Question

1. Draw the structures of all isomeric alcohols of molecular formula C₅H₁₂O and give their IUPAC names.
2. Classify the isomers of alcohols in the above question as primary, secondary and tertiary alcohols.

Answer 1

i. The isomeric alcohols with molecular formula C₅H₁₂O are –

(a) \[\ce{\underset{Pentanol (1^\circ)}{CH3 - CH2 - CH2 - CH2 - CH2 - OH}}\]

 

(b) \[\begin{array}{cc}
\ce{CH3 - CH2 - CH2 - \overset{∗}{C}H - CH3}\\
\phantom{............}|\\
\phantom{...............}\ce{\underset{Pentan-2-ol (2^\circ)}{OH}}\
\end{array}\]

 

(c) \[\begin{array}{cc}
\ce{CH3 - CH2 - CH - CH2 - CH3}\\
|\phantom{..}\\
\phantom{..}\ce{\underset{Pentan-3-ol (2^\circ)}{OH}}\
\end{array}\]

 

(d) \[\begin{array}{cc}
\ce{H3C - H2C - H\overset{∗}{C} - CH2OH}\\
\phantom{.....}|\\
\phantom{.........}\ce{\underset{2-Methylbutan-1-ol (1^\circ)}{CH3}}\
\end{array}\]

 

(e) \[\begin{array}{cc}
\ce{CH3}\phantom{............}\\
|\phantom{...............}\\
\ce{\underset{3-Methylbutan-1-ol (1^\circ)}{CH3 - CH - CH2 - CH2 - OH}}\\
\end{array}\]

 

(f) \[\begin{array}{cc}
\ce{CH3}\phantom{....}\\
|\phantom{.......}\\
\ce{CH3 - C - CH2 - CH3}\\
|\phantom{.......}\\
\ce{\underset{2-Methylbutan-2-ol (3^\circ)}{OH}}\phantom{....}\
\end{array}\]

 

(g) \[\begin{array}{cc}
\ce{CH3}\phantom{...}\\
|\phantom{......}\\
\ce{CH3 - C - CH2 - OH}\\
|\phantom{......}\\
\ce{\underset{2, 2-Dimethylpropan-1-ol (1^\circ)}{CH3}}\phantom{..}\
\end{array}\]

 

(h) \[\begin{array}{cc}
\phantom{.}\ce{CH3}\phantom{...}\ce{OH}\\
|\phantom{......}|\phantom{..}\\
\ce{\underset{3-Methylbutan-2-ol (2^\circ)}{CH3 - CH - \underset{∗}{C}H - CH3}}\
\end{array}\]

Isomers (b), (d) and (h) contain chiral carbon atoms; thus, they exhibit enantiomerism.

ii. Isomers (a), (d), (e) and (g) are primary alcohols.

Isomers (b), (c) and (h) are secondary alcohols.

Isomer (f) is a tertiary alcohol.