Premium
NMR and theoretical (MNDO and Ab Initio ) studies of lone‐pair electron‐π‐electron interactions: The conformation of 9‐methoxyfluorene
Author(s) -
Bakke Jan M.,
Rønneberg Hanne,
Chadwick Derek J.
Publication year - 1987
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.1260250315
Subject(s) - mndo , chemistry , lone pair , heteronuclear molecule , ab initio , electron pair , alkane stereochemistry , computational chemistry , chemical shift , ab initio quantum chemistry methods , conformational isomerism , crystallography , coupling constant , stereochemistry , electron , nuclear magnetic resonance spectroscopy , molecule , organic chemistry , crystal structure , physics , particle physics , quantum mechanics
Abstract The results of NMR investigations based on the heteronuclear 3 J(CH 3 , H‐9 ) coupling constant, the methyl group chemical shift, lanthanide‐induced shifts and MNDO calculations indicate that 9‐methoxyfluorene exists predominantly in the trans conformation in which the methyl group is oriented in an antiperiplanar relationship with respect to H‐9. Previous experimental work on the 9‐hydroxy analogue demonstrated a similar conformational preference, which is also indicated by the results of MNDO and ab initio calculations presented here. The origin of the preference probably lies in a repulsive interaction between the electrons of the aromatic π‐systems and the lone‐pair electrons of the hydroxyl or methoxyl oxygen.