VIBRATIONAL-SPECTRA AND CONFORMATIONS OF CYCLOPROPYLAMINE

The infrared (4000-150 cm-1) and Raman (4000-50 cm-1) spectra of gaseous, liquid, and solid cyclopropylamine have been recorded along with the infrared spectra of matrix-isolated samples. The vibrational spectra of all phases are consistent with the predominance of a conformer having the NH2 group trans to the ring C-C bonds as suggested by previous microwave studies. The torsional mode for trans-cyclopropylamine has been observed at 254 cm-1, and hot bands associated with this low-frequency fundamental are apparent throughout the spectra of the vapor phase. There are a number of weak bands which can be attributed to a second conformer, and the assignment of torsional transitions for gouche-cyclopropylamine has allowed the calculation of a suitable potential function for internal rotation. The derived value for ΔH is 592 cm-1, and this is consistent with variable temperature studies carried out for the liquid and vapor states. The internal rotational isomerism is discussed in terms of the bonding schemes which are applicable to cyclopropyl ring compounds. © 1979 American Chemical Society.