The gas-phase structure of azetidine: Microwave spectroscopy, and electron diffraction and normal coordinate analysis

High resolution Fourier transform infrared spectra and analysis of the ν14, ν15 and ν16 bands of azetidine

“…This is in agreement with ab initio calculations [12,13], Raman intensities [14] and a subsequent far infrared study [15]. The microwave and electron diffraction experiments of Günther et al [16] confirmed the presence of the equatorial conformer and determined its structure to have a ring puckering angle of 29.7°although their microwave spectrum also contained a weak unassigned feature which was thought to be due to the axial conformer. The more recent microwave and ab initio investigation of López et al [17] analyzed the rotational spectrum in the ground and several excited ring puckering vibrational states.…”

“…The ground state structure has C s point group symmetry with a ring puckering angle of 29.7°relative to the ab-plane of the molecule [16]. The three modes studied in this work correspond to motions that are principally due to ring puckering (m 16 ), ring deformation (m 15 ) and b-CH 2 rocking (m 14 ) although the two latter modes also have significant character that corresponds to NH out-of-plane bending and a-CH 2 twisting [18].…”

“…This is not surprising as the ab initio force field calculations of Dutler et al [18] suggest that the m 14 and m 15 modes are comprised of 40% and 30% NH out-of-plane bending character, respectively. [11,15,16,18]. The scaled ab initio force field calculations of Dutler et al [18] predicted the band origins to have frequencies of 739.4, 636.6 and 198.7 cm À1 , respectively, although the authors comment that the agreement for the ring puckering mode was surprising and likely fortuitous as such modes cannot be modeled realistically with harmonic force fields.…”

“…In addition to the extensive investigation of the ring puckering mode of azetidine, the higher frequency modes have been calculated via ab initio methods and the infrared spectrum has been measured in the gas phase [16,18], in solution [18,19] and in a solid argon matrix [20]. Dutler et al [18] recorded the gas phase infrared spectrum from 400 to 3400 cm À1 at a resolution of 0.12 cm À1 and 0022-2852/$ -see front matter Ó 2010 Elsevier Inc. All rights reserved.…”

Internal dynamics in azetidine: A microwave and ab initio study

“…The conformation and ring-puckering potential function of azetidine has been studied using different spectroscopic methods, 2-8 electron diffraction, 6,9 and ab initio calculations. [10][11][12] The ring-puckering vibration was first analyzed by Carreira and Lord.…”