Molecular and computational structure characterizations of (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol

Article abstract of DOI:10.1007/BF03245899

The (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol compound was synthesized and characterized by X-ray Diffraction, IR and Electronic spectroscopy. X-Ray and IR results showed that the title compound preferred the enol form in solid state. UV-Vis abso

Full text of DOI:10.1007/BF03245899

J. Iran. Chem. Soc., Vol. 8, No. 3, September 2011, pp. 674-686.
JOURIrNaAnLiaOnF THE
Chemical Society
Molecular and Computational Structure Characterizations
of (E)-2-Ethoxy-6-[(4-fluorophenylimino)methyl]phenol
Ç. Albayraka,*, B. Kosara, M. Odabasoglub and O. Buyukgungorc
aFaculty of Education, Sinop University, 57000, Sinop, Turkey
bChemical Technology Program, Pamukkale University, 20070, Kınıklı-Denizli, Turkey
cDepartment of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit-Samsun, Turkey
(Received 26 April 2010, Accepted 1 September 2010)
The (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol compound was synthesized and characterized by X-ray Diffraction,
IR and Electronic spectroscopy. X-Ray and IR results showed that the title compound preferred the enol form in solid state. UV-
Vis absorption spectra of the title compound were recorded in different solvents. The results showed that the molecule existed
only in enol form even in the solvent media. Electronic structure and spectroscopic properties of the title compound were
investigated from calculative point of view. The gas phase geometry optimization was obtained based on X-ray geometry by DFT
method with B3LYP applying 6-311G(d,p) basis set. Geometry optimizations in the solvent media were obtained with the same
level of theory by the polarizable continuum model (PCM). TD-DFT calculations starting from the optimized geometry were
made in both gas and solution phase to measure the excitation energies of enol and keto tautomers. Vibrational frequency and
natural bond orbital analysis (NBO) were performed and the thermodynamic properties of the title compound were obtained at the
optimized geometry with the same level of theory.
Keywords: Schiff base, X-Ray analysis, IR and UV-Vis spectroscopy, DFT, TD-DFT
INTRODUCTION
electrical currents, and ion transport through membranes [6].
In addition, they are widely used as ligands in the field of
coordination chemistry [7] as well as in diverse fields of
chemistry and biochemistry owing to their biological activities
[8].
The aim of this work is to investigate the tautomeric forms,
spectral properties and molecular structure of (E)-2-ethoxy-6-
[(4-fluorophenylimino)methyl]phenol and report the results
from both theoretical and experimental points of view.
The ortho-hydroxy Schiff bases derived from the
condensation of primary amines with carbonyl compounds are
important compounds which show tautomerism via the
intramolecular proton transfer from an oxygen atom to the
neighboring nitrogen atom. These compounds can exist in
three different structures, that is, enol, keto and zwitterionic
forms in the solid state [1-3]. The ortho-hydroxy Schiff bases
also show thermochromism and photochromism via the
intramolecular proton transfer [4,5]. Photochromic compounds
are used in optical switches and optical memories, variable
EXPERIMENTAL
Synthesis
*Corresponding author. E-mail: calbayrak@sinop.edu.tr
The compound (E)-2-ethoxy-6-[(4-fluorophenylimino)

Albayrak et al.
methyl]phenol was prepared by refluxing a mixture of a
publication no. CCDC 768527. Copies of the data can be
obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk).
solution containing 3-ethoxysalicylaldehyde (0.5 g, 3 mmol)
in 20 ml ethanol and a solution containing aniline (0.33 g, 3
mmol) in 20 ml ethanol. The reaction mixture was stirred for 1
h
under reflux. The crystals of (E)-2-ethoxy-6-[(4-
fluorophenylimino)methyl]phenol, suitable for X-ray analysis,
were obtained from the slow evaporation of ethyl alcohol
(yield%, 86; m.p.: 356-358 K).
Computational Procedures
All computations were done using Gaussian 03W program
package running under Windows XP [11]. Full geometry
optimization of the title molecule was obtained using DFT
method with Becke’s three-parameters hybrid exchange-
correlation functional (B3LYP) [12] employing 6-311G(d,p)
basis set [13-15] as implemented in Gaussian 03W. The
crystallographically obtained geometrical data of the molecule
were used for the optimization. The optimized geometry of the
molecule, the total molecular energy, and the dipole moment
were obtained from the optimization output. The ground state
geometry optimization of the title compound for the gas phase
was calculated using DFT method with B3LYP adding 6-
311G(d,p).
Apparatus
The melting point was determined by StuartMP30 melting
point apparatus. FT-IR spectrum of the title compound was
recorded on a Bruker 2000 spectrometer in KBr disk. UV-Vis
absorption spectra were recorded on a Thermo scientific
BioGenesis UV-Vis spectrometer using a 1 cm path length of
the cell.
X-Ray Crystallography
A suitable sample of 0.52 × 0.41 × 0.25 mm3 size was
selected for the crystallographic study. All diffraction
measurements were made at room temperature (293 K) using
graphite monochromated MoKα radiation and a STOE IPDS 2
diffractometer. Reflections were collected in the rotation mode
and cell parameters were determined by using X-AREA
software [9]. Absorption correction was made by the
integration method via X-RED software [9]. The structure was
solved by direct methods using SHELXS-97 [10]. The
refinement was made by full-matrix least-squares method on
the positional and anisotropic temperature parameters of the
non-hydrogen atoms, or equivalently corresponding to 171
crystallographic parameters. All non-hydrogen atom
parameters were refined anisotropically and all H atoms,
except for H1, were located in their idealized positions and
refined using a riding model with C-H distances in the range
0.93-0.96 Å, Uiso(H) values in the range 1.2Ueq(C) or
1.5Ueq(C) (for methyl group). The data collection conditions
and the parameters of the refinement process are listed in
Table 1.
The solution phase geometry optimizations were obtained
with the same level of theory by the polarizable continuum
model (PCM). TD-DFT calculations starting from the gas
phase and solution phase optimized geometry, using the same
level of theory, were made in both gas and solution phase to
calculate excitation energies of enol and keto tautomers. The
excitation energies of the title compound for enol and keto
forms were obtained by TD-DFT calculation. In addition, gas-
phase vibrational frequency and natural bond orbital analysis
for enol form were performed by using the same level of
theory. In addition, thermodynamic properties of the title
compound were obtained by applying the same level of theory.
RESULTS AND DISCUSSION
Structure Determination
The crystal data and refinement details of (E)-2-ethoxy-6-
[(4-fluorophenylimino)methyl]phenol compound are given in
Table 1. The selected bond lengths and angles are given in
Table 2. The molecular structure of this compound is shown in
Fig. 1 with the atom numbering scheme. As can be seen in
Fig. 1, the molecule adopts E configuration about the C=N
double bond.
Supplementary Data
Crystallographic data (excluding structure factors) for the
structure in this paper have been deposited with the
Cambridge Crystallographic Data Centre as the supplementary
The C7-N1 bond length of 1.279(3) Å and C9-O1 bond
675

Molecular and Computational Structure Characterizations of
Table 1. Crystal Data, Data Collection and Refinement Details
Chemical formula
C15H14FNO2
Monoclinic, P21/c, 4
11.5578(9) Å
12.5684(7) Å
9.7863(7) Å
113.023(6)º
1308.35(16) Å3
1.32 mg m-3
MoKα, 0.71073 Å
0.097 mm-1
293 K
Crystal system, Space group, Z
a
b
c
β
V
Dx
Radiation, λ
μ
T
Tmin, Tmax
0.9561, 0.9802
544
F(000)
Diffractometer
STOE IPDS II
ω
Scanning mode
Scan range
-14 < h < 14, -15 < k < 15, -12 < l < 12
1.62, 28.0°
θmin, θmax
Number of measured/independent reflections, Rint
19354/2711, 0.077
1824
Number of reflections with 2σ(I)
Number of refined parameters
171
S
1.083
R[F2 > 2σ(F2)]
wR (F2)
0.054
0.120
0.107, -0.167 e Å-3
Δρmax, Δρmin
Fig. 1. A view of (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol, with the atom numbering scheme.
676

Albayrak et al.
Table 2. The Selected Bond Lengths, Angles and Torsion Angles (Ǻ,°)
DFT/B3LYP
Enol form
DFT/B3LYP
Keto form
1.2524
X-Ray
C9-O1
1.349(2)
1.279(3)
1.412(3)
1.361(3)
1.433(3)
1.438(3)
1.395(3)
1.406(3)
1.403(3)
1.376(3)
1.379(4)
1.365(5)
1.354(3)
121.94(17)
117.62(18)
124.16(18)
122.85(19)
121.7(2)
117.80(18)
-159.94(18)
22.8(3)
1.3363
1.2887
1.334
1.4042
N1-C7
N1-C1
1.4071
1.3553
C10-O2
1.3584
1.4257
C14-O2
1.4275
1.3921
C7-C8
1.4488
1.4644
C8-C9
1.4134
1.4337
C8-C13
1.4123
1.4658
C9-C10
1.4185
1.3696
C10-C11
C11-C12
C12-C13
F1-C4
1.389
1.4309
1.4051
1.359
1.3768
1.3508
1.3518
127.928
117.8006
122.9619
123.1929
122.7551
121.3814
165.0778
-15.5089
-179.979
179.555
0.1263
C1-N1-C7
N1-C1-C2
N1-C1-C6
N1-C7-C8
O1-C9-C8
O1-C9-C10
C2-C1-N1-C7
C6-C1-N1-C7
N1-C1-C2-C3
N1-C1-C6-C5
N1-C7-C8-C9
C8-C7-N1-C1
121.3842
117.8607
123.2288
122.7873
122.7218
118.0842
145.6804
-36.7235
179.7921
-179.1267
-0.7365
177.2932
-178.06(17)
177.6(2)
-2.5(3)
178.9236
-177.86(17)
677

Molecular and Computational Structure Characterizations of
length of 1.349(2) Å are consistent with the distances of the C-
clearly shorter than the sum of the van der Waals’ radii for N
and O [20].
We used Parst [21] to analyze the intermolecular hydrogen
N double bond and the C-O single bond as presented for the
related compounds previously studied [16-18]. The C7-N1
double bond and C9-O1 single bond distances in (E)-2-ethoxy-
6-[(4-fluorophenylimino)methyl]phenol show that the
molecule exists in enol form in the solid state. A significant
intramolecular interaction was noted involving phenolic atom
O1 and nitrogen atom N1 which constituted a six-membered
ring S(6) [19]. The O1-N1 distance of 2.611(2) Å is indicative
of strong intramolecular hydrogen bonding. This length is
bond interactions in the crystal structure. The intermolecular
hydrogen-bonded geometry and the details of C-H…O
interactions for the title compound are listed in Table 3. (E)-2-
ethoxy-6-[(4-fluorophenylimino)methyl]phenol molecules are
2
linked to R2 (28) containing a total of 28 atoms, two donors
and two acceptors [19] as shown in Fig. 2. Furthermore, C-
H…π interactions between π electrons of aromatic ring and
Table 3. Hydrogen Bonding Geometry (Ǻ,°)
D-H…A
D-H
0.84(2)
0.960
H…A
1.84(2)
2.627
D…A
2.611(2)
3.383
∠D-H…A
152(2)
135.89
O1-H1…N1
C15-H(15C)…F1i
C14-H(14A)…Cgii
Calculated
0.9706
2.817
3.615(3)
140.10
0.992
1.737
2.630
147.80
O1-H1…N1
Symmetry code: (i) -x+1, -y+2, -z+1; (ii) x, 1/2-y, -1/2+z. Cg is the centroid of C8-C13 ring.
Fig. 2. A partial packing diagram for (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol, with C-H..F hydrogen bonds
and shown as dashed lines. H atoms not included in intermolecular hydrogen bonding have been omitted for clarity.
[Symmetry codes: (i) -x+1, -y+2, -z+1].
678

Albayrak et al.
the methyl hydrogen exist in the crystal structure (Fig. 3).
distance of 1.349(2) Å indicates single bond character and the
C-N distance is 1.279(3) Å that shows double bond character.
The results obtained from the optimization of the enol form
are in reasonable agreement with the experimental as can be
seen in Fig. 4.
The X-ray and optimized structures of the title compound
were superimposed for visual comparison as shown in Fig. 4.
The selected bond lengths and angles for the optimized
structure and the X-ray geometry of the molecule are listed in
Table 2. The corresponding C9-O1 and C7-N1 distances of the
enol form at the optimized geometry are 1.3363 Å, and 1.2887
Å while these distances for the keto form are 1.2524 Å and
1.334 Å, respectively. From the X-ray geometry, the C-O
Natural Bond Orbital (NBO) Analysis
NBO analysis is important for the understanding of
hydrogen bonding and delocalization effect from the lone pairs
Fig. 3. A partial packing diagram for (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol, with C-H..π bonds shown as
dashed lines. H atoms not included in intermolecular hydrogen bonding have been omitted for clarity. [Symmetry
codes: (ii) x, 1/2-y, -1/2+z].
Fig. 4. Superimposition of gas phase optimized (red) and experimental geometry (black) of title compound.
679

Molecular and Computational Structure Characterizations of
polarity of the solvent strengthens intramolecular hydrogen
bond, and weakens and elongates the O-H sigma bond.
(donor) to antibonding orbitals (acceptor). The interaction
between the donor and acceptor orbitals can be used to
measure delocalization. The stabilization energy derived from
the interactions between the donor and acceptor orbitals was
estimated by second order perturbation interaction energy (E2)
in natural bond orbital (NBO) at optimized geometry. For each
donor NBO (i) and acceptor NBO (j), the stabilization energy
E2 associated with delocalization between donor and acceptor
was estimated by Eq. 1 [22]:
IR Absorption Spectrum
IR spectrum of the title compound is given in Fig. 5. It is
noteworthy that there exist two absorption bands. One of these
in 2000-3000 cm-1 region is attributed to the υ(O-H) stretching
frequencies which broaden owing to the formation of strong
intramolecular hydrogen bonding O-H…N in the structure and
the other, located at 1618 cm-1, is attributed to υ(C=N)
stretching which shifted to the lower frequency of 1618 cm-1
due to the formation of strong intramolecular hydrogen
bonding O-H…N in the structure. The IR spectrum of the
molecule shows also the presence of υ(C-O) stretching at 1255
cm-1. These values are in accordance with the literature [23].
The vibrational frequencies of the title compound were
calculated by using the same level of theory. The scale factor
of 0.9682 was applied to vibrational frequencies [24].
Vibrational bands have been made by using Gaussview. The
experimental and the calculated frequencies are given in Table
5. The calculated results from frequency analysis for C=N,
O-H and C-O stretching show significant deviations from the
experimental values due to intramolecular hydrogen bond
between N and O.
F2(i, j)
εj-εi
E2 = ΔEij = - qi
(1)
Where qi is the donor orbital occupancy, εi, εj are diagonal
elements (orbital energies) and F(i, j) is the off-diagonal NBO
Fock matrix element.
NBO analysis of the title compound was performed by
applying same level of theory for the enol form in different
solvents and gas phase. The interactions between donor N1
lone pair and acceptor H1-O1 bond for the title compound in
various solvents and gas phase are shown in Table 4. NBO
analysis for the title compound shows that there is a strong
interaction nN1→σ*O1-H1. This interaction increases with the
increase of polarity of the solvent and as a result O1-H1 bond
weakens and lengthens. Table 4 shows the calculated
delocalization energies of title compound in various solvents.
The delocalization energy of the title compound increases
with the increase of polarity of the solvent. The increasing of
delocalization energy of the title compound indicates that it is
more stable in the polar solvent. In addition, N…O distance
shortens with the increase of polarity of the solvent. The
increase of nN1→σ*O1-H1 delocalization with the increase of
UV-Vis Absorption Spectra
For the evaluation of both the energies and dipole
moments of enol and keto forms to be compared with each
other, optimizations pertaining to each form of the title
compound were performed. The geometric optimization in the
solvent media was carried out using DFT/B3LYP method with
6-311G(d,p) basis set by adding the polarizable continuum
Table 4. Second Order Perturbation Theory Analysis of the Fock Matrix in NBO Basis and Intramolecular Hydrogen
Bond Lengths in Different Solvents
Solvent
Donor
Acceptor
E2 (Kcal mol-1)
O-H (Å)
N...H (Å)
N...O (Å)
Gas phase
Benzene
Chloroform
EtOH
LP(1)N1
LP(1)N1
LP(1)N1
LP(1)N1
LP(1)N1
BD*(1)O1-H1
BD*(1)O1-H1
BD*(1)O1-H1
BD*(1)O1-H1
BD*(1)O1-H1
23.44
24.88
25.83
26.96
27.19
0.9918
0.9940
0.9954
0.9970
0.9973
1.73692
1.72410
1.71644
1.70787
1.70583
2.62983
2.62183
2.61732
2.61213
2.61091
DMSO
680

Albayrak et al.
Fig. 5. The IR spectrum of (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol.
Table 5. The Experimental and the Calculated Frequences of IR Spectra (cm-1)
Assignments
Experimental
DFT/B3LYP
O-H str.
2000-3000
3067
3228
3186-3207
3109
C-H str. (aromatic)
C-H (CH3) str.
3001
N=C-H (imino) str.
2929
3034
C-H (CH2) str.
2976
2990
C=N str. + O-H bend. + C=C str.
C=C str. + C=N str.
1618
1668
1582
1639
C=C str. + C=N str. + O-H bend.
C=C str. + C-O1 str. + O-H bend.
O-H bend. + C-H (aromatic) bend.
N=C-H bend. (imino)
C-O1 str. + C=C str. + N=C-H bend.
C-O2 str.
1503
1617-1537
1493
1461
1367
1462
1394
1398
1341
1321
1255
1281
C-F str + C-H (aromatic) bend
C-N str. + C-H (aromatic) bend.
C-H bend. (aromatic)
1212
1251
1187
1218
1113-1077
904-844
789
1117-1099
856-842
819-772
735
C-H bend. (aromatic)
C-H bend. (aromatic)
C-H bend. (aromatic)
736
Str.: stretching, bend.: bending.
681

Molecular and Computational Structure Characterizations of
Table 6. The Energies and Dipole Moments of Enol and Keto Form in Gas Phase and Solution
Enol form
Keto form
Energy (Hartree)
Dipole moment (D)
2.8370
Energy (Hartree)
Dipole moment (D)
2.0862
Gas phase
Benzene
CHCl3
-885.28598146
-885.29190723
-885.29628059
-885.30073532
-885.30122807
-885.27894254
-885.28670373
-885.29249958
-885.29851305
-885.29899360
3.2754
3.6586
4.0947
4.1573
2.6172
3.1463
3.7974
3.8735
EtOH
DMSO
model (PCM). The total energies and dipole moments of enol
and keto forms in the solvent media are shown in Table 6. As
shown in this table, the total energies of enol and keto forms
decrease with the increase of polarity of the solvent, in other
words, stability of the molecule increases. In addition, dipole
moments for both enol and keto forms increase with the
increase of polarity of the solvent. We calculated the first 10
spin-allowed singlet-singlet excitations for both enol and keto
forms of the title compound by TD-DFT approach. TD-DFT
calculations were started from gas phase and solution phase
optimized geometry using the same level of theory and carried
out in both gas and solution phase to obtain excitation
energies. Among the methods to calculate excitation energies
for organic compounds as well as inorganic ones, TD-DFT is
of particular interest owing to the satisfactory results achieved
with the experiment and low cost of computational demands
[25-28].
In Fig. 6, the calculated transitions for both enol and keto
forms are given for comparison with the experimental
spectrum in EtOH. The percentage contributions of molecular
orbitals to the formation of the bands were extracted from the
output by using SWizard Program [29]. For both forms,
wavelength (λ), oscillator strength (f) were selected to be
larger than 0.1. The major contributions of the calculated
transitions are given in Table 7. According to the results, the
calculated excitation energies of enol form are at 224 nm
[HOMO→LUMO+3(43%), HOMO-1→LUMO+2(18%)], at
276 nm [HOMO-2→LUMO(66%)], at 323 nm [HOMO-1→
LUMO(82%)] and at 365 nm [HOMO→LUMO(89%)], and
Wavelength (nm)
Fig. 6. The comparison of calculated transitions for enol form
) and keto form ( ) of (E)-2-ethoxy-6-[(4-
(
fluorophenylimino)methyl]phenol
experimental spectrum in EtOH.
with
the
that of the keto form are at 234 nm [HOMO→LUMO+
3(77%)], at 333 nm [HOMO-2→LUMO(6%), HOMO-1→
LUMO(81%)] and at 449 nm [HOMO→LUMO(81%)] (Fig.
6). The frontier molecular orbitals of enol and keto form for
the title molecule are shown in Fig. 7 in the EtOH.
The UV-Vis electronic spectra of (E)-2-ethoxy-6-[(4-
fluorophenylimino)methyl]phenol in various organic solvents
(EtOH, DMSO, Benzene and CHCl3) were recorded within
200-600 nm range. The characteristic UV-Vis absorption
682

Albayrak et al.
Table 7. For Enol and Keto Forms Wavelength, Oscillator Strength, Major Contributions of Calculated Transitions
Experimental
Calculated
Keto form
Enol form
Major
Major
contribution
contribution
λ (nm)
λ (nm) (f)
λ (nm) (f)
Gas phase
-
223.48(0.3680)
H→L+3 (37%)
H→L+2 (30%)
H-1→L+2 (18%)
H-2→L (67%)
H-4→L (15%)
H-1→L (5%)
232.72(0.2469)
H→L+3(77%)
H-7→L (6%)
-
274.98(0.2132)
-
-
322.91(0.5439)
361.20(0.1265)
225.63(0.3861)
H-1→L (82%)
H→L (88%)
333.84(0.5515)
442.85(0.2354)
235.63(0.2249)
H-1→L (73%)
H →L (81%)
H →L+3(77%)
H-7→L (8%)
Benzene
CHCl3
EtOH
H→L+3 (57%)
H-1→L+2(16%)
H→L+2 (13%)
H-2→L(68%)
H-4→L(14%)
H-1→L (83%)
H→L (89%)
H→L+3(52%)
H→L+2(17%)
H-1→L+2(17%)
H-2→L (68%)
H-4→L (15%)
H-1→L (83%)
H→L (89%)
H→L+3(43%)
H→L+2(24%)
H-1→L+2(18%)
H-2→L (66%)
H-4→L (16%)
H-1→L (82%)
278
276.67(0.1922)
316
360
242
324.96(0.5871)
370.65(0.1372)
224.82(0.3811)
335.82(0.6362)
459.18(0.2418)
235.01(0.2313)
H-1→L (84%)
H→L (81%)
H→L+3 (77%)
H-7→L (8%)
280
276.23(0.1939)
316
360
224
324.23(0.5824)
367.72(0.1292)
223.90(0.3694)
334.42(0.6317)
454.47(0.2324)
234.09(0.2350) H→L+3 (77%) H-
6→L (8%)
H-1→L (82%)
H→L (81%)
278
314
358
276.04(0.1875)
323.19(0.5831)
332.91(0.6229) H-1→L (81%) H-
2→L (6%)
449.45(0.2190)
234.41(0.2437)
365.06(0.1201)
224.17(0.3806)
H→L (89%)
H→L+3 (45%)
H→L+2 (24%)
H-1→L+2(17%)
H-2→L (67%)
H-4→L (16%)
H-1→L (83%)
H→L (81%)
H→L+3 (77%)
H-6→L (6%)
DMSO
284
316
360
276.33(0.1877)
324.40(0.6040)
365.44(0.1274)
334.65(0.6353) H-1→L (81%) H-
2→L (6%)
451.33(0.2299)
H→L (89%)
H→L (81%)
683

Molecular and Computational Structure Characterizations of
Fig. 7. The molecular orbitals of (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol for enol form and keto form in
EtOH.
bands of the molecule in EtOH, DMSO, Benzene and CHCl3
are given in Table 7. Representative spectra are shown in Fig.
8. The absorption band is observed at 316 nm followed by a
shoulder at 360 nm in all solvents. The influence of the solvent
is important for intramolecular hydrogen bonds. Some
solvents such as DMF and DMSO show hydrogen bond
breaking effect. Such an effect by the solvent, leads to the
destruction of intramolecular hydrogen bond and subsequently
to the formation of anion [30,31].
Therefore, we have recorded the UV-Vis spectrum in
EtOH by adding NaOH so that we can understand whether the
anion of the title compound exists or not. A new absorption
band in basic media appeared at 395 nm (Fig. 8). This shows
that the absorption band at 360 nm does not arise from
forming of anion of the title compound. This can be explained
by the fact that the compound has a very strong intramolecular
hydrogen bond and the title compound does not convert to
anion even by DMSO [30]. In addition, the second band at 360
nm can be formed by the molecules rendering intramolecular
proton transfer from enol form to keto form possible. In the
calculated excitation energies, one can see that the HOMO→
LUMO transition for keto form occurs above 449 nm. But in
the experimental spectra, there is no absorption in this region
(Fig. 6). This indicates that the compound (E)-2-ethoxy-6-[(4-
fluorophenylimino)methyl]phenol is not in keto form in
Wavelength (nm)
Fig. 8. The solvent effect on UV-Vis spectra of (E)-2-ethoxy-
6-[(4-fluorophenylimino)methyl]phenol in
DMSO, ( ) EtOH, ( ) CHCl3, ( ) Benzene,
) EtOH+NaOH.
(
)
(
solution.
In view of TD-DFT calculations for enol form, four
excitation energies at 224 nm, at 276 nm, at 323 nm and at 365
nm arise from HOMO→LUMO+3(43%), HOMO-1→
LUMO+2(18%); HOMO-2→LUMO(66%);
HOMO-1→
684

Albayrak et al.
Table 8. Thermodynamic Properties of Title Compound at Different Temperature
T (K)
H0m (Kcal mol-1)
S0m (cal mol-1 K-1)
C0p,m (cal mol-1 K-1)
100
200
298.15
300
400
1.813
5.589
11.267
11.393
19.228
28.857
86.481
111.877
134.704
135.126
157.533
178.951
26.106
45.694
66.058
66.438
85.861
102.180
500
LUMO(82%) and HOMO→LUMO(89%) transitions,
respectively. These transitions were experimentally observed
as bands at 224 nm, at 278 nm, at 314 nm and a shoulder at
358 nm. The results obtained by the calculation for enol form
are in reasonable agreement with the experimental as seen in
Fig. 6 and the compound adopts enol form in solution.
form in the solid state both on the basis of X-ray and IR
spectroscopic data. UV-Vis spectra of the title compound were
recorded in various solvents. Whether the title compound was
in the keto or enol forms was also examined utilizing UV-Vis
spectroscopic measurements conducted in different solvents.
The results show that the molecule exists only in enol form
even in solvent media. In addition, DFT/B3LYP optimization
was performed based on X-ray geometry. TD-DFT
calculations starting from optimized geometry were carried
out in both gas and solution phase to calculate excitation
energies of enol and keto tautomers. Vibrational frequency
analysis was performed at the optimized geometry with the
same level of theory. 6-311G(d,p) basis set was applied
throughout the calculations. The results obtained by the
calculation for enol form showed a satisfactory consistency
with the experimental data.
Thermodynamic Properties
The heat capacity (C0p,m), entropy (S0 ) and enthalpy (H0 )
m
m
that are the standard thermodynamic functions were performed
using DFT/B3LYP method with 6-311G(d,p). The results are
shown in Table 8. The heat capacities, entropies and
enthalpies were obtained by increasing the temperature from
100 K to 500 K. According to the results, the increase of
temperature increases heat capacities, entropies and enthalpies
due to increasing intensities of molecular vibration.
The correlation equations between heat capacities,
entropies, enthalpies and temperature are shown below and
can be used for analyzing heat capacities, entropies and
enthalpies at different temperatures.
REFERENCES
[1] A. Özek, Ç. Albayrak, M. Odabaşoğlu, O.
Büyükgüngör, Acta Crystallogr. C63 (2007) o177.
[2] B. Koşar, Ç. Albayrak, M. Odabaşoğlu, O.
Büyükgüngör, Acta Crystallogr. E61 (2005) o1097.
[3] E. Temel, Ç. Albayrak, O. Büyükgüngör, M.
Odabaşoğlu, Acta Crystallogr. E62 (2006) o4484.
[4] I. Moustakali-Mavridis, E. Hadjoudis, A. Mavridis, Acta
Crystallogr. B34 (1978) 3709.
C0p,m = 3.61284 + 0.2262T - 5.64766 × 10-5T2, R2 = 0.99918
S0m = 60.47976 + 0.26761T - 6.16926 × 10-5T2, R2 = 0.99995
H0m = -0.06255 + 0.00873T + 9.8323 × 10-5T2, R2 = 0.99998
CONCLUSIONS
The compound (E)-2-ethoxy-6-[(4-fluorophenylimino)
methyl]phenol was synthesized and the corresponding
molecular structure was experimentally characterized by
means of X-ray Diffraction, IR and UV-Vis spectroscopy
techniques. It was concluded that this compound is in enol
[5] E. Hadjoudis, M. Vitterakis, I. Moustakali-Mavridis,
Tetrahedron 43 (1987) 1345.
[6] H. Dürr, H. Bouas-Laurent, Photochromism, Molecules
and Systems, Amsterdam, Elsevier, 1990.
[7] A.D. Garnovskii, A.L. Ninorozhkin, V.I. Minkin,
685

Molecular and Computational Structure Characterizations of
Coordin. Chem. Rev. 126 (1993) 1.
(1971) 724.
[8] R. Lozier, R.A. Bogomolni, W. Stoekenius, Biophys. J.
15 (1975) 955.
[15] M.J. Frisch, J.A. Pople, J.S. Binkley, J. Chem. Phys. 80
(1984) 3265.
[9] Stoe & Cie. X-AREA (Version 1.18) and X-RED32
(Version 1.04). Darmstadt, Germany, 2002.
[16] Ç. Albayrak, M. Odabaşoğlu, O. Büyükgüngör, Acta
Crystallogr. E61 (2005) o423.
[10] G.M. Sheldrick, SHELXS 97 and SHELXL 97 Program
for Crystal Structure Solution and Refinement,
University of Göttingen, Germany, 1997.
[17] E. Temel, Ç. Albayrak, M. Odabaşoğlu, O.
Büyükgüngör, Acta Crystallogr. E63 (2007) o2642.
[18] C.C. Ersanlı, Ç. Albayrak, M. Odabaşoğlu, A.
Erdönmez, Acta Crystallogr. E60 (2004) o389.
[19] M.C. Etter, Accounts Chem. Res. 23 (1990) 120.
[20] A. Bondi, J. Phys. Chem. 68 (1964) 441.
[21] M. Nardelli, J. Appl. Crystallogr. 28 (1995) 659.
[22] M. Snehalatha, C. Ravikumar, I. Hubert-Joe, N. Sekar,
V.V. Jayakumar. Spectrochim. Acta A 72 (2009) 654.
[23] R.M. Silverstein, F.X. Webster, D.J. Kiemle,
Spectrometric Identification of Organic Compounds, 7th
ed., John Wiley & Sons, New York, 2005.
[24] J.P. Merrick, D. Moran, L. Radom, J. Phys. Chem. A
111 (2007) 11683.
[25] V.N. Nemykin, J.G. Olsen, E. Perera, P. Basu, Inorg.
Chem. 45 (2006) 3557.
[26] G. Menconi, N. Kaltsoyannis, Chem. Phys. Lett. 415
(2005) 64.
[27] Z.F. Li, Y.C. Zhu, K. Yuan, J.W. Kang, Chinese J.
Struct. Chem. 27 (2008) 63.
[28] J.H. Pan, Y.M. Choun, H.L. Chiu, B.C. Wang, Tamkang
J. Sci. Eng. 8 (2005) 175.
[29] SI. Gorelsky, SWizard program, Revision 4.5 http://
www.sg.chem.net/, University of Ottawa, Ottawa,
Canada, 2010.
[30] Ç. Albayrak, I.E. Gümrükçüoğlu, M. Odabaşoğlu, N.O.
İskeleli, E. Ağar, J. Mol. Struct. 932 (2009) 43.
[31] A. Douhal, M. Sanz, L. Torma, J.A. Organero, Chem.
Phys. Chem. 6 (2005) 419.
[11] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria,
M.A. Robb, J.R. Cheeseman, J.A. Montgomery, T.J.
Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M.
Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M.
Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, C.
Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O.
Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W.
Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P.
Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.
Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K.
Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman,
J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J.
Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith,
M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M.
Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W.
Wong, C. Gonzalez, J.A. Pople, (2004) Gaussian 03,
Revision E.01. Gaussian, Inc., Wallingford CT.
[12] P.J. Stephens, F.J. Devlin, C.F. Chabalowski, M.J.
Frisch, J. Phys. Chem. 98 (1994) 11623.
[13] P.C. Hariharan, J.A. Pople, Theor. Chim. Acta 28 (1973)
213.
[14] R. Ditchfield, W.J. Hehrc, J.A. Pople, J. Chem. Phys. 54
686