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Ch.6 - Alkyl Halides; Nucleophilic Substitution
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.6 - Alkyl Halides; Nucleophilic SubstitutionProblem 6c
Chapter 6, Problem 6c

For each pair of compounds, predict which compound has the higher boiling point. Check [TABLE 6-2] to see if your prediction was right; then explain why that compound has the higher boiling point.
c. 1-bromobutane and 1-chlorobutane

Verified step by step guidance
1
Identify the two compounds in question: 1-bromobutane and 1-chlorobutane. These are alkyl halides where bromine and chlorine are attached to a butane chain.
Consider the molecular weight of each compound. 1-bromobutane has a higher molecular weight than 1-chlorobutane because bromine is heavier than chlorine.
Analyze the intermolecular forces present. Both compounds exhibit van der Waals forces, but 1-bromobutane will have stronger dispersion forces due to its larger electron cloud compared to 1-chlorobutane.
Check the boiling points in the provided table. 1-bromobutane has a boiling point of 102°C, while 1-chlorobutane has a boiling point of 78°C.
Explain the difference in boiling points: The higher boiling point of 1-bromobutane is due to its greater molecular weight and stronger dispersion forces, which require more energy to overcome during the phase transition from liquid to gas.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Boiling Point

The boiling point of a compound is the temperature at which its vapor pressure equals the external pressure, causing it to change from liquid to gas. It is influenced by intermolecular forces, molecular weight, and structural characteristics. Generally, compounds with stronger intermolecular forces, such as hydrogen bonding or dipole-dipole interactions, exhibit higher boiling points.
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Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between molecules. The main types include London dispersion forces, dipole-dipole interactions, and hydrogen bonding. In the case of halogenated compounds like 1-bromobutane and 1-chlorobutane, the strength of these forces significantly affects their boiling points, with stronger dipole-dipole interactions leading to higher boiling points.
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Molecular Weight

Molecular weight, or molar mass, is the mass of a molecule calculated as the sum of the atomic weights of its constituent atoms. Generally, as molecular weight increases, the boiling point tends to increase due to the greater surface area and stronger London dispersion forces. In comparing 1-bromobutane and 1-chlorobutane, the difference in molecular weights contributes to their boiling point differences.
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Related Practice
Textbook Question

For each pair of compounds, predict which compound has the higher boiling point. Check [TABLE 6-2] to see if your prediction was right; then explain why that compound has the higher boiling point.

b. isopropyl chloride and tert-butyl bromide

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Textbook Question

Show how free-radical halogenation might be used to synthesize the following ­compounds. In each case, explain why we expect to get a single major product.

(a) 1-chloro-2,2-dimethylpropane (neopentyl chloride)

(b) 2-bromo-2-methylbutane

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Textbook Question

Show how you might use SN2 reactions to convert 1-chlorobutane into the following compounds.

b. 1-fluorobutane

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Textbook Question

The light-initiated reaction of 2,3-dimethylbut-2-ene with N-bromosuccinimide (NBS) gives two products:

a. Give a mechanism for this reaction, showing how the two products arise as a ­consequence of the resonance-stabilized intermediate.

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Textbook Question

Under appropriate conditions, (S)-1-bromo-1-fluoroethane reacts with sodium methoxide to give pure (S)-1-fluoro-1-methoxyethane.

a. Why is bromide rather than fluoride replaced?

b. Draw perspective structures (as shown on the previous page for 2-bromobutane) for the starting material, the transition state, and the product.

c. Does the product show retention or inversion of configuration? d. Is this result consistent with reaction by the SN2 mechanism?

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Textbook Question

The light-initiated reaction of 2,3-dimethylbut-2-ene with N-bromosuccinimide (NBS) gives two products:

b. The bromination of cyclohexene using NBS gives only one major product, as shown on the previous page. Explain why there is no second product from an allylic shift.

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