Reaction of 2-acetyl-indane-1,3-dione with aniline - Schiff base or enamine?

Article abstract of DOI:10.1016/S0022-2860(03)00175-3

The structure of the product of the condensation reaction between 2-acetylindan-1,3-dione and aniline has been investigated in the gas phase, solution and solid state using a combination of quantum-chemical calculations, NMR and IR spectroscopies, and X-ray crystallography. Energetics of both isomers and all tautomers of the product of the reaction are predicted at HF/3-21G//HF/3-21G and HF/6-31G**//HF/3-21G levels. Geometric optimizations at HF/6-31G** level are also performed for favorable tautomers. Quantum-chemical calculations indicate that the enamine isomer, 2-[1-(N-phenylamino)-1-ethylidene]-indane-1,3-dione is favored. This is confirmed by ¹³C NMR spectroscopy in non-polar and polar solvents, and in the solid state by X-ray crystallography.

Full text of DOI:10.1016/S0022-2860(03)00175-3

Journal of Molecular Structure 654 (2003) 11–20
www.elsevier.com/locate/molstruc
Reaction of 2-acetyl-indane-1,3-dione with aniline - Schiff
base or enamine?
a,
a
b
a
*
´
Venelin Enchev , Galya Ivanova , Gordana Pavlovic , Marin Rogojerov ,
Anife Ahmedovac, Mariana Mitewac
aInstitute of Organic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
bFaculty of Textile Technology, University of Zagreb, Pierrotijeva 6, HR-10000 Zagreb, Croatia
cDepartment of Chemistry, Sofia University ‘St Kliment Ohridski’, 1126 Sofia, Bulgaria
Received 11 December 2002; accepted 7 February 2003
Abstract
The structure of the product of the condensation reaction between 2-acetylindan-1,3-dione and aniline has been investigated
in the gas phase, solution and solid state using a combination of quantum-chemical calculations, NMR and IR spectroscopies,
and X-ray crystallography. Energetics of both isomers and all tautomers of the product of the reaction are predicted at HF/3-
21G//HF/3-21G and HF/6-31G**//HF/3-21G levels. Geometric optimizations at HF/6-31G** level are also performed for
favorable tautomers. Quantum-chemical calculations indicate that the enamine isomer, 2-[1-(N-phenylamino)-1-ethylidene]-
indane-1,3-dione is favored. This is confirmed by 13C NMR spectroscopy in non-polar and polar solvents, and in the solid state
by X-ray crystallography.
q 2003 Elsevier Science B.V. All rights reserved.
Keywords: 2-Acetyl-indane-1,3-dione; Enamine; Ab initio; NMR; X-ray
1. Introduction
bases is predominately shifted to the oxoenamino
(NH) tautomer [3–6]. The type of the dominant
tautomer is not dependent on either the stereochem-
istry of the molecule or on the sort of the substituent
at the nitrogen atom, but on the kind of aldehyde used.
The oxoenamino tautomer is always observed when
the Schiff base is derived from 2-hydroxy naphtha-
laldehyde and aniline.
The ortho-hydroxy Schiff bases derived from
salicylaldehyde and related aromatic aldehydes form
intramolecular hydrogen bonds, which reveal very
interesting photo - and thermochromic properties [1],
and biological activity [2]. In most cases the
hydroxyimino (OH) tautomer is more stable. There
are, however, IR and NMR investigations that suggest
that the equilibrium in some ortho-hydroxy Schiff
Recently [7,8] we reported experimental and
theoretical studies of excited state intramolecular
proton transfer in 2-acetyl-indane-1,3-dione (2AID).
It was found that 2AID exists as the 2-(1-hydro-
xyethylidene)indane-1,3-dione tautomer [7,9]. 2AID
*
Corresponding author. Fax: þ359-2-700225.
E-mail address: venelin@orgchm.bas.bg (V. Enchev).
0022-2860/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-2860(03)00175-3

12
V. Enchev et al. / Journal of Molecular Structure 654 (2003) 11–20
should give a Schiff base as the product of the
condensation reaction with aniline as has been
reported [10]. However, Dudek and Dudek [11]
established that the reaction of 2-acetyldimedon
with anilin yielded an enamine as a product. We
have reinvestigated the structure of this product by
means of ab initio quantum-chemical calculations,
NMR and IR spectroscopies, and X-ray crystal-
lography. We found that the condensation occurs at
the 1-hydroxyethylidene moiety and the product of
the reaction is 2-[1-(N-phenylamino)-1-ethylidene]-
indane-1,3-dione.
nematic liquid crystal ZLI-1695 (Merck, mixture of 4-
cyano-40-alkylbicyclohexyls) and isotropic solvent
CCl4 were investigated. The isotropic solution was
recorded in an 18 mm KBr cell. The polarized IR
spectra of the anisotropic solution were measured
using a 25 mm KBr cell whose windows were rubbed
and polished in one direction. The polarized spectra
were recorded parallel AkðnÞ and perpendicular A’ðnÞ
to the rubbing direction. The reduced IR linear
dichroic spectra were produced by the stepwise
reduction procedure primarily suggested by Tulstrup
and Eggers [12]. It is based on the interactive
subtraction of both polarized spectra: AkðnÞ 2
c·A’ðnÞ: The step variation of c in the difference
makes it possible to eliminate simultaneously bands
with the same polarization. The parameter m then
becomes equal to the dichroic ratio Ru ðu ¼ x; y; zÞ of
the eliminated bands. The basic application of the
reduced linear dichroic spectra refers to the symmetry
assignment of the IR bands. Reduced spectra also
contain in principle the possibility for determination
of vibrational transition moment directions of solute
molecules.
2. Experimental
2.1. Synthesis of 2-[1-(N-phenylamino)-1-
ethylidene]-indane-1,3-dione
A mixture of 2.256 g (0.012 M) 2AID, 1.1 ml
(0.012 M) aniline and 150 ml dry benzene was
refluxed through a Dean-Stark trap for 5 h. The
mixture was then evaporated under reduced pressure
to dryness. The resulting yellow crystal residue was
purified by recrystalization from methanol. Yield
2.3. NMR measurements
1
1.26 g. (40%), yellow crystals. M.p. 139–140 8C; H
NMR (250 MHz): CDCl3, d ¼ 12.27 (br. s, 1H, NH),
7.6–7.7 (m, 4H), 7.2–7.4 (m, 5H), 2.59 (s, 3H, CH3);
CD3CN, d ¼ 12.23 (br. s, 1H, NH), 7.63 (br. s, 4H),
7.3–7.5 (m, 5H), 2.52 (s, 3H, CH3); DMSO-d6,
d ¼ 12.17 (br. s, 1H, NH), 7.6–7.7 (m, 4H), 7.4–7.5
(m, 5H), 2.56 (s, 3H, CH3); CD3OD, d ¼ 7.55 (br. s,
4H), 7.2–7.4 (m, 5H), 2.48 (s, 3H, CH3); UV
(CH3CN) lmax ¼ 230.5, 295.0, 336.0 nm.
The NMR spectra were obtained on a Bruker
Avance DRX-250 spectrometer operating at 250.13
1
and 62.90 MHz for H and 13C, respectively, using a
dual 5 mm probe head. The chemical shifts are
referenced to tetramethylsilane (TMS). The measure-
ments were carried out at ambient temperature (ca.
300 K), in several solvents (CDCl3, CD3OD, CD3CN,
CD3CN þ D2O and DMSO-d6). The sample concen-
1
The deuteration of 2-[1-(N-phenylamino)-1-ethy-
lidene]-indane-1,3-dione was achieved by dissolving
of 50 mg of the compound in 1 ml chloroform and
stirring with 0.5 ml D2O. The organic phase was
separated and treated with another portion of 0.5 ml
D2O. The procedure was repeated to complete
trations 0.01–0.05 M for H and saturated solutions
for 13C NMR spectra were used. The standard Bruker
library pulse programs were used for all 1D and 2D
NMR experiments: zg, dept, noemul, cosy45,
cosydftp, noesytp, invbtp and inv4lplrnd. The typical
conditions for the 1D experiment were: 308 pulses, 1 s
relaxation delays, 16 K time domain points, zero-
filled to 32 K. Hard pulses with 908 pulse widths of
11.4 ms for 1H and 6.0 ms for 13C at a power level of
3dB below the maximum output were used. The 2D
1H/1H homonuclear correlation spectra (COSY) were
performed with a spectral width of ca 1000 Hz,
relaxation delay 2 s, mixing pulse width 458, number
of increments 256 or 512 and FT size 1 K £ 1 K. The
1
deuteration, and was monitored by H NMR.
2.2. IR measurements
IR spectra were measured on a Bruker IFS-113
FTIR spectrometer in the 4000–400 cm21 spectral
region at a resolution of 2 cm21. 7.5% Solutions of the
investigated compound and its deuterated analog in

V. Enchev et al. / Journal of Molecular Structure 654 (2003) 11–20
Table 1
13
2D 1H/13C heteronuclear multiple quantum corre-
lation (HMQC) spectra were measured with spectral
Crystal data and structure refinement for 2-[1-(N-phenylamino)-1-
widths of 1500 Hz for H and 15,000 Hz for 13C, a
relaxation delay of 1.5 s, 256 increments and an FT
1
ethylidene]-indane-1,3-dione
Empirical formula
C17H13NO2
1
size of 1 K £ 256 W. The 2D H/13C heteronuclear
Formula weight
263.28
Crystal habit and colour
Crystal size, (mm3)
Crystal system, space group
Prism, yellow
multiple bond correlation (HMBC) spectra were
1
0.30 £ 0.30 £ 0.20
Monoclinic, P21=c (No. 14)
recorded with spectral widths of 3000 Hz for H and
25,000 Hz for 13C, a relaxation delay of 1.5 s, 256
increments and an FT size of 4 K £ 256 W. The
samples for the NOE experiments were prepared by
bubbling argon through the solution for 10 min to
remove traces of oxygen. Several irradiations were
performed in one experiment with automatic cycling
through frequency lists for each multiplet (the
irradiation time was 5 s) and for the off-resonance
position. Thirty-two scans with two dummy scans for
each frequency list were acquired and then the
experiment was repeated 20 times. To the difference
FID between the on-and off-resonance irradiation free
induction decays, a line broadening of 0.5 Hz was
applied before Fourier transformation.
Unit cell dimensions
ꢀ
a=A
ꢀ
b=A
10.0685(3)
6.7344(2)
ꢀ
c=A
20.2129(6)
b=8
V=A
93.255(1)
ꢀ 3
1368.33(7)
Z
4
r
calc/Mgm23
1.278
m/mm21
F(000)
0.084
552
Temperature/K
293(2)
˚
Radiation, l(Mo Ka)/A
Diffractometer
0.71073
Nonius KappaCCD
(capillary optics)
v
Scan type
u range for data collection/8
Limiting indices
5–28
212 # h # 12, 2 8 # k # 8,
2 26 # l # 26
5703/3090 ½Rint ¼ 0:0317ꢀ/1952
2.4. Single crystal X-ray diffraction experiment
Reflections collected/
unique/observed ½I . 2sðIÞꢀ
Completeness to u/%
Absorption correction
Refinement method
The general and crystal data as well as summary
of intensity data collection and structure refinement
are listed in Table 1. The data collection was carried
out on a Nonius KappaCCD diffractometer (capil-
lary optics) at 293 K. Program Denzo-SMN was
used for data reduction [13]. A total of 159 frames
was measured at 270 s per frame at a crystal-
detector distance of 28 mm (3 sets of v scans, 1.88
rotation). Scaling was carried out, but no absorption
correction was applied. The structure was solved by
direct methods using the SHELXS program [14].
The refinement procedure, based on the least-
squares full-matrix method against all reflections,
was performed with anisotropic thermal parameters
for all non-hydrogen atoms using the program
SHELXL97 [15].
98.6
None
Full-matrix least-squares on F2
Data/restraints/parameters
3090/0/186
a,b
Final R indices ½I . 2sðIÞꢀ
R1 ¼ 0:0488; wR2 ¼ 0:1175
R1 ¼ 0:0895; wR2 ¼ 0:1401
1.009
Rindices (all data)
Goodness of fit on F2; Sc
g1; g2 in weighting schemed
Extinction coefficient, xe
0.0637, 0.1598
0.064(11)
23
˚
Drmin:;max:/e A
0.131 and 2 0.119
,0.001
ðD=sÞmax.
a
R ¼ SllFol 2 lFcll=SlFol:
b
c
d
e
wR ¼ ½SðFo2 2 Fc2Þ =SwðFo2Þ ꢀ
:
2
2 1=2
S ¼ S½wðFo2 2 Fc2Þ =ðNobs 2 NparamÞꢀ
:
2
1=2
w ¼ 1=½s2ðFo2Þ þ ½ðg1PÞ þ g2PꢀwhereP ¼ ðFo2 þ 2Fc2Þ=3:
2
Fc2 ¼ kFc½1 þ 0:001xFc2l3=sinð2uÞꢀ
where x is extinction
21=4
coefficient and k ¼ 1.09381.
The hydrogen atoms were located from the
difference Fourier maps as small positive electron
densities, and finally refined by applying a riding
map at the final stage of refinement procedure. The H
atom was located as a small positive electron density
2
3
˚
˚
model [Csp –H 0.93 A; Csp –H 0.96 A with
Uiso(H) ¼ 1.2 or 1.5 Ueq(C) for Csp2 and Csp3,
respectively]. The position of the H1N hydrogen atom
along the intramolecular O· · ·N hydrogen bond vector
was carefully checked from the difference Fourier
23
˚
˚
(0.42 e A ) and refined freely [N–H 0.90(2) A]. The
hydrogen atoms of methyl C11 group are disordered
with two positions rotated from each other by 608 with
fixed occupation factors at 0.5. These hydrogen atoms

14
V. Enchev et al. / Journal of Molecular Structure 654 (2003) 11–20
Fig. 1. Tautomeric forms of 3-(N-phenylamino)-2-acetyl-indene-1-one 1 and 2-(ethylideneaminophenyl)-indan-1,3-dione 2.
Table 2
Calculated total energies, ET; zero-point energies, ZPE (a.u.), relative total energies, DET and enthalpies DH0 (kcal/mol) at different
computational levels for the isomers and tautomers of 2-[1-(N-phenylamino)-1-ethylidene]-indane-1,3-dione, shown in Fig. 1
Species
HF/3-21G//HF/3-21G
HF/6-31G**//HF/3-
21G
HF/6-31G**//HF/6-31G**
ET
ZPE
DET
DH0
ET
DET
ET
ZPE
DET
DH0
1A1
1A2
1B
2850.739791
2850.747062
2850.731918
2850.726721
2850.723746
2850.709159
2850.756439
2850.768333
2850.737155
2850.729307
2850.713180
17.91
13.35
22.85
26.11
27.98
37.13
7.46
2855.539232
2855.542129
2855.534703
2855.533836
2855.509880
2855.508484
2855.549666
2855.559317
2855.534967
2855.535194
2855.509431
12.60
10.78
15.44
15.99
31.02
31.90
6.06
0.279523
12.64
2855.546450
0.277498
9.28
9.44
1C
1D
1E
1F
0.280385
0.280793
0.279448
7.23
0.00
2855.553474
2855.561246
2855.539861
0.276729
0.277227
0.276710
4.88
0.00
4.60
0.00
2A
2B
0.00
0.00
19.56
24.49
34.61
18.25
15.28
15.13
31.30
13.42
13.12
2C
2D

V. Enchev et al. / Journal of Molecular Structure 654 (2003) 11–20
15
positions were generated using the SHELXL97 HFIX
123 instruction.
relative and total energies of isolated molecules are
given in Table 2.
At all levels of calculation (Table 2) 2-[1-(N-
phenylamino)-1-ethylidene]-indane-1,3-dione, 2A, is
predicted as the most stable. The next stable structure
in energy is 3-(N-phenylamino)-2-acetyl-indene-1-
one, 1F. The difference in energy is 7.46 and
4.88 kcal/mol calculated at HF/3-21G and HF/
6-31G** levels, respectively. When ZPE correction
is taken into account, i.e. DH0; these differences are
7.23 and 4.60 kcal/mol, respectively. The solvent
effect does not lead to substantial changes in relative
energies. The energy difference between 1F and 2A
was calculated to be 4.80, 4.37, 3.87 and 3.41 kcal/
mol in ethanol, chloroform, water and dimethylsulf-
oxide, respectively. The structure 1A1, which Il’ina
and Tarasevich [10] suggest is 12.60 kcal/mol (at HF/
6-31G**//HF/3-21G level) higher in energy than the
most stable one, 2A (Table 2).
The calculated structure of 2A is shown on Fig. 2(b)
and selected bond distances and angles are listed in
Table 3. It was found that the molecule is non-planar
and the torsional angle C10–N–C12–C13 (Fig. 2(b)
and Table 3) was predicted to be 90.58 and 90.428 at
HF/3-21G and HF/6-31G** levels, respectively.
The apparent contradiction between our theoretical
results and the previously suggested structure [10]
was the reason why a reinvestigation of the structure
of the product of the reaction between 2AID and
aniline was carried out. For comparative purpose we
carried out the synthesis using two procedures. Firstly,
using the method described by Il’ina and Tarasevich
[10] and secondly using the method described in
Section 2. The spectral data (IR, NMR) were used to
confirm the identity of the products of both reactions.
In the 1H NMR spectra in CDCl3 of the products from
both reactions we observed resonance peaks in the
aromatic spectral region (7.2–7.7 ppm), at 2.59 ppm
for the methyl group and 12.27 ppm for the proton of
the imino group. The assignment for the resonance
peak at 12.27 ppm is in disagreement with the
published data [10], where it was assigned to the
proton of hydroxyl group. The NOE measurements of
the compound showed an enhancement of the
resonances of NH (1%) and aromatic (H13 and
H17) protons (2%), when the methyl protons were
irradiated. The experimental NOE interactions
were qualitatively observed as cross-peaks on
Publication material and molecular graphics were
generated using the PLATON98 program [16].
2.5. Quantum-chemical calculations
Geometric structures of all isomers and tautomers
were optimized at the HF/3-21G level in C1
symmetry. The gradient optimizations were termi-
nated when the gradient value over all the optimized
parameters was reduced to 1.1024 Hartree Bohr21
.
Single-point calculations were then carried out at
the HF/6-31G**//HF/3-21G level. Selected species
were again reoptimized at the HF/6-31G** level. In
order to characterize the stationary points as local
minima and to evaluate the zero-point vibrational
energy (ZPE) the harmonic vibrational frequencies
were calculated at the same level of theory using a
numerical derivative procedure. The ZPEs were
scaled by a correction factor of 0.893. The effect of
solvent on the relative stabilities of the tautomers
was studied using the polarized continuum model
(PCM) proposed by Tomasi et al. [17]. In our
investigations only the electrostatic contributions
were taken into account. The calculations were
carried out using the GAMESS program [18].
The NMR nuclear shieldings of 2-[1-(N-phenyla-
mino)-1-ethylene]-indane-1,3-dione were calculated
at the HF/6-31 þ G* level using the GIAO [19,20]
method and HF/6-31G** optimized geometry. For
this calculation the GAUSSIAN 98 program [21] was
used. The structure of Si(CH3)4 (as standard) was also
optimized at the HF/6-31G** level.
3. Results and discussion
The condensation reaction of 2AID with aniline
should give a Schiff base or enamine. The possible
isomeric (1 and 2) and their tautomeric forms (1A–1F
and 2A–2D) are shown on Fig. 1. According to [10]
the product of the reaction is the tautomer 1A1
(Fig. 1). In order to obtain an insight into the
relative stabilities of the possible species, ab initio
quantum-chemical calculations at HF/3-21G and HF/
6-31G** levels were carried out. The calculated

16
V. Enchev et al. / Journal of Molecular Structure 654 (2003) 11–20
Fig. 2. Structure of 2-(ethylideneaminophenyl)-indan-1,3-dione, 2A: (a) The ORTEP drawing of the X-ray molecular structure of the both
conformers of 2A with the atom numbering scheme. Displacement ellipsoids are shown at the 50% probability level. (b) ab initio HF/6-31G**
calculated structure.
the two-dimensional NOESY spectrum. These data
indicate that the methyl protons and NH as well as
H13 and H17 are in close proximity.
assignment was facilitated by analysis of the HMQC
and HMBC spectra, which provide one and multiple
1
bond H/13C connectivities. The changes in the 13C
The 13C NMR data as well as those calculated by
the GIAO method at the ab initio HF/6-31 þ G* level
are listed in Table 4. The 13C NMR chemical shifts
chemical shifts caused by the substitution of the imino
proton by deuterium (deuterium isotope effects, DIE)
have been investigated and the results are presented in

V. Enchev et al. / Journal of Molecular Structure 654 (2003) 11–20
17
Table 3
˚
Selected bond lengths (A), bond angles and torsion angles (8) for 2-[1-(N-phenylamino)-1-ethylene]-indane-1,3-dione, derived from X-ray
crystallography and ab initio (HF/3-21G and HF/6-31G** level) calculations. Estimated standard deviations are given in parentheses. For
numbering of the atoms see Fig. 2
Parameter
X-ray
HF/3-21G
HF/6-31G**
Parameter
X-ray
HF/3-21G
HF/6-31G**
Distance
C1–C2
Bond angles
C2–C1–C6
1.381(3)
1.371(4)
1.387(4)
1.388(3)
1.384(2)
1.379(3)
1.4900(19)
1.498(3)
1.467(2)
1.440(2)
1.392(2)
1.494(3)
1.330(2)
1.431(2)
1.376(2)
1.370(3)
1.362(3)
1.374(4)
1.381(3)
1.379(3)
1.2337(19)
1.224(2)
2.751(1)
1.3901
1.3877
1.3905
1.3720
1.3806
1.3727
1.4925
1.5016
1.4631
1.4554
1.3693
1.5090
1.3388
1.4328
1.3844
1.3836
1.3841
1.3841
1.3841
1.3841
1.2269
1.2192
2.7269
1.3881
1.3918
1.3880
1.3797
1.3825
1.3805
1.4941
1.5005
1.4711
1.4629
1.3799
1.5038
1.3355
1.4271
1.3865
1.3850
1.3853
1.3853
1.3852
1.3865
1.2074
1.2000
2.7644
118.0(2)
117.73
120.77
120.85
117.78
121.36
109.10
109.86
121.51
109.03
120.38
106.56
123.00
105.44
125.57
117.93
119.98
120.08
119.90
119.99
120.08
119.97
127.84
130.31
117.60
120.96
120.99
117.65
121.36
108.46
109.89
121.43
109.05
120.01
106.81
123.88
105.80
126.29
117.62
119.96
120.11
119.89
119.96
120.12
119.96
128.15
130.31
C2–C3
C1–C2–C3
120.6(2)
C3–C4
C2–C3–C4
121.9(2)
C4–C5
C3–C4–C5
117.48(19)
120.33(17)
108.12(13)
109.17(15)
121.64(15)
108.69(14)
120.22(14)
107.65(13)
123.65(14)
106.20(14)
125.63(14)
120.22(14)
119.95(17)
120.0(2)
C5–C6
C4–C5–C6
C1–C6
C7–C8–C9
C6–C7
C6–C5–C9
C5–C9
C1–C6–C5
C8–C9
C5–C6–C7
C7–C8
C8–C10–N
C8–C10
C10–C11
C10–N
N–C12
C12–C17
C16–C17
C15–C16
C14–C15
C13–C14
C12–C13
C7–O1
C9–O2
O1· · ·N
C6–C7–C8
C7–C8–C10
C5–C9–C8
C10–N–C12
N–C10–C8
C12–C17–C16
C17–C16–C15
C16–C15–C14
C12–C13–C14
C15–C14–C13
C17–C12–C13
O1–C7–C8
120.4(2)
118.85(18)
120.3(2)
120.48(16)
127.63(13)
129.45(17)
O2–C9–C8
Torsion angles
C10–N–C12–C13
79.0(2)
90.58
90.42
Fig. 3. The deuterium isotope effects are defined as
nDC(D) ¼ dC(H)–dC(D), n being the number of
intervening bonds between the observed nuclei and
the isotope in use. The deuteration occurs at the NH
position leading to ND. The C10 and C12 carbons,
being located close to NH proton, show the highest
sensitivity to H/D substitution. A stronger isotope
effect was observed for C7 than for C9, which could
be explained by the presence of hydrogen bonding
between the proton of the imino group and the
carbonyl group in C7 position. Similar isotope
3DC(D) effects for C11, C13 and C17 were observed.
The 1H and 13C NMR spectral data obtained
(chemical shift of the NH proton, NOE and DIE)
confirm the structure 2A (Fig. 1).
ethylidene]-indane-1,3-dione were also measured.
The 1H NMR spectra of the compound showed
resonance peaks in the aromatic spectral area (7.2–
7.7 ppm), at about 2.54 ppm (^0.05 ppm depending
on the solvent) for the methyl group and at 12.27,
12.23 and 12.17 ppm for the proton of the imino group
in CDCl3, CD3CN and DMSO solutions, respectively.
The 13C NMR data are presented in Table 4. Just a
slight difference between the proton and carbon
chemical shifts in the different solutions was
observed.
In order to identify deformation frequency band,
N–H, the IR spectra of 2A and its imino deuterated
d
analog were compared. In Fig. 4(A) are presented the
IR spectra of both substances in the region 1750–
1450 cm21. The isotopic frequency shift of dNH
(Table 5) is clearly observed. The reduced linear
The 1H and 13C NMR spectra in CD3OD, CD3CN
and DMSO-d6 solutions of 2-[1-(N-phenylamino)-1-

18
V. Enchev et al. / Journal of Molecular Structure 654 (2003) 11–20
Table 4
Experimental and calculated (HF/6-31 þ G*)13C NMR chemical
shifts (in ppm) of 2-[1-(N-phenylamino)-1-ethylidene]-indane-1,3-
dione. For numbering of the atoms see Fig. 2
Carbon
Solvent
Calculated
CDCl3 CD3 OD CD3CN DMSO
C1
121.3
133.2
132.9
121.1
138.8
139.9
194.3
103.8
190.6
166.0
15.8
122.4
134.7
134.5
122.1
140.0
141.1
195.6
104.5
192.7
168.4
16.1
121.9
134.2
133.9
121.6
139.6
140.7
194.7
104.2
190.9
167.4
15.9
121.2
133.8
133.5
121.0
138.2
139.3
193.2
103.0
189.7
166.3
15.5
121.8
C2
130.0
C3
130.6
C4
122.1
C5
140.4
C6
138.2
C7
189.6
C8
94.2
C9
184.3
C10
C11
C12
173.6
14.0
136.1
137.4
126.7
130.7
129.0
137.1
126.4
130.2
128.3
135.9
125.5
129.5
127.6
135.0
C13, C17 125.5
C14, C16 129.4
129.6, 129.5
127.4, 127.5
127.4
C15
127.5
dichroic spectra of 2A and its imino deuterated analog
in the carbonyl and out-of-plane regions revealed
interesting structural information about the mutual
orientation of the two benzene rings (one from the
indanedione fragment and the other one from the
aniline fragment, Fig. 4(B) and (C)). The disappear-
ance of the low frequency band at 1643 cm21 occurs
almost simultaneously with the reduction of the band
at 692 cm21 that corresponds of the out-of plane
vibration of the benzene ring of the aniline fragment.
This implies that the corresponding transition
moments have almost the same orientation. This
result is in agreement with the ab initio calculated data
(Table 3).
Fig. 4. Selected IR data: (A) IR spectra of 2-(ethylideneaminophe-
nyl)-indan-1,3-dione, 2A, and its imino deuterated analog in CCl4 in
the 1750–1450 cm21 region; (B) The reduced IR LD spectra of 2A
in the 1760–1500 cm21 region; (C) The reduced IR LD spectra of
imino deuterated 2A in benzene ring out-of-plane frequency region.
Fig. 3. Deuterium isotope effects on 13C chemical shifts for 2-
(ethylideneaminophenyl)-indan-1,3-dione.

V. Enchev et al. / Journal of Molecular Structure 654 (2003) 11–20
19
90.58 in the gas phase calculations (Table 3). There is
generally good agreement in bond lengths and angles
between the crystal structure and the corresponding
calculated values in the gas phase.
Table 5
Experimental and calculated IR frequencies (in cm21) of 2A. Ab
initio calculated frequencies are scaled by factor 0.893
n
Calculated
HF/3-21G
Measured
CCl4
The crystal structure of 2-[1-(N-phenylamino)-1-
ethylidene]-indane-1,3-dione, shown in Fig. 5, is built
up from discrete centrosymmetric dimers held
ZLI-1695
KBr
N–H· · ·O1i
nN–H
nN–D
3248
2379
1727
1679
1601
3268
2311
1695
1642
1610
1520
3320
–
together
by
intermolecular
2354
1694
1643
1607
(i ¼ 1 2 x, 2 y, 2 z) hydrogen bonds (N· · ·O:
n
CyO (C9–O2)
CyO (C7–O1)
1686
1641
1601
–
˚
˚
3.136(2) A; (N)H· · ·O: 2.462(19) A; /N–H(N)–O:
132.3(15)8). Therefore the hydrogen atom from N–H
group participates in both inter-and intra-molecular
hydrogen bonding stabilizing the dimeric structure
(Fig. 5). The hydrogen atoms from the methyl group
are disordered with two positions rotated from each
other by 608. Both conformers, shown in Fig. 2, are
present in the unit cell with the same abundance. Only
one conformer is shown in Fig. 5.
n
dN–H
dN–D
The X-ray data show that in the solid state the
compound also exists in the enamine tautomeric form
2A (Fig. 2(a)). There is evidence of intramolecular
N–H· · ·O hydrogen bonding (IHB) involving the
imine proton and the carbonyl O1 atom (N–H:
˚
0.90 A; (N)H· · ·O1: 2.02 A; N· · ·O: 2.751 A; /N–
˚
˚
3.1. Supporting information available
H–O: 138.48). The forming of IHB leads to a slight
˚
lengthening of the C7–O1 (1.234 A) bond distance
˚
with respect to C9–O2 (1.224 A) [22]. The selected
Characterization data for compound 2A, some
1
representative H and 13C NMR, IR, MS, UV–Vis
molecular parameters determined by means of X-ray
crystallography and quantum-chemical calculations at
the HF/3-21G and HF/6-31G** levels are presented in
Table 3. The X-ray data show the benzene ring from
the aniline moiety is twisted around the C12–N bond
by 78.10(9)8 in the crystalline state compared ca.
spectra, X-ray structure factor tables and table of
Cartesian coordinates are available from the authors.
Atomic coordinates and equivalent isotropic displace-
ment parameters, calculated hydrogen atom par-
ameters, anisotropic thermal parameters and bond
lengths and angles have been deposited at the
Fig. 5. Crystal packing of 2-(ethylideneaminophenyl)-indan-1,3-dione molecules.

20
V. Enchev et al. / Journal of Molecular Structure 654 (2003) 11–20
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Acknowledgements
The crystallographic data were collected on the
KappaCCD Nonius diffractometer in the Laboratory
of Inorganic Chemistry, Faculty of Chemistry and
Chemical Technology, University of Ljubljana, Slo-
venia. We acknowledge with thanks the financial
contribution of the Ministry of Science and Technol-
ogy, Republic of Slovenia through grant Packet X-
2000 and PS-511-103, which made the purchase of the
apparatus possible.
[14] G.M. Sheldrick, Acta Crystallogr. A46 (1990) 467.
[15] G.M. Sheldrick, SHELXL97, 1997, Program for the Refinement
¨
of Crystal Structures. University of Gottingen, Germany
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S. Su, T.L. Windus, M. Dupuis, J.A. Montgomery Jr.,
J. Comput. Chem. 14 (1993) 1347.
We wish to thank Dr Isaac Abrahams (Structural
Chemistry Group, Department of Chemistry, Queen
Marry University, London) for the helpful
discussions.
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Jr. R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam,
A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi,
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