Microwave spectrum, molecular structure, and theoretical calculation of cyclohexanone oxime ( chair form)

Abstract

The microwave spectra of cyclohexanone oxime and d 1 (=NOD) and d 4(2,2,6,6- d 4) derivatives were observed in the frequency range from 8 to 40 GHz in the ground and excited vibrational states. The rotational constants were determined to be A = 3799.844(48), B = 1513.7912(23), and C = 1189.6118(29) MHz for normal species, A = 3791.835(88), B = 1461.0324(47), and C = 1157.5653(53) MHz for d 1 species, and A = 3364.141(49), B = 1487.9551(34), and C = 1154.0965(44) MHz for d 4 species in the ground vibrational state. The planar moments, P bb ( P bb = ( I c + I a − I b )/2) of normal, d 1, and d 4 species were determined to be 111.9885(26), 111.9817(46), and 124.2394(49) uÅ 2, respectively. The almost same values of P bb of normal and d 1 species suggest that the hydroxyl hydrogen atom is very close to the a– c plane. From the r s coordinates of the hydroxyl hydrogen atom, the OH bond was found to be at the trans position with respect to the C N double bond. The conformation of cyclohexanone oxime was determined to be chair form by comparing the observed and calculated rotational constants, Δ I, and planar moments, and taking account of the calculated the relative energy difference, Δ E. The structural parameters, the three bond lengths, three bond angles, and three dihedral angles, were adjusted to the nine rotational constants observed. The bond angle of ∠C 2C 1N is much wider than that of ∠C 6C 1N by about 10°. The dihedral angles of ∠C 1C 2C 3C 4, ∠C 2C 3C 4C 5, and ∠C 3C 4C 5C 6 were determined to be 53.3(5), −57.2(5), and 57.2(5)°. Two vibrational modes were assigned to the ring-bending and ring-twisting ones, which are almost harmonic up to v = 3.