Conformations of conjugated hydrocarbons. Part 2. A spectroscopic and thermodynamic study of cis- and trans-penta-1,3-diene

Abstract

Vibrational spectra of both cis- and trans- penta-1,3-diene have been recorded over a range of temperatures for three phases. Complete vibrational assignments for both compounds have been made and new thermodynamic functions calculated over a range of temperatures by statistical methods. No spectroscopic or thermodynamic evidence of a high energy conformer for either compound has been found. Assignment of torsions leads to values (in kJ mol^–1) for cis- and trans- penta-1,3-diene respectiveiy of 12.3 and 10.4 for the three-fold barrier height V₃ and 133 and 120 for the two-fold barrier parameter V*.