2,3-Dimethyl-1,2,3,4-tetrahydronaphthalenes and 4,5-dimethylcyclohexenes. Proton magnetic resonance and stereochemistry

Abstract

The proton magnetic resonance spectra of cisand trans-2,3-dimethyl-l,2,3,4tetrahydronaphthalenes and cisand trans-4,5-dimethylcylcohexenes exhibit a chemical-shift difference in the signal corresponding to the protons adjacent to the methyl groups. This proton signal in the spectra of the trans isomers is about 0.5 ppm toward higher field from the corresponding signal in the spectra of the c k isomers. This chemical shift is attributed to the predominant axial orientation of these hydrogens in the half-chair conformation of the trans isomers in contrast to the average axial-equatorial orientation in the corresponding conformation of the cis isomers. This difference is interpreted in terms of the unequal shielding of axial and equatorial substituents resulting from the magnetic anisotropy effect of the carbon-carbon single bond. These compounds retained their conformational mobility to the practical temperature limit of -127 to -169'.The stereospecific synthesis of these compounds is described.

New aromatic musk odorants: Design and synthesis

“…This correlation was confirmed by decoupling experiments. Our configurational assignment of 71 and 72 is also in agreement with analogous cases [26] ('H-NMR of 71 and 72: 1.58 and 1.88 ppm (H-C(2,3))).…”