1,4-Dimethylenespiropentane: A Unique Model System for Studying Fermi Resonance in Raman Optical Activity

• Published in: Chemphyschem Vol. 8; no. 8; pp. 1161 - 1169
• Main Authors: Hug, Werner, Haesler, Jacques, Kozhushkov, Sergei I., de Meijere, Armin
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 04.06.2007; WILEY‐VCH Verlag; Wiley
• Subjects: Ab initio calculations; Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Electronic structure of atoms, molecules and their ions: theory; Exact sciences and technology; Fermi resonance; Molecular properties and interactions with photons; Molecular spectra; Physics; Raman and rayleigh spectra (including optical scattering); Raman spectroscopy; solvent effects; Raman spectra; ab initio caiculations· Fermi resonance; Fermi resonance; Vibrational modes; Theoretical study; Hydrocarbons; Ab initio calculations; Raman spectroscopy, solvent effects; Spiran; Solvent effects
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200600678

The C2‐symmetric title compound, a small, rigid hydrocarbon molecule with two distinct, strongly interacting vibrational chromophores, represents a unique model system for testing computational approaches to Raman optical activity (ROA) beyond the isolated molecule and the harmonic approximation. We show that the experimental Raman and ROA spectra are marked by the presence of strong Fermi resonances, and that the shape and relative size of the bands which we attribute to such resonances strongly depend on the solvent environment of the molecule. On the other hand, the dominant computed ROA couplet, arising from the CC stretching vibrations, is absent in the spectra measured in the condensed phase. The strong dependence of the computed size of the couplet on the description of the diffuse part of the electron distribution suggests that this absence is due to nonspecific interactions in the condensed phase. Compare and contrast: Experimental Δ curves give the ratio of Raman optical activity to Raman scattering. Curves measured for backscattering for neat (−)‐(M)‐ (see picture, red) and (+)‐(P)‐1,4‐dimethylenespiropentane (black) on two different instruments are essentially mirror images of each other, which demonstrates the high instrumental precision of the measurements and the similar enantiomeric purity of the samples.