Near‐Infrared Vibrational Circular Dichroism: NIR‐VCD

Testing the vibrational exciton and the local mode models on the instructive cases of dicarvone, dipinocarvone, and dimenthol vibrational circular dichroism spectra

“…Reference can be made to our previous, experimental and theoretical studies 25–28,43 and to the experimental and computational study by Devlin et al ., 44 as well as, limited to absorption, to the seminal overtone investigations of alcohol and diol OH stretchings 45,46 . In Figure 9, we compare the experimental IR/NIR absorption and VCD spectra in the OH stretching fundamental (Δv = 1) and first overtone (Δv = 2) regions of (1 S ,2 S ,5 R ,1 S ′,2 S ′,5 R ′)‐dimenthol and of (+)‐(1 S ,2 R ,5 S )‐ and (−)‐(1 R ,2 S ,5 R )‐menthol, with the corresponding calculated spectra of (1 S ,2 S ,5 R ,1 S ′,2 S ′,5 R ′)‐dimenthol and of (1 R ,2 S ,5 R )‐menthol, according to the local mode approximation 25–28 . This approximation for IR‐VCD and NIR‐VCD spectra has been discussed in previous studies 25–28 and implies the calculations of mechanical and electrical anharmonicities.…”

“…In Figure 9, we compare the experimental IR/NIR absorption and VCD spectra in the OH stretching fundamental (Δv = 1) and first overtone (Δv = 2) regions of (1 S ,2 S ,5 R ,1 S ′,2 S ′,5 R ′)‐dimenthol and of (+)‐(1 S ,2 R ,5 S )‐ and (−)‐(1 R ,2 S ,5 R )‐menthol, with the corresponding calculated spectra of (1 S ,2 S ,5 R ,1 S ′,2 S ′,5 R ′)‐dimenthol and of (1 R ,2 S ,5 R )‐menthol, according to the local mode approximation 25–28 . This approximation for IR‐VCD and NIR‐VCD spectra has been discussed in previous studies 25–28 and implies the calculations of mechanical and electrical anharmonicities. Application of the local mode model to the present case of two nearby OH bond stretchings is to be taken with some care, even though, according to Kjaergaard 45 and Abbate et al ., 47 is expected to work increasingly better with increasing overtone order.…”

“…The spectra were recorded in CDCl 3 /CCl 4 solutions in 0.2‐ and 0.1‐mm path‐length BaF 2 cells with concentrations ranging from 0.05 to 0.1 M. For the OH stretching fundamental region infrasil®/quartz rectangular 0.1‐ to 0.5‐mm‐thick cuvettes were employed, on the same Jasco FVS6000 apparatus with solutions as just above. For acquiring NIR‐VCD spectra, the home built dispersive apparatus previously used in analogous circumstances was employed, 25–28 a suprasil®/quartz cell 0.5 cm wide was employed, and five scans were acquired in the CD and absorption baseline (ABL) mode, 26 the latter being subtracted from the former. The solvent spectrum recorded in the same manner was finally subtracted out.…”

“…Indeed, we will investigate to what extent the VCDEC model applies in the CO stretching spectroscopic region in 1 and 2 . For compound 3 , VCD spectra in the OH stretching fundamental and first overtone regions have been recorded, and the local mode model has been employed to interpret the VCD data 11,25 . The ECD spectra have also been recorded, and a discussion will be presented as to whether the phenomena of vibrational and electronic excitons are related and to which extent.…”

Vibrational optical activity: From discovery and development to future challenges

“…Subsequently, through additional changes in detectors (Ge), FT‐VCD was extended continuously from 800 cm −1 in the mid‐IR to 10 000 cm −1 in the near‐visible region . This coverage overlaps the near‐IR coverage of ECD instrumentation both commercial and custom adapted by Abbate et al…”