The conformation and the electronic structure of several α-heterosubstituted acetone oximes (XCH2(CH3)C=NOH (X = H (1), F (2), Cl (3), CH3O (4), C2H5S (5) and (CH3)2N (6)) have been determined by means of a multidisciplinary approach based on ultraviolet photoelectron (UP), electron transmission (ET) and dissociative electron attachment (DEA) spectroscopies and fully optimized ab initio 6-31G** and MP2/6-31G** calculations. The vertical ionization energy (IE) and electron affinity (EA) values related to the HOMO (πC=N) and LUMO (π∗C=N) have been determined by the ΔSCF and ΔMP2 (IE only) procedures. The studied compounds prefer an anti (E) configuration between the OH and the CH2X group, and a gauche conformation of the C-X bond with respect to the double bond, except 2 and 4 for which a syn (Z) planar structure is nearly degenerate with the E one. The spectral data, coupled with the results of the calculations indicate that the properties of the acetone oximes are mainly governed by the mixing between the orbitals localized at the X and C=N fragments and by electrostatic interactions between hydrogen and electronegative atoms. When X has poor donor and poor mesomeric acceptor properties (X = F and OMe), the prevailing interaction is the strong charge transfer mixing of the hydroxyl oxygen lone pair with the π∗C=N orbital, and the X group moves in the main molecular plane.
UV-photoelectron, electron transmission, and dissociative electron attachment spectroscopies of acetone oximes
DAL COLLE, Maurizio;DISTEFANO, Giuseppe;
1998
Abstract
The conformation and the electronic structure of several α-heterosubstituted acetone oximes (XCH2(CH3)C=NOH (X = H (1), F (2), Cl (3), CH3O (4), C2H5S (5) and (CH3)2N (6)) have been determined by means of a multidisciplinary approach based on ultraviolet photoelectron (UP), electron transmission (ET) and dissociative electron attachment (DEA) spectroscopies and fully optimized ab initio 6-31G** and MP2/6-31G** calculations. The vertical ionization energy (IE) and electron affinity (EA) values related to the HOMO (πC=N) and LUMO (π∗C=N) have been determined by the ΔSCF and ΔMP2 (IE only) procedures. The studied compounds prefer an anti (E) configuration between the OH and the CH2X group, and a gauche conformation of the C-X bond with respect to the double bond, except 2 and 4 for which a syn (Z) planar structure is nearly degenerate with the E one. The spectral data, coupled with the results of the calculations indicate that the properties of the acetone oximes are mainly governed by the mixing between the orbitals localized at the X and C=N fragments and by electrostatic interactions between hydrogen and electronegative atoms. When X has poor donor and poor mesomeric acceptor properties (X = F and OMe), the prevailing interaction is the strong charge transfer mixing of the hydroxyl oxygen lone pair with the π∗C=N orbital, and the X group moves in the main molecular plane.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
