Ethynyl group, electronic effects

X. THE ELECTRONIC EFFECTS OF ACETYLENIC GROUPS A. The Characteristics of the Ethynyl Group... 

The substituent and geometric effects on the electronic spectra of silylenes are well modeled by ab initio MO calculations, in all essential respects . For some substituents such as vinyl and ethynyl groups, the MO calculations are inaccurate because of contamination of the UHF states by higher-lying triplet states. Removal of this contamination by the method of spin projection gave results in good agreement with expaimental trends ... 

As the other steps in cross-coupling reactions, the rate of the reductive elimination step is also influenced by the steric and electronic effects induced by the ancillary ligands bound to the metal center. Consequently, the influence of the steric and electronic properties of these ligands on this step has been theoretically investigated by several groups. Ananikov, Musaev and Morokuma analyzed by means of the ONIOM approach the C-C coupling from the complexes c -[Pd(R)2(L) ] (R = Me, Ph, vinyl, ethynyl L = PPhs, PCys, PMes and PH3 n = 1,2) [116]. According... 

What is the effect of vinyl substitution on the first electronic transition of a silylene The relevant calculations and the available experimental data for vinyl substituted silylenes are presented in Fig. 4. The calculations predict that substitution of a methyl group in Mc2Si by a vinyl group induces a red-shift of 47 nm, significantly larger than the red-shift of only 11 nm predicted for a similar ethynyl substitution. Substitution of the second methyl group by a vinyl group causes an additional red-shift of 38 nm. 

A strong electron-releasing effect of the silatranyl group is displayed in the upheld shift of the yS- and signals of the vinyl, ethynyl, and phenyl groups of silatranes... 

---