As chemical investigations move into new fields, such as radical ions, the understanding of even fundamental reactions sometimes undergoes revisions. Here, the mechanisms for the interconversion of the s-cis and s-trans rotamers of several 1,3-butadiene radical cations are investigated with hybrid density functional theory and are shown to exhibit a complexity far exceeding rotamer interconversion in the neutral analogues. In particular, rehybridization of the central carbons during the interconversion process results in a oxo-parameter mechanism, where one parameter is the rotation around the central bond, and the other parameter is the rehybridization. To convert rotamers, the rehybridized centers must invert. The origin of this effect is traced to one of the most basic concepts in chemistry, conjugation. Substituent effects on the rehybridization and the rotation mechanism are studied by investigations of (2,3-X,X) disubstituted butadienes, where X = -CH3, -NH2, -OH, -F, -SiH3. Cation-stabilizing substituents are found to reduce the rehybridization, ranging from negligible reduction for -F to practically eliminated rehybridization for -SiH3. The same behavior is also encountered in the simplest conjugated cation and radical, that is, allyl cation and allyl radical. The effect of rehybridization on classical transition state versus dynamic control of the reaction is discussed, as well as the suitability of using model studies when treating high-energy open-shell species.