First ionization potentials and conjugation in molecules of ethylene derivatives containing organoelemental substituents of Group IV elements

Abstract

Unlike the .EHOMO energies, the first vertical ionization potentials (1 I) of monosubstituted ethylenes depend not only on both the inductive and resonance effects but also on the polarizability of the substituents, which can be characterized by the Ga parameters. The OR +, (sp*, and <se parameters for 12 silicon-, germanium-, and tin-containing groups were determined using the equations relating the It values and the o), ~R +, ~p+, and oa parameters of the substituents in the molecules of organic compounds. The conjugation of oNanoelemental substituents with the double bond is stronger than that with benzene ring; the CR § parameters in the ethyiene and benzene series are related by a linear dependence.Key words: ionization potential; silylethylenes, germylethylenes, stannylethylenes; o-constants of substituents, correlation equations.The modem model of conjugation (see, for instance, Ref. 1) in the organoelemental compounds of the R3ER=, type (E = Si, Ge, Sn, and Pb; R is an organic radical; R~, is an unsaturated group: Ph, CH=CH2, C~=CR, fury l, rhienyl, etc.) is based on the concept of dual (simultaneously acceptor and donor) resonance properties of organoelemental substituents R3E (E is a Group IV element) toward the reaction (or indicator) centers R=. The resonance acceptor effect (d,r~-conjugation) is the interaction between the vacant nd-orbitals of E atoms and the antibonding (s*-orbitals of the E--R bonds of the R3E substituent containing an R=, group. The resonance donor effect ((s,~z-conjugation) is due to the interaction between o-orbitals of the E--R bond in R3E with fragment R~. The overall effect (simultaneous effect of the d,zt-and cbx-conjugation) cannot be characterized by universal parameters, since the conjugation between R3E and R=, depends on the nature of the organic radical, unsaturated group, and the Group IV element; in the case of fixed R, E, and Rx. it depends on the magnitude of the negative effective charge on R=. I Of two components (the acceptor and donor one) of the overall resonance effect, only the ~,Tt-conjugation is dependent on the charge on R~. 1-4 Hence, va .rtdng the negative effective charge on ~ in a wide range makes it possible to observe not only changes in the relative contributions of the two indicated components of the overall resonance effect, but (in the limiting case) also inversion of the sign of the overall effect.t-7 The problem of inversion of the donor-acceptor properties of the R3E substituents remains inadequately studied despite its importance for both creation of a general theoD" of conjugation in organic compounds of Group IV elements and for studying the ionic reactions with participation of such type derivatives.Investigation of the ionization potentials of the R3ER=, type compounds can make an appreciable contribution to the solution of this problem and accumulation of data on the resonance parameters of the R3E substituents. Thus, an analyis of the first ionization potentiais of benzene derivatives (P~, = Ph) made it possible to obtain new informat...

Conjugation in radical cations of benzene, ethylene, and acetylene derivatives. Nonuniversality of the resonance parameters of group 14 organoelement substituents

“…At the same time, they can be used to estimate the CrR+(lll) and ~R+(ll) values that have only been reported in Ref. 8 and in this work.…”