Knowledge Bank

Ab Initto molecular orbital calculations have been carried out to predict the infrared spectra (frequencies and intensities) of a number of chemically related molecules. These include two different ethanethiol conformers, diethylsulfide, and their chlorinated $derivatives,1$ a number of fluorinated and alkylated derivatives of $H3PO$ and $H2POH,2$ and several cytosine tautomers and methylated and fluorinated $derivatives.3$ Hence, we may examine the values calculated for force constants and dipole moment derivatives for chemically similar bonds (C-H, C-S, C-Cl, P-H, P-O, C-N, etc.) in these chemically different, but related, molecules to determine the limits that may be expected for the concept of transferability of these parameters. Selected examples from these systems will be presented and discussed.