Stabilization of carbocations through donation of ð electrons from adjacent carbon orbitals results in well-known species such as the allyl and benzyl cations. Adjacent nonbonding (n) electrons on heteroatoms also can provide considerable stabilization, as in oxonium ions such as CH2dO+CH3 and iminium ions such as CH2dN+(CH3)2. Less well known is stabilization of carbocations by ó orbitals. In its most common example this interaction provides stabilization of tertiary over secondary over primary carbocations. According to the valence bond representation of this interaction, a filled ó orbital donates electrons to an empty ð orbital, as in 1 and 2 (R ) H).