Vibrational Spectra and Structure of Small-Ring Compounds. XII. Propylene Imine and Propylene Imine-d1

The infrared spectra of propylene imine and propylene imine‐d₁ have been recorded from 33 to 4000 cm⁻¹ in the gas phase and from 250 to 4000 cm⁻¹ in the liquid phase. The Raman spectrum of the liquid phase has also been recorded. The assignment of the 27 normal vibrations has been made based upon band position, intensity, and isotopic shift. The cis and trans isomers have been observed and the barrier to internal rotation of the methyl group in the cis and trans forms has been calculated to be 2.97 and 2.51 kcal/mole, respectively. The intensity of the 3220 cm⁻ line of propylene imine has been studied as a function of temperature. The $\mathrm{\Delta H°}$ for H–bond formation is found to be − 1262 cal/mole. Thermodynamic functions have been calculated for the temperature range 200°–1000°K on the basis of a rigid rotator, harmonic oscillator model for all vibrations except the internal rotation for which appropriate corrections have been made.