8. (14 points) Consider the IR spectra and the structures below For each structu

Question

8. (14 points) Consider the IR spectra and the structures below For each structure: predict the key IR vibrations in wavenumbers. One or more vibration may be present. Match the compound with the corect spectra. Write "none" if the correct spectrum is not present. Calculate the DBE for the first compound. Show your calculation. expected bands: other than CH Comect Specrum: Spectrum [1 Spectrum [2 100 100 50 90 4000 3500 3000 2500 2000 15 1000 500 4000 3500 30ODD 2500 2000 1500 1000 500 Waanumbor (am Wavenumber (om Spactrum 3 Spectrum 14 100 50 50 4000 3600 3000 2500 2000 1500 1000 500 4000 3500 3000 2500 2000 1500 1000 600 Wavenumbor (om Wvenumber (am

Explanation / Answer

There are 4 molecules given

1st molecule ( 1st from left) ; Expected band is O-H strech , which occurs at 3400-3600 cm-1 broad

Hence spectrum 1 macthes with molecule 1

2nd molecule : expected bands are C=O strech at 1700 cm-1. Hence spectrum 4 matches

3rd molecule : expected bands C=O at 1700 cm-1 and OH strech broad one near 3100 cm-1-3200 cm-1 . hence spectrum 3 matches with it

4th molecule : Expected band C triple bond N strech near 2200 cm-1. Hence answer is None ( since no spectrum has peak in area of 2200 cm-1)

Now we calculate DBE of 1st compound

Degree of unsaturation or double bond equivalence DBE can be calculated by formula

DBE = ( nC x 2 + 2 - nH) / 2 where nC = number of carbons = 5,

nH = number of H = 12

Oxygen is considered equivalent to 0 H ,

now DBE = ( 5 x 2 + 2 - 12) / 2 = 0

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