Theoretical studies on the effect of sequential benzannulation to corannulene

Abstract

Exploratory semi-empirical SCF calculations are done on mono, di, tri, tetra, and pentabenzocorannulenes to assess the effect of sequential benzannulation to the corannulene moiety. Computed results predict a gradual reduction in the bowl-to-bowl inversion barrier in each step of the successive benzannulations and eventually for pentabenzocorannulene the barrier is only 1.4 kcal mol⁻¹ at the MNDO level. This is also followed by gradual flattening of the central corannulene skeleton and the strain energy in benzannulated corannulenes is found to be more due to the steric repulsions between the peri-hydrogens due to the tessellation of six-membered rings. Molecular mechanics calculations are performed to evaluate the strain energy of the various benzocorannulenes. The strain energy build-up in a sequential bridging 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 evaluated starting from the pentabenzocorannulene, C₄₀H₂₀, to a very deep bowl, C₄₀H₁₀, which is the main structural motif of C₆₀.