Fourier-transform infrared, vibrational circular dichroism of sugars. A spectra-structure correlation

✍ Scribed by Darlene M. Back; Prasad L. Polavarapu

• Publisher: Elsevier Science
• Year: 1984
• Tongue: English
• Weight: 274 KB
• Volume: 133
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(84)85193-9

✦ Synopsis

It is now established that the circular dichroism in vibrational transitions (v.c.d.) of chiral molecules is a measurable phenomenon'.

In v.c.d. measurements (3n -6) vibrational transitions can be probed, whereas, in conventional cd. measurements in the visible region, only a few electronic transitions can be probed. For sugars, in particular, there is either one accessible electronic transition (associated with a C=O group) or none at all. The application of c.d. spectroscopy to sugars has therefore been very limited, but this limitation can be overcome through c.d. measurements in abundant vibrational transitions, and this confers on v.c.d. spectroscopy a unique status in providing stereochemical information on sugars.

It may be anticipated that correlations analogous to those relating the molecular optical rotation to the sequential arrangement of hydroxyl groups* might also be apparent in v.c.d. spectra. However, as there are numerous vibrational transitions, which one(s) of the v.c.d. bands might follow the aforementioned correlations are not immediately obvious. A vibration that encompasses the ring skeleton, and involves the C-O bonds (in axial or equatorial dispositions), is more likely to follow the expected correlations.

As the v.c.d. effect is generally three to four orders of magnitude smaller than the conventional, electronic c.d. effect, the measurement of v.c.d. requires special instrumentation.

The multiplex advantage of Fourier-transform infrared (F.t.-i.r.) spectroscopy can be utilized to achieve significantly enhanced signal quality in v.c.d. measurements.

During the past two years, we have investigated the v.c.d. of some simple sugars, using a F.t.-i.r. spectrometer, and now present some of these results and the first F.t.-i.r.-v.c.d. measurements on sugars*. *For v.c.d. measurements m the C-H stretching-vibrational region of sugars. employing a dispersive, infrared spectrometer, see ref. 3.