3) Which functional group is absent in the IR spectrum shown below? 35 4 45 wael

Question

3) Which functional group is absent in the IR spectrum shown below? 35 4 45 waelength (am) 7 8 9 10 11 12 13 14 15 16 5 5.5 6 60- N 800 6l 4000 3500 3000 2500 2000 1800 1600 1400 1200 1000 wavenumber (em h7 C B. C-O (carbonyl) oo 1SO c C. C-H (aldehyde) D. C-H (alkane) 00,-2700 4) Which bond typically has the lowest stretching frequency? 5) The infrared spectrum of CHCH-CHCH,CH2CH3 will not have an absorption in which frequency range?,22 B. 3300 -3200 cm1 toongh D3100-3000 cmr' fonan C A. 1680 1640 cm C C 2950- 2850 cm

Explanation / Answer

3) The fuctional group missing is O-H(alcohol) as it comes at around 3600 cm-1 and is an extremely broad spectrum due to hydrogen bonding. All the other peaks meantioned are clearly depicted in the graph. C=O around 1700, C-H (alkane) at 2950 and C-H(aldehyde) at 2800-2900 cm-1.

4) C-O has the lowest stretching frequency among the four as the bond is the most polar, and hence lowest energy is required to stretch the bond.

5) The compound will not have an absorption frequenct at 3300-3200 cm-1. A corrosponds to C=C, C corrosponds to C-H(alkane) and D corrosponds to C-H(alkene).

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