Hello:
I am comparing the Raman spectra of deuterated ethanol (OD) and normal ethanol (OH) and noted that the C-O stretch at 1094 cm-1 is shifted to 1105 cm-1upon deuteration. I need an explanation for that. My initial thinking is that the bending mode C-O-H (EtOH) is contributing at 1094 cm-1 and this band shifts to higher wavenumber upon deuteration. Is this explanation correct? I would appreciate a couple of references to whatever the correct reasoning is.
Thanks
Umesh
check the links below and hope to be useful to you
http://www.slideshare.net/yomology/raman-spectroscopy
http://pubs.acs.org/doi/abs/10.1021/j100285a047
Mohamed:
Thank you very much for the links. Looks like there is another factor to consider -the role of H-bond. I will follow up to see what progress can I make on this issue.
Umesh
Dear Umesh,
Bonds involving deuterium and tritium are somewhat stronger than the corresponding bonds in hydrogen. The C-D bond is about 10 times stronger than the C-H bond, which means the C-D bond is more resistant than the C-H bond. This is why D2Owould have higher melting point (3.82 °C), boiling point (101.72 °C), density (1.017 g/cm3), temperature of maximum density (11.6 °C), heat of vaporization (10,864 cal/mol) and viscosity than H2O.
The wavelengths of all deuterium spectroscopic lines are shorter than the corresponding lines of light hydrogen. Thus, the wavenumber of all deuterium spectroscopic lines would be bigger than the corresponding lines of light hydrogen.
The fact that there is a net shift to higher wavenumber in deuterated ethanol, tells you there is a net compression in the resultant vibrational modes which could not have been due to possible combined bending of C-O-H (EtOH) modes and the stretching of C-O modes. Deuterated ethanol is behaving just like a single cellulose microfibril in compression in a Raman light spot within a 2D network of cellulose microfibrils being increasingly put in tension.
Thus, the questions to ask here would be: 'what modes must the C-O modes and the C-O-D modes be in to result in a net compression vibrational mode?'
Ref:
http://cdn.intechopen.com/pdfs-wm/35655.pdf
Akwasi
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