Distinctive Normal Harmonic Vibrations of [2.2]Paracyclophane

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 1997-10, Vol.101 (44), p.8233-8241
• Main Authors: Walden, Susan E, Glatzhofer, Daniel T
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp9720395

The hybrid Hartree−Fock/density functional method B3LYP and 4-31G(d) basis set were used for geometry optimizations and vibrational analysis of both the D2 and D 2 h conformers of [2.2]paracyclophane. The unprecedented full geometry optimization with a split valence basis set and a method that includes electron correlation shows the equilibrium structure of [2.2]paracyclophane to be the twisted D 2 conformation with a calculated twist angle (CringCbridgeCbridgeCring) of 3.9°. We present the first complete assignment of all 90 normal harmonic vibrations of [2.2]paracyclophane. Upon examination of the calculated normal modes and comparison with prior assignments for paracyclophanes and p-xylene, we have identified vibrations that are cyclophane specific modes. Our calculated harmonic frequencies and relative intensities are in excellent overall agreement with the experimental IR spectrum. We have thus demonstrated the potential of hybrid Hartree−Fock/density functional theory as an electron-correlated method suitable and practical for characterizing even the large, highly strained, structurally and electronically unique parent of the [2.2]paracyclophane family.