The preferred conformations of some p-substituted S-phenyl *-ethylsulfonylthioacetates p-Ph-SC(O)CH2SO2Et (X= NO2 1, Cl 2,.Br 3, H 4, Me 5 and OMe 6) are determined through *CO infrared analysis and ab initio HF/6-31G**calculations, which showed the occurrence of two stable conformations i.e. the gauche2 (syn) and the gauche1 (anti), being the former the most stable one. The lower frequency and more intense component of the doublet for the carbonyl absorption is then attributed to gauche2 (syn) while the higher frequency and less intense component to the gauche1 (anti) conformer. Experimental and theoretical data of the corresponding p-substituted-S-phenyl thioacetates (X= NO2 10, Cl 11,.Br 12, H 13, Me 14 and OMe 15), not bearing an *-ethylsulfonyl group, have lead to similar results confirming the frequency assignments. The progressive increase of the gauche2 (syn)/gauche1 (s-anti) infrared population ratio for compounds 1-6, on going at the para position from electron attracting to electron donating substituents, along with a larger negative carbonyl frequency shifts (**) for the gauche2 (syn) conformer relative to the gauche1(anti) conformer, and the ab initio data for the corresponding thioacetate methylsulfones 7-9 are interpreted in terms of the predominance of the summing up of the O*-(CO)…S*+(SO2) and H*+(SO2Me)...O*-(CO) interactions over the O*-(SO2)...C*+(CO) interaction which stabilises the gauche2 (syn) conformer into a larger extent than the gauche1 (anti) conformer. X-ray single crystal diffraction analyses for the S-phenyl- (4) and p-methyl-S-phenyl *-ethylsulfonylthioacetates (5) indicate that these compounds exist in the solid state as a slightly distorted gauche2 (syn) conformation, which is stabilised by dipole moment coupling along with the intermolecular hydrogen bond interactions.
Conformational and electronic interaction studies of some para-substituted S-phenyl alpha-ethylsulfonylthioacetates
DISTEFANO, Giuseppe;DAL COLLE, Maurizio
2003
Abstract
The preferred conformations of some p-substituted S-phenyl *-ethylsulfonylthioacetates p-Ph-SC(O)CH2SO2Et (X= NO2 1, Cl 2,.Br 3, H 4, Me 5 and OMe 6) are determined through *CO infrared analysis and ab initio HF/6-31G**calculations, which showed the occurrence of two stable conformations i.e. the gauche2 (syn) and the gauche1 (anti), being the former the most stable one. The lower frequency and more intense component of the doublet for the carbonyl absorption is then attributed to gauche2 (syn) while the higher frequency and less intense component to the gauche1 (anti) conformer. Experimental and theoretical data of the corresponding p-substituted-S-phenyl thioacetates (X= NO2 10, Cl 11,.Br 12, H 13, Me 14 and OMe 15), not bearing an *-ethylsulfonyl group, have lead to similar results confirming the frequency assignments. The progressive increase of the gauche2 (syn)/gauche1 (s-anti) infrared population ratio for compounds 1-6, on going at the para position from electron attracting to electron donating substituents, along with a larger negative carbonyl frequency shifts (**) for the gauche2 (syn) conformer relative to the gauche1(anti) conformer, and the ab initio data for the corresponding thioacetate methylsulfones 7-9 are interpreted in terms of the predominance of the summing up of the O*-(CO)…S*+(SO2) and H*+(SO2Me)...O*-(CO) interactions over the O*-(SO2)...C*+(CO) interaction which stabilises the gauche2 (syn) conformer into a larger extent than the gauche1 (anti) conformer. X-ray single crystal diffraction analyses for the S-phenyl- (4) and p-methyl-S-phenyl *-ethylsulfonylthioacetates (5) indicate that these compounds exist in the solid state as a slightly distorted gauche2 (syn) conformation, which is stabilised by dipole moment coupling along with the intermolecular hydrogen bond interactions.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
