Sidechain moves can be proposed in various ways, such as to random torsional angles, or via selection from a potential torsional distribution which is biased in some way. In the case of sidechain rotations, random moves would likely result in many proposed moves being rejected because they would place the torsion in a state with a particularly high energy. Because each NCMC move proposal has an associated cost, regardless of whether the move is ultimately accepted or not, it is advantageous to propose rational moves (i.e. moves to favorable rotameric states) rather than random ones. In addition to avoiding move proposals to high energy states, we also want to avoid using NCMC to attempt small, favorable moves within the same rotamer state; while small moves are more likely to be accepted, they are readily (and more economically) accessed using traditional MD. Fortunately in the case of sidechain flips, the rotamer states are well-known; the structural conformations of the 20 natural amino-acids have been extensively characterized; here we use this a priori knowledge of low energy rotamer states to conditionally bias move proposals to known, alternate rotamer states.