A STUDY OF SUBSTITUENT EFFECTS ON HYDROGEN-TO-ARENE NONBONDED INTERACTIONS

The polycylic aromatic hydrocarbon 9,14-diphenylbenzo[b]triphenylene is strongly twisted due to nonbonded interactions between hydrogen atoms on the polycyclic nucleus and the pi systems of the phenyl groups. Ten derivatives of 9,14-diphenylbenzo[b]triphenylene, with a wide variety of substituents on the phenyl groups, were synthesized and crystallographically characterized in order to test for the presence of electronic substituent effects on the magnitude of these hydrogen-to-arene nonbonded repulsions. The observed end-to-end twists in these compounds were the following: 9,14-diphenylbenzo[b]triphenylene (3) 40.4 +/- 0.4-degrees; 9,14-bis(4-nitrophenyl)-bezo[b]triphenylene (4), adopted a nontwisted conformation; 9,14-bis(4-methoxyphenyl)benzo[b]triphenylene (5), 36.8 +/- 1.3-degrees;9,14-bis[4-(methylthio)phenyl]benzo[b]triphenylene (6), 40.5+/-0.6-degrees;9,14-bis(4-chlorophenyl)-benzo[b]triphenylene (7), 39.4 +/- 0.5-degrees; 9,14-bromophenyl)benzo[b]triphenylene (8), 39.4+/-0.8-degrees;9,14-bis[4-(trifluoromethyl)phenyl]benzo[b]triphenylene (9), 36.3+/-1.5-degrees and 33.0 +/- 1.5-degrees (two crystallographically independent molecules); 9,14-bis(4-cyanophenyl)benzo[b]triphenylene (10), 38.2+/-0.5-degrees; 9,14-bis(4-methyl-phenyl)benzo[b]triphenylene (11), 43.1 +/- 0.4-degrees; 9,14-bis(4-nitrophenyl)-11-methylbenzo[b]triphenylene (12), 40.4 +/- 0.9-degrees and 33.4+/-0.9-degrees (two crystallographically independent molecules). The effects of the substituents and of crystal packing forces on the solid-state conformations of these compounds are discussed.