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Substituent‐induced chemical shifts (SCS) by the phenyl group in sterically congested styrene derivatives
Author(s) -
Knorr Rudolf,
Stephenson David S.,
Böhrer Petra,
Hoang ThiPhung
Publication year - 1993
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260310415
Subject(s) - chemistry , substituent , steric effects , chemical shift , styrene , stereochemistry , proton nmr , medicinal chemistry , organic chemistry , copolymer , polymer
The two 13 C NMR methyl signals of the sterically congested 9‐benzylidene‐1,8‐dimethylfluorene (1a) have the surprisingly small separation of only 0.37 ppm; for 9‐benzylidene‐2,7‐dimethylfluorene the corresponding methyl separation is 0.04 ppm. An alternative analysis of 1a with respect to 1,8‐dimethylfluorene shows that the perturbing syn ‐phenyl substituent has caused a downfield ( + 0.47 ppm) 13 C shift but an upfield 1 H shift ( − 0.97 ppm) of the compressed 1‐CH 3 group. For further comparisons, NMR assignments were also made for 2,7‐dimethylfluorene, 1,8‐dimethylfluoren‐9‐one and 2‐(1,1‐dimethylethyl)‐3,3‐dimethyl‐1‐phenylbut‐1‐ene.