Theoretical Prediction and the First IR Matrix Observation of Several L-Cysteine Molecule Conformers

For the first time the argon‐matrix low‐temperature IR spectra of cysteine are recorded. They reveal a quite complicated spectral pattern, which can also be reproduced in the N2 matrix. Assignment of the observed spectra is undertaken on the basis of comparison of the experimental and calculated B3LYP/aug‐cc‐pVDZ anharmonic IR spectra. The presence of at least three, and possibly even six or more, cysteine conformers with and without intramolecular hydrogen bonding is confirmed. On the basis of the calculated vibrational circular dichroism spectra, we predict this technique to be more distinctive for conformers than IR absorption is. Cold conformers: Argon‐matrix low‐temperature IR spectra of cysteine are recorded and compared to calculated spectra. The presence of at least three cysteine conformers, both with and without intramolecular hydrogen bonding, can be observed. The presence of several conformers is illustrated in the picture, which shows the ν(SH) stretching vibrations.