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NMR studies of sulphur heterocycles. II —substituent effects in the thieno[2,3‐b] [1]benzothiophene and thieno[3,2‐b] [1]benzothiophene systems
Author(s) -
Ewing D. F.,
Gregory D. N.,
Scrowston R. M.
Publication year - 1974
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270060512
Subject(s) - benzothiophene , substituent , thiophene , chemistry , chemical shift , ring (chemistry) , computational chemistry , sulfur , stereochemistry , medicinal chemistry , organic chemistry
Substituent chemical shifts for the title systems have been determined at infinite dilution in CDCl 3 from a study of 40 derivatives. An excellent correlation is found between the ortho effect of substituents in the thiophene ring and the corresponding effects in thiophene itself, indicating negligible perturbation by the fused rings. Long range effects of 2‐ and 3‐substituents on the 5‐ and 6‐protons are electronic in origin, but cannot be interpreted in terms of simple resonance theory. These long range effects correlate linearly with σ p °. An O, S‐ cis conformation for the formyl group in 2‐formyl‐thieno[2,3‐6][1]benzothiophene is adduced on the basis of chemical shifts.