Vibrational analysis of 2-fluoropropane and 2-fluorobutane

Vibrational spectra were obtained for 2-fluorobutane in the vapor, liquid, and solid states. The S_HH and Spy conformers are present in the solid, and the S_HH conformer is present in the liquid and in lower concentration in the vapor. Vibrational assignments were made with the aid of normal coordinate calculations that fit thirty-six frequencies of 2-fluoropropane and S_HH 2-fluorobutane with an average error of 3.7 cm^?1. Only a few vibrations of 2-fluorobutane seem to be dependent on conformation. The “C—F stretching” frequency cannot be used to distinguish the conformers because of extensive interaction between this coordinate and others.