Linear and nonlinear chiroptical effects

by 1977- Al-Basheer, Watheq Ahmad

v Chiroptical effects of linear and nonlinear nature are investigated by employing a variety of spectroscopic methods, such as linear and nonlinear circular dichroism, optical rotation, vibrational Raman scattering, infrared absorption and Vibrational Circular Dichroism. (2+1) Resonance Enhanced Multiphoton Ionization Circular Dichroism (REMPICD) is a direct demonstration of the nonlinear chiroptical effects of a sample of R-(+)-3-methylcyclopentanone. Solvent effects on circular dichroism is studied for 35 common solvents, which is significantly attributed to the solutesolvent electrostatic and Van der waals interactions for CD and ORD of R3MCP. Hartree-Fock and Density Function Theoretical calculations of R3MCP CD and ORD in solvation are also employed to support the experimental findings. Enantiomers (R, S) of chiral molecules are known to exhibit optical activity effects which are equal in magnitude and opposite in sign. For some carbonyl molecules (possessing the C=O) the equatorial and axial conformers also exhibit CD and ORD of opposite sign but not necessarily the same absolute magnitude. Studies of the temperature variation of the CD and Raman spectra are shown to be a useful technique to study the conformer’s populations and energy difference. IR absorption and Vibrational Circular Dichroism (VCD) of carvone, and limonene, are also studied as an example of molecules having different conformers. IR and VCD Density Function theory (DFT) calculations of the vibrational levels are compared with experimental results in order to establish the dominate (lowest energy) conformer.