How many isomers of C5H11 OH will be primary alcohols ? [1992]a)5b)4c)2d)3.Correct answer is option 'B'. Can you explain this answer?

Question

Answer

Answer

1. CH3-CH2-CH2-CH2-CH2-OH
2. CH3-CH2(CH3)-CH2-CH2-OH
3. CH3-CH2-CH2(CH3)-CH2-OH
4. CH3-C(CH3)2-CH2-OH.

Answer

Primary alcohols have the general formula R-CH2OH, where R represents an alkyl group. In the case of C5H11OH, we are looking for isomers in which the OH group is attached to a primary carbon (i.e., the carbon atom directly bonded to only one other carbon atom).

To determine the number of primary alcohol isomers for C5H11OH, we need to consider the different ways we can arrange the C and H atoms in a chain of five carbon atoms, while ensuring that the OH group is attached to a primary carbon.

Let's analyze the possible arrangements step by step:

1. Start with the longest carbon chain: In this case, it is a chain of five carbon atoms (pentane).

2. Consider the position of the OH group: The OH group can be attached to any of the five carbon atoms in the chain.

3. Count the number of possible isomers for each position of the OH group:

a) If the OH group is attached to the first carbon atom in the chain, we have a primary alcohol (1-pentanol).

b) If the OH group is attached to the second carbon atom in the chain, we have a secondary alcohol (2-pentanol).

c) If the OH group is attached to the third carbon atom in the chain, we have a secondary alcohol (3-pentanol).

d) If the OH group is attached to the fourth carbon atom in the chain, we have a secondary alcohol (4-pentanol).

e) If the OH group is attached to the fifth carbon atom in the chain, we have a primary alcohol (5-pentanol).

4. Count the number of primary alcohol isomers: From the above analysis, we can see that there are two primary alcohol isomers, namely 1-pentanol and 5-pentanol.

Therefore, the correct answer is option 'B' (4).

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