Microwave spectrum, molecular structure, and theoretical calculation of anti-2-cyclohexen-1-one oxime

The microwave spectra of 2-cyclohexen-1-one oxime and its deuterated (NOD), species were observed in the frequency range from 8 to 40 GHz in the ground vibrational state. The rotational constants were determined to be A = 4399.83 (12), B = 1507.832 (4), and C = 1166.821 (6) MHz for normal species and A = 4400.10 (34), B = 1454.06 (2), and C = 1134.38 (1) MHz for deuterated species. The inertial defects (ΔI = Ic − Ia − Ib) of normal and deuterated species were determined to be −16.907 (6) and −16.909 (18) u Å2, respectively. The ΔI value suggests a plausible molecular structure in which the NOH group and five carbon atoms of the cyclohexene ring are coplanar, but one of the carbon atoms deviates from this plane. The anti form was determined by comparing the observed and calculated rotational constants, ΔI, and ΔE (relative energy). From the rs coordinates of the hydroxyl hydrogen atom, the OH bond was found to be at the trans position with respect to the CN double bond. The structural parameters of the two bond lengths and three bond angles of anti form were adjusted to the six rotational constants observed. It was found that the bond angle of ∠C(H2)CN is much wider than that of ∠C(H)CN by about 10°. The rotational constants (B and C) of anti form calculated using MP2/6-31G (d, p) level were in good agreement with those observed.