Anisochrony of Isopropyl Methyl Groups in 1-Isopropyl-Substituted Tetralins and Indans

Article abstract of DOI:10.1002/omr.1270211106

1-Isopropyl-5-methylindan, 1-isopropyl-7-methylindan and 1-isopropyl-1,2,3,4-tetrahydronaphthalene show a large anisochrony (magnetic non-equivalence) of the isopropyl methyl signals at room temperature in their 1H NMR spectra.A decrease in magnitude of this anisochrony is observed, in each case, in the temperature range 30-150 deg C.However, for 1-isopropyl-8-methyltetralin, the magnitude of the non-equivalence of the isopropyl methyl signals is unexpectedly small.These latter signals converge at 85 deg C and then diverge in the opposite direction over the range 85-150 deg C.This alteration in anisochrony with temperature change for all cases is observed as a continuous downfield migration of one signal which, in turn, results from variations in conformation populations.