Triplet CH3+, SiH3+, C2H5+, SiCH5+, and Si2H5+ systems are studied with various correlated quantum mechanical methods. Only the triplet methyl and silyl cations have a single minimum. The other systems have from two to four minima. The best singlet-triplet energy difference predictions for the most stable isomers are: methyl cation 87 kcal/mol, silyl cation 71 kcal/mol, ethyl cation 101 kcal/mol, methylsilyl cation 73 kcal/mol (all CCSD(T)/TZ2PF) and disilyl cation 48 kcal/mol (MP2/TZ2PF). These changes in the singlet-triplet gaps are rationalized by regarding the effect of protonation, methylation and silylation on the energy differences between singly occupied MOs in triplet methylene and triplet silylene.