Studies in nuclear magnetic resonance spectroscopy. Part VIII. Conformations and coupling constants in 1,2-disubstituted 3,3-dimethylbutanes

Abstract

The 100 MHz spectra of a series of 1,2-disubstituted 3,3-dimethylbutanes have been analyzed exactly as ABC systems by use of iterative computer techniques. The chemical shifts are shown to agree reasonably well with those predicted from systems with similarly oriented substituents. The gauche(J_g) and trans(J_t) coupling constants were shown to be of the same sign and opposite in sign to J_gem. The values of the vicinal coupling constants and their relative insensitivity to concentration change suggest that these compounds exist predominantly as single conformers, viz. with gauche oriented 1,2-substituents. Neither J_g nor J_t correlates with the electronegativities or sizes of the substituents. Small differences observed in these parameters in this series of compounds may therefore reflect different relative populations of conformers.