Ab initio calculations have been performed to study the stereoselective selenenylation reaction of alkenes with chiral selenium electrophiles. The interaction of the heteroatom of the chiral side chain with the selenium atom in the reagent has been investigated by a detailed conformational analysis. Calculations of the seleniranium intermediates with different substituted alkenes have been performed as well. The reversal of selectivity changing from aromatic to aliphatic alkenes as substrates in the selenenylation reaction has already been proven by experiment and is now supported by the calculations described herein.