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Lack of manifestation of an anomeric effect in 2‐diphenylphosphinoyl‐1, 3‐dioxane and 2‐diphenylphosphinoyl‐1, 3‐oxathiane 1
Author(s) -
Juaristi E.,
FloresVela A.,
Labastida V.,
Ordoñez M.
Publication year - 1989
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.610020406
Subject(s) - chemistry , conformational isomerism , steric effects , counterpoise , substituent , anomer , anomeric effect , stereochemistry , crystallography , oxygen atom , medicinal chemistry , computational chemistry , density functional theory , organic chemistry , molecule , basis set
The spectroscopic evidence for the predominance of the equatorial conformers in the title compounds was confirmed by the study of derivatives containing counterpoise substituents, and by chemical equilibration of anancomeric models. Δ G 27 o°C [P(O)Ph 2 ] ≳ 3·2 kcal/mol was determined in the dioxane, and Δ G 55 o°C [P(O)Ph 2 ] = 1·42 ± 0·12 kcal/mol in the oxathiane. It follows then that the strong anomeric interaction observed previously in SCP segments does not show up in the six‐membered heterocycles 2 and 7 , which contain OCP moieties. This may be due to an inherent inability of oxygen to act as an electron donor to the axial P(O)Ph 2 substituent, or to a dominant repulsive steric interaction in the axial conformers.