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Hydrocarbons of varying lengths and shapes form fatty acids and other structural

ID: 508427 • Letter: H

Question

Hydrocarbons of varying lengths and shapes form fatty acids and other structural compounds. Two structures for C_8H_18 are shown below. Which one has a higher boiling point and why? n-octane: linear, unbranched alkanes experience more surface area contact than comparable branched alkanes and have greater Van der Waals forces acting on them. n-octane: the atom pairs in octane have a smaller electronegativity difference than those in 2, 3, 4-trimethylpentane. 2, 3, 4-trimethylpentane: the boiling point of an alkane is inversely proportional to chain length and directly proportional to number of substituents. 2, 3, 4-trimethylpentane: the increased branching gives the molecule a greater net dipole moment than n-octane.

Explanation / Answer

Answer is (A) as weak intermolecular forces depend on surface area, and branching of chain makes the molecule more compact and thereby decreases the surface area