IR spectroscopy: Choose at least one signal in the diagnostic region of this IR

Question

IR spectroscopy: Choose at least one signal in the diagnostic region of this IR spectrum, and indicate (by labeling it/them on the spectrum) what it/they tell you (i.e. what functional group or type of bond is indicated by each peak). Be as specific as possible-e.g. is it a single, double, or triple bond? What are the hybridization states of the atoms involved (if that information is on your reference sheet)? 2. 100 80 60 40 20 1500 Wavenumber [cm 1000 400 4000 2016-3092.2T 3000 2000 Name one kind of bond that you can be sure is not present based on the IR spectrum. Indicate at what wavenumber range you would expect to see the peak for that kind of bond.

Explanation / Answer

Region II (3000-2000) - the presence of sharp peaks in the range of 2950-2800 cm-1 are attributed to the C-H stretching vibrations in alkanes. the compound contains only single bond character and hence the carbon atoms are found to be sp3 hybridized.

Region IV (1500-1000) - the peak around 1465 cm-1 can be attributed to CH2 bending vibrations and peak around 1375 cm-1 can be due to CH3 bending vibrations.

Region V - The peak around 650 can be assigned to C-Br stretching vibrations.

Hence the compound may be alkyl halide.

Further the absence of peaks above 3000 confirms the absence of double bonds and triple bonds. whose C-H stretching vibrations lie in that range. alkene C-H 3010-3100, alkyne C-H 3300.

Also the absence of peaks in the region between 1500-2000 confirms the absence of carbonyl group.C=O stretching for aldehyde = 1725, ketone 1715, carboxylic acid 1730, ester 1735-1750 and amide 1680-1630 cm-1

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