Problems of conformation and stereoselection are key elements in both the understanding of the role of biologically important compounds, and in the design of their synthesis. Two particularly important components of the overall problem are barriers to rotation adjacent to unsaturated centers, and non-bonded interactions. It is proposed to carry out detailed ab initio molecular orbital calculations dealing with both of the above, to make detailed analyses of the results of the calculations, and then apply the results in developing better procedures for molecular modelling. In addition, the effect of reagents such as H- and H+ on the conformations and rotational barriers will be explored in order to directly attack the problem of stereoselection. In all cases, the computational results will be related to experimental observations, either those already available, or new observations which are suggested by the results of the calculations.