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Mechanisms of conformational chirality inversion in bicyclo[4.2.1]nonan‐9‐one and bicyclo[4.2.2]decane as studied in two‐parametric torsional energy surfaces
Author(s) -
Ōsawa Eiji
Publication year - 1982
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540030315
Subject(s) - bicyclic molecule , chemistry , cyclooctane , decane , ring flip , stereochemistry , cyclohexane , nonane , enantiomer , molecule , bent molecular geometry , computational chemistry , crystallography , ring (chemistry) , organic chemistry
With the purpose of deciphering conformational inversion processes of typical mobile bicyclic molecules, torsional energy surfaces near the enantiomers of bicyclo[4.2.1]nonan‐9‐one ( 1 ) and bicyclo‐[4.2.2]decane ( 2 ) were prepared using molecular mechanics with an improved two‐bond drive technique. Inversion of 1 takes place most favorably via a C s transition state with the tetramethylene chain over the ethano bridge [ 1B , Δ H ± 6.1 (calculated) vs. 6.8 (observed) kcal/mol]. An alternative pathway involving a C s local energy minimum ( 1C ), in which the tetramethylene chain is bent over the carbonyl, has a barrier 2.4 kcal higher than 1B . The global energy minimum conformation of 2 has boat–chair cyclooctane and twist–boat cyclohexane rings ( BCTB ), and enantiomerizes into its mirror image ( BCTB ') via three intermediates: TCTB , CB , and TCTB '. The highest point in the proposed pathway, a saddlepoint CB , is calculated to lie 8.0 kcal/mol above BCTB (observed Δ H ± 7.8 kcal/mol). The advantage of the two‐parametric over the one‐parametric torsional energy surface is discussed.