Question

16 multiple choice 2 points which of the following compounds has the highest boiling points? cyclopentane n-pentane neopentane isopentane

Explanation:

Boiling point of alkanes (and cyclic alkanes) is related to molecular surface area and branching. Cyclopentane (cyclic, $C_5H_{10}$) has a more compact, cyclic structure with greater surface contact than the acyclic pentane isomers? Wait, no—wait, pentane isomers: n - pentane (straight - chain, $C_5H_{12}$), isopentane (branched), neopentane (highly branched). Wait, cyclic compounds vs acyclic? Wait, cyclopentane is $C_5H_{10}$, pentanes are $C_5H_{12}$. Wait, no, the question has cyclopentane (cyclic, formula $C_5H_{10}$) and the pentanes (alkanes, $C_5H_{12}$). Wait, no, maybe I made a mistake. Wait, actually, for the same carbon count (but here cyclopentane has 5 C, same as pentanes, but different H count: cyclopentane is $C_5H_{10}$, pentanes are $C_5H_{12}$). Wait, no, the key is intermolecular forces. Cyclopentane has a cyclic structure, and for the pentane isomers: straight - chain n - pentane has the most surface area (least branching), so highest boiling point among pentanes. But cyclopentane: let's check molecular weight? Wait, cyclopentane: molar mass $5\times12 + 10\times1 = 70$ g/mol. Pentanes: $5\times12+12\times1 = 72$ g/mol. Wait, higher molar mass for pentanes. Wait, but maybe the question has a typo? No, the options are cyclopentane, n - pentane, neopentane, isopentane. Wait, actually, among the pentane isomers (n - pentane, isopentane, neopentane), n - pentane has the highest boiling point because it has the least branching (maximizes surface area for London dispersion forces). But cyclopentane: let's check boiling points. Cyclopentane boiling point is about 49 °C, n - pentane is about 36 °C? Wait, no, that can't be. Wait, no, I think I mixed up. Wait, cyclopentane: formula $C_5H_{10}$, molar mass 70. n - pentane: $C_5H_{12}$, molar mass 72. Wait, but maybe the question is considering cyclic vs acyclic with same C? No, maybe the options are mislabeled? Wait, no, the correct answer: among the pentane isomers (n - pentane, isopentane, neopentane), n - pentane has the highest boiling point. But cyclopentane: let's check actual boiling points. Cyclopentane: ~49 °C, n - pentane: ~36 °C. Wait, that's higher. Wait, maybe the question is about cyclic and acyclic with same C atoms (5 C). So cyclopentane (cyclic, $C_5H_{10}$) has a higher boiling point than n - pentane ($C_5H_{12}$)? Wait, no, molar mass: cyclopentane 70, n - pentane 72. But intermolecular forces: cyclic compounds can have different packing. Wait, maybe the question is a mistake, but according to the options, if we consider the pentane isomers (n - pentane, isopentane, neopentane) and cyclopentane. Wait, no, the correct answer here: cyclopentane has a higher boiling point than n - pentane? Wait, no, let's check: Cyclopentane boiling point: 49.3 °C, n - pentane: 36.1 °C. So cyclopentane has a higher boiling point. So the answer is cyclopentane.

Answer:

cyclopentane