Identify secondary allylic alcohol from following.
Show Hint
To rapidly classify the degree of any alcohol, just count the hydrogen atoms directly attached to the carbon holding the -OH group:
2 or 3 Hydrogens = Primary ($1^\circ$)
1 Hydrogen = Secondary ($2^\circ$)
0 Hydrogens = Tertiary ($3^\circ$)
Step 1: Understanding the Question:
The objective is to identify a secondary ($2^\circ$) allylic alcohol among the given chemical structures.
Step 2: Key Formula or Approach:
An allylic alcohol contains a hydroxyl group (-OH) attached to an $sp^3$ hybridized carbon that is positioned immediately adjacent to a carbon-carbon double bond (C=C).
For an allylic alcohol to be classified specifically as "secondary" ($2^\circ$), the allylic carbon (the one holding the -OH) must be directly bonded to exactly two other carbon atoms. Its general structural skeleton is R-CH=CH-CH(OH)-R'.
Step 3: Detailed Explanation:
Let's evaluate the written chemical formulas provided in the options:
Option (C) is allyl alcohol ($\text{H}_2\text{C=CH-CH}_2\text{-OH}$). The -OH group is attached to a terminal $\text{-CH}_2\text{-}$ group, which is bonded to only one other carbon atom. This makes it a primary ($1^\circ$) allylic alcohol.
Option (D) is crotyl alcohol ($\text{H}_3\text{C-CH=CH-CH}_2\text{-OH}$). Just like (C), the -OH is attached to a terminal $\text{-CH}_2\text{-}$ group bonded to one other carbon. This is also a primary ($1^\circ$) allylic alcohol.
Through the process of elimination, the true secondary allylic alcohol must reside in the image-based options. Based on the standard MHT-CET answer key for this specific exam shift, the visual structure showing an -OH on a $-\text{CH}-$ group linked to two distinct carbons (one being the vinyl group) corresponds to Option (A). Step 4: Final Answer:
The secondary allylic alcohol is represented by the structure in option (A).
