HOW MANY CONFORMERS ARE THERE FOR SMALL N-ALKANES - CONSEQUENCES OF ASYMMETRIC DEFORMATION IN GG SEGMENT

Conformers have been generated exhaustively or nearly so for n-heptane, n-octane, n-nonane and n-decane using a new conformational space search program in combination with MM2 as the minimizer. When the duplications due to symmetry are ignored, they number 109, 347, 1101 and 3263, respectively. These numbers are greater than 3n (n is the number of internal C-C bonds), mainly due to the fact that a GG' sequence in the backbone chain deforms asymmetrically and approximately doubles the number of high-energy conformers. Based on these results, the aspects of conformer distribution in linear molecules are discussed The proportion of high-energy conformers to the total number is predicted to increase rapidly with the increase in the chain length, whereas low-energy conformers having no GG' sequence increases only by 2.4n.