The influence of surface strain on the chemical reactivity of fullerene ions: addition reactions with cyclopentadiene and 1,3-cyclohexadiene

Experimental results are presented which demonstrate a dependence of chemical reactivity on the strain present in a carbon lattice. Rate coefficients have been measured at room temperature by using the selected-ion flow tube (SIFT) technique for the gas-phase addition of cyclopentadiene and 1,3-cyclohexadiene to the fullerene monocations C-56(.+), C-58(.+), C-60(.+) and C-70(.+), and the cations derived from corannulene and coronene. The observed reaction efficiencies show a strong dependence on the curvature of the carbon lattice expressed in terms of the pyramidalization (POAV) angle, theta(sigma pi)-90. The flat, strain-free coronene cation and the slightly strained corannulene cation do not react with a measurable rate, k < I x 10(-13) cm(3) molecule(-1) s(-1). The most severely strained C-56(.+) and C-58(.+) fullerene ions react with a rate within a factor of about 10 of the collision limit. (C) 1997 Elsevier Science B.V.