Vibrational circular dichroism in ephedra molecules. Experimental measurement and ab initio calculation

1994 ◽  
Vol 99 ◽  
pp. 131 ◽  
Author(s):  
Teresa B. Freedman ◽  
N. Ragunathan ◽  
Susan Alexander
Keyword(s):  
Circular Dichroism ◽  
Ab Initio ◽  
Experimental Measurement ◽  
Ab Initio Calculation ◽  
Vibrational Circular Dichroism ◽  
Circular Dichroïsm

Ab Initio Calculation of Vibrational Circular Dichroism Spectra Using Gauge-Invariant Atomic Orbitals

1995 ◽  
Vol 99 (41) ◽  
pp. 14918-14922 ◽  
Author(s):  
K. L. Bak ◽  
F. J. Devlin ◽  
C. S. Ashvar ◽  
P. R. Taylor ◽  
M. J. Frisch ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Ab Initio ◽  
Ab Initio Calculation ◽  
Vibrational Circular Dichroism ◽  
Circular Dichroism Spectra ◽  
Gauge Invariant ◽  
Atomic Orbitals ◽  
Circular Dichroïsm

Electronic and Vibrational Circular Dichroism of Model β-Lactams: 3-Methyl- and 4-Methylazetidin-2-one

1996 ◽  
Vol 50 (5) ◽  
pp. 630-641 ◽  
Author(s):  
Jennifer McCann ◽  
Arvi Rauk ◽  
Gennadii V. Shustov ◽  
Hal Wieser ◽  
Danya Yang
Keyword(s):  
Circular Dichroism ◽  
Ab Initio ◽  
Electronic Transition ◽  
Vibrational Circular Dichroism ◽  
Protic Solvent ◽  
Free Energies ◽  
Chiroptical Properties ◽  
Circular Dichroïsm ◽  
Rotational Strengths ◽  
Simple Modeling

The chiroptical properties of the simplest chiral β-lactams, 3- and 4-methylazetidin-2-one, 1 and 2, respectively, were investigated. The experimental vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra were measured and compared with ab initio predictions. Both compounds were found to form dimers with calculated binding enthalpies and free energies of about −51 kJ/mol and −6 to −8 kJ/mol, respectively. The experimentally measured IR and VCD spectra were measured in concentrated nonpolar (CCl4) solution and are in agreement with the predicted IR and VCD spectra of the dimeric forms, 12 and 22, but not the monomers. The most intense dimer VCD bands originate from in-plane N-H wags, which perturb the H-bonded cyclic array. At the more dilute concentrations employed for the ECD spectra, the experimental ECD spectra in heptane were interpreted satisfactorily as arising from a mixture consisting predominantly of monomers. In protic solvent (H2O, MeOH), the ECD spectra are consistent with H-bonded monomers. Simple modeling suggests that the rotational strengths of the first electronic transition gain most of their intensity from the nonplanarity of the amide chromophore, the contributions of which follow a spiral rule previously enunciated.

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