Textbook Question
Which of the following compounds forms hydrogen bonds between its molecules?
1. CH3CH2OCH2CH2OH
2. CH3CH2N(CH3)2
3. CH3CH2CH2CH2Br
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2. Molecular Representations
Intermolecular Forces
5:02 minutesProblem 10b
Textbook Question
List each set of compounds in order of increasing boiling point.
b. Octane, (CH3)3C—C(CH3)3 and CH3CH2C(CH3)2CH2CH2CH3
Verified step by step guidance1
Understand that boiling point is influenced by molecular weight, intermolecular forces, and molecular structure. Larger molecules and those with stronger intermolecular forces typically have higher boiling points.
Identify the molecular structure of each compound: Octane (C8H18) is a straight-chain alkane, (CH3)3C—C(CH3)3 is 2,2,3,3-tetramethylbutane, a highly branched alkane, and CH3CH2C(CH3)2CH2CH2CH3 is 2,2-dimethylhexane, a less branched alkane.
Consider the effect of branching on boiling point: Straight-chain alkanes generally have higher boiling points than branched alkanes due to greater surface area allowing for stronger van der Waals forces.
Compare the molecular weights: Octane has a molecular weight of 114 g/mol, 2,2,3,3-tetramethylbutane has a molecular weight of 114 g/mol, and 2,2-dimethylhexane has a molecular weight of 114 g/mol. Since the molecular weights are similar, focus on branching.
Arrange the compounds in order of increasing boiling point based on branching: 2,2,3,3-tetramethylbutane (most branched, lowest boiling point), 2,2-dimethylhexane (less branched), and octane (straight-chain, highest boiling point).
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5mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Boiling Point
Boiling point is the temperature at which a substance transitions from a liquid to a gas. It is influenced by molecular weight, intermolecular forces, and molecular structure. In organic compounds, stronger intermolecular forces like hydrogen bonding or dipole-dipole interactions typically result in higher boiling points.
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Intermolecular Forces
Intermolecular forces are attractions between molecules, including van der Waals forces, dipole-dipole interactions, and hydrogen bonds. In hydrocarbons, van der Waals forces are predominant, and the strength of these forces increases with larger surface area and molecular weight, affecting boiling points.
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03:01How Van der Waals forces work.
Molecular Structure
Molecular structure refers to the arrangement of atoms within a molecule, impacting its physical properties. In alkanes, branching reduces surface area contact between molecules, leading to weaker van der Waals forces and lower boiling points compared to straight-chain isomers with similar molecular weights.
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