Q.Consider the compounds I to VII:
I. CH3—CH2—CH2—CH2—OH
II. CH3—CH2—CH(OH)—CH3
III. (CH3)3C—OH
IV. CH3—CH(CH3)—CH2—OH
V. CH3—CH2—O—CH2—CH3
VI. CH3—O—CH2—CH2—CH3
VII. CH3—O—CH(CH3)2
Which of the above compounds form pairs of metamers?

The key idea is Metamerism, a type of structural isomerism where compounds have the same molecular formula and the same functional group, but differ in the nature of the alkyl groups attached to the polyvalent atom or functional group.

1. First, determine the molecular formula and functional group for each compound. All given compounds have the molecular formula $\text{C}_4\text{H}_{10}\text{O}$.

   • Compounds I, II, III, IV are alcohols (contain -OH group). Alcohols do not exhibit metamerism as the hydroxyl group is monovalent.
   • Compounds V, VI, VII are ethers (contain -O- group). Ethers are known to exhibit metamerism.

2. Next, examine the alkyl groups attached to the oxygen atom in the ether compounds:

   • V. $\text{CH}_3\text{CH}_2\text{—O—CH}_2\text{CH}_3$: Alkyl groups are ethyl ($\text{C}_2\text{H}_5$) and ethyl ($\text{C}_2\text{H}_5$).
   • VI. $\text{CH}_3\text{—O—CH}_2\text{CH}_2\text{CH}_3$: Alkyl groups are methyl ($\text{CH}_3$) and n-propyl ($\text{C}_3\text{H}_7$).
   • VII. $\text{CH}_3\text{—O—CH(CH}_3\text{)}_2$: Alkyl groups are methyl ($\text{CH}_3$) and isopropyl ($\text{C}_3\text{H}_7$).

3. Finally, identify pairs where the alkyl groups attached to the oxygen atom are different. …

To identify metamers, we first need to understand what they are and how they differ from other types of isomers.

Understanding Metamerism

1. Isomers: Compounds that have the same molecular formula but different structural arrangements of atoms.
2. Structural Isomers: A broad category of isomers where the atoms are connected in different ways. Metamers are a specific type of structural isomer.
3. Metamers: These are structural isomers that share the same molecular formula and the same functional group, but differ in the nature of the alkyl groups attached to the polyvalent atom of the functional group.
   • A polyvalent atom is an atom that can form more than one bond, allowing different alkyl groups to be attached to it.
   • Common functional groups that exhibit metamerism include ethers (where oxygen is the polyvalent atom), ketones (where the carbonyl carbon is the polyvalent atom), and secondary/tertiary amines.
   • Alcohols, for example, do not exhibit metamerism because the oxygen atom in the hydroxyl group ($-\text{OH}$) is only bonded to one carbon atom (it's monovalent in terms of carbon attachment).

Step-by-Step Analysis of Compounds

Let's analyze each compound to determine its molecular formula, functional group, and IUPAC name. This will help us group similar compounds and then check for metamerism.

From the table, we observe two distinct groups of compounds:

1. Alcohols (I, II, III, IV): All have the molecular formula $\text{C}_4\text{H}_{10}\text{O}$ and are alcohols.
2. Ethers (V, VI, VII): All have the molecular formula $\text{C}_4\text{H}_{10}\text{O}$ and are ethers.

Identifying Metameric Pairs

1. Alcohols (I, II, III, IV)

Compounds I, II, III, and IV are all alcohols with the molecular formula $\text{C}_4\text{H}_{10}\text{O}$.

• I (Butan-1-ol) and II (Butan-2-ol) are position isomers.
• I (Butan-1-ol) and IV (2-Methylpropan-1-ol) are chain isomers.
• II (Butan-2-ol) and III (2-Methylpropan-2-ol) are chain isomers.

However, alcohols do not exhibit metamerism because the oxygen atom in the hydroxyl group ($-\text{OH}$) is only bonded to one carbon chain. There are no different alkyl groups around a polyvalent functional group atom to vary. Therefore, none of the alcohol compounds (I, II, III, IV) form metameric pairs with each other or with any other compound.

2. Ethers (V, VI, VII)

Compounds V, VI, and VII are all ethers with the molecular formula $\text{C}_4\text{H}_{10}\text{O}$. In ethers, the oxygen atom is polyvalent, bonded to two alkyl groups. Metamerism occurs when these alkyl groups differ. …