The effect of neighboring 1-and 2-adamantyl group substitution on the conformations and stereodynamics of N-methylpiperidine. Dynamic NMR spectroscopy and molecular mechanics calculations

When a 1-adamantyl or a 2-adamantyl substituent is introduced at the 2-posi tion in N-methylpiperidine, four different chair conformations are possible . Experimental observation using dynamic NMR spectroscopy and molecular mec hanics calculations agree that the chair conformation with an equatorial ad amantyl group and an axial methyl group is by far the most stable, but in b oth cases a minor population of a second conformation is demonstrated and c haracterized. Interaction between adamantyl and methyl groups is much more conformation-determining than any preference for equatorial over axial loca tion which predominates in simpler 2-substituted N-methylpiperidines.