FTIR investigation of solvent effects of N-methyl and N-tert-butyl benzamide

Article abstract of DOI:10.1134/S0022476614080319

Infrared spectroscopy studies of N-methyl benzamide and N-tert-butyl benzamide in 12 organic solvents were undretaken to investigate solvent-solute interactions. The wavenumbers of carbonyl stretching vibration ν(C=O) in different solvents were correlated

Full text of DOI:10.1134/S0022476614080319

Journal of Structural Chemistry. Vol. 55, No. 8, pp. 1616-1622, 2014.
Original Russian Text © 2014 B. Jović, A. Nikolić, S. Petrović, B.Kordić, T. Đaković-Sekulić, N. Stojanović.
FTIR INVESTIGATION OF SOLVENT EFFECTS
OF N-METHYL AND N-tert-BUTYL BENZAMIDE
a
B. Jović , A. Nikolić , S. Petrović , B.Kordić ,
a
b
a
a
T. Đaković-Sekulić , and N. Stojanović
a
Infrared spectroscopy studies of N-methyl benzamide and N-tert-butyl benzamide in 12 organic solvents
were undretaken to investigate solvent-solute interactions. The wavenumbers of carbonyl stretching
vibration ν(C=O) in different solvents were correlated with the solvent acceptor number (AN), the linear
solvation energy relationships (LSER), Catalan solvent parameters (SA, SB and SPP) and Buckingham
equation. For both studied amides significant correlation of the position of the carbonyl band with empirical
parameters was obtained. Based on obtained results it was assumed that the amide self-association and the
steric effects are most important factors that determine position of carbonyl groups band in the IR spectra.
DOI: 10.1134/S0022476614080319
Keywords: N-methyl benzamide, N-tert-butylbenzamide, Solvent effect, solvent parameters.
INTRODUCTION
N-substituted amides are important as the simplest model molecules having a peptide group. Intermolecular
interactions of the amide group is an important factor in determining the structure of biomolecules. Numerous empirical and
theoretical studies [1-4] have been devoted to the intermolecular interactions of N-substituted amides. Solvent effects on
carbonyl groups of many secondary amides have not yet been systematically studied. In this paper it was attempted to
examine solvent effects on the infrared spectra of two N-substituted amides with different N-substituents in 12 organic
solvents.
Several empirical parameters have been used in this work to give better insight into the nature of intermolecular
interactions of N-substituted amides. The Gutman’s acceptor number AN was proposed [5] as quantitative empirical
31
parameter of solvent electrophilicity based on P NMR chemical shifts of triethylphosphine oxide in different solvent. The
fairly good linear correlations of AN with position of carbonyl stretching vibration ν(C=O) have been found for large number
of substances in different organic solvents [6-8].
ν = ν0 + αAN
(1)
The solvent parameters of the Kamlet–Taft solvatochromic relationship [9] measure separately the hydrogen bond
donor acidity (α), hydrogen bond acceptor basicity (β), and dipolarity/polarizability (π*) properties of solvents as contributing
to overall solvent polarity, δ is a polarizability correction term for polychlorinated aliphatic and aromatic solvents.
a
Department of Chemistry Biocemistry and Environmental protection, Faculty of Sciences, University of Novi Sad,
b
21000 Novi Sad, Serbia. Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Beograd,
Serbia; branislav.jovic@dh.uns.ac.rs. The text was submitted by the authors in English. Original article submitted March 25,
2014.
1616
0022-4766/14/5508-1616 © 2014 by Pleiades Publishing, Ltd.

ν = ν0 + (sπ* + dδ) + aα + bβ
(2)
The magnitudes of regression coefficients (a, b, d, s) The Catalan et al. [10] proposed solvent properties scales based
on carefully selected positively solvatochromic pairs of test dyes and include values for about 200 organic solvents. In this
paper: dipolarity/polarizability SPP, solvent basicity SB, and solvent acidity SA solvatochromic parameters were correlated
with position of carbonyl group band in order to estimate acid-base and polarisability properties of investigated solvents. can
describe relative contribution of the indicated parameters.
ν = ν0 + aSA + bSB + pSPP
(3)
The Kirkwood-Bauer-Magat (KBM) equation [11] has been used often in studies of IR carbonyl vibration shifts but
is not satisfactory for polar solvents. The deviations from the KBM equation have been attributed to formation of molecular
complexes. KBM equation have been modified and improved by a number of authors, in this study extended Buckingham
equation [12], was used:
2
⎛
⎞
ε −1
n −1
⎛
⎞
ν = C + C
1
+ C
3
(4)
⎜
⎝
⎟
⎠
2
⎜
⎝
⎟
⎠
2
2ε +1
2n +1
EXPERIMENTAL
N-methyl and N-tert-butyl benzamide were synthesised by Schotten-Baumann reaction of acylation of the
corresponding amines with alkyl chloride. The purity of these N-monosubtituted amides was cheked by GC and mass
spectrometry. For all samples used in this work the purities as judged by GC were 99.2% or better.
All solvents were obtained from commercial sources (Aldrich, Fluka, Merck, > 97%) and have been redestilled prior
to use.
–1
Infrared absorbtion spectra (2000-1600 cm ) have been obtained using a Thermo-Nicolet Nexus 670 instrument. A
DTGS detector was employed in IR measurements. For all spectra, 50 scans were recorded and averaged with a resolution of
–1
2 cm for each spectrum. The concetrations of the N-substituted amides in the pure solvents were between 0.003 and
–3
0.02 mol·dm . Samples were placed in 0.057 and 0.116 mm path length NaCl cells and the measurements were performed at
–1
298 K. The reported frequencies were reproducible within 0.2 cm . The IR spectra of pure solvents were recorded under the
same conditions. The Thermo-Nicolet Omnic software version 6.0 was used for spectral data treatment.
RESULT AND DISCUSSION
Fig. 1. The observed frequencies of the ν(C=O) of (a) N-methyl and (b) N-tert-butylbenzamide in 12
different organic solvents.
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The FTIR spectra of the selected N-substituted benzamides in 12 different solvents are shown in Fig. 1. The
observed frequencies of the ν(C=O) of N-substituted amides and the solvent parameters are presented in Table 1.
TABLE 1. The Observed Frequencies of the ν(C=O) of N-Substituted Amides and the Solvent Parameters of Investigated
Organic Solvents
NMB
NtBA
Solvent
AN
8.6
n
ε
π*
δ
α
0
β
0
SA
0
SB
SPP
ν(C=O) ν(C=O)
1
Carbontetra-
chloride
1680.1
1676.2
1.4612 2.2
0.28
0.5
0.044 0.632
2
3
Chloroform
1660.3
1667.1
1660.1 23.1 1.4458 4.8
1663.8 20.4 1.4241 8.9
0.58
0.85
0.5 0.44
0.5 0.3
0
0
0.047 0.071 0.786
0.040 0.178 0.876
Methylene
chloride
Dichloroe-
thane
4
1669.9
1666.0 16.7 1.4448 10.4 0.81
0.5
0
0
0.030 0.126 0.890
5
6
7
8
9
Hexane
1689.4
1689.1
1676.7
1677.3
1671.9
1684.4
1683.7
1674.0
1674.8
1668.8
0
1.3749 1.9
1.3876 1.9
1.5011 2.3
–0.11
–0.08
0.59
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.056 0.519
0.083 0.526
0.124 0.667
0.128 0.655
0.591 0.838
Heptane
Benzene
Toluene
0
0
8.2
3.3
8.0
0.1
0.11
0.55
1.4969
1.4072
2.4
7.6
0.54
Tetrahidro-
furan
0.58
10
Diethyl ether
1676.5
1674.6
3.9
1.3524
4.2
0.27
0
0
0.47
0
0.562 0.694
11
12
Acetone
1667.1
1672.2
1663.6 12.5 1.3586 20.6 0.62
1669.1 9.3 1.3724 6.0 0.45
0
0
0.08 0.48
0.45
0
0
0475 0.881
0.542 0.795
Ethyl acetate
0
Fig. 2. The plot of the ν(C=O) of N-methyl
(•) and N-tert-butylbenzamide (◦) versus
Guttman acceptor number AN.
The IR region of the carbonyl group vibration is generally complex. Existence of different bands and band shoulders
in this region can be attributed to the following effects: self-association through hydrogen bonding, forming a solvent-solute
complex, existence of stable conformers and the Fermi resonance [13-15].
The plot of the ν(C=O) versus Guttman acceptor number (AN) is shown in Fig. 2. The linear equation parameters
and correlation coefficients of each amide are shown in Table 2.
As it can be noticed in Table 2 and Fig. 2, the carbonyl group band shifts to lower frequency with increasing
electrophilicity of the solvent. The influence of solvent polarity on the frequency shift of the carbonyl C=O group was similar
for both amides. Comparison of the α values indicates that N-tert-butyl benzamide shows slightly higher sensitivity to solvent
polarity.
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TABLE 2. The Guttman Equation Parameters and Correlation Coefficient
ν
α
R
0
N-methyl benzamide
N-tert-butyl benzamide
1684.7
1680.5
–1.037
–0.939
0.896
0.910
TABLE 3. The Multilinear LSER Equation Parameters and Correlation Coefficient
ν
0
s
d
a
b
R
N-methyl benzamide
N-tert-butyl benzamide
1687.4
1683.1
–14.91
–13.79
–7.02
–7.55
–28.01
–22.14
–15.85
–14.07
0.954
0.954
Fig. 3. The plot of the ν(C=O) of (a) N-methyl and (b) N-tert-butylbenzamide versus α and π* Kamlet–Taft
solvatochromic parameters.
The multilinear LSER equation parameters and correlation coefficients of each amide are shown in Table 3. The
plots of the ν(C=O) versus hydrogen bond donor acidity (α) and dipolarity/polarizability (π*) parameters are shown in Fig. 3.
On the basis of the magnitudes of the parameter values for the solvatohromic equation, it could be estimated that it is
the possibility for a solvent to donate hydrogen atom for hydrogen bonding which contributes most to the shift of the
carbonyl band. In this study solvents with “classical” hydrogen donor groups such as OH and NH groups are not investigated,
so it can be assumed CH groups act as hydrogen donors. Hydrogen bonding involving CH groups have been proven in
numerous papers [15].
The plots of the ν(C=O) versus Catalan SA and SPP parameters are shown in Fig. 4. The linear equation parameters
and correlation coefficients for both amides are shown in Table 4.
2 2
The plot of the ν(C=O) versus f(є)=(ε – 1/2ε + 1) and the f(n)=(n – 1/2n +1) of the Buckingham equation is shown
in Fig. 4. The multilinear Buckingham equation parameters and correlation coefficients of each amide are shown in Table 4.
TABLE 4. The Catalan Multilinear Equation Parameters and Correlation Coefficient
ν
a
b
p
R
0
N-methyl benzamide
N-tert-butyl benzamide
1708.2
1704.5
180.35
127.94
–4.62
–1.79
–42.28
–43.41
0.926
0.953
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Fig. 4. The plot of the ν(C=O) of (a) N-methyl and (b) N-tert-butylbenzamide versus SA and SPP Catalan
parameters.
From Table 5 and Fig. 4 it can be seen that good correlation was obtained with the modified KBM, Buckingham
equation. If we use KBM equation which takes into account only dielectric constants, poor correlation is obtained. This result
indicates that more effects has to be taken in to account for carbonyl group shift in different solvents: nonspecific
interactions, hydrogen bonding, and steric effects.
N-substituted benzamides have a proton donor and acceptor functional groups, and their dipole moments are 3.6 D
[16], and represent a group of organic compounds with a high possibility of formation of different molecular complexes.
Self-association of N-substituted benzamides was investigated in carbon tetrachloride and benzene [17]. It was
found that in the case of N-tert-butyl benzamide self-association is about four times stronger in non-polar CCl than in
4
benzene, due to formation of N–H···π hydrogen bonds. Self-association of different amides and N-substituted amides was
also studied, and a similar trend was found in nonpolar solvents [13, 14]. In this study we investigated amides in diluted
–3
solutions in the concentration range stretching from 0.003 to 0.02 mol dm , while amides self-association via hydrogen
bonding has been proven at much lower concentrations [15]. Based on data obtained in this work and literature data, it can be
Fig. 5. The plot of the ν(C=O) of (a) N-methyl and (b) N-tert-butylbenzamide versus (ε – 1/2ε+1) and the
2 2
(n – 1/2n +1) of the Buckingham equation.
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TABLE 5. The Multilinear Buckingham Equation Parameters and Correlation Coefficient
C
C
C
3
R
1
2
N-methyl benzamide
N-tert-butyl benzamide
1740.2
1728.9
–79.69
–73.56
–197.76
–167.37
0.824
0.874
assumed that the dominant effect that determines the position of the C=O groups in the IR spectra is self-association of N-
substituted amides.
With increasing of the solvent polarity self-association of secondary amides is less favored because of the possibility
of creating associates with the solvent, in other words, active competition for the proton donor and acceptor groups between
amide and solvent molecules can be assumed. In a test series of N-substituted amides, the lowest association constants were
obtained for the secondary amides with bulky substituents [2]. Impact of the steric effect on amide self-association should be
the same for the formation of molecular complexes between amide and solvent molecules. Based on the results obtained in
this work it can be assumed that the steric effect has greater influence on the possibility of formation of self-associates than
on the formation of molecular complexes between secondary amide and solvent molecules.
CONCLUSIONS
Solvent effects on the infrared spectra of N-methyl and N-tert-butyl benzamide in 12 organic solvents have been
examined. Several empirical parameters have been used in order to achieve a better insight into the nature of carbonyl group
interactions of the selected amides. Comparison of the obtained parameter values for both amides indicates that N-tert-butyl
benzamide shows slightly higher sensitivity to the solvent polarity. The results also indicate that more effects have to be taken
into account for N-methyl and N-tert-butyl benzamide carbonyl group shift: hydrogen bonding, nonspecific interactions, and
substituent effects. Based on differences in the obtained parameter values for the model applied and literature data, it can be
estimated that self-association and steric effects are the most important factors that determine the position of carbonyl group
band in the IR spectra of the N-substituted benzamides with different substituents.
This work was financially supported by the Ministry of Education and Science of Serbia (Projects No 172013).
REFERENCES
1. B. Jović, A. Nikolić, and S. Petrović, J. Mol. Struct., 1044, 140-143 (2013).
2. B. Jović, A. Nikolić, and B. Holló, J. Struct. Chem., 54, 431-436 (2013).
3. S. Gadžurić, A. Nikolić, M. Vraneš, B. Jović, M. Damjanović, and S. Dožić, J. of Chem. Thermodyn., 51, 37-44 (2012).
4. E. B.Burgina, V. P. Baltakhinov, E. V.Boldyreva, and T. P. Shakhtschneider, J. Struct. Chem., 45, 64-73 (2004).
5. V. Gutmann, The Donor-Acceptor Approach to Molecular Interactions, Plenum Press, New York (1978).
6. Q. Liu, W. Sang, and X. Xu, J. Mol. Struct., 608, 253-257 (2001).
7. M. S. Zakerhamidi, S. Ahmadi-Kandjani, M. Moghadam, E. Ortyl, and S. Kucharski, J. Mol. Struct., 996, 95-100
(2011).
8. C. Conti, R. Galeazzi, E. Giorgini, and G. Tosi, J. Mol. Struct., 744-747, 417-423 (2005).
9. M. J. Kamlet, J. L. Abboud, and R. W. Taft, J. Am. Chem. Soc., 99, 8325-8327 (1977).
10. J. Catalán, Handbook of Solvents G. Wypch (Ed.), ChemTech Publishing, Toronto (2001).
11. L. Onsager, J. Am. Chem. Soc., 58, 1486-1491 (1936).
12. A. D. Buckingham, Trans. Faraday Soc., 56, 753-761 (1960).
13. A. Nikolic, M. Tarjani-Rozsa, N. U. Perišić, A.Petrik, and D.G. Antonović, J. Mol. Struct., 219, 245-250 (1990).
14. A. D. Nikolić, M. Tarjani, N. Perišić-Janjić, and S. D. Petrović, J. Mol. Struct., 174, 129-134 (1988).
1621

15. G. A. Jeffrey, Oxford University Press, New York (1997).
16. CRC Handbook of Physics and Chemistry, 52nd edition, Chemical Rubber Co., Cleveland (1971).
17. A. Nikolić, M. Rozsa-Tarjani, A. Komaromi, J. Csanadi, and S. Petrović, J. Mol. Struct., 2267, 49-54 (1992).
18. J. G. Lin, S. Q. Zang, Tian, et al., CrystEngComm., 9, 915-921 (2007).
19. Y. Yang, P. Du, J. F. Ma, et al., Cryst. Growth Des., 11, 5540-5553 (2011).
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