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The nonplanarity of n ‐doped polyenes and of carbanions with alkali metal counterions
Author(s) -
Burke Luke A.,
KroghJespersen Karsten
Publication year - 1988
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.560340810
Subject(s) - chemistry , polyacetylene , lithium (medication) , dilithium , carbanion , alkali metal , computational chemistry , ab initio , crystallography , corannulene , lithium atom , ion , molecule , stereochemistry , deprotonation , organic chemistry , ionization , medicine , endocrinology , polymer
Using ab initio RHF‐SCF‐MO theory with the 3‐21G basis set and geometry optimization with a gradient method, trans pentadienyl lithium and sodium have been shown to have a carbon backbone in which the middle carbon atom falls ca. 40° out of the plane of the other carbon atoms. The free anion was found to be planar. Optimization of the dilithium octateraene complex (C 8 H 10 Li 2 ) with C 2 symmetry gave a structure where the hydrocarbon backbone is distorted out of plane and folded about the lithium atoms. A partially optimized C 8 H 10 Li 2 where the C and H atoms are constrained to remain in‐plane lies ca. 0.6 eV above the folded structure. The consequences of the distortion are discussed for the applicability to longer polyenes and n ‐doped polyacetylene. In a vibrational analysis of C 5 H 7 Li and C 5 H 7 Na and of allyl Li and allyl Na, two very intense bands near 800 cm –1 appear which are not present in the flat, free allyl and pentadienyl anions. The similarity to the broad band at 800 cm –1 which appears in doped polyacetylene is discussed.