E. Olefirowicz, E. Eliel
Dec 26, 1997
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0
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4
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Journal
Journal of Organic Chemistry
Abstract
Conformational equilibria in 1-, 3-, and 4-methyl-1,2,3,4-tetrahydroisoquinolines (THIQs) and the diastereomeric pairs of their 1,3- and 1,4-dimethyl homologs have been determined by measurement of H3/H4(trans) coupling constants and have been confirmed by molecular mechanics [MMP2(85)] calculations. The experimental −ΔG° values (a → e) for the monomethyl compounds (computed values in parentheses) in kcal mol-1 are Me-1, 0.56 (0.46); Me-3, 1.63 (1.53); and Me-4, −0.32 (−0.22). Agreement of experimental and calculated values is very good as is the additivity of values for the dimethyl compounds (Table 1). Values for the corresponding hydrochlorides are Me-1, 0.19 (−0.34); Me-3, l.15 (1.46); and Me-4, 0.35 (0.10) kcal mol-1. The less than satisfactory agreement of experimental with computed data here is probably due to neglect of solvation. The very small or negative ΔG° values for Me-1 and Me-4 were ascribed not only to the pseudoaxial (rather than axial) nature of Me(ax) and the absence of a syn-axial hyd...