1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-pentane-2,4-dione - Synthesis, spectroscopic, theoretical and structural elucidation

Article abstract of DOI:10.1002/poc.1266

1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-pentane-2,4-dione is spectroscopically and structurally elucidated by means of linear-polarized IR spectroscopy (IR-LD) of oriented solids as a colloidal suspension in nematic liquid crystal. Structural info

Full text of DOI:10.1002/poc.1266

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2007; 20: 1108–1113
Published online 26 September 2007 in Wiley InterScience
(
www.interscience.wiley.com) DOI: 10.1002/poc.1266
1
,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-
pentane-2,4-dione—synthesis, spectroscopic,
theoretical and structural elucidation
Tsonko M. Kolev1,2* and Plamen Angelov1
1
Department of Organic Chemistry, Plovdiv University, 24 Tzar Assen Street, Plovdiv, Bulgaria
Institute of Organic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Sofia, Bulgaria
2
Received 29 March 2007; revised 10 August 2007; accepted 11 August 2007
ABSTRACT: 1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-pentane-2,4-dione is spectroscopically and structu-
rally elucidated by means of linear-polarized IR spectroscopy (IR-LD) of oriented solids as a colloidal suspension in
nematic liquid crystal. Structural information and IR-spectroscopic assignment are supported by quantum chemical
ꢀ
ꢀ
calculations at MP2 and B3LYP level of theory and 6-311þþG basis set. The geometry is characterized with an
.
. .
˚
inramolecular hydrogen bond of NH O ¼¼ C with length of 2.526 A and a NHO angle of 140.5(1)8. The
NH—C(CH )C ¼¼ C—C ¼¼ O(CH ) fragment is nearly flat with a maximal deviation of total planarity of 10.48.
3
3
Copyright # 2007 John Wiley & Sons, Ltd.
KEYWORDS: 1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-pentane-2,4-dione; IR-LD spectroscopy; solid-state;
1
colloidal suspension in nematic liquid crystal; quantum chemical calculations; H-NMR
5
by Gilli and co-authors to explain the abnormally strong
INTRODUCTION
.
..
intramolecular NH O ¼¼ C bonds formed in b-enaminones
and related compounds. This type of intramolecular
H-bond and the possible rotamers and tautomers make the
title compound an interesting object for LD-IR studies.
1
Enaminones, as defined by Greenhill are compounds that
combine the ambient electrophilicity of enones with the
ambient nucleophilicity of enamines. For this reason their
chemical reactivates are very diverse and they have found
2–4
numerous synthetic applications.
The potential bio-
logical activity motivates structural and spectroscopic
studies of these derivatives. Structural and theoretical
EXPERIMENTAL
Synthesis
5–7
studies on enaminones have been published previously,
but to the best of our knowledge linear dichroic infrared
IR-LD) spectroscopy has been used only on one object,
-ethylamino-2-(4-nitro-benzoyl)-but-2-enoic acid phe-
(
4-Phenethylamino-pent-3-en-2-one (2). Acetyla-
cetone (0.300 g, 3 mmol) was added to a solution of
2-phenylethyl amine (0.364 g, 3 mmol) in DCM (10 ml).
Then Na SO (1 g) was added and the mixture was stirred
3
7
nylamide, which belongs to this interesting class of
organic compounds. In this paper we describe the appli-
cation of the solid-state LD-IR technique for structural
investigation of 1,1,1-trichloro-3-(1-phenethylamino-
ethylidene)-pentane-2,4-dione (Scheme 1) – an enam-
inone with interesting structural features. This compound
was synthesized as a part of synthetic methodology
2
4
overnight at 25 8C. After that, the sodium sulfate was
filtered off and the solvent was removed by distillation. 2
was isolated as 0.597 g of yellow oil (98%).
1
H-NMR d (ppm) ¼ 1.83 (s, 3H), 2.01 (s, 3H), 2.85 (t,
2H, J ¼ 7.0 Hz), 3.43–3.51 (m, 2H), 5.01 (s, 1H), 7.25–
8
project according to Scheme 2. The compound studied is
7.61 (m, 5H) and 10.85 (Br, 1H).
an example of resonance assisted hydrogen bonding,
which is a synergistic interplay between p-delocalization
and hydrogen bond strengthening originally introduced
1
,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-
pentane-2,4-dione (3). To a cooled (0–5 8C) and
stirred solution of the enaminone 2 (0.203 g, 1 mmol)
and Et N (0.14 ml, 1 mmol) in CH Cl (5 ml) was slowly
added trichloroacetyl chloride (1 mmol). The reaction
mixture was allowed to reach room temperature and the
*
Correspondence to: T. M. Kolev, Institute of Organic Chemistry,
Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Building 9,
113 Sofia, Bulgaria.
3
2
2
1
E-mail: kolev@orgchm.bas.bg
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 1108–1113

1
,1,1-TRICHLORO-3-(1-PHENETHYLAMINO-ETHYLIDENE)-PENTANE-2,4-DIONE— STRUCTURE AND PROPERTIES 1109
experimental IR-spectroscopic band assignment and
especially for obtaining of structural information has
been demonstrated in series of organic systems and metal
1
4
15
16
complexes, Cu(II) complexes, polymorphs, codeine
1
7
derivatives, peptides their Au(III) complexes, hydro-
18,19
chlorides and hydrogensquarates.
IR-LD spectroscopy
and the interpretation of the linear-polarized IR spectra
20–23
by so-called reducing-difference procedure
Scheme 1. Chemical diagram of 1,1,1-Trichloro-3-(1-
phenethylamino-ethylidene)-pentane-2,4-dione
are
1
0–23
described.
1
H-NMR measurements, referred to TMS, were made at
98 K with a Bruker DRX-250 spectrometer using 5 mm
2
tubes and CDCl as solvent.
Quantum chemical calculations were performed with
stirring continued overnight. The mixture was then
washed with water (200 ml), dried (Na SO ) and the
solvent was removed on a rotavap. Column chromatog-
3
2
4
24
GAUSSIAN 98 program package. The visualization is
achieved by ChemCraft program. The theoretical
9
approximation approach has been described. The geo-
25
raphy on neutral alumina in Et O: petroleum gave 3 as
2
yellow crystals (0.279 g, 80%, m.p. 70–71 8C).
1
H-NMR d (ppm) ¼ 1.88 (s, 3H), 2.22 (s, 3H), 2.95 (t,
metry of the studied compound was optimized at two
levels of theory: second-order Moller–Pleset perturbation
theory (MP2) and density functional theory (DFT) using
2
and 12.03 (Br,1H).
H, J ¼ 6.8 Hz), 3.56–3.70 (m, 2H), 7.25–7.50 (m, 5H)
ꢀꢀ
6-311þþG basis set. DFT method employed is B3LYP,
which combines Becke’s three-parameter non-local
exchange functional with the correlation function of
Lee, Yang and Parr. Molecular geometries of the studied
species were fully optimized by the force gradient method
using Bernys’ algorithm. For every structure the
stationary points found on the molecule potential energy
hyper surface were characterized using standard analyti-
cal harmonic vibrational analysis. The absence of
imaginary frequencies, as well as of negative eigenvalues
of the second-derivative matrix, confirmed that the
stationary points correspond to minima of the potential
energy hyper surfaces. The calculated vibrational
frequencies and infrared intensities were checked for
agreement with the experimental data. The DFT method
provides more accurate vibrational data, as the calculated
Materials and methods
ꢁ1
4
000–400 cm solid-state IR spectra were recorded on a
ꢁ1
Bruker 113 v FT-IR spectrometer (resolution 2 cm , 250
scans) equipped with a Specac wire-grid polarizer. Oriented
solid samples were obtained by the new method
applied in linear-polarized IR spectroscopy, i.e. a colloidal
9,10
0
suspension in a nematic liquid crystal of the 4 -cyano-
0
4
-alkylbicyclohexyl type (ZLI 1695, Merck). The
validation of the method, based on a colloidal suspension
in nematic liquid crystal for accuracy, precision and the
influence of the liquid crystal medium on peak positions
and integral absorbances of the guest molecule bands
11
ꢁ
1
ꢁ1
have been presented. Optimization of experimental
conditions and an experimental design for quantitative
evaluation of the impact of four input factors has been
standard deviations are 10 cm (B3LYP) and 13 cm
(MP2), respectively. For this reason the B3LYP/
ꢀ
ꢀ
6
-311þþG
data are presented, where for better
11,12
presented.
The number of scans, the rubbing-out of
correspondence between the experimental and theoretical
values, a modification of the results using the empirical
scaling factor 0.9614 is done.
KBr-pellets, the amount of studied compounds included
in the liquid crystal medium and the ratios of Lorentzian
to Gaussian peak functions in the curve fitting procedure
on the spectroscopic signal at five different frequencies
11,12
have been studied.
The nature and balance of the
forces in the nematic liquid crystal suspension system, the
mathematical model for their clearance, morphology of
the suspended particles and the influence of the space
system types on the degree of orientation, i.e., ordering
RESULTS AND DISCUSSION
Theoretical data
13
parameter have been shown using 5 liquid crystals and
5 compounds. Applicability of the last approach for
Molecular structures. According to the quantum
chemical calculation only one potential energy hyper
1
Scheme 2. Reaction scheme
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 1108–1113
DOI: 10.1002/poc

1
110
T. M. KOLEV AND P. ANGELOV
Table 1. Calculated
ꢀ
ꢀ
(MP2/6-311þþG )
geometry
˚
parameters as bond lengths (A) and angles (8) of compound
studied using atom numbering of Scheme 3
Name definition
Values
Name definition
Values
R(1,2)
R(1,3)
R(2,7)
R(3,4)
R(4,5)
R(4,6)
R(5,7)
R(6,8)
R(8,9)
R(9,10)
R(10,11)
R(10,12)
R(11,13)
R(11,14)
R(13,17)
R(13,18)
R(14,15)
R(14,16)
R(18,19)
R(18,20)
R(18,21)
—
1.397
1.396
1.397
1.401
1.401
1.518
1.396
1.547
1.475
1.333
1.417
1.512
1.451
1.465
1.234
1.590
1.520
1.268
1.869
1.866
1.879
—
A(2,1,3)
A(1,2,7)
A(1,3,4)
A(3,4,5)
A(3,4,6)
A(5,4,6)
A(4,5,7)
A(4,6,8)
120.1 (8)
119.7 (1)
120.6 (2)
118.8 (8)
120.5 (7)
120.5 (4)
120.6 (0)
109.9 (5)
120.0 (9)
109.5(3)
125.7 (8)
120.2 (6)
116.9 (3)
122.4 (6)
123.2 (1)
118.9 (5)
117.6 (7)
126.7 (3)
118.7 (1)
113.9 (5)
119.7 (4)
121.9 (3)
118.3 (2)
107.0 (9)
116.8 (5)
109.2 (8)
106.9 (4)
107.1 (6)
109.0 (8)
A(2,7,5)
A(6,8,9)
A(8,9,10)
Scheme 3.
surface minimum of the studied compound is obtained
Scheme 3). When energy is corrected by zero point
vibration energy contribution the form shows an E of
A(9,10,11)
A(9,10,12)
A(11,10,12)
A(10,11,13)
A(10,11,14)
A(13,11,14)
A(11,13,17)
A(11,13,18)
A(17,13,18)
A(11,14,15)
A(11,14,16)
A(15,14,16)
A(13,18,19)
A(13,18,20)
A(13,18,21)
A(19,18,20)
A(19,18,21)
A(20,18,21)
(
rel
ꢁ
1
1
.0 kJ mol . The predicted geometry shows an intramo-
.
. .
lecular hydrogen bond of NH O ¼¼ C type (Scheme 3)
˚
with bond length of 2.526 A and a NHO angle of
140.5(1)8. The computed geometry parameters, i.e., bond
lengths and angles are collected in Table 1. The
NH—C(CH )C ¼¼ C—C ¼¼ O(CH ) fragment is nearly flat
3
3
with a maximal deviation of total planarity of 10.48, thus
proposing a co-linear orientation of the out-of-plane (o.p.)
transition moments in the frame of the fragment.
However, the direction of the aromatic o.p. transition
moments are near to perpendicular oriented due to the
corresponding space disposition of both moieties of
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1
00.38. Total dipole moment of 6.078 Debye is calculated
Dihedral angles (8)
and the distribution of the group charges is presented in
Scheme 4.
D(3,1,2,7)
D(2,1,3,4)
D(1,2,7,5)
D(1,3,4,5)
D(1,3,4,6)
D(3,4,5,7)
D(6,4,5,7)
D(3,4,6,8)
D(5,4,6,8)
D(4,5,7,2)
D(4,6,8,9)
D(6,8,9,10)
D(8,9,10,11)
D(8,9,10,12)
D(9,10,11,13)
D(9,10,11,14)
D(12,10,11,13)
0.2
0.1
0.2
0.0
177.4
0.0
177.4
88.7
88.6
0.1
179.9
176.2
172.3
0.6
174.4
10.4
13.0
D(12,10,11,14)
162.1
135.4
54.1
39.7
130.6
170.9
10.0
4.5
174.4
123.0
3.2
121.1
48.5
168.3
67.2
—
D(10,11,13,17)
D(10,11,13,18)
D(14,11,13,17)
D(14,11,13,18)
D(10,11,14,15)
D(10,11,14,16)
D(13,11,14,15)
D(13,11,14,16)
D(11,13,18,19)
D(11,13,18,20)
D(11,13,18,21)
D(17,13,18,19)
D(17,13,18,20)
D(17,13,18,21)
—
Vibrational analysis. The theoretical IR spectrum of
the studied compound in gas phase is presented in Fig. 1.
Table 2 contains the IR-characteristic bands and their
assignment. Comparison between the calculated spec-
trum and the experimental one (Fig. 1, Table 2) in solid
state is made. The predicted IR spectrum is characterized
with the highest absorption maximum at 3021 cm
assigned to 20a stretching in-plane (i.p.) mode of
aromatic system. The bands in 3100–2950 cm corre-
spond to other i.p. maxima of aromatic fragments, and the
asymmetric and symmetric stretching peaks of CH
ꢁ
1
ꢁ
1
3
—
—
ꢁ
1
and CH groups are obtained in 2950–2800 cm region.
2
The 1700–1400 cm region shows the highest frequency
ꢁ1
ꢁ1
and intensive peaks at 1699 and 1627 cm belonging to
n
the intermolecular interactions. The obtained differences
between theoretically and experimentally obtained values
of 2 cm indicate a good theoretical approximation of
the presented approach.
peaks of C ¼¼ O(Cl ) and C ¼¼ O(CH ) groups. Both
C ¼¼ O
3
3
ꢁ1
maxima are with mixed character with participation of
dNH motion (Scheme 5A and B). Other maxima are
assigned as i.p. transition moments of benzene ring
with A and B symmetry class, which are noted as 8a,
1
2
26,27
8
b, 19a, 19b in Wilson’s nomenclature
as well as to
)
Experimental conventional and
linear-polarized IR data
stretching mode of the double C ¼¼ C bond (n
C ¼¼ C
(
benzene ring are obtained at 725 cm (11-gCH) and
Table 2). B -out-of-plane (o.p.) peaks of m-substituted
1
ꢁ1
The experimental IR-spectroscopic pattern is characteri-
zed with a strong overlapping, and the adequate
ꢁ
1
98 cm (4-g ). These maxima are uninfluenced from
6
Ar
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 1108–1113
DOI: 10.1002/poc

1
,1,1-TRICHLORO-3-(1-PHENETHYLAMINO-ETHYLIDENE)-PENTANE-2,4-DIONE— STRUCTURE AND PROPERTIES 1111
Scheme 4. Calculated group charges
Scheme 5. Visualization of selected transition moment
directions in 1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-
pentane-2,4-dione
reducing-difference procedure for their interpretation.
For the assignment of modes of both phenyl fragments is
26,27
used the Wilson’s notation.
The difference IR-LD
spectrum (Fig. 2) of the compound showed good
orientation of the crystalline sample in the liquid crystal
medium and resulted in adequate conclusions using the
criteria marked. All the obtained data of mono-
substituted phenyl fragment correlated well with data for
Figure 1. Theoretical IR spectrum of 1,1,1-Trichloro-3-
11,12
(
1-phenethylamino-ethylidene)-pentane-2,4-dione
2
7
interpretation of the IR-spectroscopic bands is achieved
by preliminary procedures of deconvolution and curve
fitting. The experimental confirmation of IR-characteristic
band assignment (Table 2) is achieved by means of
linear-polarized IR spectra and the application of
other compounds containing the discussed fragments.
ꢁ
1
The 3500–3100 cm IR-spectroscopic region is charac-
ꢁ
1
terized with a broad absorption band at 3413 cm
belonging to nNH, affected by moderate interactions. The
ꢁ1
theoretical value of 3466 cm is also low frequency
ꢀ
ꢀ
Table 2. Theoretical
1
(B3LYP/6-311þþG )
and
experimental
solid-state
IR-spectroscopic
data
of
,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-pentane-2,4-dione
ꢁ
1
)
ꢁ1
n (cm )
n (cm
Assignment
Theoretical
Experimental
Assignment
Theoretical
Experimental
nNH
n
3466
1699
1627
1613
1600
1590
1509
1444
3413
1695
1600
1610
1598
1583
1507
1447
3 (B2)
1 (A1)
1255
1000
811
666
660
725
698
—
1254
1000
823
671
698
727
700
—
C ¼¼ O(CCl3)
n
g
g
C ¼¼ O(CH3)
C ¼¼ O(Cl3)
8
8
n
a (A )
1
b (B2)
C ¼¼ O(CH3)
NH
g
11 (B1)
4 (B1)
—
C ¼¼ C
1
9a (A )
1
9b (B2)
1
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 1108–1113
DOI: 10.1002/poc

1
112
T. M. KOLEV AND P. ANGELOV
shifted due to the intramolecular interaction. In contrast to
.
typical enolic form like in curcumine, where the OH O
. .
2
8
˚
bond is extremely short with bond length of 2.440 A and
no n IR band presents in the IR spectrum in solid
OH
29
. . .
state, here a moderate NH O ¼¼ C bond affects the peak
position similarly to b-enaminones described by Gilli and
5
co-authors. The presence of only one n band suggests
the stabilization of only one form, i.e. with
NH
.
N—H O hydrogen bond.
. .
The application of reducing-difference procedure to
polarized IR-LD spectra resulted in: (i) elimination of the
ꢁ1
bands at 727 and 700 cm (Fig. 3(2)) belonging to
1-gCH and 4-gAr o.p. modes (B ) of m-substituted
benzene in same dichroic ratio, confirming their shown
1
1
ꢁ1
origin. However the intensive peak at 798 cm
negative oriented. (ii) Its elimination (Fig. 3(3)) resulted
is
ꢁ1
in a disappearance of the peak at 671 cm , suggesting an
origin from gNH and g motion. This result is in
C ¼¼ O(CH3)
accordance with the theoretically predicted geometry in
Scheme 3. (iii) The reduction of the highest frequency
ꢁ
1
Figure 2. Non-polarized IR (1) and difference (2) IR-LD
spectrum of 1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-
pentane-2,4-dione
peaks in 1700–1500 cm region in different dichroic
ratio also supported the proposed structure of the studied
compound.
CONCLUSION
The experimental polarized IR data have shown that
heteronuclear resonance assisted intramolecular hydro-
gen bonding is preferred rather than intermolecular inter-
actions in solid state. It is shown that in contrast to typical
.
. .
enolic form like in curcumine, where the OH O bond is
2
8
˚
extremely short with bond length of 2.440 A and no n
OH
2
IR band presents in the IR spectrum in solid state, here a
9
.
. .
moderate NH O ¼¼ C bond affects the peak position
similarly to b-enaminones. The presence of only one n
NH
band suggests the stabilization of only one form, i.e. with
.
. .
N-H O hydrogen bond. The conclusions drawn are
corroborated by extended DFT and ab initio MP2
quantum chemical calculations at B3LYP and MP2
levels of theory and 6-31þþGꢀꢀ basis set.
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,1,1-TRICHLORO-3-(1-PHENETHYLAMINO-ETHYLIDENE)-PENTANE-2,4-DIONE— STRUCTURE AND PROPERTIES 1113
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