Theoretical studies on the effect of sequential benzannulation to corannulene

AT4 Exploratory semi-empirical SCF calculations are done on mono, di, tri, tetra, and pentabenzocorannulenes to assess the effect of sequential benzan nulation to the corannulene moiety. Computed results predict a gradual redu ction in the bowl-to-bowl inversion barrier in each step of the successive benzannulations and eventually for pentabenzocorannulene the barrier is onl y 1.4 kcal mol(-1) at the MNDO level. This is also followed by gradual flat tening of the central corannulene skeleton and the strain energy in benzann ulated corannulenes is found to be more due to the steric repulsions betwee n the peri-hydrogens due to the tessellation of six-membered rings. Molecul ar mechanics calculations are performed to evaluate the strain energy of th e various benzocorannulenes. The strain energy build-up in a sequential bri dging starting from pentabenzocorannulene en route to C40H10 are done. AM1 consistently overestimates the inversion barrier and based on the previous related calculations MNDO is adjudged to be the better choice to employ on this class of compounds. The sequential strain energy build-up is also eval uated starting from the pentabenzocorannulene, C40H20, to a very deep bowl, C40H10, which is the main structural motif of C-60 (C) 2001 Elsevier Scien ce B.V. All rights reserved.