Fenchone, camphor, 2-methylenefenchone and 2-methylenecamphor: a vibrational circular dichroism study.
We report and discuss the infrared (IR) vibrational circular dichroism (VCD) spectra of the enantiomeric pairs of the olefin derivatives of fenchone (1,3,3-trimethyl-2-methylenebicyclo[2.2.1]heptane) and camphor (1,7,7-trimethyl-2-methylenebicyclo[2.2.1]heptane), respectively, together with those of the parent molecules. The VCD spectra were taken in three spectral regions: the mid-IR region, encompassing the fundamental deformation modes, the region of CH-stretching fundamental modes and the NIR-region between 1100 and 1300 nm, which corresponds to the second CH-stretching overtone. The VCD and absorption spectra in the first two regions are analyzed by use of current density functional theory (DFT) calculations. The NIR region is analyzed by a protocol that consists of the use of DFT-based calculations and in assuming local mode behavior: the local mode approach is found appropriate for interpreting the absorption spectra and, for the moment, acceptable for calculating NIR-VCD spectra. The analysis of the first region allows us to track the contribution of the C=O group in the vibrational optical activity of C-C stretching modes; notable differences are indeed found in olefins and ketones. On the contrary, in the other two regions the VCD spectra of olefins and ketones are more similar: in the normal mode region of CH stretching fundamentals the spectra are determined by the mutual orientation of the CH bonds; in the second overtone local mode region olefins and ketones signals show some differences.
Longhi
Giovanna
G
Dipartimento di Scienze Biomediche e Biotecnologie, Università di Brescia, viale Europa 11, 25123 Brescia, Italy.
Abbate
Sergio
S
Gangemi
Roberto
R
Giorgio
Egidio
E
Rosini
Carlo
C
D001892:Camphanes; D002164:Camphor / Q000031:analogs & derivatives* / Q000737:chemistry*; D002942:Circular Dichroism; D003198:Computer Simulation; D008956:Models, Chemical; D008968:Molecular Conformation; D009636:Norbornanes / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D019265:Spectroscopy, Near-Infrared; D013237:Stereoisomerism; D014732:Vibration
C522047:2-methylenecamphor; C522048:2-methylenefenchone; D001892:Camphanes; D009636:Norbornanes; C027327:fenchone; D002164:Camphor