A new Schiff base compound N,N′-(2,2-dimetylpropane)- bis(dihydroxylacetophenone): Synthesis, experimental and theoretical studies on its crystal structure, FTIR, UV-visible, 1H NMR and 13C NMR spectra

Article abstract of DOI:10.1016/j.saa.2011.05.080

The Schiff base compound, N,N′-(2,2-dimetylpropane)- bis(dihydroxylacetophenone) (NDHA) is synthesized through the condensation of 2-hydroxylacetophenone and 2,2-dimethyl 1,3-amino propane in methanol at ambient temperature. The yellow crystalline precipi

Full text of DOI:10.1016/j.saa.2011.05.080

Spectrochimica Acta Part A 81 (2011) 144–150
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A new Schiff base compound N,Nꢀ-(2,2-dimetylpropane)-
bis(dihydroxylacetophenone): Synthesis, experimental and theoretical studies
on its crystal structure, FTIR, UV–visible, 1H NMR and 13C NMR spectra
Vahid Saheb∗, Iran Sheikhshoaie
Department of Chemistry, Shahid-Bahonar University of Kerman, Kerman 76169, Iran
a r t i c l e i n f o
a b s t r a c t
The Schiff base compound, N,Nꢀ-(2,2-dimetylpropane)-bis(dihydroxylacetophenone) (NDHA) is synthe-
sized through the condensation of 2-hydroxylacetophenone and 2,2-dimethyl 1,3-amino propane in
methanol at ambient temperature. The yellow crystalline precipitate is used for X-ray single-crystal
determination and measuring Fourier transform infrared (FTIR), UV–visible, 1H NMR and 13C NMR spec-
tra. Electronic structure calculations at the B3LYP, PBEPBE and PW91PW91 levels of theory are performed
to optimize the molecular geometry and to calculate the FTIR, 1H NMR and 13C NMR spectra of the com-
pound. Time-dependent density functional theory (TDDFT) method is used to calculate the UV–visible
spectrum of NDHA. Vibrational frequencies are determined experimentally and compared with those
obtained theoretically. Vibrational assignments and analysis of the fundamental modes of the compound
are also performed. All theoretical methods can well reproduce the structure of the compound. The
1H NMR and 13C NMR chemical shifts calculated by all DFT methods are consistent with the experi-
mental data. However, the NMR shielding tensors computed at the B3LYP/6-31+G(d,p) level of theory
are in better agreement with experimental 1H NMR and 13C NMR spectra. The electronic absorption
spectrum calculated at the B3LYP/6-31+G(d,p) level by using TD-DFT method is in accordance with the
observed UV–visible spectrum of NDHA. In addition, some quantum descriptors of the molecule are calcu-
lated and conformational analysis is performed and the results were compared with the crystallographic
data.
Article history:
Received 27 December 2010
Received in revised form 22 May 2011
Accepted 25 May 2011
Keywords:
Schiff base
X-ray diffraction
DFT calculations
UV–visible
FTIR
NMR
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
dyes, acid–base and redox indicators, metalochromic reagents,
liquid crystals and histological stains [12–14]. Their structures
Schiff base compounds have received considerable scrutiny
from both theoretical and experimental standpoints. They have
been used in several areas such as homogenous catalysis, bioinor-
ganic chemistry and dye lasers. These compounds were prepared
by Schiff for the first time [1]. They are also used in the synthesis
of antibiotics, antiallergic, antiphlogistic and antitumor substances
[2–4]. Schiff bases are among the most widely investigated ligands
in coordination chemistry [5]. In addition, they have attracted con-
siderable attention due to their potential applications in modern
technology for the preparation of nonlinear optical (NLO) materials
[6–11].
are often considered as a representative model for the active
site of biologically important metal-containing enzymes [15].
In the present study, the Schiff base compound N,Nꢀ-(2,2-
dimetylpropane)-bis(dihydroxylacetophenone) (Fig. 1) has been
synthesized and characterized by IR, 1H NMR, 13C NMR spec-
troscopy and X-ray single-crystal determination. The molecular
conformation of the synthesized compound is stabilized by
O–H. . .N type hydrogen bonds. The most stable conformer, here-
after called NDHA, is the subject of our experimental and theoretical
studies.
In the past decade, by increasing development of computa-
tional chemistry, Density Functional Theory (DFT) has been used
extensively to calculate a wide variety of molecular properties
such as equilibrium structure, charge distribution, UV–visible,
FTIR and NMR spectra, and provided reliable results which are in
accordance with experimental data [16]. In this research, three
DFT methods are used to perform theoretical calculations on the
structure, FTIR, 1H NMR and 13C NMR spectra and some additional
The electronic absorption spectra of azo compounds, espe-
cially those containing phenolic moieties have been the main
subject of extensive studies due to their applications as textile
∗
Corresponding author. Tel.: +98 341 3222033; fax: +98 341 3222033.
E-mail address: vahidsaheb@mail.uk.ac.ir (V. Saheb).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.05.080

V. Saheb, I. Sheikhshoaie / Spectrochimica Acta Part A 81 (2011) 144–150
145
Fig. 1. The crystal structure of N,Nꢀ-(2,2-dimetylpropane)-bis(dihydroxylacetophenone) (NDHA) Schiff base compound.
Table 1
properties of the title compound. The methods include Beck’s
Crystal and experimental data for the NDHA Schiff base compound.
three-parameter exchange functional [17] with Lee et al.’s [18]
correlation functional (B3LYP); Perdew and Wang’s 1991 exchange
with gradient-corrected correlation functional (PW91PW91)
[19]; and Perdew et al.’s exchange and correlation functional
[20] (PBEPBE).
Z = 2
C21H26N2O2
F0 0 0 = 364
Mr = 338.44
Triclinic, P1
Dx = 1.225 Mg m−3
˚
˚
a = 7.7847 (9) A
b = 9.1857 (12) A
c = 13.3801 (14) A
˛ = 79.547 (4)◦
ˇ = 77.508 (3)◦
ꢃ = 85.537 (4)◦
Mo K␣ radiation, ꢀ = 0.71075 A
Cell parameters from 6952 reflections
ꢁ = 3.2–27.5◦
˚
˚
ꢂ = 0.08 mm−1
2. Experimental
T = 193 K
Block, yellow
2.1. Materials and measurements
3
˚
0.40 mm × 0.30 mm × 0.10 mm
V = 917.89 (18) A
Extinction correction: none
Primary atom site location:
structure-invariant direct
methods
All of the chemicals and reagents were purchased from Fluka
and Merck chemical companies and were used without further
purification. 1H NMR and 13C NMR spectra were recorded on
a Bruker DRX-400 MHz ultrashield spectrometer using CDCl3 as
a solvent and Me4Si as an internal standard. FT-IR (KBr pellet,
450–4400 cm−1) spectrum was taken with Perkin-Elmer Model
RX-I FT-IR spectrometer. The electronic spectra were recorded
on a Beckman DU-7000 UV-vis spectrophotometer. Elemental
analysis (C, H, and N) data were obtained with an Exeter Ana-
lytical CE-440 elemental analyzer. Melting points were taken
using an electro thermal IA 9100 apparatus in an open capillary
tubes.
2900–3040 (ꢄ, OH). The detailed descriptions of FT-IR and NMR
spectrums of the synthesized compound are given in the next
sections.
2.3. X-ray diffraction data of N,Nꢀ-(2,2-dimetylpropane)-
bis(dihydroxylacetophenone) Schiff base compound
The yellow single crystals of NDHA were obtained by slow evap-
oration of solvent from methanol solution of the compound at
room temperature. All of the measurements were performed using
graphite-monochromatized Mo K␣ radiation at 193 K: C18H14N4O,
2.2. Synthesis
N,Nꢀ-(2,2-dimetylpropane)-bis(dihydroxylacetophenone)
(NDHA) was prepared according to the following procedure:
˚
Mr 338.44, Triclinic, space group P1, a = 7.7847 (9) A, b = 9.1857 (12)
3
A, c = 13.3801 (14) A, V = 917.89 (18) A , Z = 2, dcalc = 1.225 Mg m−3
,
˚
˚
˚
ꢂ = 0.08 mm−1, crystal size = 0.40 mm × 0.30 mm × 0.10 mm. A total
of 6952 reflections were collected (ꢁ = 3.2–27.5◦), (Rint = 0.0644).
The structure was solved by direct methods (SHELXS-97) [21] and
refined by full-matrix least-squares techniques against F2 (SHELXL-
97) [22]. The final R indices of R1 = 0.2325 and wR2 = 0.1861
were obtained. The crystal packing fragment for NDHA is shown
in Fig. 2. Tables 1–2 show some X-ray crystallographic data of
NDHA.
To
a
well
stirred
solution
of
10 mmol
of
2-
hydroxylacetophenone in 1.2 mL absolute MeOH was added a
solution of 5 mmol 2,2-dimethyl 1,3-amino propane in 0.51 mL
absolute MeOH at abient temperature for 1 h. The purity of
the product was monitored by TLC using silica gel. The prod-
uct,
N,Nꢀ-(2,2-dimetylpropane)-bis(dihydroxylacetophenone)
(NDHA) (Fig. 1) was prepared as a yellow powder with high
yield. The solid yellow precipitate was filtered, washed with cold
MeOH, dried in vacuum desiccators and subjected to elemen-
tal microanalysis. Yield 46% with a mp. 128–130 ◦C. Anal. Calc.
for C21H26N2O2: C, 74.51, H, 7.76, N, 8.28, found: C, 74.46, H,
7.72, N, 8.25%. 1H NMR (CDCl3): ı 1.250–3.565 (s, 6H, methyl),
14.564 (s, 1H, OH), 6.807–7.556 (s, 4H, phenyl). FT-IR (KBr, cm−1):
3. Theoretical
All geometries were optimized at the B3LYP, PBEPBE and
PW91PW91 levels of theory along with standard 6-31+G(d,p)

146
V. Saheb, I. Sheikhshoaie / Spectrochimica Acta Part A 81 (2011) 144–150
Table 2
◦
˚
Selected bond lengths (A), angles ( ) and torsion angles in comparison with calcu-
lated values.
Parameters
X-ray analysis B3LYP
PW91PW91 PBEPBE
Bond lengths
C10–C12
C11–H11
C13–H13
C14–C16
C15–H15
C16–C17
C17–C18
C17–H17
C18–C19
C18–H18
C19–C20
C19–H19
C20–C21
C20–H20
O2–C21
O2–H02
1.527
1.039
1.022
1.482
0.950
1.396
1.383
0.984
1.390
0.991
1.374
0.986
1.400
0.982
1.344
1.020
1.289
1.462
1.56
1.541
1.541
1.101
1.010
1.474
1.095
1.417
1.394
1.092
1.410
1.092
1.393
1.093
1.413
1.092
1.340
1.060
1.311
1.450
1.542
1.094
1.010
1.480
1.089
1.412
1.389
1.084
1.403
1.085
1.388
1.086
1.405
1.085
1.343
1.011
1.295
1.461
1.102
1.110
1.473
1.097
1.418
1.395
1.093
1.411
1.093
1.394
1.095
1.414
1.094
1.343
1.049
1.310
1.460
N2–C14
N2–C13
H01···N1
H19···O1
2.54
Fig. 2. Crystal packing fragment of the NDHA Schiff base compound.
Bond angles
C10–C11–H11
H11A–C11–H11B
N2–C13–C10
C10–C13–H13
N2–C13–H
110.7
111.0
110.5
110.4
110.3
112.3
110.9
108.3
117.6
119.1
112.0
122.3
118.7
120.3
120.0
120.5
118.6
118.5
105.2
121.0
110.5
113.2
110.2
110.2
118.2
118.1
112.1
122.0
118.5
120.1
120.3
121.5
117.9
118.0
105.4
122.7
108.2
112.6
109.0
107.1
116.6
118.4
113.4
121.9
118.8
120.5
120.5
121.6
117.8
118.8
103.5
125.2
107.8
113.1
108.5
110.2
117.6
118.9
112.2
121.8
118.8
120.5
120.5
121.6
117.8
118.7
103.9
122.8
basis set. The harmonic vibrational frequencies and their rela-
tive intensities were calculated by B3LYP and PBEPBE methods
and the results were compared with experimental FTIR spectra.
The most widely used technique for calculating NMR shielding
tensors is the GIAO (Gauge Including Atomic Orbital) method
[23,24]. This method was used for calculating 1H NMR and
13C NMR chemical shifts at the B3LYP, PW91PW91 and PBEPBE
levels with the 6-31+G(d,p) basis set. Solvent (CHCl3) was
considered as a uniform dielectric constant 4.9 and Polarized Con-
tinuum Model (PCM) [25] was employed to calculate the NMR
chemical shifts. Time-dependent density functional theory (TD-
DFT) was used to compute excitation energies and oscillator
strengths for electronic transitions from ground to excited states
[26–28].
N2–C14–C16
C16–C14–C15
C14–C15–H15
C18–C17–C16
C18–C17–H17
C19–C18–H18
C20–C19–C18
C19–C20–H20
C21–C20–H20
O2–C21–C20
C21–O2–H02
C14–N2–C13
Dihedral angles
C14–N2–C13–C10
C12–C10–C13–N2
C13–N2–C14–C16
N2–C14–C16–C17
C15–C14–C16–C17
C19–C20–C21–O2
C19–C20–C21–C16
C17–C16–C21–O2
178.3
−57.4
−179.7
−179.0
0.4
179.6
−61.2
−179.4
−179.5
0.4
179.9
0.0
−179.9
179.6
−61.0
−179.5
−179.6
0.3
179.8
0.0
−179.8
179.8
−61.0
−179.3
−179.7
0.1
179.9
0.0
−179.9
DFT calculations at the B3LYP/6-31G(d) level are performed
to locate the lowest-energy conformations on the potential
energy surface (PES) and to estimate the conformational flexi-
bility of the compound. Some quantum chemical descriptors for
tautomers (HOMO, LUMO, dipole moment, molecular volumes
and heat of formation) are calculated at the B3LYP/6-31+G(d,p)
level. The geometry and charge distribution of the conju-
gated base of the molecule were also investigated. All the
calculations were carried out with the GAUSSIAN03 software
[29].
179.7
−1.0
−179.4
As shown in Table 2, the calculated bond lengths and bond
angles at all levels of theory are in reasonable agreement with
the crystallographic data. The molecule is optimized in gas phase
and the deviations in molecular geometries are attributed to
intramolecular interactions in the crystalline structure. The strong
4. Results and discussion
˚
˚
The crystal structure analysis of the synthesized material con-
firmed the structure of compound as N,Nꢀ-(2,2-dimetylpropane)-
bis(dihydroxylacetophenone). The X-ray crystallographic data
of NDHA are shown in Tables 1–2. All spectroscopic data
for NDHA are in good accordance with the X-ray crys-
O–H. . .N hydrogen bond (O2–H2 = 1.02 A, H2. . .N2 = 1.59 A) causes
for a planar six-membered ring formation. This short intramolec-
ular hydrogen bond belongs to the strong resonance-assisted
hydrogen bondings [30]. In order to evaluate the strength of this
hydrogen bond, the PES of the molecule was explored by scanning
the torsional angle ꢁ1 (H1–O1–C1–C6) at the B3LYP/6-31+G(d,p)
level. As can be seen from Fig. 3, the resulting potential energy
profile shows one global minimum (NDHA), two global maxima
and two local minima (C2). The energies of the local minima and
the global maxima are 74.5 kJ mol−1 and 101.3 kJ mol−1 higher than
NDHA, respectively. The large barrier-height for rotating about ꢁ1
(H1–O1–C1–C6) torsional angle implies a strong hydrogen bonding
in this system.
tallographic data. Scheme
1 shows the mechanism of the
reaction between 2-hydroxylacetophenone and 2,2-dimethyl
1,3-amino propane in absolute methanol. NDHA compound
is formed by the reaction of
C O with amino group and
gives an imine. Some experimental selected bond lengths and
bond angles are shown in Table 2 in comparison with the
calculated values at the B3LYP, PBEPBE and PW91PW91 lev-
els.

V. Saheb, I. Sheikhshoaie / Spectrochimica Acta Part A 81 (2011) 144–150
147
CH3
H3C
CH3
CH3
NH2
H3C
H2N
N
CH3
N
H3C
CHO
HO
2
+
OH
OH
Scheme 1. Schematic representation of the preparation of N,Nꢀ-(2,2-dimetylpropane)-bis(dihydroxylacetophenone) (NDHA) with its chemical diagram.
Table 3
120
1 (H1-O1-C1-C6)
Vibrational frequencies of NDHA in comparison with the calculated values the B3LYP
110
100
90
80
70
60
50
40
30
20
10
0
and PBEPBE levels of theory.a
C2
Experiment
B3LYP/6-31G(d)
PBEPBE/6-31+G(d,p)
Assignment
760
791
840
927
997
736
819
832
883
974
733
782
833
910
998
OB(HCC)
IB(HCC)
OB(HCC)
OB(HOC)
R(HCH)
IB(HCC)
IB(HCC)
IB(HCC)
T(HCH)
4 (C7-N1-C9-C10)
3 (C1-C6-C7-N1)
1062
1080
1131
1162
1218
1239
1261
1305
1324
1346
1371
1389
1449
1468
1509
1580
1615
2834
2903
2963
2983
3043
1047
1061
1146
1173
1215
1249
1256
1296
1314
1338
1376
1396
1442
1471
1505
1581
1616
2811
2902
2974
2991
3047
1067
1070
1121
1153
1196
1248
1275
1310
1323
1351
1371
1380
1445
1468
1516
1591
1612
2824
2911
2970
2986
3040
2 (N1-C9-C10-C13)
IB(HCC)
IB(HCC)
T(HCH)
C1
NDHA
NDHA
-10
IB(HCC)
IB(HCC)
W(HCH)
W(HCH)
W(HCH)
IB(HCC)
SC(HCH)
IB(HCC)
IB(HOC)
BS(C N)
BS(O–H)
BS(C–H)
BS(O–H)
BS(O–H)
BS(O–H)
-150
-100
-50
0
50
100
150
Torsional Angle (Degree)
Fig. 3. The potential energy profile for rotation about torsional angles ꢁ1
(H1–O1–C1–C6), ꢁ2 (N1–C9–C10–C13), ꢁ3 (C1–C6–C7–N1) and ꢁ4 (C7–N1–C9–C10).
NDHA to C1 is 26.8 kJ mol−1. This result clarifies that the compound
is relatively flexible in rotating about C9–C10 and the equiva-
lent C10–C13 bonds. To understand why the conformer NDHA is
observed experimentally, the molecular volume for two conform-
ers were calculated at the B3LYP/6-31+G(d,p) level by Gaussian
software [29] which calculates molecular volume defined as the
volume inside a contour of 0.001 electrons/bohr3 density. The val-
ues of 255.1 cm3 mol−1 and 268.4 cm3 mol−1 were obtained for
volumes of NDHA and C1, respectively. The smaller volume of
NDHA relates to close packing effect and a stronger intramolec-
ular interaction as found in our previous study [31]. The energy
of the molecule increases continuously by more than 70.0 kJ mol−1
through scanning the angle ꢁ3 (C1–C6–C7–N1) due to vanishing
of the strong resonance-assisted N1. . .H1 hydrogen bonding. The
potential energy profile obtained by scanning the torsional angle
ꢁ4 (C7–N1–C9–C10) is also depicted in Fig. 3. As can be seen, the
a
BS: bond stretching, SC: scissoring, R: rocking, W: wagging, T: twisting, IB: in-
plane bending, OB: out-of-plane bending.
The flexibility of the molecule for conversion to different con-
formers was determined by scanning the torsional angles ꢁ2
(N1–C9–C10–C13), ꢁ3 (C1–C6–C7–N1) and ꢁ4 (C7–N1–C9–C10)
between −180◦ and 180◦ in every 10◦. The 1D potential energy
profiles in Fig. 3 show that the most stable conformers are NDHA
and C1. The conformer C1 which is as stable as the main conformer
NDHA is formed through scanning the angle ꢁ2 (N1–C9–C10–C13).
The barrier height calculated at the B3LYP/6-31+G(d,p) level from
Table 4
Experimental isotropic 1H NMR chemical shifts of NDHA in comparison with calculated theoretical values.
Experiment
B3LYP/6-31G*
B3LYP/6-1+G**
PW91PW91/6-31+G**
PBEPBE/6-31+G**
Assignment
1.2903
2.4096
3.5414
6.8172
6.9622
7.3121
7.5497
14.5641
1.1657
2.2033
3.6235
6.6235
6.7581
7.1635
7.3356
14.7568
1.2435
2.2313
3.4634
6.8475
7.1263
7.4665
7.6455
14.9322
1.0934
2.3954
3.7493
6.8484
7.1139
7.3006
7.5655
15.2058
1.2505
2.2600
3.5964
6.7762
6.9957
7.3821
7.5871
15.3298
11&12
8&15
9&13
4&18
2&20
3&19
5&17
OH

148
V. Saheb, I. Sheikhshoaie / Spectrochimica Acta Part A 81 (2011) 144–150
molecule is flexible in varying the angle ꢁ4 from 180◦ to 100◦. How-
ever, energy of the molecule increases rapidly with decreasing ꢁ4
to less than 100◦ because the internal rotation is hindered by steric
interaction of methyl groups. The geometries of different conform-
ers, the keto-amine tautomer of NDHA and the transition state
connecting keto-amine tautomer to NDHA (enol-imine) conformer,
optimized at the B3LYP/6-31+G(d,p) level of theory, are shown in
Fig. 4. The keto-amine form, with energy being 13.3 kJ mol−1 higher
than conformer NDHA, could be formed through a saddle point with
a barrier height of 15.2 kJ mol−1
.
The experimentally observed Fourier transform infrared (FTIR)
peaks of NDHA are given in Table 3 and compared with the
most intense harmonic vibrational frequencies calculated at
the B3LYP/6-31+G(d,p) and PBEPBE/6-31+G(d,p) levels of the-
ory. The frequencies calculated by B3LYP/6-31+G(d,p) method
are scaled by 0.9594 to compensate the shortcomings due
to basis set truncation and neglect of electron correlation
and mechanical anharmonicity [32,33]. The vibrational fre-
quencies computed by PBEPBE/6-31+G(d,p) method are not
scaled. The frequencies obtained by both theoretical meth-
ods are in accordance with the observed FTIR spectrum. By
comparing the computed and experimental vibrational frequen-
cies, each absorption peak could be assigned to
a normal
mode of vibration of the compound. The results of the vibra-
tional bands assignments are given in the fourth column of
Table 3.
Fig. 5 shows the 1H NMR spectrum of the title compound. Exper-
imentally, eight peaks are observed because the molecule has a
symmetric structure, with many hydrogen atoms being in the same
electronic environment. The rotation of methyl groups causes their
hydrogen atoms show unique NMR peaks as well. The computed
1H NMR chemical shifts at the B3LYP/6-31G(d), B3LYP/6-31+G(d,p),
PBEPBE/6-31+G(d,p) and PW91PW91/6-31+G(d,p) levels of theory
along with experimental data are given in Table 4. As can be seen,
the results obtained by using all DFT methods are in reasonable
agreement with experimental values. The 13C NMR spectrum of the
compound is demonstrated in Fig. 6. The isotropic chemical shifts
calculated by all DFT methods are given in Table 5 and compared
with the experimental data. In order to compute the 13C NMR chem-
ical shifts, each couple of carbon atoms on equivalent locations of
the molecule have been considered as equivalent and their average
of chemical shifts are calculated. The predicted 13C NMR peaks by
B3LYP/6-31+G(d,p) are in accordance with the experimental data.
The calculated 1H NMR and 13C NMR magnetic shielding tensors
are compared with the experimental values and assignments are
performed and the results are given in Tables 4 and 5.
To clarify the relation between theoretical and experimental
values of NMR shielding tensors, the experimental data are plot-
ted versus computed values. As shown in Fig. 7, there is a good
linear relationship between experimental and theoretical chemi-
cal shifts. Similar plots for other calculated NMR peaks are given in
supplementary content.
The UV–visible spectrum of the synthesized Schiff base shows
two bands at 322 and 389 nm which correspond to enol-imine
and keto-amine tautomers, respectively. These values are similar
to those found in related compounds [34]. Electronic absorption
spectrum of NDHA and its keto-amine tautomer are calculated by
time-dependent DFT (TD-DFT) method at the B3LYP/6-31+G(d,p)
level of theory. The predicted absorption wave lengths for enol-
imine and keto-amine tautomers are at 317.22 and 382.44 nm,
respectively.
The quantum descriptors for tautomers are given in Table 6.
The gap between the highest occupied molecular orbital (HOMO)
and the lowest unoccupied molecular orbital (LUMO) is rational-
ized as a measure of molecular hardness [35]. Stable molecules
are characterized by large HOMO–LUMO energy gaps. The large
Fig. 4. The optimized geometries of NDHA, the conformer C1 (via rotation about
torsional angle ꢁ2), the conformer C2 (via rotation about torsional angle ꢁ1), keto-
amine tautomer of NDHA, transition state for conversion of enol-imine to keto-
amine tautomer and the conjugated base.

V. Saheb, I. Sheikhshoaie / Spectrochimica Acta Part A 81 (2011) 144–150
149
Fig. 5. Experimental 1H NMR spectrum of NDHA.
Table 5
Experimental isotropic 13C NMR chemical shifts of NDHA in comparison with calculated theoretical values.
Experiment
B3LYP/6-31G*
B3LYP/6-31+G**
PW91PW91/6-31+G**
PBEPBE/6-31+G**
Assignment
15.031
25.098
36.345
14.4397
24.0181
39.5614
15.4147
24.5522
39.4378
62.569
113.2469
116.0637
118.8357
123.4934
128.2478
162.6213
168.9637
13.9729
25.2329
43.6347
63.0902
111.555
115.06
116.4924
122.4342
126.381
159.8327
166.9229
14.3738
24.8666
38.8823
C8&C15
C11&C12
C10
58.071
59.6574
63.4568
C9&C13
C4&C18
C2&C20
C6&C16
C5&C17
C3&C19
C1&C21
C7&C14
117.491
119.084
119.652
128.529
133.008
164.509
172.859
110.4188
112.6294
114.5788
122.2032
125.7573
155.9394
165.9652
111.8742
115.4591
116.6281
120.1017
125.91597
158.6314
165.5774
Table 6
Calculated quantum descriptors of tautomers.
Enol-form
Keto-form
conformer (L1)
conformer
HOMO/(eV)
LUMO/(eV)
−5.96
−1.65
4.31
4.50
−980.2
255.1
−5.50
−1.90
3.60
5.08
−966.9
285.7
ꢅE (HOMO–LUMO)/eV
M (Debye)
ꢅHfꢁ (kJ mol−1
)
Molecular volume (cm3 mol−1
)
HOMO–LUMO gaps in two tautomers reveal that they should
be stable molecules. The visualized isosurface of HOMO and
LUMO orbitals are given in supplementary content. The calcu-
lated enthalpies of formations show that the enol-imine tautomer
is more stable than the keto-amine tautomer. The geometry and
charge distribution (Mulliken population analysis) of the conju-
gated base of NDHA is also demonstrated in Fig. 4. The charge
density is mostly concentrated on oxygen and nitrogen which
Fig. 6. Experimental 13C NMR spectrum of NDHA.

150
V. Saheb, I. Sheikhshoaie / Spectrochimica Acta Part A 81 (2011) 144–150
16
14
12
10
8
References
1H NMR (B3LYP)
exp = 0.963( 0.058) calcd - 0.173( 0.044)
R = 1.000
[1] H. Schiff, Ann. Chem. Pharm. 3 (Suppl.) (1864) 343.
[2] D. Barton, W.D. Ollis, Comprehensive Organic Chemistry, vol. 2, Pergamon,
Oxford, 1979.
[3] R.W. Layer, Chem. Rev. 63 (1963) 487–510.
[4] C.K. Ingold, Structure and Mechanism in Organic Chemistry, Second ed., Cornell
Univ, Ithaca, 1969.
[5] D. Lorcya, N. Belleca, M. Fourmiguea, N. Avarvari, Coord. Chem. Rev. 253 (2009)
1398–1438.
[6] H. Reyes, C. Garcia, N. Farfan, R. Santillan, P.G. Lacroix, C. Lepetit, K. Nakatani, J.
Organomet. Chem. 689 (2004) 2303–2310.
[7] S. Di Bella, I. Fragala, I. Ledoux, J. Zyss, Chem. Eur. J. 7 (2001) 3738–3743.
[8] J.F. Lamere, P.G. Lacroix, N. Farfan, J.M. Rivera, R. Santillan, K. Nakatani, J. Mater.
Chem. 16 (2006) 2913–2920.
6
[9] G.P. Lacroix, Eur. J. Inorg. Chem. 2001 (2000) 339–348.
[10] A. Elmali, A. Karakas, H. Unver, Chem. Phys. 309 (2005) 251–257.
[11] F. Cariati, U. Caruso, R. Centore, A. De Maria, M. Fusco, B. Panunzi, A. Roviello,
A. Tuzi, Inorg. Chim. Acta 357 (2004) 548–556.
4
2
[12] S.A. Houlden, I.G. Csizmadia, Tetrahedon 25 (1969) 1137–1153.
[13] H. Dinc¸ alp, F. Toker, I. Durucasu, N. Avcıbas¸ ı, S. Icli, Dyes Pigments 75 (2007)
11–24.
[14] S. Ernst, H. Disteldorf, X. Yang, Micropor. Mesopor. Mater. 22 (1998) 457–464.
[15] R.N. Krasikova, O.F. Kuznetsova, O.S. Fedorova, V.I. Maleev, T.F. Saveleva, Y.N.
Belokon, Bioorg. Med. Chem. 16 (2008) 4994–5003.
0
0
2
4
6
8
10
12
14
16
Theoretical Chemical Shift (ppm)
[16] W. Koch, M.C. Holthausen, A Chemist’s Guide to Density Functional Theory,
Second ed., WILEY/VCH Verlag GmbH, Weinheim, 2001.
[17] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652.
Fig. 7. A plot of experimentaland theoretical1H NMR chemicalshifts at the B3LYP/6-
31+G(d,p) level.
[18] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785–789.
[19] J.P. Perdew, K. Burke, Y. Wang, Phys. Rev. B 54 (1996) 16533–16539.
[20] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865–3868.
[21] G.M. Sheldrick, SHELXS-97. Program for the Solution of Crystal Structures, Uni-
versity of Göttingen, Germany, 1997.
is indicative that the title compound is a powerful chelating
agent.
[22] G.M. Sheldrick, SHELXL-97. Program for the Refinement of Crystal Structures,
University of Göttingen, Germany, 1997.
5. Conclusion
[23] K. Wolinski, J.F. Hilton, P. Pulay, J. Am. Chem. Soc. 112 (1990) 8251–8260.
[24] J.L. Dodds, R. McWeeny, A.J. Sadlej, Mol. Phys. 41 (1980) 1419–1430.
[25] S. Miertus, E. Scrocco, J. Tomasi, Chem. Phys. 55 (1981) 117–129.
[26] R.E. Stratmann, S.G.E. cuseria, M.J. Frisch, J. Chem. Phys. 109 (1998)
8218–8224.
[27] R. Bauernschmitt, R. Ahlrichs, Chem. Phys. Lett. 256 (1996) 454–464.
[28] M.E. Casida, C. Jamorski, K.C. Casida, D.R. Salahub, J. Chem. Phys. 108 (1998)
4439–4449.
[29] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
J.A. Montgomery Jr., T. 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, Gaussian 03, Revision C.01, Gaussian, Inc.,
Wallingford, CT, 2004.
The Schiff base N,Nꢀ-(2,2-dimetylpropane)-bis(dihydroxyla-
cetophenone) (NDHA) has been synthesized and characterized by
FTIR, 1H NMR, 13C NMR spectroscopy and X-ray single-crystal
determination. Quantum chemical methods such as B3LYP, PBEPBE
and PW91PW91 methods are used to obtain geometrical param-
eters and calculate the FTIR, 1H NMR, 13C NMR spectra of the
compound. The computed spectra are compared with the exper-
imental observations.
The bond lengths, bond angles and dihedral angles computed by
all theoretical methods are in agreement with the X-ray crystallo-
graphic data. The normal mode vibrational frequencies calculated
at the B3LYP and PBEPBE levels of theory are in accordance with
the recorded FTIR spectrum. In addition, vibrational bands assign-
ments and analysis of the fundamental modes of the compound
are performed. The chemical shifts of the 1H NMR and 13C NMR
spectra predicted by all of the DFT methods are in accordance with
the experimental NMR spectra. However, the chemical shifts calcu-
lated by B3LYP/6-31+G(d,p) method are in better agreement with
the experimental data.
[30] G. Gilli, F. Bellucci, V. Ferretti, V. Bertolasi, J. Am. Chem. Soc. 111 (1989)
1023–1028.
[31] I. Sheikhshoaie, V. Saheb, Spectrochim. Acta Part A 77 (2010) 1069–1076.
[32] J.A. Pople, H.B. Schlegel, R. Krishnan, J.S. Defrees, J.S. Binkley, M.J. Frisch,
R.A. Whiteside, Int. J. Quantum Chem. Quantum Chem. Symp. 15 (1981)
269.
Acknowledgment
[33] K.K. Irikura, R.D. Johnson III, R.N. Kacker, J. Phys. Chem.
8430–8437.
A 109 (2005)
[34] S.H. Alarcon, D. Pagani, J. Bacigalupo, A.C. Olivieri, J. Mol. Struct. 475 (1999)
233–240.
[35] R.G. Pearson, Proc. Natl. Acad. Sci. U.S.A. 83 (1986) 8440–8441.
We are grateful to Shahid Bahonar University of Kerman
Research Council for the financial support of this research.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.05.080.