The rotational spectra of thetransandgaucheforms of 1-chloropropane have been analyzed in the frequency range 8–40 GHz using Stark, waveguide FTMW, and pulsed molecular beam FTMW spectrometers. The spectra of35Cl,37Cl, and the three13C isotopomers have been observed for both conformers. The complete quadrupole Cl-coupling tensors have been determined and discussed within the structural considerations. For thegaucheform the barrier to internal rotation of the methyl group has been determined to be 2908(4) cal/mol fromA–Esplittings observed in the first excited torsional state. TwoA–Esplittings have been observed only in the ground state of thetransform. From these splittings a barrier of 2760 cal/mol has been estimated.