Photoelectron Spectra and Electronic Structures of Some Acceptor-Substituted Cyclopropanes:Linear Correlation of Substituent Effects on MO Energies with Molecular Structures

摘要

The relationship between electroni and geometrial structures in acceptor-substituted cyclopropanes has been investigated by B3LYP DFT calculations and photoelectron (PE) spectroscopy The spectra of cyclopropanecarbaldehyde (2) cyclopropanecarboxylic acid (3) cyclopropanecarboxylic acid methyl ester (4) nitrocycloperopane (5) isothiocyantocylopropane (6) cyanocyclopropane (7) and 1,1-dicyanocyclopropane (8) have been analyzed The first ionization potential (IP_1) of compounds 2-5 was found to be 0.1-0.4 eV higher than that of the analogous isoproply derivatives indicatin-contrary to expectation-that in these compounds the cyclopropyl group acts as a waker delectron donor than an isopropyl proup In the other compounds IP values are 0.4-1.1 eV lover than in the open-chain congeners The qWalsh orbitals omega_A and omega_A of the three-emembered ring are substantially stabilized to different extents by interatins with substituent orbitalso and this is reflected in shortened distal and elongated vicinal C-bonds Although the nitro group in compound 5 causes large stabilizations of both omega_s and omega_a their energy difference triangel open_omega remains rather small this is in agreement with a relatively small difference triangle openr of the C-C bond lengthes For the ivestigated monosubstitute cyclo propanes 2-7 the largest effects with respect to triangle openr are caused by the formyl group in carboxaldehyde 2. Comparison of the results for nitrile s 7 adn 8 indicates thast the effects of the cyano groups are additive Alinerar relation ship between triangel openomega and triangle openr wa established by B3LYP DFT calculations on geo-metrically distorted cylopropane (1) and from the PE data of 2-8.