Question 17.4.5: How will you differentiate between the following pairs using......

Engineering Chemistry: Fundamentals and Applications [EXP-169979]

How will you differentiate between the following pairs using IR spectra?

(a) $CH_3CH_2CHO$ and $CH_2\xlongequal[]{}CH CH_2OH$

(b) $CH_3CH_2OH$ and $CH_3CHO$

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(a) $CH_3CH_2CHO$ will show absorption band at 1740–1720 $\mathrm{cm}^{–1}$ for C=O group.

$\quad CH_2=CH CH_2OH$ will show the following absorption bands

• ~ 1050 $\mathrm{cm}^{–1}$ for primary alcohols (C–O stretching and bending)

• At 3100–3000 $\mathrm{cm}^{–1}$ , C=C str.

• At 905 $\mathrm{cm}^{–1}$ for vinyl group $(H_2C = C - C - H)$ str.

• Band at 3200–3500 for OH group.

(b) $CH_3CH_2OH$ will show the following bands.

• C – H str at 2960–2850 $\mathrm{cm}^{–1}$

• Band at 3300–3400 $\mathrm{cm}^{–1}$ due to OH group.

• $CH_3CHO$ shows the following absorption bands

• Band at 1745 $\mathrm{cm}^{–1}$ due to C=O str.

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