Microwave spectrum, barriers to internal rotation, molecular structure, and theoretical calculation of (E)- and (Z)-acetaldehyde oxime, CH3CHNOH

Microwave spectra of six isotopic species of (E)- and (Z)-acetaldehyde oxime (CH3CDNOH, CH3CH15NOH, CH313CHNOH, 13CH313CHNOH, CD3CHNOH, and CD3CDNOH) were observed in the frequency range of 26.0-40.0 GHz. Adding to normal species and CH3CHNOD, the rs coordinates of H1, N, C1, C2, and H3 atoms (refer to Fig. 1) of (E) and (Z) isomers in A-state were calculated using Kraitchman's equation. The structural parameters, three bond lengths and three bond angles of (E)- and (Z)-acetaldehyde oxime in A-state were determined. The structural parameters obtained are as follows: for E isomer, r(C1N): 1.265(15) Å, r(C1-C2): 1.510(11) Å, r(C1-H1): 1.110(9) Å, ∠C2C1N: 117.7(8)°, ∠H1C1N: 118.1(5)°, and ∠C2C1H1: 124.2(7)°, and for Z isomer, r(C1N): 1.275(4) Å, r(C1-C2): 1.510(14) Å, r(C1-H1): 1.091(8) Å, ∠C2C1N: 124.3(7)°, ∠H1C1N: 113.6(5)°, and ∠C2C1H1: 122.1(7)°. The bond angle ∠C2C1N in Z isomer is much larger than that of (E) isomer, because of the steric repulsion between the methyl and hydroxyl groups in (Z) isomer. The steric repulsion may be related to the low barrier height (V3) of the methyl group in Z isomer.