The aromaticity of several heterosubstituted cyclopropenes and corresp
onding protonated forms was investigated using ab initio calculations
at the G2-MP2 level of theory, topological charge density, and NBO ana
lysis. It was shown that according to geometric, energetic, charge den
sity, and magnetic criteria these systems are remarkably aromatic, esp
ecially the protonated forms. It was shown that the aromatic delocaliz
ation of double bond in the cyclopropene ring can be well modeled usin
g a three-center two-electron bond in the framework of NBO analysis pr
oposed by Reed and Weinhold.