Restricted Rotation about the C(13)-Aryl Single Bond in 13-Aryl13 H-dibenzo[a, i] fluorenest

Abstract

Three 13-aryl-13 H-dibenzo[a, i]fluoren-13-ols ( 3 ) (13-(2-methylphenyl)- (3 a), 13-(3methylpheny1)- (3 b), and 13-(2-methyl-1-naphthyl)-, 13 H-dibenzo[a, Cfluoren-13-01 (3 c))were synthesized by the reaction of 13 H-dibenzo[a, i]fluoren-13-one ( 2 ) with three aryllithiums. Reduction of ( 3 ) with HI in acetic acid gave the -corresponding 13-aryl-13 Hdibenzo[a, i]fluorenes ( 4 ).,
The rotational barrier (δG^≠) abo ut the Cso-Cso single bond in 13-(2-methylpheny1)-13 Hdibenzo[a, i]fluorene (4 a) was determined by means of the DNMR method (δG^≠ap, sp =18.6 6 kcal/mol, δG^≠spap=18.70 kcal/mol). Furthermore, the rates of isomerization for th e process of ap--. sp and sp--*ap of isolated (3 c) and (4 c) were measured at various temperatures on their 'H-NMR spectra, respectively, and the δG^≠ values for each process were obtained c): δG^≠ap-sp =24.96 kcal/mol, δG^≠sp-ap=23.24kcal/mol. (4c): δG^≠ap-sp=34.78kcal/mol, δG^≠sp-ap=34.52 k cal/mol)