Quantum chemical interpretation of the stereospecific effects characteristic of the polymerization in acrylonitrile-RLi and methyl acrylate-RLi systems

With the aim to find the causes of the different stereochemical behavior characteristic of the anionic acrylonitrile (AN) and methyl acrylate (MA) growing chains, the following model systems were investigated using the MNDO 1

1 Modified neglect of diatomic overlap.

(method: 1) compounds XCH₂CH₂CH(X)Li simulating racemic (r) and meso (m) diads of AN (X = CN) and MA (X = COOCH₃) at the active end of the growing chain; (2) intermediate complexes of a MA r-diad with a MA molecule in the mutual orientations which should lead to the formation of a rr- or rm-triad; (3) compounds XCH₂(CH₂CH(X))₂Li simulating mm-, mr-, rm-, or rr-triads of MA and their complexes with H₂O and ethylenediamine (EDA). It was found that reaction of a MA r-diad with a MA molecule should preferably lead to the formation of a rm-triad in the absence of EDA and to the formation of a rr-triad in the presence of EDA. For AN none of the possible transformations of active diads into triads was found to be preferred. These results are in qualitative agreement with the experimental data.