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Structure of charge‐transfer reaction complexes in anionic polymerization of isoprene: Quantum chemical calculations
Author(s) -
Kalninsh K. K.,
Podolsky A. F.
Publication year - 2005
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.20518
Subject(s) - isoprene , excited state , chemistry , polymerization , ab initio , valence (chemistry) , ion , photochemistry , computational chemistry , atomic physics , polymer , copolymer , organic chemistry , physics
A new mechanism of isoprene anionic polymerization is proposed. Its central moment is thermal electronic excitation of a living polyisoprene–isoprene complex into the quasi‐degenerate electronically excited state (S · T) 1 , which is of the charge (electron) transfer character. It is asserted that the probability of chemical bond formation is determined by the free valence index on carbon atoms and by the geometry of reacting complex in the excited state (S · T) 1 . Semi‐empirical AM1 and ab initio 6‐31G* quantum chemical calculations revealed low energies of triplet excited levels (<10 kcal/mole). Comparison of isoprene polymerization on free anions and on solvated ion pairs shows that both types of active centers produce vinyl 1,2 (4,3)‐units. Free anions generate predominantly 1,2‐units, whereas solvated ion pairs tend to form units with the 4,3‐structure. Analysis of energies of excited isoprenyl lithium + isoprene complexes shows that the formation of 1,4 (4,1)‐ cis ‐polyisoprene in an inert media is most preferable. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005