Vibrational spectra have been obtained for quite a few monobromo1–15and dibromoalkanes16–32, most of which were shown to exhibit rotational isomerism. However, very few tribromo23,33,34and tetrabromoalkanes28,35,36have been studied. Therefore, IR spectra have been obtained for 1,2,4,5-tetrabromopentane (TBP), and molecular mechanics calculations have been made for the six spectroscopically distinguishable conformers of this molecule that have all five carbons coplanar, in order to learn something about the molecule's conformational behavior. The calculations were made with the MM2 program written by Allinger and Yuh and converted by Petillo to run on a microcomputer.37The six conformers of TBP can be represented by the following skeletal formulas, where a + indicates a bromine on one side of the plane of carbons and a − indicates a bromine on the other side of that plane: