C-13 NMR-SPECTRA AND ELECTRONIC-STRUCTURE OF ALKENYLALANES

The parameters of C-13 NMR spectra of linear and cyclic alkenylalanes synthesized from mono- and disubstituted acetylene and the simplest al kylalanes have been obtained. A strong paramagnetic effect of the alum inum atom on shielding of alpha- and beta-carbon atoms at the double b ond has been observed for the dimeric form of organoaluminum compounds (OAC) in inert solvents, unlike that for the monomeric form solvated in electron-donor solvents (Et2O, THF, and Et3N). The results were int erpreted in terms of the model of the electron density redistribution on going from the dimeric structure of OAC to the monomeric one. The P M3 method describes most adequately (as compared to MNDO and AM1) the equilibrium geometry of cyclic dimers of OAC.