Question

Which of the following is a secondary allylic alcohol?

• A. $H_{2}C = CH - CH_{2} - OH$
• B. $CH_{3} - CH = CH - CH_{2} - OH$
• C.

  

• D.

  

Hint:

To classify an allylic alcohol, first identify the allylic carbon (the carbon bearing the -OH group and adjacent to a $C=C$ double bond). Then, count the number of alkyl or carbon groups directly attached to this allylic carbon (excluding the -OH group and considering the $C=C$ portion as one substituent if it's the chain). One alkyl group is primary, two are secondary, and three are tertiary.

Answer 1

The Correct Option is C

Step 1: Definition of allylic alcohol An allylic alcohol is an alcohol in which the hydroxyl group (${-}\mathrm{OH}$) is attached to a carbon atom adjacent to a carbon--carbon double bond ($\mathrm{C=C}$). This adjacent carbon is called the \textit{allylic carbon}.
Step 2: Classification of allylic alcohols Allylic alcohols are classified based on the number of carbon groups attached to the carbon bearing the $-\mathrm{OH}$ group:

• Primary: Attached to one carbon and two hydrogens
• Secondary: Attached to two carbons and one hydrogen
• Tertiary: Attached to three carbons and no hydrogen

Step 3: Analysis of given options

• A. $\mathrm{H_2C = CH - CH_2 - OH$}
  The $-\mathrm{OH}$ is on $\mathrm{CH_2}$, which is bonded to one carbon and two hydrogens.
  $\Rightarrow$ Primary allylic alcohol
• B. $\mathrm{CH_3 - CH = CH - CH_2 - OH$}
  The $-\mathrm{OH}$ is on $\mathrm{CH_2}$, bonded to one carbon and two hydrogens.
  $\Rightarrow$ Primary allylic alcohol
• C. $\mathrm{H_2C = CH - CH(CH_3) - OH$}
  The $-\mathrm{OH}$ is on $\mathrm{CH}$, which is bonded to two carbon groups and one hydrogen.
  $\Rightarrow$ Secondary allylic alcohol
• D. $\mathrm{CH_2 = CH - C(CH_3)_2 - OH$}
  The $-\mathrm{OH}$ is on a carbon bonded to three carbon groups and no hydrogen.
  $\Rightarrow$ Tertiary allylic alcohol

Step 4: Conclusion The compound that is a secondary allylic alcohol is: \[ \boxed{\text{Option C \]