Conformations and internal rotation of simple 1-alkenylnaphthalenes, studied by dynamic nuclear magnetic resonance spectroscopy, nuclear Overhauser effects, and molecular mechanics calculations

Abstract

A wide range of proton–proton nuclear Overhauser effects have been measured for 1-naphthylethylene and its gem, cis, and trans monomethyl derivatives, and the mean interplane angle in each case is determined. The rotational barrier in the α,β,β-trimethyl derivative is 14.3 kcal mol^–1, determined with the help of a chiral shift reagent. The MMP2 program is used to calculate a four-minima potential energy diagram for all these molecules. The measured rotational barrier is reproduced well, while mean interplane angles derived from the n.O.e. measurements agree well with the mean interplanar angle derived from calculations of stable conformations.