The determination of configuration of certain quaternary salts derived from N-benzyl piperidines by nuclear magnetic resonance spectroscopy

Abstract

By conformational analysis of N-benzyl benziodides derived from 2-methyl-, 3-methyl-, and 4-phenyl-piperidine, 2-methylpyrrolidine, trans-decahydroquinoline, and nortropane, and of the diastereoisomeric N-benzyl-N-methyl-camphidinium iodides, coupled with consideration of the effects of the magnetic anisotropy of the benzene rings on the chemical shifts of significant protons in the preferred conformations, configurational assignments (at nitrogen) for the camphidinium salts and for diastereoisomeric N-benzyl N-dideuteriobenzyl salts in all the other systems named except nortropane become possible. The results accord with preferred axial quaternisation (by primary alkylating agents) in all the systems where unambiguous configurational deductions could be made.