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 compounds studied 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 the 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.

X-ray diffraction analyses of 2-substituted cyclohexanone oximes C5H9(X)C=NOH [X = SMe (1), NMe2 (2)] and of the parent compound [X = H (3)] showed that their cyclohexyl rings are in a slightly distorted chair conformation. These compounds assume in the solid state the (E) configuration bearing the 2-substituents in the axial conformation. Compounds (1) and (2) exist as dimeric and polymeric hydrogen-bond associates, respectively. Low-temperature X-ray analysis of the cyclohexanone oxime (3) showed that the molecules are associated forming two independent trimers. The dimer in (1) and the trimer in (3) are built up via [O-H...N=C] hydrogen bonds, while the polymer of (2) is via the [OH...NMe2] hydrogen bond. The comparative IR nu(OH) and nu(C=N) analysis of the title compounds, in the solid state and in CCl4 solution, fully supports the nature of the associates for (1)-(3) obtained by X-ray diffraction. The IR azomethyne frequency shift analysis (Deltanu(C=N)) also suggests the occurrence of the pi(C=N)/sigma*(C-X) orbital interaction which stabilizes the axial conformations of (1) and (2).

Plano de pesquisa inicial. 2.2-Equilíbrio conformacional nas oximas de cis-2-cloro (2-bromo)-4metil-cicloexanonas e compressão estérica CH3 / X 1,3 sin diaxial. 23 2.3-Compostos sob estudo 28 2.4-Espectroscopia de RMN de 1H 29 2.4.1-Oxima de cis-2-cloro-4-tércio-butil-cicloexanona 29 2.4.2 Outras oximas de configuração cis 2.4.3-Oximas de configuração trans 2.4.4-Oximas de cicloexanonas a-heterossubstituídas 39 2.5-Determinação do equilíbrio conformacional por RMN de 1H 2.5.1-Método 2.5.2-Aplicação do método à oxima da 2-c1oro-cicloexanona .47 2.5.3-Aplicação do método à oxima e O-metiI oxima da trans-2-c1oro-3-metil-cicloexanona .48 2.6-O emprego do grupo 4-tércio-butila como modelo de conformação rígida 49 2.7-Espectroscopia de RMN de 13C 52 2.7.1-Atribuição 2.7.2-Emprego de 8c-4 no cálculo da porcentagem de confôrmeros axiais 2.7.3-Ressonância na função oxima 60 2.7.4-População dos confôrmeros axiais 2.8 Aspectos vibracionais 2.8.1-Estiramento CN 66 2.8.2-Estiramento NO 75 2.8.3-Bandas de estiramento OH 78 2.8.3.1-Acidez relativa 2.8.3.2-Basicidade relativa 83 2.9-Transições 7t~7t* nos éteres metílicos de oximas de cicloexanonas a-heterossubstituídas 86 2.10-CÁLCULOS AB INITIO 2.10.1 Geometrias calculadas e por difração de raio-X 88 2.1 0.2-Cargas calculadas para as oximas e O-metil oximas de 2-X-cicloexanonas 97 2.10.3-Ordens de ligação e frequências de estiramento 98 2.10.4-Energia relativa entre os confôrmeros e momentos de dipolo 101 2.10.5-Análise dos orbitais de fronteira 102 CAPíTULO 3 Conclusões CAPiTULO 4 Parte Experimental. 111 Solventes e reagentes Pontos de Fusão e Análises Elementares Medidas no ultravioleta Medidas no infravermelho