V. NUMMERT ET AL.
acetonitriles,[31] acetophenones, and benzaldehydes.[32–36]
Guy[27] obtained excellent correlations for the 13C NMR chemical
shift in ortho-substituted thiocyanatobenzenes with the induc-
tive, resonance, and the steric substituent parameters. The
influence of substituents in an alkyl chain on the carbonyl carbon
13C NMR chemical shift was studied mainly for the case of esters
containing substituents in the acyl part.[37–39]
Earlier (as shown in References [1–6]) we found the log k values
for the alkaline hydrolysis of phenyl esters of ortho-substituted
benzoic acids, X-C6H4CO2C6H5, and substituted phenyl esters of
benzoic acid, C6H5CO2C6H4-X, to be correlated with the Charton
equation using the Taft inductive (sI) and resonance (s8R)
constants, and the steric scale for ortho substituents, EBs . In the
alkaline hydrolysis of substituted benzoates in pure water,
the ortho inductive effect and the meta and para polar effect in
the acyl part were 1.5-fold and the steric influence was 2.7-fold
higher than the corresponding influences in the aryl part of
phenyl benzoates. In the alkaline hydrolysis of phenyl esters of
ortho-substituted benzoic acids, X-C6H4CO2C6H5, in water the
resonance term was negligible ((r8R)ortho ca. 0.3). In the case of
phenyl esters of ortho-substituted benzoic acids, X-C6H4CO2C6H5,
Sigma-Aldrich 99.8 atom% deuterated NMR solvent CDCl3
containing 1% of TMS as internal reference was used. Samples
were prepared at a concentration of 0.1 M solute. Both the
chemical shifts (1H and 13C) were referenced to internal TMS. The
spin–spin coupling constants (J values) are given in Hz. 13C NMR
spectra of 55 ortho-, meta-, and para-substituted phenyl
benzoates, X-C6H4CO2C6H5 (X ¼ H, 2-NO2, 2-CN, 2-F, 2-OCH3,
2-NH2, 4-NO2, 4-F, 4-Cl, 4-Br, 4-CH3, 4-OCH3, 4-NH2, 3-NO2, 3-Cl,
3-CH3), C6H5CO2C6H4-X (X ¼ 2-NO2, 2-CN, 2-F, 2-Cl, 2-I, 2-CF3,
2-CH3, 2-C(CH3)3, 2-OCH3, 2-N(CH3)2, 2-CO2CH3, 4-NO2, 4-CN, 4-F,
4-Cl, 4-CH3, 4-OCH3, 3-NO2, 3-Cl, 3-CH3, 3-NH2), alkyl benzoates,
C6H5CO2R (R ¼ CH3, CH2C6H5, CH2CH2OCH3, CH2CH2Cl, CH2CꢁCH,
CH2CF3, CH2CHCl2, CH2CCl3, CH2Cl, CH2CN), methyl benzoates,
X-C6H4CO2CH3 (X ¼ H, 2-Cl, 2-Br, 2-I), and ethyl benzoates,
X-C6H4CO2C2H5, (X ¼ H, 2-NO2, 2-CN, 2-Cl, 2-CF3) were recorded
(as shown in Table S1). Carbonyl carbon 13C NMR chemical shifts,
dCO, for phenyl esters of ortho-, meta-, and para-substituted
benzoic acids, X-C6H4CO2C6H5, ortho-, meta-, and para-
substituted phenyl esters of benzoic acid, C6H5CO2C6H4-X,
substituted alkyl benzoates, C6H5CO2R, and methyl and ethyl
esters of substituted benzoic acids (X-C6H4CO2CH3,
X-C6H4CO2C2H5) are given in Tables 1–3.
the infrared stretching frequencies of the carbonyl group, nCO
,
for the cis and trans conformers of ortho derivatives appeared
¼
to be correlated with dual parameter equations: (nCO cis
)
Synthesis of compounds
(nCO)o þ 16.4sI ꢀ 22.6EBs and (nCO trans
)
¼ (nCO)o þ 12.6sþp ꢀ 11.9EsB.[7]
Recently, we found[8] good correlations between the log k values of
the alkaline hydrolysis of ortho-substituted phenyl benzoates and
theinfraredstretchingfrequenciesofthecarbonylgroup,nCO,when
the additional resonance and steric scales were included.
To study the influence of substituent effects on the carbonyl
carbon 13C NMR chemical shifts, the values of the chemical shifts,
dCO, for ortho-, meta-, and para-substituted phenyl benzoates,
(X-C6H4CO2C6H5,), methyl and ethyl benzoates (X-C6H4CO2CH3,
X-C6H4CO2C2H5), phenyl acetates (CH3CO2C6H4-X), and alkyl
benzoates (C6H5CO2R) were submitted to a correlation analysis
involving the scales for the corresponding inductive, resonance,
and steric factors.
The second purpose of the present work was to compare the
substituent effects on the carbonyl carbon 13C NMR chemical
shift, dCO, in substituted phenyl benzoates with those in the rates
of the alkaline hydrolysis and the infrared stretching frequencies
of carbonyl group, nCO. For that purpose, the log k values for the
alkaline hydrolysis of ortho-, meta-, and para-substituted phenyl
benzoates and alkyl benzoates in water, aqueous 0.5 M Bu4NBr
and 2.25 M Bu4NBr as well as the IR frequencies, nCO, were
correlated with the corresponding carbonyl carbon 13C NMR
The preparation procedure and characteristics of ortho-, meta-,
and para-substituted phenyl benzoates (X-C6H4CO2C6H5,
C6H5CO2C6H4-X) and alkyl benzoates (C6H5CO2R) have been
previously described.[4,40–42] Methyl 2-chlorobenzoate, methyl
2-bromobenzoate, and methyl 2-iodobenzoate were obtained
commercially (Aldrich). Benzyl benzoate was obtained from Sigma
and ethyl 2-(trifluoromethyl)benzoate was a reagent from ABCR
GmbH&Co. Cyanomethylbenzoate, C6H5CO2CH2CN, wasprepared
from benzoic acid and chloroacetonitrile in the presence of
triethylamine.[43,44] Theyieldwas28.8%,b.p. 163–1658C/15 mmHg
(Reference,[43] 152–154 8C/11 mm Hg). IR nCO ¼ 1731.8 in DMSO.
The 2,2,2-trifluoroethyl benzoate, C6H5CO2CH2CF3, was obtained
by the treatment of 2,2,2-trifluoroethanol with benzoyl chloride in
pyridine. The yield was 38.4%, b.p. 107–109 8C/27 mm Hg
(Reference,[45] 84–868C/19 mm Hg, Reference,[46] 50–528C/4 mm
Hg). IR nCO ¼ 1734.8 in DMSO. The 2,2,2-trichloroethyl benzoate,
C6H5CO2CH2CCl3, and 2,2-dichloroethyl benzoate, C6H5CO2CH2
CHCl2, were synthesized by the treatment of 2,2,2-trichloro-
ethanol or 2,2-dichloroethanol with benzoyl chloride in pyridine as
described for the synthesis of 2,2,2-trifluoroethyl benzoate.
2,2,2-Trichloroethyl benzoate, C6H5CO2CH2CCl3; yield 84.0%.
IR nCO ¼ 1732.3 in DMSO. 2,2-Dichloroethyl benzoate,
C6H5CO2CH2CHCl2; yield 36.5%, b.p. 185 8C/27 mm Hg. IR
nCO ¼ 1726.5 in DMSO. The 2-CO2CH3-phenyl benzoate, C6H5
CO2C6H4CO2CH3, was prepared from methyl salicylate and benzoyl
chloride in pyridine at 0 8C with stirring. A white solid was obtained
by recrystallization from ethanol, m.p. 928C (Reference,[47] 92 8C).
Ethyl 2-nitrobenzoate, 2-NO2-C6H4CO2CH2CH3, was synthesized as
previously described.[48] Yield 47.4%, b.p. 179–180 8C/25mm Hg
(Reference,[48] 178–1798C/23 mm Hg). Ethyl 2-chlorobenzoate,
2-Cl-C6H4CO2CH2CH3, waspreparedaspreviouslydescribed,[48] b.p.
143–1488C/25 mmHg(Reference,[49] 122–125 8C/15 mmHg). Ethyl
2-cyanobenzoate, 2-CN-C6H4CO2CH2CH3, was synthesized from
phthalic acid monoamide and ethanol in pyridine in the presence
of p-toluenesulfonyl chloride.[50] A white crystalline solid was
purified by recrystallization from benzene-pentane: m.p.62–65 8C
(Reference,[50] 64.5–668C, Reference,[51] 62–658C).
chemical shift, dCO
.
In the present work, the carbonyl carbon 13C NMR chemical
shifts, dCO, values for 55 ortho-, meta-, and para-substituted
phenyl benzoates, (X-C6H4CO2C6H5, C6H5CO2C6H4-X), methyl and
ethyl benzoates (X-C6H4CO2CH3, X-C6H4CO2C2H5), and alkyl
benzoates (C6H5CO2R) were recorded.
EXPERIMENTAL
NMR measurements
1
The standard H and proton-decoupled 13C NMR spectra were
recorded using a Bruker Avance II 200 spectrometer at 4.7 T
magnetic field at the corresponding resonance frequencies for 1H
200.13 MHz and for 13C 50.33 MHz. For the samples,
a
Copyright ß 2009 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 1155–1165