Steric origin of isotope effects in nuclear magnetic resonance shifts induced by lanthanide shift reagents; effect of deuteriation of methyl substituted pyridines

Abstract

Deuteriation of all the methyl groups, or the 2- and 6-methyl groups, in 2,4,6-trimethylpyridine causes a large (ca. 6%) isotope effect on the lanthanide-induced shift for the 3- and 5-hydrogen atoms, whereas the effect of deuteriation of the 4-methyl group is not detectable (<0·2%); a steric origin is proposed for the secondary isotope effect in lanthanide-induced shifts.