AbstractThe Raman spectra (3400–10 cm−1) of liquid and solid 3‐methyl‐3‐vinylcyclopropene, C3H2(CH3)CHCH2, and its isotopomer C3D2(CH3)CHCH2were recorded. The temperature dependence of some band intensities and qualitiative depolarization ratios show that the thermodynamically preferred conformation iss‐trans. The structural parameters and conformational stability ofs‐transandgaucherotamers were obtained fromab initiocalculations by employing both 3–21G and 6–31G* basis sets. Barriers to internal rotation and fundamental vibrational frequencies were calculated utilizing the 3–21G basis set. Theab initioresults are consistent with the experimentally indicated greater stability of thes‐transrelative