Acetone (CH3COCH3) and prop-2-en-1-ol (H2C=CHCH2OH) are isomers. How could you distinguish them by IR spectroscopy? S t r a t e g y Identify the functional groups in each molecule, and refer to Table 10.1.

Question

Acetone [latex](CH_{3}COCH_{3})[/latex] and prop-2-en-1-ol [latex]H_{2}C=CHCH_{2}OH[/latex] are isomers. How could you distinguish them by IR spectroscopy?

S t r a t e g y

Identify the functional groups in each molecule, and refer to Table 10.1.

Table 10.1 Characteristic IR Absorptions of Some Functional Groups
Functional Group	Absorption ([latex]cm^{-1}[/latex])	Intensity	Functional Group	Absorption ([latex]cm^{-1}[/latex])	Intensity
Alkane C–H	2850–2960	Medium	Amine N–H C–N	3300–3500 1030–1230	Medium Medium
Alkene =C–H C=C	3020–3100 1640–1680	Medium Medium	Carbonyl compound C=O Aldehyde Ketone Ester Amide Carboxylic acid	1670–1780 1730 1715 1735 1690 1710	Strong Strong Strong Strong Strong Strong
Alkyne C–H C[latex]\equiv[/latex] C	3300 2100–2260	Strong Medium	Carboxylic acid O–H	2500–3100	Strong, broad
Alkyl halide C–Cl C–Br	600–800 500–600	Strong Strong	Nitrile C[latex]\equiv[/latex] N	2210–2260	Medium
Alcohol O–H C–O	3400–3650 1050–1150	Strong, broad Strong	Nitro NO2	1540	Strong
Arene C–H Aromatic ring	3030 1660–2000 1450–1600	Weak Weak Medium

Accepted Answer

Acetone has a strong C=O absorption at 1715 c[latex]m^{-1}[/latex], while prop-2-en-1-ol has an –OH absorption at 3500 c[latex]m^{-1}[/latex] and a C=C absorption at 1660 c[latex]m^{-1}[/latex].

Question 10.4: Acetone (CH3COCH3) and prop-2-en-1-ol (H2C=CHCH2OH) are isom...

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