Question

How many molecules are secondary alcohol? 

• A. 2
• B. 3
• C. 4
• D. 5

Hint:

First check whether the drawn group is truly an -OH or actually part of a -COOH, since they look similar in skeletal formulas. Once you know it is a real alcohol, count the hydrogens on the carbon holding the -OH -- two carbon neighbours (1 H on that carbon) means secondary, this is faster than tracing the whole chain each time.

Answer 1

The Correct Option is B

Step 1: Definition of secondary alcohol.
An alcohol is called a secondary alcohol when the carbon atom bearing the –OH group is attached to two other carbon atoms.
Step 2: Analyze each given structure.
Compound (a):
The –OH group is attached to a carbon bonded to only one carbon atom. Hence, it is a primary alcohol.
Compound (b):
The –OH group is attached to a carbon bonded to two carbon atoms. Hence, it is a secondary alcohol.
Compound (c):
The –OH group is attached to a carbon bonded to two alkyl groups. Hence, it is a secondary alcohol.
Compound (d):
Both –OH groups are attached to terminal carbon atoms. Hence, it is a primary alcohol.
Compound (e):
The –OH group is attached to a carbon bonded to two carbon atoms of the ring. Hence, it is a secondary alcohol.
Step 3: Count secondary alcohols.
Secondary alcohols are compounds (b), (c) and (e).
Total = 3

Answer 2

Concept:

• A secondary alcohol has its -OH on a carbon that is bonded to exactly one hydrogen and two other carbon atoms.
• A quick check for this: count the H atoms sitting on the carbinol carbon itself -- a primary carbinol carbon carries 2 H, a secondary one carries 1 H, and a tertiary one carries 0 H.
• Before counting anything, confirm the group drawn is really an -OH. A carbon carrying both a C=O and an -OH together is a carboxylic acid (-COOH), a completely different group, and must be excluded first.

Step 1: Screen structure (a).
The ring carbon in (a) carries both a double-bonded O and an -OH on the same carbon -- that combination is a carboxylic acid, not an alcohol. Structure (a) is dropped from the count immediately.

Step 2: Check structure (b).
The carbinol carbon sits in the middle of the chain, bonded to a $CH_3$ group on one side and the rest of the chain on the other, with 1 H on it. Two carbon neighbours means this carbon is secondary.

Step 3: Check structure (c).
The same skeleton, drawn from the other end: the carbinol carbon is again flanked by two carbon chains and carries 1 H. Two carbon neighbours means this is also a secondary alcohol.

Step 4: Check structure (d).
Both -OH groups sit on the end carbons of the chain. An end carbon is bonded to only one other carbon, so each carbinol carbon here carries 2 H -- both are primary, so (d) adds nothing to the secondary count.

Step 5: Check structure (e).
The carbinol carbon hangs off the ring, bonded to one ring carbon and one $CH_3$ group, with 1 H on it. Two carbon neighbours means this is a secondary alcohol too.

Final Answer: Secondary alcohols are (b), (c) and (e), so the total is 3.