Knowledge Bank

Although the existence of endo and exo isomers of 2-methyl-bicyclo[2.1.0]pentane has been known for several years, positive identification of the species (which are easily separated chromatographically) had not been $achieved.1$ We have succeeded in observing and analyzing the microwave spectra of these molecules and have made the correct isomeric assignments. Rotational constants (in MHz) for the endo and exo isomers are: A = 6257.36, B = 3412.19, C = 2843.34; and A = 7418.75, B = 3101.66, C = 2652.57, respectively. Dipole moment components have been determined for each of the two isomers by means of Start effect measurements. These results will be interpreted in accordance with the structure and dipole moment values for the parent bicyclic species.