Microwave spectrum, molecular structure, dipole moment, and theoretical calculation of cyclopentanone oxime

The microwave spectra of cyclopentanone oxime (C5H8NOH) and its deuterated species (C5H8NOD) were observed in the frequency region from 9 to 40 GHz. Only a-type R-branch transitions were assigned in the vibrational ground and excited states. The rotational constants of normal species were determined to be A = 5870.80(33), B = 1917.021(8), and C = 1526.784(8) MHz in the vibrational ground state, and A = 5870.16(43), B = 1842.707(9), and C = 1479.401(9) MHz for deuterated species. The dipole moments were determined as μa = 0.80(10), μb = 0.20(10), and μc = 0.40(10) D. The ring-puckering vibrational states were observed up to v = 6. The vibrational mode was nearly harmonic. The fundamental frequency of the ring-puckering mode was found to be 70(20) cm−1. The molecular structure of cyclopentanone oxime was determined to be a twisted configuration by comparing the observed and calculated rotational constants, planar moment of inertia, Pcc, and rs coordinates of the hydroxyl hydrogen atom. On the molecular geometry, the bond angle, ∠C2C1N6 (Fig. 1), is larger than ∠C5C1N6 by ca. 6°, because of the steric repulsion between the methylene group of C2 atom and hydroxyl group.