is rotated around the
6
9
were solved and refined by direct methods using SHELX-
7 package [12]. For the crystals all non-hydrogen atoms were
◦
◦
C(2) O(2) bond by −77.4(2) and 81.3(2) , respectively, in
molecules 4A and 4B. Thus, apart from minor differences in
the size of torsion angles and the direction of the torsion of sub-
stituents in respect of the C(2) O(2)-bonds, the geometry of the
molecules 4A and 4B is similar.
refined anisotropically. H-atoms, located in ꢀF maps, were
included into structure factor calculations with fixed positional
and thermal parameters in structures 2, 7 and refined as rid-
ing atoms. All figures were made using the program PLATON
The independent molecules 4A and 4B in the crystal
[
13]. Crystals 4 and 7 are isostructural, so for 4 the figures
. . .
ꢀ
of hydrazone 4 form cyclic dimers of the type 4A 4B
have not been represented. All crystallographic data (excluding
structure factors) for the structures are deposited with the Cam-
bridge Crystallographic Data Centre (deposition number CCDC
ꢀ. . .
. . .
(
7
or 4A 4B) due to N H O hydrogen bonds (Fig. 2,
). The parameters of the hydrogen bonds are the follow-
. . .
ꢀ
ing: N(1A)–H(1A) O(1B ) [1 + x, y, z − 1], N(1A)–H(1A)
2
71697-271700).
. . .
ꢀ ꢀ
˚ ˚ ˚
.92 A, H(1A) O(1B ) 1.96 A, N(1A) O(1B ) 2.874(4) A,
. . .
0
.
. .
ꢀ
◦
. . .
ꢀꢀ
˚
ꢀꢀ
angle N(1A)–H(1A) O(1B ) 173 ; N(1B)–H(1B) O(1A )
.
. .
˚
3
. Results
[x − 1, y, 1 + z], N(1B)–H(1B) 0.86 A, H(1B) O(1A) 2.03 A,
. . . ꢀꢀ . . .
˚
N(1B) O(1A ) 2.887(4) A, angle N(1B)–H(1B) O(1A )
◦
3
.1. X-ray analysis
172 .
The crystals of hydrazone 7 are isostructural to the crystals
of hydrazone 4 (see Table 2). However the disorder of tert-butyl
substituents in molecules 7 is not observed (Fig. 1, 7). The pres-
ence of ortho-hydroxy groups in the phenyl ring of hydrazone
7 does not lead to a change in the crystal packing. The con-
formation of the independent molecules 7 is also similar to the
According to the X-ray data hydrazide 2 exists in the crystal
phase only as a ZN–C(O)-conformer (Fig. 1, 2). This conforma-
tion is stabilized by intramolecular hydrogen bonds between
the amide hydrogen atom and the oxygen atom of the phenoxy
groups (Fig. 2, 2) As a result the phenyl ring (plain P1) and

S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
253
Table 2
Single-crystal X-ray data for structures 2, 4, 6 and 7
Parameter
2
4
6
7
Chemical formula
Color, shape
Lattice type
C12H18N2O2
Colorless, prismatic
Monoclinic
P21/a
C19H22N2O2
Colorless, prismatic
Triclinic
C19H21N3O4
Light yellow prismatic
Monoclinic
Pa
C19H22N2O3
Colorless prismatic
triclinic
Space group
P-1
P-1
Cell dimensions
a = 8.154(4) A˚
b = 9.55(1) A˚
c = 16.68(1) A˚
a = 9.175(6) A˚
b = 12.37(1) A˚
c = 16.88(1) A˚
a = 10.55(1) A˚
b = 6.362(3) A˚
c = 14.389(9) A˚
a = 8.967(9) A˚
b = 12.67(1) A˚
c = 16.71(2) A˚
◦
◦
◦
◦
β = 91.86(4)
α = 89.90(6)
β = 75.25(6)
β = 108.51(9)
α = 89.39(9)
β = 75.72(8)
◦
◦
◦
◦
γ = 72.85(6)
γ = 74.25(8)
Volume ( A˚ 3)
Z
1298 (2)
4
1765 (3)
4 (two independent molecules)
915 (2)
2
1768 (3)
4 (two independent molecules)
Formula weight
Calculated density (g/cm )
μ (Cu K␣) (mm
F(0 0 0)
222.29
1.137
0.598
480
310.40
1.168
0.574
664
355.40
1.290
0.717
376
326.40
1.226
0.639
696
3
−1
)
Radiation, λ ( A˚ )
θ, Measurement interval ( )
Cu K␣, λ = 1.54184 A˚
2.72–74.22
◦
2.72–57.23
6.96–65.00
2.72–74.22
Scan angle
ω
Reflections limits
−10 ≤ h ≤ 10
−10 ≤ h ≤ 8
−13 ≤ k ≤ 13
−18 ≤ l ≤ 0
−12 ≤ h ≤ 11
0 ≤ k ≤ 7
−11 ≤ h ≤ 10
−15 ≤ k ≤ 15
−20 ≤ l ≤ 0
0
0
≤ k ≤ 11
≤ l ≤ 20
0 ≤ l ≤ 16
Total reflections measured
Reflections with F > 2σ(I)
2910
1392 [>3σ(I)]
145
Not applied
Included not refined
R1 = 0.065
wR2 = 0.077
4739
3903
452
1675
1583
272
6984
3555 [>3␴(I)]
433
2
Number of parameters
Absorption correction
Hydrogen treatment
Mixed
R1 = 0.054
wR2 = 0.161
Mixed
R1 = 0.051
wR2 = 0.127
Included not refined
R1 = 0.055
wR2 = 0.065
2
Final R-factors [F > 2σ(I)]
Goodness of fit on F2
2.275
1.027
1.103
1.936
conformation of the molecules 4. The main geometric parame-
ters of molecules 4 correspond to those of molecules 7 within
the limits of experimental errors.
The analysis of intra- and intermolecular interactions in crys-
tal 7 showed that the hydroxyl group forms an intramolecular
H-bond with the imine nitrogen atom. Similar as in crystal 4
intermolecular hydrogen bonds bind molecules 7A and 7B in
the dimers (Fig. 2, 7).
. . .
˚
. . .
˚
N(2A) 1.59(3) A, O(15A) N(2A) 2.633(4) A, angle
. . .
◦
. . .
O(15A)–H(15A) N(2A) 138(2) ; O(15B)–H(15B) N(2B),
. . .
˚
˚
O(15B)–H(15B) 1.13(3) A, H(15B) N(2B) 1.74(3) A, O(15B)
. . .
. . .
◦
˚
N(2B) 2.643(4) A, angle O(15B)–H(15B) N(2B) 133(2) ;
. . .
ꢀ
N(1A)–H(1A) O(1B ) [−x, 2 − y, 1 − z], N(1A)–H(1A)
. . .
ꢀ ꢀ
˚ ˚ ˚
.15(2) A, H1A O1B 1.69(2) A, N(1A) O(1B ) 2.820(3) A,
. . .
1
. . .
ꢀ
◦
. . .
ꢀꢀ
ꢀꢀ
angle N(1A)–H(1A) O(1B ) 169(2) ; N(1B)–H(1B) O(1A )
. . .
[
−x, 1 − y, 1 − z], N(1B)–H(1B) 1.16(3), H(1B) O(1A )
The parameters of the hydrogen bonds are the following:
. . .
ꢀꢀ
˚ ˚
.72(3) A, N(1B) O(1A ) 2.876(3) A, angle N(1B)–H(1B)
1
.
. .
˚
. . .
ꢀꢀ
◦
O(15A)–H(15A) N(2A), O(15A)–H(15A) 1.22(3) A, H(15A)
O(1A ) 175(2) .
In molecule 6 hydrazone and amide fragments are located in
one plain P2 as in molecules mentioned above. However the
introduction of a nitro group into the benzylidene fragment leads
to conformational changes in comparison to hydrazones 4 and
Table 3
◦
Dihedral angles ( ) between planes P1(C3–C4–C5–C6–C7–C8), P2(O2–
C2–C1–O1–N1–N2–C13)a and P3(C14–C15–C16–C17–C18–C19) for the
structures 2, 4, 6 and 7
7. For 6 (Fig. 1, 6) as well as in the molecules of hydrazide 2 an
EC(1)–C(2)-conformation [(torsion angle O(1)–C(1)–C(2)–O(2)
is equal 176.6(3) ] is observed, instead of a ZC(1)–C(2)-
Molecule
P1/P2
P1/P3
P2/P3
◦
2
5.7 (8)
–
–
conformation for hydrazones 4 and 7. In molecule 6 the torsion
of the tert-butylphenyl fragment around the C(3) O(2) bond is
essentially greater than in molecules 4 and 7 [(torsion angle
4
4
6
7
7
a
b
80.99 (9)
83.43 (8)
35.5 (2)
80.96 (8)
84.87 (8)
73.61 (8)
85.29 (8)
13.8 (7)
76.25 (9)
83.24 (9)
8.1 (6)
10.2 (4)
21.7 (3)
5.3 (9)
11.2 (4)
a
b
◦
C(2)–O(2)–C(3)–C(4) is equal to −45.3 (8)], but the devia-
tion of the tert-butylphenoxy moiety from coplanarity with the
a
For compound 2 plane P2 (O2–C2–C1–O1–N1–N2).
hydrazone–amide fragment is much smaller (Table 3).

2
54
S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
Fig. 1. Geometry of the molecules 2, 6, 7 and atomic numbering scheme (crystals 4 and 7 are isostructural).
Compared to hydrazones 4 and 7, the phenyl ring of the
arylideneimino fragment in hydrazone 6 is much more twisted
dihedral angles P2/P3 is equal 21.7(3)) relative to the optimal
position for conjugation. Due to realization of the ZN–C(O)-
the amide and the ether (−OCH2) groups in hydrazone are
formed in spite of the fact that a pronounced turning of the 4-
tert-butylphenyl fragment around the C(2) O(2) and O(2) C(3)
bonds is observed. This intramolecular H-bond formed in the
crystal by the amide group as in molecule 2 is complemented by
(
.
. .
conformation intramolecular NH O hydrogen bonds between

S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
255
an intermolecular H-bond with the C O group of the adjacent
molecule (Fig. 2, 6).
only NH groups, but no NH2 groups are present. It should be
notedaccordingtoliteraturedataXC(O)NHNH2 groupmaygive
only two bands for free vibrations ν(NH) and ν(NH2) in region
The parameters of the H-bonds are the following:
.
. .
. . .
. . .
−1
˚
˚
N(1)–H(1) O(2), N–H 0.96 A, H O 2.16 A, N(1) O(2)
3500–3400 cm [14,15]. The above-mentioned frequencies of
.
. .
◦
. . .
ꢀ
˚
2
.569(5) A, angle N(1)–H(1) O2 104 ; N(1)–H(1) O(1 )
these absorption bands of the hydrazide 2 in crystalline phase
are significantly lowered. This indicates that they all belong
to fragments involved in hydrogen bonding. The presence of
.
. .
. . .
ꢀ
˚
(
1/2 + x, 1 − y, z): H O 2.17, N(1) O(1 ) 3.079(5) A, angle
. . .
ꢀ
◦
N(1)–H(1) O(1 ) 157 . A chain along the X-axis is formed via
−1
intermolecular H-bridges.
absorption band with a maximum at ∼1540 cm (amide II
band δ(NH)), which can be observed as a shoulder on the strong
−
1
peak at 1518 cm (ν(CC) phenyl group), is an indication on the
ZN–C(O)-conformation of the amide NH group [15].
3
.2. IR investigation
According to Bellamy–Williams correlation [15], the fre-
quencies ν and ν of the NH amine groups for “free” or equal
For investigation of conformational properties, intra- and
as
s
2
intermolecular interactions depending on H-bonds the absorp-
tion bands of NH, NH2 and C O groups in IR spectra are
informative. To study such interactions IR spectra of compounds
N H bonds follow Eq. (1):
νs = 345.53 + 0.876νas
(1)
2
–9 were recorded in solid (polycrystalline) phase and in CCl4
solution (Fig. 3).
Hence νs(NH2) for the described solid state should be:
−
1
Thespectrumofhydrazide2inthesolidstate(Fig. 3, 2)shows
νs = 345.53 + 0.876 × 3340 = 3271 cm . We observed a band
−
−1
1
−1
the νas(NH2) as a shoulder (3340 cm ) on the strong peak at
at 3205 cm . It indicates that the NH2 groups of the primary
−1
3
322 cm and νs(NH2) at 3205 cm . The δ(NH2) absorption
amine fragments take part in an asymmetric H-bonds, which is
in agreement with the data from the X-ray analysis (Fig. 2, 2).
When going to solution in CCl4 the spectrum of hydrazide 2
in the selected areas of ν(NH), ν(NH2) and ν(C = O) absorp-
tion changes pronouncedly (Fig. 3, 2). All above-mentioned
−
1
−1
forms a shoulder at ∼1650 cm on the ν(C O) (1660 cm
)
−
1
absorption band. A strong peak at 3322 cm belongs to ν(NH).
This assignment results from the comparison of the relative
intensities of ␯(NH) in the spectra of compounds 3–9, where
Fig. 2. Hydrogen bonds in the structures 2, 6 and 7 (crystals 4 and 7 are isostructural).

2
56
S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
Fig. 2. (Continued)
absorption bands of associated NH2 and NH practically dis-
appear already at a concentration of ∼10 M. Instead of them
It is necessary to note again that the presence of the peak
−
2
−1
−1
δ(NH) at ∼1540 cm in the solid phase and 1545 cm in
−
1
a strong peak ν(NH) at 3452 cm with a shoulder νas(NH2)
solution indicates the ZN–C(O)-form of the amide fragment. The
−1
−1
−1
at ∼3445 cm and a weak peak νs(NH2) at 3338 cm with
comparison of the value of the ν(NH) frequency 3322 cm in
−
1
−1
shoulders at 3367 and 3292 cm can be observed. Hence all
intermolecular bonds have been disrupted and, as follows from
the observed bands in comparison to literature data [14], only
non-associated molecules with possible intramolecular hydro-
gen bonds are present. In agreement with it, the frequency of the
solid phase and 3452 cm in CCl4 solution with literature data
[14] also shows that hydrazide 2 in crystalline form and in CCl4
solution exists only in ZN–C(O)-conformation. The presence of a
single conformer in solution is also confirmed by a characteristic
singlet peak ν(C O).
In acylhydrazones of acetone NH2 group is absent and a non-
equivalent isomerization around C N double bond is excluded.
The region of NH stretching vibrations in the IR spectra is sim-
−
1
δ(NH2) band decreased to 1627 cm and ν(C O) increased to
693 cm
According to Bellamy–Williams Eq. (1) free νs(NH2) should
−1
1
.
−
1
−1
−1
be about 3363 cm . Hence the shoulder at 3367 cm can
probably be assigned to those molecules, which are free of
hydrogen bonds involving the −NH2 group. The frequency of
plified, but those of carbonyl absorptions (1692 cm ) in solid
−1
get more complicated due to the ν(C N) vibration (1646 cm
)
−1
(Fig. 3, 3). The absorption peak δ(NH) at 1543 cm is of
analytical importance. The peak is a characteristic for the
ZN–C(O)-conformer of the amide fragment. At the same time
ν(NH) absorption band is double and has maxima at 3245
−
1
the peak 3338 cm indicates the presence of an intramolecular
hydrogen bond of the NH2 group with any proton acceptor in
the non-associated molecules in this case. Another shoulder at
−1
−1
3
292 cm disappears during dilution and most probably cor-
and 3222 cm . The low value frequency is a characteris-
responds to the short chain block of the associates bound by
intermolecular hydrogen bonds.
tic for the EN–C(O)-configuration of the amide group in H-
cyclodimers [15,16]. So it can be concluded that hydrazone 3

S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
257
Fig. 2. (Continued).
in the solid state, according to the ratio of intensities of the
shrinks during dilution, being outstripped in intensity by the
former peak. For this reason the first one has to be assigned
to ZN–C(O)- and the second to the EN–C(O)-conformer and their
associates.
−
1
−1
doublet 3245 cm /3222 cm , consists of a mixture of about
equal parts of H-bridged dimers of EN–C(O)-conformers and of
intermolecularly bonded ZN–C(O)-conformers.
In contrast to the case of 2, the ν(NH) vibration bands of the
intermolecular hydrogen bonds remain but shift to 3195 cm
as the hydrazone 3 concentration in CCl4 is decreased from
Thus the hydrazone of acetone 3 in the solid state exists as a
mixture of equal parts of the EN–C(O)- and ZN–C(O)-conformers.
However in solution as the dilution increases, the ZN–C(O)-form
becomes slightly dominant.
For acetylhydrazones of aromatic aldehydes in crystal and
solution of different polarity only one EC N-isomer is usually
realized [5,6,17], which is in agreement with the X-ray data for 4,
6, 7. It should be noticed that the spectral behaviour of aldehyde
hydrazones 4, 5, 7 is similar in contrast to the behaviour of
hydrazones 6, 8, 9. Therefore the spectra of the benzylidene
derivative 4 and some spectral peculiarities of compounds 6, 8,
9 have been investigated in more detail.
−
1
−
2
−3
to 10 M (Fig. 3, 3). The vibration bands disappear
1
0
−
4
only at 10 M. This value of frequency is typical for the
EN–C(O)-conformers of amides and is in agreement with litera-
ture data about stronger intermolecular hydrogen bonds formed
by the EN–C(O)-conformers in comparison with the ZN–C(O)-
conformers of secondary amides [15]. The fact that the band
with a maximum at 3195 cm does not shift to higher fre-
quencies during dilution is typical for cyclic H-dimers of the
EN–C(O)-conformers, which are not bound via additional inter-
molecular H-bonds [16]. The concentration decrease of 3 is
also accompanied by the appearance of weak peaks of mul-
−
1
X-ray analysis of the monocrystal of hydrazone 4 showed that
the molecules of this compound exist as H-cyclo-dimers of the
EN–C(O)-conformers. In the IR spectra of 4 in solid state a peak
−
1
tiplet in region ∼3400 cm . Considering their relative inten-
−
1
sities, the peaks have to be assigned in the following way:
with a maximum at 3193 cm can be clearly observed (Fig. 3,
4) which is caused by intermolecular hydrogen bonds in the
EN–C(O) cyclo-H-dimer. There are some striking peculiarities of
the IR spectra in the range of N–H stretching vibrations. More
−
1
3
413 and 3452 cm —␯(NH) vibrations of monomers of the
ZN–C(O)-conformers with and without intramolecular NH
.
. .
O
hydrogen bonds between the amide and the ether group respec-
−
1
−1
tively, 3391 cm —monomers of the EN–C(O)-conformer, band
longwave and intensive additional absorption at ∼3090 cm
−
1
−1
at 3359 cm —overtone of the carbonyl absorption. The car-
bonyl peak at 1713 cm grows, and the peak at 1697 cm
was registered along with the EN–C(O) peak at ∼3195 cm
−
1
−1
in spectra of arylaldehyde hydrazones 4, 5, 7, 8. For 9 the

2
58
S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
Fig. 3. IR spectra of compounds 2-9 (a) in nujol and (b) in CCl4 at concentrations: (1) 10 2 M; (2) 10 M; (3) 10 M. For the solutions only the regions of ν(NH),
−
−3
−4
ν(C O) are shown.

S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
259
Fig. 3. (Continued).
−
1
peak at ∼3090 cm is only observed. In spectra of hydrazones
For hydrazone 6, which contains a nitro group in the ben-
zylidene fragment a rather strong main absorption peak at
−
1
6
vice versa—the high-frequency peak at 3268 cm is more
−
1
−1
−1
intensive than low-frequency peak at ∼3090 cm . Accord-
3268 cm with a shoulder at ∼3200 cm in the ν(NH) region
of polycrystalline phase is observed (Fig. 3, 6). The frequency
of this peak for 6 in comparison with compounds 4, 5, 7 is
much higher. Obviously it is caused by the ZN–C(O)-form of the
molecule, in which the hydrogen atom of the NH group accord-
ing to X-ray data is connected by bifurcated H-bonds (Fig. 2, 6).
ing to literature data, it is due to Fermi resonance between
␯
(NH) vibration and overtone – 2δ(NH) of ZN-C(O)-conformer or
composite tone - ␯(C O) + δ(NH) of EN–C(O)-conformer. How-
ever, the corresponding absorption of secondary amides as a
rule is much weaker than the main absorption in region above
3200 cm [15]. The observed reverse phenomenon for our
compounds obviously results from the aromatic character of
imine group substituents in discussed row. In fact the range of
000–3100 cm is a characteristic for unsaturated (aromatic
and similar ones) ν( CH) vibrations. The resonance effect com-
plicated by their participation leads obviously to anomalous
absorption of stretching vibrations at ∼3090 cm for EN–C(O)-
conformers in the solid state. It may be an important diagnostic
criterionfortheseconformers. Theν(NH)mainbandofZN–C(O)-
forms is replaced at higher frequencies region than for EN–C(O)-
forms and usually doesn’t give such effect. That is observed in
the case of hydrazone 6.
In the solutions of hydrazone 4 at concentrations below
M the absorption of the cyclo-H-dimers is not observed.
The peak ν(NH) at 3433 cm , which appears when going
from the solid state to solution and which dominates among
others in this region, represents the ZN–C(O)-form. The peak
of its partner at 3349 cm , can be assigned to the EN–C(O)-
conformer. The intensity of the low-frequency component of
doublet ν(C O) (1723 and 1697 cm ) decreases under dilution,
accompanied by a slightly decreasing of the intensity of peak
349 cm . This is probably the case of overlapping this latter
with overtone –2ν(C O). The peaks for ν(C O), as in the case
of hydrazone 3, have to be assigned to the ZN–C(O)-at 1723 cm
and to the EN–C(O)-conformer together with associates forms at
697 cm , respectively. The relative low frequency of the peak
−
1
−1
∼
The shoulder at ∼3200 cm may indicate the presence of H-
cyclodimers of the EN–C(O)-conformers in polycrystalline state.
However it is also reasonable that the combination- and over-
−
1
−1
3
tones in the region ∼3200 cm can be observed. Since X-ray
analysis of the monocrystal 6 showed only ZN–C(O)-conformer.
The above-mentioned ν(NH) peaks for solid state 6 disap-
−
1
−1
pear and new ones (a major peak at 3429 cm , belonging to
−1
the ZN–C(O)-form, and a second at 3346 cm for the EN–C(O)
-
form) appear when going to CCl solution. At the same time the
4
−1
band for ν(C O) splits into peaks at 1728 and 1702 cm with
increasing relative intensity of the first peak during dilution. The
−
1
peak at 1728 cm obviously belongs to ZN–C(O)-conformers of
the free molecules, the another – to EN–C(O)- and associated
forms. The δ(NH) absorption can hardly be used for an investi-
gation because of overlapping with the region of the very strong
−3
1
0
−
1
−
1
−1
ν (NO ) absorption at ∼1520 cm and ν (NO ) at 1343 cm
as
2
s
2
(Fig. 3, 6).
−
1
The, presence of an ortho-hydroxy substituent in the phenyl
ring of the salicylidene hydrazone 7 is responsible for the broad
dome-shaped ν(OH) band in the IR spectrum of the crystal 7.
This band is underneath the ν(NH), ν( CH), ν(−CH) absorp-
−
1
−1
−1
3
tions in the region ∼3300–2800 cm with a center at around
−
1
∼3100 cm . The other bands typical for ν(OH) vibrations and
−
1
−1
usually observed in the region 3200–3650 cm [15] have not
been registered. In CCl solutions the broad dome-shaped ν(OH)
4
−1
1
␯
band remains. This means that the hydrogen atom of the ortho-
−
1
(NH) for the EN–C(O)-conformer at 3349 cm can be caused
hydroxy group forms very strong intramolecular hydrogen
2
by the presence of long chain conjugation in the molecule. The
same conclusions can be also drawn from IR spectra of 4-bromo-
and 2-hydroxyphenylhydrazones 5, 7 (Fig. 3, 5, 7).
bonds with sp -hybridized free electron pair of the nitrogen atom
−1
−1
)
of the azomethine group (ꢀν = 3610–3050 cm = 560 cm
that was clearly recognized by X-ray analysis The rule of

2
60
S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
with a maximum at 3215 cm 1 for the cyclic H-dimer of the
EN–C(O)-conformer disappears upon dilution. So the IR spec-
trum becomes simpler. At the same time the sharp peaks
−
Johannsen (Eq. (2)) [18] was applied for the determination of
this intramolecular hydrogen bond energy:
2
−1
−
1
free
(
ꢀH) = 1.92[(ꢀν) − 40] kJ mol
(2)
at 3349 and 3433 cm
for ν (NH) of the EN–C(O)- and
ZN–C(O)-form, respectively, are increasing. The ratio of the peak
intensities of the conformers in contrast to the previous cases
for 2–8 is inverse, namely the EN–C(O)-conformer dominates.
As in the case of spectra 8 in CCl4, a doublet ν(C O) at
724 cm /1703 cm appears and its lower frequency com-
ponent is decreasing upon dilution. Consequently compound
in crystal phase exists as an EN–C(O)-conformer with very
strong hydrogen bonds. There is an equilibrium of both amide
structures with a predominance of the EN–C(O)-form in solu-
tions of 9 probably due to some electronic effects of 2-pyridine
fragment.
Following the Johannsen Eq. (2), the energy of inter-
molecular hydrogen bond in the cyclic H-dimers of EN–C(O)-
form of investigated compounds can be approximately
.
. .
For intramolecular hydrogen bonds OH N C in hydrazone 7
−
1
the −ꢀH calculated ∼30 kJ mol
.
The hydrazone 8 containing 4-pyridine fragment shows in
solid state a spectral similarity with the phenyl analogue 4.
It concerns the fragments NH and C O (Fig. 3, 8). In the
region of ν(NH) vibrations for compound 8, as well as for
−
1
−1
1
9
−
1
hydrazone 4, a peak at 3194 cm
of the cyclic H-dimers
of EN–C(O)-conformers is observed. However, in contrast to
−
1
4
the probable amide II peak δ(CNH) = 1549 cm
of the
ZN–C(O)-conformation of the secondary amide structure also
has to be mentioned. At the same time, ν(NH) peaks in the
−
1
region ∼3300 cm
for the ZN–C(O)-amide structure, which
were observed for compounds 2 and 3 in the solid state, have
not been registered for 8. However in hydrazone 8 an absorp-
2
estimated to be equal: (ꢀH) = 1.92[(3350 − 3200) − 40];
−
1
−
1
tion in the region at ∼3100 cm is observed. Probably, the
ZN–C(O)-conformer of compound 8 in the solid state along with
the usual intermolecular hydrogen bond forms also hydrogen
bonds with the N-atom of the pyridine fragment of the molecule.
The N-atom of the pyridine fragment is known as one of the
strongest proton acceptors [15]. This probably leads to an addi-
tional shift ν(NH) to lower frequencies (∼3100 cm ) for the
ZN–C(O)-conformer and the enhancement of Fermi resonance
with 2δ(NH).
−
ꢀH ≈ 14.5 kJ mol . Thus the whole energy of intermolec-
ular hydrogen bonds in the cyclic H-dimer can be deter-
−
1
mined as 14.5 × 2 = 29 kJ mol . The average energy of the
H-bond in intermolecularly bonded associates of ZN–C(O)-
conformers for 3 and 6 is obtained from the expression:
2
−1
(
ꢀH) ≈ 1.92[(3421 − 3245) − 40]; −ꢀH ≈ 16.1 kJ mol
.
−
1
One can roughly estimate the share of the ZN–C(O)- and
EN–C(O)-forms in solution by the intensity ratio of the ν(NH)
absorption bands. Thus, the ratio of ZN–C(O)/EN–C(O) at a con-
−
4
This conclusion is confirmed by spectra in CCl4 solution.
centration of ≈10 M was determined as follows: hydrazide 2–
−
1
Therein the intensity of the peak at 3103 cm is step-by-step
1
–
00/0%; 3 – 66%/34%; 4 – 69/31%; 5 – 63/37%; 6 – 78/22%; 7
64/36%; 8 – 75/25%; 9 – 40/60%.
free
decreased with dilution and, as in 4, a ν (NH) doublet appears:
onepeakat3430 cm assignedtothe ZN–C(O)-conformer(more
intense for diluted solution) and another one at 3347 cm
assigned to the EN–C(O)-conformer. Additionally also a doublet
for ν(C O) at 1720 cm /1703 cm appears. In more con-
−
1
−
1
4. Conclusion
−
1
−1
centrated solution a small peak of the cyclic H-dimer with a
maximum at 3211 cm can be noted.
A new series of 4-tert-butylphenoxyacetylhydrazones has
been synthesized by reaction of 4-tert-butylphenoxyacetylhy-
drazide with aromatic aldehydes and acetone. Characteristic
spectral parameters and structural peculiarities of the inves-
tigated molecules have been determined by means of X-ray
analysis and IR spectroscopy. It was found that in solid state and
CCl4 solution 4-tert-butylphenoxyacetylhydrazide exists only
as a ZN–C(O)-conformer. However its hydrazone derivatives in
solid state exist as EN–C(O) or ZN–C(O)-form as well as a mixture
of these conformers. The EN–C(O)-conformer of 4-tert-butyl-
phenoxyacetylhydrazone of salicylic aldehyde has intramolec-
−
1
Unexpectedly, for hydrazone 9, containing 2-pyridine frag-
−
1
ment, only one absorption band with a maximum at 3084 cm
in solid is observed in the region of ν(NH) in contrast to 2–8
Fig. 3, 9). This band is broadened, as it usually happens for
(
hydrogen bonded XH groups, and, as in the previous case for
compound 4, 5, 7 and 8, it overlaps with the aromatic ν( CH)
absorption but to a greater degree. The additional peaks in the
−
1
region of ∼1550 cm , which could be assigned to δ(NH) in the
ZN-C(O)-structure, cannot be observed except for νPh and νPy
−
1
. . .
−1
(
1606, 1586 and 1564 cm ). The peak of ν(C O) has maxi-
ular H-bonds OH N (−ꢀH = ∼30 kJ mol ), which do not
hinder the formation of cyclic hydrogen bonded dimers. The
ZN–C(O)-conformer of 4-tert-butylphenoxyacetylhydrazide and
−
1
mum at 1705 cm and is symmetric. Therefore one can suppose
that the pyridine acceptor dominates in the NH proton bonding
in hydrazone 9. The lower frequency absorption bands of the
multiple bonds of the pyridine fragments—1598 cm (8) and
586 cm (9) also support this statement. It can be clearly seen
4-tert-butylphenoxyacetylhydrazone of 4-nitrobenzaldehyde in
−
1
. . .
solid state has an intramolecular hydrogen bond of the NH O
−1
1
type between the amide hydrogen atom and the oxygen atom
of the phenoxy group. The presence of this intramolecular bond
is probably the reason for the predominance of the ZN–C(O)-
conformers in dilute CCl4 solution in almost all investigated
hydrazones. The energy of the intermolecular hydrogen bond
in the cyclic H-dimers of the EN-C(O)-conformers and asso-
that EN–C(O)-conformers form cyclic H-dimers, in which the NH
groups are involved in probably bifurcated H-bonds with partic-
ipation of the nitrogen atom of the pyridine fragments.
In CCl4 solution of hydrazone 9 the absorption in the region
−1
of 3084 cm
gradually decreases; a weak band of ν(NH)

S.N. Podyachev et al. / Spectrochimica Acta Part A 66 (2007) 250–261
[4] U. Ragnarsson, Chem. Soc. Rev. 30 (2001) 205.
261
ciates of the ZN–C(O)-conformers has been estimated as 14.5
and 16.1 kJ mol , respectively.
−
1
[
[
5] G. Palla, G. Fredieri, P. Domiano, Tetrahedron 42 (1986) 3649.
6] U. Himmerlreich, F. Tschwatschal, R. Borsdorf, Monatsh. Chem. 124
1993) 1041.
7] E.A. Alekseeva, V.A. Bacherikov, A.I. Gren, A.V. Mazepa, V.Y.
Gorbatyuk, S.P. Krasnoshchekaya, Russ. J. Org. Chem. 36 (2000)
1321.
The diagnostically important IR spectral criteria required for
the conformational analysis of acethylhydrazones have been
established.
(
[
[
Thus, the nature of the substituent in the acetylhydrazone
fragment of the molecules determines the character of hydrogen
bonds, the conformational properties and characteristic spectral
parameters of the investigated hydrazones.
8] S.N. Podyachev, B.I. Buzykin, D.V. Osyanina, V.V. Syakaev, S.N.
Sudakova, I.A. Litvinov, R.R. Shagidullin, L.V. Avvakumova, W.D.
Habicher, A.I. Konovalov, X International Seminar on Inclusion Com-
pounds Book of Abstract, Kazan, Russia, 2005, p. 132.
[
9] A. Yamada, T. Murase, K. Kikukawa, T. Arimura, S. Shinkai, J. Chem.
Soc. Perkin Trans. 2 5 (1991) 793.
Acknowledgements
[
[
[
10] S.S. Tiwari, A.K. Sen Gupta, K. Jaswant, J. Indian Chem. Soc. 51 (1974)
02.
11] L.H. Straver, A.J. Schierbeek, MOLEN. Structure Determination System.
Program Description, Nonius B.V., Delft, 1994. V. 1.
12] G.M. Sheldrick, SHELX-97 (Release 97-2). Programs for Crystal Structure
Analysis, University of G o¨ ttingen, Germany, 1997.
13] A.L. Spek, Acta Cryst. (A) 46 (1990) 34.
4
This work was supported by the Russian Fund for Basic
Research (grants 04-03-32992a, 04-03-32156aofi a, 04-03-
3
2156a) and a grant of the Academy of Science of the Republic
of Tatarstan (07-7.1-264).
[
[
14] E. Titov, A. Grekov, I. Rybachenkov, V. Shevchenko, Teor. Eksp. Khim. 4
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