C-13-NMR STUDIES ON CONFORMATIONAL EQUILIBRIA IN ISOPROPYL METHYL-ETHER

The energy difference between the two rotational isomers, i. e. , C//s and C//1, of isopropyl methyl ether has been elucidated from the observed vicinal **1**3C-**1H coupling constant. The conventional Gutowsky method based on the simple rotational isomeric state model tends to give an underestimate, especially when the energy difference is large. A more elaborate treatment, which takes account of the overall profile of the torsional potential energy curve, has been attempted. Adoption of J//T equals 11. 0-12. 0 Hz for the trans coupling gave a value of 2. 2 plus or minus 0. 2 kcal mol** minus **1 for the energy difference E//C(3)-E//C(1). This result is consistent with the range (2. 4 plus or minus 0. 6 kcal mol** minus **1) estimated by the matrix-isolation method as reported by M. Nakata et al.