The cyclopropane moiety appears in many natural products that are purported to form through cationic cascade reactions. The strained σ-array of the cyclopropane moiety gives rise to substantial electron density off of the main bonding axis, and hence begs the question - to what extent does a cyclopropane ring stabilize a cationic center? Quantum chemical calculations (B3LYP/6-31G(d) and MP2/6-31G(d)) were used to describe several cyclopropyl carbinyl cations of strained six-membered ring systems (see below), and in the ultimate test of donating ability, the cyclopropane ring was allowed to “compete” with a π-framework for delocalization of positive charge.
Siebert, M.R. and Tantillo, D.J. Journal of Physical Organic Chemistry, 2007, 20, 384-394. “Brother vs. Brother: Competitive Stabilization of Carbocationic Centers by Flanking Cyclopropanes and π-Systems.” 10.1002/poc.1155.