posted on 2019-02-13, 00:00authored byPavel Michal, Radek Čelechovský, Michal Dudka, Josef Kapitán, Milan Vůjtek, Marie Berešová, Jaroslav Šebestík, Karthick Thangavel, Petr Bouř
Spectroscopy
of vibrational optical activity has been established
as a powerful tool to study molecular structures and interactions.
In most cases, only fundamental molecular transitions are analyzed.
In the present study, we analyze a broader range of vibrational frequencies
(40–4000 cm–1), which could be measured on
a new Raman optical activity (ROA) instrument. An unexpectedly strong
vibrational Raman optical activity of 2-chloropropionitrile has been
observed within the low-frequency region (40–150 cm–1). On the basis of combined molecular dynamics and density functional
theory simulations, it could be assigned to intermolecular vibrations.
A detailed analysis also revealed connection between spectral shapes
and molecular structure and flexibility, such as bending of the CCN
group. At the other edge of the scale, within ∼1500–4000
cm–1, for the first time, many combination and overtone
ROA bands have been observed for 2-chloropropionitrile and α-pinene.
These were also partially assigned, using quantum-chemical computations.
The band assignment was confirmed by a comparison with Raman, absorption,
and vibrational circular dichroism spectra. The measurement in the
broader vibrational range thus significantly extends the information
that can be obtained by optical spectroscopy, including intermolecular
interactions of chiral molecules and liquids.