Premium
Effects of neutral and charged substituents on the infrared carbonyl stretching frequencies in phenyl and alkyl benzoates in DMSO
Author(s) -
Nummert Vilve,
Piirsalu Mare,
Vahur Signe,
Toom Lauri,
Leito Ivo,
Koppel Ilmar A.
Publication year - 2017
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3608
Subject(s) - chemistry , substituent , benzoates , alkoxy group , aqueous solution , medicinal chemistry , alkyl , inductive effect , ion , infrared , dimethyl sulfoxide , organic chemistry , physics , optics
The carbonyl infrared stretching frequencies for 57 meta ‐, para ‐ and ortho ‐substituted phenyl benzoates, C 6 H 5 CO 2 C 6 H 4 ‐X and alkylbenzoates, C 6 H 5 CO 2 R, containing besides neutral substituents the charged substituents in phenoxy and alkoxy part in dimethyl sulfoxide (DMSO) have been recorded. The carbonyl stretching frequencies, ν CO , for meta ‐ and para ‐substituted phenyl esters of benzoic acids in the case of neutral substituents were found to correlate well with the substituent constants, σ °. The ν CO values for ortho derivatives correlated with the inductive substituent constants, σ I , only. The values of constants for charged substituents, σ ° ± , calculated on the basis of the ν CO and the 13 C NMR chemical shifts, δ CO , in DMSO agree well with the σ ° ± values for the corresponding ion pairs reported by Hoefnagel and Wepster and those determined from the log k values of the alkaline hydrolysis in 4.4 M NaCl solution at 50 °C. Thus, the values of substituent constants for ion pairs of charged substituents estimated on the basis of aqueous data could be successfully used in non‐aqueous solution (DMSO) simultaneously with neutral substituents in case the charged substituents were not completely ionized and are in ion pair form. Copyright © 2016 John Wiley & Sons, Ltd.