An DFT studies of conformational stability, vibrational frequencies and normal mode analysis of 3-bromo-1-butene

The conformational stability, vibrational frequencies and corresponding normal mode analysis for all three conformers of 3-bromo-1-butene, H2CCHCH(CH3)Br, were investigated using the 6-311++G(d,p) basis set by the BLYP and B3LYP methods. From the calculations, the enthalpy differences (ΔH) between the most stable HE (hydrogen atom eclipses the double bond) and the higher energy ME (methyl group eclipses the double bond) conformations have been obtained to be 4.20 (BLYP) and 3.74 kJ mol−1 (B3LYP). The same calculation yields a ΔH of 11.25 (BLYP) and 9.64 kJ mol−1 (B3LYP) between the HE and the least stable BrE (bromine atom eclipses the double bond) form. The normal mode analysis for vibrational frequencies is proposed for all three conformers using the force constants from BLYP/6-311++G(d,p) calculations. Additionally, the complete equilibrium geometries, the infrared intensities and the Raman activities were also obtained from the calculations.