FTIR spectroscopic study of hydrogen bonding and solvent induced frequency shifts of N-tert-butylacetamide

Article abstract of DOI:10.1016/j.molstruc.2012.10.009

This paper reports the results of FTIR study of N-tert-butylacetamide in carbon tetrachloride solution and in presence of seven different molecules as H acceptors. The spectroscopic characteristics for NH?O hydrogen bonded complexes are given. Also, the equilibrium constants for 1:1 complex formation, at 25 °C were determined by using IR measurements. Frequency shifts of carbonyl stretching vibration ν(CO) of N-tert-butylacetamide in the same organic H acceptors was also investigated. The wavenumbers of carbonyl stretching vibration ν(CO) were correlated with the solvent acceptor number (AN) and the linear solvation energy relationships (LSERs).

Full text of DOI:10.1016/j.molstruc.2012.10.009

Journal of Molecular Structure 1044 (2013) 140–143
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
FTIR spectroscopic study of hydrogen bonding and solvent induced frequency shifts
of N-tert-butylacetamide
Branislav Jovi c´ , Aleksandar Nikoli c´ , S. Petrovi c´ b
a,
⇑
a
a
Department of Chemistry, Faculty of Sciences, University of Novi Sad, Trg Dositeja Obradovi ´c a 3, 21000 Novi Sad, Serbia
Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Beograd, Serbia
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 16 October 2012
This paper reports the results of FTIR study of N-tert-butylacetamide in carbon tetrachloride solution and
in presence of seven different molecules as H acceptors. The spectroscopic characteristics for NAHꢀ ꢀ ꢀO
hydrogen bonded complexes are given. Also, the equilibrium constants for 1:1 complex formation, at
25 °C were determined by using IR measurements. Frequency shifts of carbonyl stretching vibration
Keywords:
Hydrogen bonding
N-tert-butylacetamide
Solvent effect
m
(C@O) of N-tert-butylacetamide in the same organic H acceptors was also investigated. The wavenum-
bers of carbonyl stretching vibration (C@O) were correlated with the solvent acceptor number (AN) and
the linear solvation energy relationships (LSERs).
m
Ó 2012 Elsevier B.V. All rights reserved.
1
. Introduction
>99%), Ethyl acetate, Toluene, Diethyl ether (Fluka >98%), Tetrahy-
drofuran (Merck >99%), were redistilled and dried prior to use.
Using Becker’s procedure [15], the hydrogen bonding formation
constant can be determined from the difference of monomer band
N-substituted amides have been attracting scientific attention
for many years since this class of compounds can be regarded as a
simple model of biological systems with the peptide groups.
Numerous theoretical and experimental studies of hydrogen bond-
ing have been devoted to the amide group [1–8]. This paper is a part
of our continuing and systematic investigation of the secondary
amides in solutions from both, spectroscopic [9–11] and thermody-
namic [12–14] aspect. In the present work, we investigated the
absorbance of pure amide in CCl
4
solution and CCl
4
amide solution
in the presence of proton acceptor.
0
A ꢁ A
K ¼
ð1Þ
0
AC
PA
0
NAHꢀ ꢀ ꢀO and NAHꢀ ꢀ ꢀ
p interactions and the solvent effects on the
where A is the monomer absorbance for carbon tetrachloride solu-
tion containing of N-tert-butylacetamide and A is the absorbance of
infrared spectra of N-tert-butylacetamide. Spectroscopic character-
istics of NAH and C@O functional groups and several empirical
parameters have been used in this work to give better insight into
the nature of intermolecular interactions of N-substituted amides.
the same band for the solution with both N-tert-butylacetamide
0
PA
and the proton acceptor concentration (C ). Hydrogen bonding for-
mation constants and spectroscopic parameters were investigated
ꢁ1
in IR range of amide NAH vibration from 3600 to 3200 cm . In or-
der to avoid self-association, amide concentration in carbon tetra-
ꢁ3
2
. Experimental
chloride solutions was below 0.003 mol dm . Concentration of
ꢁ3
the proton acceptors varied within 0.2 and 1 mol dm . Samples
were placed in 1–5 cm (IR) UVIRSIL cells and the measurements
were performed at 298 K.
N-tert-butylacetamide was synthesised by Schotten–Baumann
reaction, by acylation of the corresponding amines with alkyl chlo-
ride. The purity of this N-monosubtituted amide was checked by
GC and mass spectrometry. Based on the GC results the sample
used in this work had purities 99.2% or better. The molecular struc-
ture of the N-tert-butylacetamide can be represented by the
scheme (see Scheme 1):
Solvent effects were investigated in IR range of amide carbonyl
ꢁ1
C@O vibration from 1800 to 1600 cm . For all spectra, 50 scans
ꢁ1
were recorded and averaged with resolution of 2 cm for each
spectrum. The concentrations of the N-substituted amides in the
ꢁ3
pure solvents were between 0.003 and 0.02 mol dm . Samples
were placed in 0.057 and 0.116 mm pathlength NaCl cells and
the measurements were performed at 298 K.
Carbon tetrahydrochloride (J.T. Baker, >99.9%) was used with-
out further purification. Acetone, Acetonitrile, Benzene, (J.T. Baker,
Infrared spectra were obtained using Thermo-Nicolet Nexus
670 instrument. A DTGS detector was employed in IR measure-
ments. The Thermo-Nicolet Omnic software version 6.0 was used
⇑
Corresponding author. Tel.: +381 21 4852737; fax: +381 21 454065.
E-mail address: branislav.jovic@dh.uns.ac.rs (B. Jovi c´ ).
0
022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.10.009

B. Jovi ´c et al. / Journal of Molecular Structure 1044 (2013) 140–143
141
are summarized in Table 1.
D
m
(NH) and
m
1/2(NH)
c
are NAH band
shift and halfwidth of the NAH complex band, respectively,
0
e
(NH)
and the integrated absorption coefficient. The observed frequen-
cies of the (C@O) of N-tert-butylacetamide in seven different or-
ganic H acceptors were also presented in Table 1.
c c
and B (NH) represent the molar absorbtion coefficient
m
ꢁ
1
The peak shoulders at about 3400 cm (for benzene and tolu-
ene, Fig. 1) actually belong to the NAH group from the hydrogen
bonded complex, by deconvolution of spectra it was found that
the red shift for these bands is 16.2 and 16.6 for toluene and
benzene.
Scheme 1. Scheme of molecular structure of N-tert-butylacetamide.
The obtained IR spectroscopic parameters clearly indicate
for all manipulation with spectral data. The reported frequencies
ꢁ1
NAHꢀ ꢀ ꢀO and NAHꢀ ꢀ ꢀ
p hydrogen bonding between NtBA and the
and half-widths were reproducible within 0.2 and 1 cm , respec-
tively. The integrated molar absorption coefficients were obtained
within ±5%. The equilibrium constants were determined with aver-
age relative standard deviation of 6%. Due to the small number of
samples, the obtained correlation coefficients were tested by two
tailed t-test with a significance level of 0.01.
investigated compounds. The stability of molecular complexes
increases in the following order: Ben < Tol < Eac < Thf < Dee <
Ace < Acn. Hydrogen bonding between the secondary amides and
different proton acceptors has been studied in many papers. Exper-
imentally was confirmed that the ether oxygen atom is a better
proton acceptor than
p aromatic electron system and a weaker
acceptor than the ketone oxygen [16,17]. The results obtained in
this study suggest that the strongest hydrogen bond is between
NtBA and acetonitrile molecule. The presence of strong specific
interactions between different substituted and non-substituted
amide molecules and acetonitrile has been proven thermodynam-
ically by some authors [18,19]. Unlike NAHꢀ ꢀ ꢀACN specific interac-
tions, OAHꢀ ꢀ ꢀACN interactions were studied spectroscopically and
3
. Results and discussion
Fig. 2 relates to the IR spectra of N-tert-butylacetamide in the
presence of different proton acceptors. The spectroscopic parame-
hydrogen bonded complexes ob-
ters for NAHꢀ ꢀ ꢀO and NAHꢀ ꢀ ꢀ
p
tained by the IR measurements and the equilibrium constants
Table 1
Spectroscopic parameters for hydrogen bonded complexes and the equilibrium constants obtained in IR measurements.
ꢁ
3
B0(NH)
(cm mol
ꢁ4
System
Hydrogen bond
type
m
(cm
(C@O)
D
(cm
m
(NH)
)
m
(cm
1/2 (NH)c
e
(NH)
c
10
c
10
K
ꢁ
1
ꢁ1
ꢁ1
2
ꢁ1
ꢁ1
(dm3 mol
ꢁ1
)
)
(cm mol
)
)
)
m
(NH) of NtBA in CCl
4
NtBA-
TOL
NtBA-
BEN
NtBA-
ACE
NAHꢀ ꢀ ꢀ
p
p
1685.2
1684.0
1675.8
16.2
8
3.92
3.8
0.55
0.31
1.13
ꢁ
1
(
cm )
NAHꢀ ꢀ ꢀ
16.6
36.2
8
2.46
1.99
2.93
13.6
NAHꢀ ꢀ ꢀO
NAHꢀ ꢀ ꢀO
47
3
448.9
NtBA-
EAC
1682.1
43.5
16
3.51
3.8
0.78
m
(C@O) of NtBA in CCl
4
NtBA-
ACN
NtBA-
DEE
NAHꢀ ꢀ ꢀ
p
1674.0
1686.5
45.9
84.8
17
28
5.76
6.61
17.2
3.9
1.35
1.03
ꢁ
1
(
cm )
NAHꢀ ꢀ ꢀO
NAHꢀ ꢀ ꢀO
1
689.1
NtBA-
THF
1681.7
85.7
35
3.67
2.9
0.85
Fig. 1. IR spectra of N-tert-butylacetamide, in the presence of seven different H acceptors.

1
42
B. Jovi ´c et al. / Journal of Molecular Structure 1044 (2013) 140–143
Fig. 2. The observed frequencies of the m(C@O) of N-tert-butylacetamide in seven different organic H acceptors.
theoretically, in terms of theoretical explanations of some experi-
mental data, some authors suggest the interaction of two mole-
cules of acetonitrile with phenol [20]. The specific interaction of
acetonitrile as a molecule with two proton acceptor sites (N atom
of the broad peak in the spectra of DEE is possibly due to the pres-
ence of secondary amide rotamers or resulting from deconvolution
of the spectral range.
The plot of the m(C@O) for versus Guttman acceptor number AN
and the
p
system) with the amide molecules represents an issue
is shown in Fig. 3. The linear equation parameters and correlation
that should be examined in the future.
coefficient is shown in the following equation.
The Gutman’s acceptor number AN was proposed [21] as quan-
titative empirical parameter of solvent electrophilicity based on
m
ðC@OÞ ¼ 1690:6 ꢁ 0:915AN R ¼ ꢁ0:9211
The multilinear LSER equation parameters and correlation coef-
ð4Þ
3
1
P NMR chemical shifts of triethylphosphine oxide in different sol-
vent. The fairly good linear correlations of AN with position of car-
bonyl stretching vibration (C@O) have been found for a large
number of substances in different organic solvents.
ficient are shown in the following equation.
m
mðC@OÞ ¼ 1694:7 ꢁ 16:05
p
ꢁ 31:92
a
ꢁ 9:41b R ¼ 0:9378
ð5Þ
m
¼
m
0
þ
aAN
ð2Þ
On the basis of the significant correlation obtained in Gutman
equation and the magnitudes of parameter values for the solv-
atohromic equation, it could be estimated that the electrophilicity
of the solvent, contributes most to the shift of carbonyl band. On
the basis of data obtained from LSER equation, contribution of
polarization effects must also be taken into account in order to
explain the carbonyl band position.
The solvent parameters of the Kamlet–Taft solvatochromic rela-
tionship [22,23] measure separately the hydrogen bond donor
acidity (
polarizability (
a
), hydrogen bond acceptor basicity (b), and dipolarity/
ꢂ
p
) properties of solvents as contributing to overall
solvent polarity, d is a polarizability correction term for polychlori-
nated aliphatic and aromatic solvents.
N-substituted acetamides have a proton donor and acceptor
functional groups and the dipole moments of 3.6 D order of
m
¼
m
0
þ ðspꢂ þ ddÞ þ a
a
þ bb
ð3Þ
The magnitudes of regression coefficients (a, b, d, s) can describe
relative contribution of the indicated parameters.
The FTIR spectra in the region of carbonyl group stretching
vibration of the N-tert-butylacetamide in seven different solvents
is shown in Fig. 2. The solvent parameters of seven investigated
organic H acceptors are presented in Table 2.
Broad peaks at about 1630 were not the subject of research, it is
very unlikely that these bands correspond to the carbonyl band red
ꢁ1
shift. In the case of toluene spectra, the band at 1630 cm corre-
sponded to C@C stretching vibration of toluene. The appearance
Table 2
The solvent parameters of seven investigated organic H acceptors.
ꢂ
Solvent
AN
p
d
a
b
Acetone
Acetonitrile
Benzene
Diethyl ether
Ethyl acetate
Tetrahidrofuran
Toluene
12.5
18.9
8.2
3.9
10.2
8.8
0.62
0.75
0.59
0.27
0.45
0.58
0.54
0
0
0
0
0
0
0
0.08
0.19
0
0
0
0.48
0.31
0.1
0.47
0.45
0.55
0.11
0
0
8.2
Fig. 3. The plot of the m(C@O) for versus Guttman acceptor number AN.

B. Jovi ´c et al. / Journal of Molecular Structure 1044 (2013) 140–143
143
magnitude [24] and represent a group of organic compounds with
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This work was financially supported by the Ministry of Educa-
tion and Science of Serbia (Project No. 172013).