Influence of substituents on the infrared stretching frequencies of carbonyl group in esters of benzoic acid

Article abstract of DOI:10.1002/poc.1112

Infrared spectra of 25 substituted phenyl esters of benzoic acid C ₆H₅CO₂C₆H₄-X (X=H, 3-Cl, 3-F, 3-CN, 3-NO₂, 3-CH₃, 3-OH, 3-NH₂, 4-Cl, 4-F, 4-NO₂, 4-CN, 4-

Full text of DOI:10.1002/poc.1112

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2006; 19: 654–663
Published online 16 November 2006 in Wiley InterScience
(
www.interscience.wiley.com) DOI: 10.1002/poc.1112
Influence of substituents on the infrared stretching
frequencies of carbonyl group in esters of benzoic acid
y
Vilve Nummert, Oksana Travnikova, Signe Vahur, Ivo Leito, Mare Piirsalu, Vahur M a¨ emets,
Ivar Koppel and Ilmar A. Koppel*
Institute of Chemical Physics, University of Tartu, Tartu, Jakobi 2, Estonia
Received 17 March 2006; revised 16 June 2006; accepted 28 June 2006
—
ABSTRACT: Infrared spectra of 25 substituted phenyl esters of benzoic acid C H CO C H -X (X—H, 3-Cl, 3-F, 3-
6
5
2 6 4
CN, 3-NO , 3-CH , 3-OH, 3-NH , 4-Cl, 4-F, 4-NO , 4-CN, 4-OCH , 4-CH , 4-NH , 2-Cl, 2-F, 2-I, 2-NO , 2-CF , 2-
2
3
2
2
3
3
2
—
2
3
CN, 2-CH3, 2-OCH , 2-N(CH ) , 2-C(CH ) ), 8 alkyl benzoates C H CO R (X—CH , CH CH , CH Cl, CH CN,
3
3 2
3 3
6
5
2
3
2
3
2
2
—— CH, CH
CH2C
(
2
—
CH
Cl, CH
CH
OCH
, CH
C
H
), and 22 phenyl esters of substituted benzoic acids X-C
H
4
CO
C
6
H
2
2
2
2
3
2
6
5
6
2
5
—
X—3-Cl, 3-NO , 3-CH 3-N(CH ) , 4-F, 4-Cl, 4-Br, 4-NO , 4-CH , 4-C(CH ) , 4-OCH , 4-NH , 2-Cl, 2-F, 2-Br, 2-I,
2 3, 3 2 2 3 3 3 3 2
ꢀ
-NO , 2-CN, 2-CF , 2-CH , 2-OCH , 2-NH ) were recorded in tetrachloromethane in the region of 400–4000 cm .
2 3 3 3 2
1
Carbonyl stretching frequencies nCO for meta- and para-substituted phenyl esters of benzoic acid and phenyl esters of
o
meta-substituted benzoic acids were shown to correlate with the substituent constants s . The influence of the through
resonance effect on nCO was found to be important in the case of þR para substituents in the benzoyl part of phenyl
benzoates as well. The carbonyl stretching frequencies of ortho derivatives in phenoxy part were shown to correlate
with the inductive substituent constant s only. In the benzoyl part of the esters the carbonyl stretching frequencies of
I
cis and trans conformers (relative to the carbonyl group) of ortho derivatives were nicely described by dual parameter
þ
B
s
B
s
equations: (n
)
¼ (n ) þ c s þ c E and (n
)
¼ (n ) þ c s þ c E (R ¼ 0.99). The trans isomers of
CO cis
CO o
1
I
3
CO trans
CO o
1
p
3
phenyl esters of ortho-substituted benzoic acids showed direct resonance similar to that for para derivatives. The
positive steric term found for both the cis and trans conformers could be considered as measure of the steric inhibition
of resonance between the phenyl ring and the carboxy-group caused by bulky ortho substituents. The existence of cis/
trans conformations was supported by frequency calculations with Density Functional Theory (DFT) method at
ꢁ
ꢁ
B3LYP/6-311þG level for the ortho-substituted benzoates. In the case of alkyl benzoates good correlations of n
CO
ꢁ
B
s
values were obtained when both the Taft s and the steric E constants were used. For meta- and para-substituted
phenyl benzoates s-trans conformation where the plane of the benzene ring in the benzoyl part of the ester is coplanar
with the carbonyl bond plane and the plane of the benzene ring in the phenoxy part is twisted nearly perpendicular
relative to the carbonyl bond plane was supported. Copyright # 2006 John Wiley & Sons, Ltd.
Supplementary electronic material for this paper is available in Wiley Interscience at http//www.interscience.wi-
ley.com/jpages/0894-3230/suppmat/
KEYWORDS: phenyl benzoates; alkyl benzoates; infrared spectra; substituent effects; DFT calculations
INTRODUCTION
substituted benzoic acids, X-C H CO C H , in pure
6 4 2 6 5
water has been studied. In the present paper we extended
the study of substituent effects to the infrared absorption
of these esters. To check up which of the substituent
descriptors could be used to correlate the infrared
carbonyl stretching frequencies nCO in ortho-, meta-,
and para-substituted phenyl esters of benzoic acid,
C H CO C H -X, phenyl esters of substituted benzoic
1
–5
In our previous papers the influence of the substituent
effects on the kinetics of the alkaline hydrolysis of
meta-, para-, and ortho-substituted phenyl benzoates,
C H CO C H -X, alkyl benzoates, C H CO R, in var-
6
5
2
6
4
6
5
2
ious media and phenyl esters of meta-, para-, and ortho-
6
5
2 6 4
acids, X-C H CO C H , and alkyl-substituted esters of
4
6
2 6 5
*
Correspondence to: I. A. Koppel, Institute of Chemical Physics,
benzoic acid, C H CO R, in the present work the infrared
6
5
2
University of Tartu, 51014 Tartu, Jakobi 2, Estonia.
E-mail: ilmar.koppel@ut.ee
Present address: Department of Physics, Uppsala University, Box
spectra for 55 esters were recorded in tetrachloromethane
solution.
The influence of substituents on the infrared carbonyl-
y
5
30, SE-751 21 Uppsala, Sweden.
Contract/grant sponsor: Estonian Science Foundation; contract/grant
number: 6701, 6705.
0
stretching frequencies n —— O of esters RCO R involving
C
2
Copyright # 2006 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2006; 19: 654–663

INFLUENCE OF SUBSTITUENTS ON THE IR STRETCHING FREQUENCIES
655
a variable substituent has been studied for methyl
11–13
One of the purposes of the current study was to check the
influence of substituent effects on IR carbonyl stretching
6
–10
9
benzoates,
phenyl acetates,
ethyl benzoates,
14–18
t-butyl benzoates,
phenyl and alkyl esters of hydro-
frequencies n
C—O
—
of ortho-, meta-, and para-substituted
19–20
cinnamic acid,
21
and phenyl dichloroacetates.
phenyl and alkyl benzoates, and propose conformations for
the esters studied on the grounds of correlation analysis. To
confirm the conclusions derived from the correlation
analysis the DFT calculations were also employed.
We could find only a few publications providing data
on the infrared carbonyl stretching frequencies of
substituted phenyl benzoates including data for ortho-,
meta-, and para-substituted derivatives in the same
The accent of our work was mainly on ortho
substituents. It is known that Hammett type relationships
are mostly applied to meta- and para-substituted
derivatives while ortho derivatives usually do not obey
Hammett type equations very well and the problem is more
complicated. In the very beginning of the study of ‘the
ortho effect,’ the infrared frequencies often used to
calculate so-called polar substituent constants for ortho
substituents as the infrared frequencies of ortho derivatives
1
7,22
series
electronegative substituents.
and for alkyl benzoates, C H CO R, with
6 5 2
23
14
Freedman observed that the carbonyl-stretching
frequencies of phenyl acetates failed to correlate with
s or s for the para-substituents and suggested that
the frequency n
ꢀ
C—O
—
is dependent only on the inductive
20
component of s. Cohen and Takahashi obtained
the excellent correlation using s8 constants to correlate
the infrared carbonyl stretching frequencies for 48 mono-
and polysubstituted phenyl hydrocinnamates for the meta
and para benzene ring substituents. In the case of ortho
28
were found to be independent of steric effects. Nowadays
it is accepted that the polar influence of ortho substituents
is only very seldom equal to that of para substituents (i.e.,
the absence of ‘ortho effect’) and the inductive and
resonance components for ortho substituents usually vary
depending on the processes and conditions.
20
substituents, the same authors used substituent con-
ꢁ
0
0
p
stants s ¼ s þ 0.39s (RCH ), assuming that the induc-
o
tive effect from ortho position exceeds that of para
2
substituents. In the case of the alkyl substituted esters of
20
3
excellent correlations exist between carbonyl stretching
frequencies and s constants for a large number of esters.
-phenylpropionic acids it was demonstrated that
EXPERIMENTAL
ꢁ
Methyl esters of ortho-halogeno and ortho-methoxy
substituted benzoic acids and esters of a-substituted
acetic acids exhibit a split of carbonyl bands which was
attributed to the presence of two different cis and trans
The spectra of 25 substituted phenyl benzoates,
C H CO C H -X, 8 alkyl benzoates, C H CO R, and
6
5
2
6
4
6
5
2
22 phenyl esters of substituted benzoic acids, X-
C H CO C H , were recorded in the region 400–
6
4
2
6
5
6,18,24–26
ꢀ1
(gauche) conformations.
In the case of carbonyl
4000 cm
trometer in approximately 0.013 M solution of tetra-
on Interspectrum PFS 2020 FT-IR spec-
compounds, a strong non-bonding interaction is con-
sidered to operate across the space between two nearly
chloromethane (Fluka, for IR-spectroscopy). A KrS cell
5
—
parallel oriented dipoles of the C—O and another polar
with path length 1.02 mm was used. The wavelength scale
of the spectrometer was calibrated using polystyrene film
(0.013 mm thick). The day-to-day reproducibility of the
bond situated in a mutually vicinal position. Pre-
the lower wave number band was assigned
6,24–26
viously
ꢀ
1
to the less polar trans (gauche) conformation and the
higher wave number to more polar cis conformation
absorption maxima was ꢂ0.3 cm .
The preparation procedure and characteristics of sub-
stituted phenyl and alkyl benzoates (Refs 1–5, 29–33 and
27
exhibiting the dipole field effect known as Corey effect.
1
13
To the best of our knowledge, there are no sufficient
data on IR absorption of carbonyl bond for ortho-, meta-,
and para-substituted phenyl benzoates and alkyl benzo-
ates in literature enabling a thorough study of the
influence of substituent effects on IR carbonyl stretching
references cited therein) as well as the H and C NMR
spectra for phenyl 4-tert-butylbenzoate, phenyl 3-dimethy-
laminobenzoate, 3-fluorophenyl benzoate, and 3-cyanophe-
nyl benzoate are available in the supplementary material.
The purity of some of the compounds, X-C H CO C H
6
4
2 6 5
—
(X—2-F, 2-Cl, 2-Br, 2-I, 2-OCH , 2-CF , H), first of all
3 3
—
frequencies n . Therefore in the present work the
C—O
infrared spectra were recorded for the following
substituted phenyl benzoates in tetrachloromethane
those that showed two peaks in the carbonyl stretching
region of the IR spectra—was additionally checked using
GC-MS method. The mass spectrum of the non-substituted
phenyl benzoate served as the reference spectrum in the
interpretation of the mass spectra of the substituted phenyl
benzoates (see supplementary material).
—
solution: C H CO C H -X (X—H, 3-Cl, 3-F, 3-CN,
6
5
2 6 4
34
3
4
2
-NO , 3-CH , 3-OH, 3-NH , 4-Cl, 4-F, 4-NO , 4-CN,
2
2
3
2
-OCH , 4-CH , 4-NH , 2-Cl, 2-F, 2-I, 2-NO , 2-CF ,
3
3
2
2
3
-CN, 2-CH3, 2-OCH , 2-N(CH ) , 2-C(CH ) ), alkyl
3 2
3
3 3
—
benzoates, C H CO R (R—CH , CH CH , CH Cl,
6
5
2
3
2
3
2
—— CH,
CH CN,
CH2C
CH CH OCH ), and X-C H CO C H (X—3-Cl, 3-
—
CH
C
H
,
CH CH Cl,
—
2
2
6
5
2 2
CALCULATIONS
2
2
3
6
4
2 6 5
NO , 3-CH 3-N(CH ) , 4-F, 4-Cl, 4-Br, 4-NO , 4-
2
3,
3 2
2
—
Energies, the absorption frequencies of the C—O group,
nCO, and the dipole moments, m, for 12 trans and cis
CH , 4-C(CH ) , 4-OCH , 4-NH , 2-Cl, 2-F, 2-Br, 2-I, 2-
2
3
3 3
3
NO , 2-CN, 2-CF , 2-CH , 2-OCH , 2-NH ).
3
2
3
3
2
Copyright # 2006 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2006; 19: 654–663
DOI: 10.1002/poc

6
56
V. NUMMERT ET AL.
conformers of ortho-substituted phenyl benzoates, 2-X-
C H CO C H , (H, CH , NH , CN, NO , OCH , Cl, F, Br,
conformers of 2-CN and 2-NO phenyl benzoates for
2
which no splitting of the carbonyl band was observable in
the spectra.
6
4
2
6
5
3
2
2
3
CF , C(CH ) , 2,6-(CH ) ) and meta- and para-sub-
3
3 3
3 2
—
stituted phenyl benzoates, X-C H CO C H (X—4-NO ,
The observed range of the (n
)
values (Tables S3
and S4) is 1709–1758 cm for ortho-, meta-, and para-
6
5
2
6
5
2
CO max
ꢀ
1
4
-NH , 4-OCH , 3-Cl) were calculated by the DFT
2
3
ꢁꢁ
ꢀ1
method at the B3LYP/6-311þG level (Table S1). The
geometry optimizations, and frequency calculations and
rotational barrier calculations for 10 trans and cis
conformers of ortho-substituted methyl benzoates, 2-X-
substituted phenyl benzoates and 1724–1748 cm for
alkyl benzoates.
Data analysis
—
C H CO CH (X—H, Cl, F, Br, NO , CN, CF , CH ,
6
4
2
3
2
3
3
OCH , NH ) were performed by the DFT method at the
3
The values of n
benzoates were treated according to the following
equations:
C—O
—
for substituted phenyl and alkyl
2
ꢁꢁ
B3LYP/6-31þG level (Table S2). The Gaussian 03
3
5
ꢁꢁ
program was used. The smaller 6-31þG basis set was
chosen for the more computation-intensive rotational
barrier calculations. It gives good agreement with the
experimental results for unsubstituted phenyl benzoate,
ðn Þ
¼
CO m;p;ortho
o
o
ðn Þ þ c
s þ c2ðorthoÞsI þ c3ðorthoÞ
s
R
(1)
CO o
1ðm;pÞ
ꢁꢁ
À
Á
and the results obtained with the larger 6-311þG basis
set are not significantly different (See also reference 36.)
Since methyl and phenyl esters of substituted benzoic
acid show very similar behavior in the correlation
analysis, the smaller system (methyl benzoate) was
chosen instead of bulky phenyl benzoate for the
calculations of rotational barriers in the ortho-substituted
esters. This approach is valid because the barrier height is
mainly determined by the steric interaction of the ortho
B
þ c4ðorthoÞ Es
ortho
ðn Þ ¼ ðn Þ þ c s
(2)
(3)
(4)
(5)
CO p
CO o
1
þ
ðn Þ ¼ ðn Þ þ c s
CO p
CO o
1
p
À
Á
þ
B
ðnCOÞortho ¼ ðnCOÞo þ c1sI þ c2sR þ c3 Es
ortho
À
Á
þ
B
s
ðn Þ
CO orthoꢀtrans
¼ ðn Þ þ c s þ c E
CO o
1
p
3
ortho
—
substituent and the O—C—O moiety. The influence of
the alkyl part of the ester is small. The rotational barriers
were calculated by constrained optimizations of the
À
Á
ꢁ
B
s
ðn Þ ¼ ðn Þ þ c s þ c E
CO R
(6)
(7)
CO o
1
2
Alk
À
Á
B
s
ðn Þ ¼ ðn Þ þ c s þ c E
CO R
CO o
1
I
2
Alk
—
—
dihedral angle (O—C—C—C) at 158 increments from 0
to 1808. This was done in such a way that all remaining
geometry parameters were allowed to be optimized. The
The carbonyl stretching frequencies n
of meta-,
CO
para-, and ortho-substituted phenyl esters of benzoic
acid, C H CO C H -X, and the phenyl esters of meta-
existence of the hydrogen bond in the cis-2-NH -benzoate
2
6
5
2 6 4
was checked with the Atoms In Molecules (AIM)
approach at the same level of theory. Geometry
optimizations were also performed for unsubstituted and
substituted benzoic acids, X-C H CO C H , were treated
6 4 2 6 5
according to Eqn (1). The nCO values in the phenyl esters
of para-substituted benzoic acids and the phenyl esters of
ortho-substituted benzoic acids were correlated according
to Eqns (2)–(5). The carbonyl stretching frequencies nCO
of substituted alkyl esters of benzoic acid, C H CO R,
2
-Cl-phenyl hydrocinnamate and 2-Cl-phenyl benzoate.
6
5
2
RESULTS
were analyzed with Eqns (6) and (7).
inductive s
3
8,39
40
The Taft’ s polar s8,
the resonance
1,5
scales were
I,
o
o
41
B
—
C—O stretching frequencies
s ½s ¼ (s8) ꢀs ], and steric (E )
R
R
para
I
s
used with Eqns (1), (4), and (5). (E )
ortho
B
X
¼ log k ꢀ
s
ortho
Hþ
H
X
H
The infrared carbonyl stretching frequencies nCO for
meta-, para-, and ortho-substituted phenyl benzoates,
C H CO C H -X, X-C H CO C H and alkyl benzoates,
log k , where k and k are the rate constants for the
þ þ þ
H H H
acidic hydrolysis of ortho-substituted and unsubstituted
þ
phenyl benzoates in water at 508C. s and s in Eqns (2)–
(3) are the Hammett and Brown and Okamoto substituent
6
5
2
6
4
6
4
2
6
5
p
C H CO R, recorded in tetrachloromethane, are listed in
6
5
2
39
þ
Tables S3 and S4.
The splitting of the carbonyl band was observed for the
—
following esters: C H CO C H -X (X—3-OH) and X-
constants, respectively. s in Eqn (5) is the resonance
substituent constant, characteristic of through-resonance
R
þ
þ
39
—
(s ¼ R ). The unsubstituted phenyl benzoate (X—H)
6
—
5
2
6
4
R
C H CO C H (X—2-OCH , 2-F, 2-Cl, 2-Br 2-I, 2-CF ).
was also included in the data treatment of the ortho-
substituted derivatives according to Eqn (1).
6
4
2
6
5
3
3
In order to get more accurate estimates of the carbonyl
stretching frequencies deconvolution of the carbonyl
bands using Igor Pro was performed. (Voigt profiles
showed better fit to the experimental data than the
Gaussian or Lorenzian profiles.) The results are shown in
Table S1. Using the deconvolution approach it was also
To correlate the nCO values of substituted alkyl esters of
benzoic acid, C H CO R, (Eqns (6) and (7)) both the Taft
37
6
5
2
ꢁ
4
42,43
s substituent constants and the induction constants
sI were used as the polar substituent parameter. The sI
4
scale was chosen in order to compare the influence of the
induction effect of the aliphatic substituents —CH X and
possible to obtain the (n
)
CO max
values for the cis and trans
2
Copyright # 2006 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2006; 19: 654–663
DOI: 10.1002/poc

INFLUENCE OF SUBSTITUENTS ON THE IR STRETCHING FREQUENCIES
657
that of meta- and para-substituted phenyls —C H X.
6
1785
780
4
Steric substituent constants for the variable substituent in
B
1
the alkyl component of the ester, (E ) were calculated
Alk
s
B
CH
Hþ
1775
1770
1765
B
s
R
3
R
Hþ
as follows: (E ) ¼ (log k ꢀlog k ), where k and
Alk
Hþ
are the rate constants for the acidic hydrolysis of
CH
3
k
R-substituted and CH -substituted alkyl benzoate or
þ
H
3
2
acetate in water.
The data treatment was carried out using a multiple
parameter linear least squares (LLSQ) procedure.
Exclusion of significantly deviating points was performed
at confidence level 0.99.
1760
1755
1750
1745
1740
ν
45
A
The results of the statistical data treatment according to
Eqns (1)–(7) for the carbonyl stretching frequencies nCO
of the esters C H CO C H -X, X-C H CO C H , and
6
5
2
6
4
6
4
2
6
5
1735
-0,4 -0,2
C H CO R are listed in Table 1.
6
0
0,2 0,4 0,6 0,8
σ , (σ )
1
5
2
For comparison the carbonyl stretching frequencies
nCO taken from the literature for meta-, para-, and ortho-
°
I ortho
6
substituted methyl benzoates, 3-phenyl propioanates,
19
o
Figure 1. Relationship between the nCO values and s or
(s ortho constants for substituted phenyl esters of benzoic
acid, C H CO C H -X, (A) and 3-phenylpropionic acids,
46–49
benzoic acids,
23
alkyl esters of benzoic acid,
)
I
24
6
5
2 6 4
C H CO R and ethyl acetates, XCH CO CH CH ,
2
6
5
2
2
2
3
C H (CH ) CO C H -X, (B). For meta and para substituents
6
5
2 2
2 6 4
were correlated via Eqns (1)–(7) as well (Table S5). The
substituent constants used for the correlations are listed in
Table S6 and Table S7.
o
(
D) s and for ortho substituents (*) s were used.
I
Figure 1 illustrates the relationship between the nCO
o
values and s or (s )
Computational results
constants for substituted phenyl
esters of benzoic and 3-phenylpropionic acids. The
I ortho
The DFT calculations show the existence of cis- and
trans-conformations (with respect to the carbonyl group)
for nearly all ortho-substituted benzoates as confirmed by
energy minima and absence of imaginary vibrations. The
B
s
relationships between the n ꢀc(E )
values and
, for phenyl esters of
CO
ortho
þ
þ
s , (s )
and (s )
para- and ortho-substituted benzoic acid are shown in
p
I ortho-cis
p
ortho-trans
Fig. 2.
computed carbonyl absorption frequencies (n
)
CO calc
of cis
Table 1. Results of the treatment of the nCO values for substituted phenyl and alkyl esters of benzoic acid with Eqns (1)–(7)
a
Ester
Eqn
(n
)
CO o
c1
c2
c3
n/n0
R
so
b
C H CO C H -X
6
1
1
1
1
2
3
4
4
4
5
6
7
6
7
1743.3 ꢂ 0.2
1742.6 ꢂ 0.3
1743.3ꢂ 0.2
1741.7 ꢂ 0.2
1740.3 ꢂ 0.6
1742.3 ꢂ 0.3
1740.0 ꢂ 1.5
1741.5 ꢂ 0.9
1740.6 ꢂ 0.6
1734.0 ꢂ 0.6
1725.8 ꢂ 1.6
1725.9 ꢂ 1.8
1726.6 ꢂ 1.5
1726.7 ꢂ 1.7
8.19 ꢂ 0.40
18.7 ꢂ 0.8
8.21 ꢂ 0.40
11.6 ꢂ 1.1
10.6 ꢂ 1.4
7.41 ꢂ 0.34
22.0 ꢂ 2.5
18.4 ꢂ 1.7
0
12.6 ꢂ 0.6
25.9 ꢂ 1.7
57.6 ꢂ 3.9
25.5 ꢂ 1.3
56.8 ꢂ 3.6
—
—
14/15c
11/11
23/25
0.984
0.985
0.991
0.983
0.944
0.993
0.971
0.991
0.994
0.995
0.989
0.987
0.993
0.993
0.174
0.173
0.130
0.186
0.330
0.122
0.239
0.133
0.108
0.104
0.150
0.160
0.133
0.160
5
2 6 4
0
18.1 ꢂ 0.5
—
0
2.0 ꢂ 0.7
—
d
e
X-C H CO C H
2 6 5
5/5
8/9
8/9
10/10
8/8
7/8
7/7
6
4
f
—
—
0
—
—
f
g
ꢀ21.5 ꢂ 3.3
ꢀ23.2 ꢂ 1.8
ꢀ8.38 ꢂ 1.70
ꢀ11.9 ꢂ 1.6
—
g,h
0
i
14.1 ꢂ 0.7
i,j
—
C H CO R
6
30.8 ꢂ 4.4
30.7 ꢂ 4.7
32.5 ꢂ 3.7
32.2 ꢂ 4.4
8/8
8/8
7/7
7/7
5
2
k
—
k
a
o
n , the total number of data subjected to the regression data treatment; n, the number of points left after exclusion of significantly deviating points, confidence
level 0.99.
b
Only meta- and para-substituted derivatives included.
Ortho-substituted derivatives included.
c
d
c
Only meta-substituted derivatives were included.
4
¼ 0.
e
f
Included para-substituted derivatives. 4-F derivative excluded.
g
n
well as unsubstituted derivative and 2-CH
CO values for cis isomers (with respect to the carbonyl group) of phenyl esters of 2-substituted benzoic acids calculated by deconvolution of carbonyl bands as
derivative (X–H, NO
, F, Cl, Br, I, OCH , CN, CF , CH ) were included (Table 1).
3
2
3
3
3
h
2-CH
3
and 2-I derivatives omitted.
CO values for trans isomers calculated by deconvolution of carbonyl bands (NO
during data treatment.
i
n
2 3 3 2
, F, Cl, Br, I, OCH , CN, CF ) included (Table 1). 2-NO derivative excluded
j
2
-NO
2
derivative omitted.
The CH CH derivative was omitted before data processing.
k
3
2
Copyright # 2006 John Wiley & Sons, Ltd.
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DOI: 10.1002/poc

6
58
V. NUMMERT ET AL.
1
1
1
1
1
1
1
1
1
755
750
745
740
735
730
725
720
715
values for 2-NO -, 2-CH -, and 2-CN-rotamers (5, 7, and
2 3
23 cm , respectively).
The energy calculations by the DFT method confirmed
that trans conformers are more stable than the corre-
sponding cis conformers in both the phenyl and methyl
esters of ortho-substituted benzoic acids for the following
B
ꢀ1
ν , ν
ortho
– cEs
p
—
substituents: X—CN, OCH , F, CF , NO Cl, Br (for
3
3
2,
phenyl 2-chloro- and 2-bromobenzoates DGtrans/cis ¼ 0),
—
whereas alkyl substituents X—CH , C(CH ) are
3
3 3
preferably located near to the carbonyl group (Tables
S1 and S2).
Relatively low rotational barriers of the ester group
with respect to the aromatic ring plane found for ortho-
substituted methyl benzoates (Table S2) and the small
energy differences of the cis and trans conformations
indicate that both conformations should be well enough
populated. The calculations reveal a trend of the
rotational barrier to depend on the size of substituents:
the larger substituents tend to decrease the barrier to the
rotation and it is the highest for the unsubstituted methyl
σ p+, (σ I)ortho, (σ +
)
ortho
-
1,5
-1
-0,5
0
0,5
1
B
s
Figure 2. Relationship between the nCO and (nCO–cE )
values and substituent constants for phenyl (&, *, ~) and
methyl esters (&, *, ~) of para- and ortho-substituted
benzoic acids. For para substituents sP (&, &), ortho cis
derivatives (s )
) (s )
ortho
benzoate (ꢃ6.6 kcal/mol). The exception is 2-NH -
2
þ
benzoate, the cis form of which forms a hydrogen bond
with the carbonyl oxygen. Therefore, this configuration is
significantly stabilized, in comparison to the trans form,
and its rotational barrier (ꢃ10.6 kcal/mol) is almost twice
as high as that for the unsubstituted ester.
(*, *) and for ortho trans derivatives (~,
I ortho
þ
~
were used.
ortho
P
and trans conformers for phenyl esters of ortho-
substituted benzoic acid, X-C H CO C H , are presented
In both the phenyl and methyl esters of ortho-
substituted benzoic acids (Tables S1 and S2) the carboxyl
groups plane was found to be nearly coplanar with the
6
4
2 6 5
in Table S1. Those for ortho-substituted methyl benzoates
X-C H CO CH are presented in Table S2. Both
6
4
2
3
computed frequencies were found to be linearly
correlated with the corresponding experimental nCO
values for the cis and trans conformers (Tables S3).
For phenyl esters of substituted benzoic acids, X-
C H CO C H , we found:
benzene ring plane for the smallest substituents CN (the
¼ ꢀ0.03) and F (Es
steric parameter EsB
in both cis and trans isomers. For the bulkiest ortho
B
¼ ꢀ0.15)
ortho
ortho
B
substituents 2-CF3 (Es
B
¼ ꢀ0.593) and 2-C(CH )
ortho
3 3
(Es
ortho
¼ ꢀ0.604) in both cis and trans isomers the
6
4
2
6
5
carboxyl group was out of the aromatic ring plane by
ðn Þ ¼ ðꢀ0:0005 ꢂ 0:0080Þ
about 388 and 538, respectively. The difference in the
CO calc
—
—
values of dihedral angle O—C—C—C calculated for
phenyl esters and methyl esters of ortho-substituted
benzoic acids is in the range 5–108 in the case of
þ ð1:302 ꢂ 0:046ÞnCO
(8)
R ¼ 0:989; s ¼ 0:15; n=n ¼ 20=21;
—
0
0
substituents X—CH , CN, NH , Cl, F, OCH , CF , NO
3
2
3
3
2
(Tables S1 and S2).
X ¼ transꢀ2ꢀCN excluded
—
The values of the dihedral angle O—C—C—C for the
—
The same relationship for methyl esters of substituted
benzoic acids, X-C H CO CH , is expressed as follows:
phenyl esters of ortho-substituted benzoic acids, X-
C H CO C H , and methyl benzoates, X-C H CO CH
3
6
4
2
3
6
4
2
6
5
6
4
2
(the values of the dihedral angle are shown in brackets)
ðn Þ ¼ ðꢀ0:0006 ꢂ 0:0001Þ
for cis and trans forms were: 2-CH : 4.28, (08), 175.48,
CO calc
3
(
1808); 2-NH : 0.48, (08), 175.58, (1808); 2-CN: 2.28, (08),
2
þ ð1:357 ꢂ 0:078ÞnCO
(9)
162.98, (1808); 2-Cl: 26.28, (24.08), 147.78, (153.78); 2-F:
1
0.88, (08), 172.28, (1808); 2-OCH : 28.38, (17.88),
3
R ¼ 0:982; s ¼ 0:188; n=n ¼ 11=12;
0
0
153.18, (166.18); 2-CF : 37.68, (36.48), 140.28, (142.38);
3
2
-NO : 81.68, 134.88, (137.88), 2-Br: 29.18, (08), 144.68,
X ¼ transꢀ2ꢀBr excluded
2
(
1808); 2-C(CH ) : 52.88, 125.98.
3
3
— —
The dihedral angle (—C—O—C—C—) between the
In agreement with the experiment, the computed nCO
frequencies for the trans rotamers are lower than those for
the cis rotamers (except 2-NH phenyl benzoate). The
ester group’s plane and the aromatic ring plane of the
phenoxy part of esters for 2-H-, 2-Cl-phenyl hydro-
cinnamate and 2-H-, 2-Cl-phenyl benzoate was computed
to be 63.38, 86.458, 63.78, and 90.58, respectively.
2
wave number difference between the two forms was of 5–
4
ꢀ1
8 cm , with the smallest differences in frequency
Copyright # 2006 John Wiley & Sons, Ltd.
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INFLUENCE OF SUBSTITUENTS ON THE IR STRETCHING FREQUENCIES
659
The hydrogen bond was proved for methyl ortho-
NH -benzoate according to criteria given in Ref. [50]
—
by —O..H— bond distance, electron density and
˚
Laplacian (1.937 A, 0.029 and 0.094 au, respectively).
This result is well in line with the high rotational barrier
of the carbonyl bond in respect to the aromatic ring
plane of benzoate in this molecule.
esters. For the alkaline hydrolysis of the same esters in
water, the inductive effect of substituents X in the alkyl
chain CH X appeared to be approximately four times
2
2
stronger than that in meta and para positions of the
2
aromatic ring.
A good correlation of the carbonyl stretching
o
frequencies nCO with s for para-substituted phenyl
esters of benzoic acid shows the absence of the through-
resonance between the electron-donating substituents and
5
carbonyl group. This is in agreement with Exner and
2
DISCUSSION
19
Cohen who proposed s-trans conformation for phenyl
esters where the carbonyl group in the phenyl ester is
nearly perpendicular to the aroxy plane (Structure 1),
which is also confirmed by the calculations. One of the
primary requirements for the resonance interaction
between two groups is mutual coplanarity of these
groups. The carbonyl stretching frequencies nCO for
phenyl and methyl esters of para-substituted benzoic acid
Influence of substituents
The nCO frequencies increase with increasing s values of
the corresponding substituent (Tables 1, S3 and S4). It
means that electron-withdrawing substituents increase
and electron-donating substituents decrease nCO values,
which is similar to the findings of previous works in this
field. Since the stretching frequencies are proportional to
the bond force constants, higher wave numbers indicate
higher formal bond orders of the carbonyl bond. The
electron-withdrawing substituents are considered to
þ
show correlation with s substituent constants in the case
p
of electron-donor substituents. Thus, the presence of the
resonance between þR substituents and the carbonyl
group indicates that the benzene ring in the benzoyl
part of the ester is coplanar with the carboxyl group
(Structure 1):
—
suppress the polarization of the C—O bond or diminish
—
the C—O bond resonance forms stabilization.
21,25,25,51
Carbonyl stretching frequencies nCO for meta- and
para-substituted phenyl esters of benzoic and propionic
acids as well as phenyl and methyl esters of meta-
substituted benzoic acids showed good correlation with
o
the s constants (R > 0.980). The influence of the
through resonance effect to nCO was found to be also
important in the phenyl esters of para-substituted
benzoic acids. It was found that the carbonyl stretching
frequencies nCO of phenyl and methyl benzoates in
the case of þR para substituents in the acyl group
The split of the experimental carbonyl stretching bands
(Table S3) in the case of some phenyl esters of ortho-
substituted benzoic acids can be explained by confor-
mational isomerism, which is supported by the calcu-
lations. At the same time the possibility of a Fermi
resonance cannot be excluded.
þ
correlated better with the Okamoto and Brown s
p
constants in comparison to the Hammett s constants
(
Tables 1 and S5).
The polar influence of meta, para, and ortho
In the case of substituents in the aroxy part of the esters,
—
(C H CO C H -X, C H CO R) (except X—3-OH) the
6 5 2 6 4 6 5 2
substituents in the benzoyl part of the ester on the
carbonyl stretching frequencies nCO was found to be only
about 1.3 times stronger than in the case of substituents in
the aroxy part of the esters. The magnitudes of c1
calculated according to Eqn (1) for meta- and para-
substituted phenyl benzoates in the case of substituents in
the aroxy part and in the case of substituents in the
benzoyl part were found to be 8.19 and 11.6, respectively.
In the case of ortho substituents, the corresponding values
splitting of the carbonyl absorption maximum was not
observed. Due to the rotation of the aromatic plane in the
phenoxy part out of the carbonyl plane by nearly 908,
there is essentially only one conformation for the ortho
derivatives possible.
The carbonyl stretching frequencies, nCO, for ortho-
substituted phenyl esters of benzoic acid, C H CO C H -
6
5
2 6 4
—
X (X—H, NO , CN, CF , N(CH ) , F, Cl, I, OCH , CH ,
2
3
3 2
3
3
C(CH ) ), showed a good correlation only with the
3
3
of c found from Eqns (1) and (4) appeared to be 18.1 and
1
inductive constant s , while resonance and steric factors
I
appeared to be insignificant (Fig. 1, Table 1):
2
both series. The same ratio was nearly 1.5 for the alkaline
2.0 (Table 1) giving the ratios (cI)ortho/(c ) ꢄ 2.0 for
I m,p
1,5
hydrolysis of substituted phenyl benzoates in water.
The inductive influence of substituents X in the alkyl
chain CH X of C H CO CH X on the carbonyl stretching
ðn Þ
¼
CO m;p;ortho
o
ð1743:3 ꢂ 0:2Þ þ ð8:21 ꢂ 0:4Þm;p
s
(10)
2
6
5
2
2
frequencies nCO was found to be 6.7 times stronger than
that of substituents in meta and para positions in the
corresponding aromatic series and 3.1 times stronger than
the influence of ortho substituents from aroxy part of the
o
þ ð18:1 ꢂ 0:5ÞorthosI þ ð2:0 ꢂ 0:7Þortho
s
R
R ¼ 0:991; s ¼ 0:130; n=n ¼ 23=25
0
0
Copyright # 2006 John Wiley & Sons, Ltd.
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DOI: 10.1002/poc

6
60
V. NUMMERT ET AL.
However, in addition to s inductive constants,
I
(Structures 2 and 3) whereas the lower frequency
component corresponds to the trans rotamer and the
higher frequency component may be attributed to the
cis rotamer.
Correlation analysis using Eqns (4) and (5) showed that
both the inductive and the steric scales were essential to
correlate the nCO values of the cis rotamers in the phenyl
esters of ortho-substituted benzoic acids, 2-X-
o
resonance s constants were also required to correlate
the nCO values for ortho-substituted phenyl esters of 3-
phenyl propionic acid (Table S5).
R
7
Similar to methyl benzoates the lower carbonyl
stretching frequency for meta-hydroxyphenyl benzoate
could be ascribed to dimers or
ꢀ1
nCO ¼ 1716.2 cm
trimers, which are formed by the intermolecular H-bond
between carbonyl oxygen and hydrogen of the meta-
hydroxyl substituent. In the hydroxyl absorption region
the spectrum of the meta-hydroxyphenyl benzoate shows
—
C H CO C H (X—H, CH , NO , CN, Cl, F, Br, I,
6
4
2
6
5
3
2
OCH , CF ), while the resonance term appeared to be
3
3
insignificant and was excluded during the data processing
(Fig. 2, Table 1):
ꢀ1
a band at 3606 cm and also a broad band with the
maximum at nCO ¼ 3441cmꢀ that could be ascribed to
hydrogen bonded associates.
1
ðn Þ
¼
CO cisꢀortho
ð1740:0 ꢂ 1:5Þ þ ð22:0 ꢂ 2:5Þ
—
In the case of the ortho substituents X—Cl, F, Br I,
sI
(11)
OCH , CF in the benzoyl part of phenyl benzoates,
3
ortho
3
B
s
2
-X-C H CO C H , the split of the carbonyl experimen-
6 4 2 6 5
ꢀ ð21:5 ꢂ 3:3Þortho
E
tal stretching bands was observed. The experimental
nCO values of phenyl esters of ortho-substituted benzoic
acid show only one carbonyl stretching band in the
carbonyl stretching region in the case of strong electron-
R ¼ 0:971; s ¼ 0:239; n=n ¼ 10=10
0
0
Correlation becomes better if 2-CH and 2-I derivatives
were omitted:
3
acceptor substituents (–I and –R substituents: NO , CN),
2
strong electron repelling substituents (þR substituent:
ðn Þ
¼
CO orthoꢀcis
ð1741:5 ꢂ 0:9Þ þ ð18:4 ꢂ 1:7ÞorthosI
NH ) and for substituents showing weak substituent effect
2
(12)
(
CH ). Two carbonyl bands were found for substituents,
3
B
s
which exhibit both the relatively strong inductive and
resonance effects. According to the frequency calcu-
lations there are two conformations possible in the case of
all ortho substituents (Tables S1 and S2).
ꢀ ð23:2 ꢂ 1:8Þortho
E
R ¼ 0:991; s ¼ 0:133; n=n ¼ 8=8
0
o
The trans conformers in the phenyl esters of ortho-
—
substituted benzoic acids (X—CN, CF , OCH , F, Cl, I,
Br) are very well described by the dual parameter Eqn (5)
Table 1):
Due to the existence of the hydrogen bond for cis-2-
NH -benzoate, the high rotational barrier and energeti-
3
3
2
cally less favorable trans-configuration may result in a
very poor population of the trans form. Separation of the
experimental carbonyl bands by deconvolution gave two
very close bands for phenyl 2-nitro- and 2-CN-benzoates
as well. There is also a good agreement with the
conformations of the corresponding ortho-substituted
(
ðnCOÞ
¼
orthoꢀtrans
þ
ð1734:0 ꢂ 0:6Þ þ ð12:6 ꢂ 0:6Þorthos
(13)
p
B
ꢀ
ð11:9 ꢂ 1:6ÞorthoEs
6,46
methyl esters and benzoic acids.
R ¼ 0:995; s ¼ 0:104; n=n ¼ 7=7
0
0
On the grounds of the infrared spectra, correlation
analysis and DFT calculations we assume that phenyl
and methyl esters of ortho-substituted benzoic acids
can exist in two conformations: ortho substituents in cis
and trans positions relative to the carbonyl group
The nCO value for trans conformation of phenyl 2-
nitrobenzoate was omitted as it was excluded during the
data treatment.
The correlations similar to Eqns (12) and (13) were
obtained for cis and trans isomers in ortho-substituted
methyl benzoates and benzoic acids (Table S5).
The strong inductive effect (c ¼ 22.0) of the ortho
1
substituents in cis position with respect to the carbonyl
—
group diminishes the C—O bond resonance forms
stabilization thus increasing essentially the carbonyl
stretching frequencies compared to the non-substituted
ester. The trans isomers of phenyl and methyl esters
of ortho-substituted benzoic acids showed direct
polar resonance effect to nearly the same extent as in
the case of þR para substituents (Tables 1 and S5, Fig. 2).
The positive steric term, found for both the cis and
trans conformers could be considered as measure of the
steric inhibition of resonance between the phenyl ring in
Copyright # 2006 John Wiley & Sons, Ltd.
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DOI: 10.1002/poc

INFLUENCE OF SUBSTITUENTS ON THE IR STRETCHING FREQUENCIES
661
benzoyl part and the carbonyl group caused by ortho
substituents. It is in accordance with the values of the
corresponding dihedral angles calculated for the phenyl
and methyl esters of ortho-substituted benzoic acids
double bond. Resonance increases the single bond
—
character of the C—O bond and consequently, lowers
its force constant resulting in the lower frequency of
carbonyl absorption.
We propose that the split of the experimental carbonyl
stretching bands in the phenyl esters of ortho-substituted
benzoic acids (Table S3) could be ascribed to the
conformational isomerism rather than to Fermi reson-
ance. The existence of cis/trans conformations was
supported by frequency calculations with Density
Functional Theory (DFT) method (Table S1). Between
46
(
bulky CF group in ortho position the carbonyl groups
Tables S1 and S2) and benzoic acids. In the case of
3
plane was found to be more twisted out of the benzene
ring plane (by 388) compared to that for the smallest
ones CN and F (in phenyl esters by 28 and 118,
respectively, and in methyl esters by 08 in both cases).
In cis isomers the steric inhibition of resonance between
of phenyl ring and carbonyl group was found to be
about twice larger than in trans isomers (Eqns (12)
and (13)).
the computed frequencies, (n
)
, for cis and trans
CO calc
rotamers, and the corresponding experimental nCO values
was found an excellent correlation (Eqn (8), R ¼ 0.989).
6,9
The through þR resonance in the case of para and trans
Similarly, earlier study of the variation of the n
CO
ortho substituents in acyl part of the esters stabilizes the
values with solvent and temperature proved that in ortho-
substituted methyl and t-butyl benzoates the split of the
split carbonyl stretching bands has been attributed to cis
and trans isomers but not to Fermi resonance.
þ
ꢀ
resonance form of carbonyl bond C —O decreasing the
corresponding carbonyl stretching frequencies nCO
Inductive effect of the electronegative substituents
.
—
increases the bond order of the C—O bond and therefore
The carbonyl stretching frequencies nCO for substituted
alkyl benzoates, C H CO R, and for ethyl esters of
the carbonyl stretching frequencies nCO become higher
compared to unsubstituted derivative. In Fig. 2 the points
for the trans ortho substituents do not fall on the same
6
5
2
2
4
substituted acetic acids, XCH CO C H were found to
2 2 5,
2
be dependent on both the inductive and the steric effects
of substituents (Tables 1 and S5). The stronger electron-
acceptor substituents in alkyl benzoates shift the carbonyl
stretching frequencies nCO towards higher values.
However, due to the steric consequences the influence
of the inductive effect is suppressed and the carbonyl
stretching frequencies of the substituted alkyls appeared
to be lower than expected.
53
straight line with para substituents. It has been proposed
that in the case of trans isomers an additional through
space interaction between the negatively charged
heteroatom of the ortho substituent and the positively
charged C atom of the carbonyl group could stabilize the
resonance form of the carbonyl bond. Furthermore, in the
case of trans rotamers of phenyl esters of ortho-
substituted benzoic acids the additional through space
interaction appeared to surpass the inductive influence of
the ortho substituents from trans position.
CONCLUSIONS
In the case of the phenyl ester of ortho-amino benzoic
acid only one carbonyl band was observed
Substituted phenyl benzoates with ortho, meta, and para
substituents as well as alkyl substituents in the ester part
(C H CO C H -X, C H CO R) showed experimentally a
ꢀ
1
(
nCO ¼ 1709.8 cm ). Very low value of n
shows
CO
strong interaction between the ortho NH substituent and
2
6
5
2
6
4
6
5
2
5
4
the carbonyl CO group. Similar to acetophenones this
could be explained by the intramolecular NH. . .O
hydrogen bond that depresses the nCO value considerably.
This hypothesis is also supported by the DFT calcu-
lations.
single infrared carbonyl stretching band. In the case of
—
ortho substituents (X—Cl, Br, I, F, OCH , CF ) in
3
3
benzoyl part in substituted phenyl benzoates, X-
C H CO C H , doublet infrared carbonyl stretching
6
4
2 6 5
bands were observed. Calculations with the DFT method
and correlation analysis proved for meta- and para-
substituted phenyl benzoates s-trans conformation where
the plane of the benzene ring in the benzoyl part of the
ester is coplanar with the carbonyl bond plane and the
plane of the benzene ring in the phenoxy part is twisted
nearly perpendicular relative to the carboxyl bond plane.
The calculations with DFT method at the B3LYP/6-
As was mentioned above, another alternative expla-
nation for the splitting of the carbonyl band, namely
25,26
Fermi resonance, cannot be excluded.
The Aryl–C
ꢀ
1
stretch appears to be at around 850–870 cm . When the
overtone of this vibration happens to be at the similar
—
—
frequency to the C—O stretch vibration, the C—O
stretch band splits resulting in the higher and lower
stretching frequency compared to the fundamental
carbonyl stretching bands. At the molecular level, this
interaction is due to an overlapping of the p orbitals. This
overlapping forms an extended system where electrons
are delocalized. The lower stretching frequencies are
considered to be caused by expanded conjugation effects.
ꢁꢁ
ꢁ
311þG and 6-31 þ G levels and correlation analysis
support the existence of cis and trans conformations with
respect to the carbonyl bond for the phenyl and methyl
esters of ortho-substituted benzoic acids. The ortho
substituent effect on nCO for cis rotamers in benzoyl part
of esters was described by the inducive s and the steric
I
B
—
The introduction of a C—C bond adjacent to the carbonyl
group results in the electron delocalization in the carbonyl
Es scales. To correlate the substituent effect in trans
þ
isomers both the s scale characteristic of the direct polar
p
Copyright # 2006 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2006; 19: 654–663
DOI: 10.1002/poc

6
62
V. NUMMERT ET AL.
B
s
resonance and steric E scale were significant. In both cis
13. Binev I, Vassileva P, Kolev TsM, Juchnovski I. J. Mol. Structure
984; 114: 371–374.
1
and trans conformers the aromatic plane in benzoyl part
of the esters was twisted out of coplanarity with respect to
the carbonyl bond plane due to the steric hindrance of
ortho substituents.
1
1
4. Freedman HH. J. Am. Chem. Soc. 1960; 82: 2454–2459.
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6. Katsarava RD, Kharadze DP, Bendiashvili TM, Urman YaG,
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1
7. Katsarava RD, Kharadze DP, Avalishvili LM, Zaalishvili MM. Izv.
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Supplementary material
1
8. Exner O, Friedl Z, Fiedler P. Collect. Czech. Chem. Commun.
983; 48: 3086–3096.
1
The following supplementary material is available in
Wiley Interscience:
1
2
9. Cohen LA, Takahashi S. J. Am. Chem. Soc. 1973; 95: 443–448.
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1. Neuvonen H, Neuvonen K. J. Chem. Soc., Perkin Trans. 2: 1999;
1
Table S1, the results of DFT B3LYP/6-311þGꢁꢁ
2
calculations of electronic energies E, Gibbs energies G
at 298 K), IR frequencies nCO, and dipole moments m for
457–1502.
22. Prangova LS, Fradkina SP, Vasiljeva IN. Zh. Obshch Khim. 1987;
57: 1853–1863.
(
substituted phenyl benzoates; Table S2, results of DFT
calculations for methyl esters of 2-substituted benzoic
acids; Table S3, infrared carbonyl stretching frequencies
nCO for substituted phenyl esters of benzoic acid and
2
2
2
3. Kereselidze DA, Bogatkov SV, Cherkasova EM. Reakts. Sposobn.
Organ. Soedin. 1972; 9: 513–520.
4. Perj e´ ssy A, Loos D, D o¨ lling W, Lacov a` M, Chovancov a` J. Reakts.
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5. Bellamy LJ. Advances in Infrared Group Frequencies. Methuen &
Co. LTD: Bungay, Suffolk, 1968.
phenyl esters of substituted benzoic acids in CCl ; Table
4
S4, infrared carbonyl stretching frequencies nCO for
substituted alkyl benzoates, C H CO R in CCl ; Table
26. Bellamy LJ. The infrared Spectra of Complex Molecules. Chapman
and Hall: 1980 p. 14713.
6
5
2
4
2
2
2
7. Corey EJ. J. Am. Chem. Soc. 1953; 75: 2301–2304.
8. Charton M. Prog. Phys. Org. Chem. 1971; 8: 235–317.
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S5, results of the literature nCO values treatment
according to Eqns (1)–(7) for substituted phenyl esters
of 3-phenylpropionic acid, methyl esters of benzoic acids,
benzoic acids, alkyl esters of benzoic acid, and alkyl
esters of acetic acid; Table S6, the substituent constants
for meta-, para-, and ortho-substituents used in corre-
lations; Table S7, the substituent constants for alkyl
substituents used in correlations. The preparation
procedure and analyses of substituted phenyl and alkyl
3
3
3
3
0. Harvey L, Gleicher GJ, Totherow WD. Tetrahedron 1969; 25:
5
019–5026.
1. Weygand-Hilgetag. Organisch-Chemische Experimentierkunst.
J.A. Barth-Verlag: Leipzig, 1964.
2. Stiles M, Miller RG, Burckhardt U. J. Am. Chem. Soc. 1963; 85:
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792–1797.
3. Humffray AA, Ryan JJ. J. Chem. Soc. (B) 1967; 468–471.
34. The NIST database http://webbook.nist.gov/.
1
13
35. Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA,
Cheeseman JR, Montgomery, JA, Jr., Vreven T, Kudin KN, Burant
JC, Millam JM, Iyengar SS, Tomasi J, Barone V, Mennucci B,
Cossi M, Scalmani G, Rega N, Petersson GA, Nakatsuji H, Hada
M, Ehara M, Toyuta K, Kukuda R, Hasegawa J, Ishida M,
Nakajima T, Honda Y, Kitao O, Nakai H, Klene M, Li X, Knox
JE, Hratchian HP, Cross JB, Bakken V, Adamo C, Jaramillo J,
Gomperts R, Stratmann RE, Yazyev O, Austin AJ, Cammi R,
Pomelli C, Ochterski JW, Ayala PY, Mokokuma K, Voth GA,
Salvador P, Dannenberg JJ, Zakrzewski VG, Dapprich S, Daniels
AD, Strain MC, Farkas O, Malick DK, Rabuck AD, Raghavachari
K, Foresman JB, Ortiz JV, Cui Q, Baboul AG, Clifford S, Cio-
slowski J, Stefanov BB, Lui G, Liashenko A, Piskorz P, Komaromi
I, Martin RL, Fox DJ, Keith T, Al-Laham MA, Peng CY, Nanayak-
kara A, Challacombe M, Gill PMW, Johnson B, Chen W, Wong
MW, Gonzalez C, Pople JA. Gaussian 03, Revision C.02. Gaussian
Inc.: Wallingford CT, 2004.
benzoates; the H and C NMR spectra for phenyl 4-tert-
butylbenzoate, phenyl 3-dimethylamino benzoate, 3-
fluoro- and 3-cyanophenyl benzoates are available as
supplementary material. This material is available at the
epoc website at http://www.wiley.com/epoc. at Wiley
Interscience.
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