Conformational Space and Dynamic Stereochemistry of Overcrowded Homomerous Bistricyclic Aromatic Enes − A Theoretical Study

摘要: The conformational spaces and dynamic stereochemistry of representative overcrowded homomerous bistricyclic aromatic enes (1, X = Y) are investigated, applying the semiempirical PM3 method. experimental energy barriers for E,Z isomerizations, enantiomerizations, inversions 1 related compounds, derived from DNMR other kinetic studies, reviewed. This study focuses on analysis minima, transition states, mechanisms isomerizations bifluorenylidene (2), dixanthylene (3), dithioxanthylene (9), bi-5H-dibenzo[a,d]cyclohepten-5-ylidene (11). four differ in sizes their central rings bridging groups. interconversions twisted, anti-folded, syn-folded conformations thermal (topomerizations), (including combinations) elucidated. calculated topomerizations 2, 3, 9, 11 25.3, 16.4, 24.3, 39.3 kcal/mol, respectively. corresponding enantiomerizations or 4.9, 15.9, 37.6 In most cases, agreement with experimentally determined values is within 1−3 kcal/mol. New proposed anti-folded 11, involving low-symmetry folded/twisted states respective intermediates.