THE VIBRATIONAL SPECTRUM OF NORBORNADIENE AND 2,3,5,6--NORBORNADIENE--$d_{4}$

Abstract

In continuing our investigation of plastic crystals, we have recorded the Raman spectrum of the liquid and the infrared spectrum of solid and gascous samples of bicyclo-2,2,1-hepta-2,5-diene (norbornadiene). Thermodynamic investigations have shown this system (solid) to possess a plastic phase transition ($\Delta S_{m}$ = 1.58 c.u. and $\Delta S_{1} = 10.57$ c.u.). Although we were not able, by using the infrared techniques, to observe this transition, it was observed in the very similar plastic crystal, norbanane. The C--II stretching region of the liquid was found to contain two sets of Fermi doublets; this could have an important bearing on further Raman investigations concerned with the classical, non-classical ion controversy. At least one isotopically substituted species (2,3,5,6-norbornadiene-$d_{4}$) will also be examined in connection with vibrational assignments in the parent system.