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Chemistry Question 66 – JEE-MAIN 2025

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Given below are two statements : Statement (I) : Neopentane forms only one monosubstituted derivative. Statement (II) : Melting point of neopentane is higher than n-pentane. In the light of the above statements, choose the most appropriate answer from the options given below :

Consider the structural symmetry of neopentane to determine the number of unique hydrogen atoms available for substitution.

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Ninja Strategy•Recall Key Properties

Recall the unique symmetry of neopentane leading to one monosubstituted product and its efficient crystal packing leading to a higher melting point compared to n-pentane.

Step 1: Analyze Statement (I) regarding monosubstitution of neopentane.✦ Active

Neopentane (2,2-dimethylpropane) has a highly symmetrical structure where a central carbon atom is bonded to four methyl groups. All 12 hydrogen atoms in these four methyl groups are chemically equivalent due to the molecule's symmetry.

CH3|CH3−C−CH3|CH3

Therefore, replacing any one hydrogen atom with a substituent will yield only one unique monosubstituted product. Thus, Statement (I) is correct.

Step 2: Analyze Statement (II) regarding the melting point of neopentane vs. n-pentane.○ Expand

Melting point is influenced by the efficiency of molecular packing in the solid state. While branching generally lowers boiling points due to reduced surface area for van der Waals forces, highly symmetrical and compact molecules like neopentane can pack very efficiently into a crystal lattice.

This efficient packing leads to stronger intermolecular forces in the solid state, requiring more energy to overcome, resulting in a higher melting point. For example, the melting point of neopentane is −16.6 ∘C, while that of n-pentane is −129.7 ∘C.

Thus, Statement (II) is correct.

Step 3: Conclude based on both statements.○ Expand

Since both Statement (I) and Statement (II) are correct, the most appropriate answer is option 1.

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