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Iodination of alkanes using iodine (I2) is usually an

Organic Chemistry | 8th Edition | ISBN: 9780321768414 | Authors: L.G. Wade Jr ISBN: 9780321768414 33

Solution for problem 57SP Chapter 4

Organic Chemistry | 8th Edition

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Organic Chemistry | 8th Edition | ISBN: 9780321768414 | Authors: L.G. Wade Jr

Organic Chemistry | 8th Edition

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Problem 57SP

Iodination of alkanes using iodine (I2) is usually an unfavorable reaction. (See Problem 4-17, for example.) Tetraiodomethane (CI4) can be used as the iodine source for iodination, in the presence of a free-radical initiator such as hydrogen peroxide. Propose a mechanism (involving mildly exothermic propagation steps) for the following proposed reaction. Calculate the value of  for each of the steps in your proposed mechanism.

The following bond-dissociation energies may be helpful:

(a) Using the BDEs in Table 4-2 (p. 143), compute the value of ΔH° for each step in the iodination of methane.

Reference: Problem 4-17:

(b) Compute the overall value of ΔH° for iodination.

(c) Suggest two reasons why iodine does not react well with methane.

Step-by-Step Solution:

Solution  57SP

Here, we are going to calculate the value of  for each of the steps in your proposed mechanism.

Step 1:

Mechanism

Here, Bond dissociation energy of bonds broken :

HO-OH = 213 kJ/mol

I-CI3 = 188 kJ/mol

Bond dissociation energy for bonds formed :

HO-I = 234 kJ/mol

o = [Bond dissociation energy for bonds broken] -[Bond dissociation energy for bonds formed]

        = +188 kJ/mol - 234 kJ/mol = -46.0 kJ/mol

Step 2:

Here, Bond dissociation energy of bonds broken :

+397 kJ/mol

Bond dissociation energy for bonds formed :

H-CI3 = 418 kJ/mol

o = [Bond dissociation energy for bonds broken] -[Bond dissociation energy for bonds formed]

        = +397 kJ/mol - 418 kJ/mol = -21 kJ/mol

Here, Bond dissociation energy of bonds broken :

I-CI3 = 188 kJ/mol

= 222 kJ/mol

o = [Bond dissociation energy for bonds broken] -[Bond dissociation energy for bonds formed]

        = 188 kJ/mol - 222 kJ/mol = -34 kJ/mol

Total enthalpy change in the propagation steps :  -34 kJ/mol + (-21 kj/mol) = -55 kJ/mol

Step 2:

Calculation of the total enthalpy change for the reaction is

 

Bond dissociation energy for bonds broken 

        Here, Bond dissociation energy of bonds broken :

+397 kJ/mol

I-CI3 = 188 kJ/mol

Total Bond dissociation energy for bonds broken = 585 kJ/mol

Bond dissociation energy for bonds formed

 +222 kj/mol

H-IC3 = 418 kJ/mol

Total Bond dissociation energy for bonds  formed  = 640 kJ/mol

Thus,

o = [Bond dissociation energy for bonds broken] -[Bond dissociation energy for bonds formed]

        =  585 kJ/mol -640 kJ/mol

        = -55 kJ/mol

Thus, overall value of ΔH° for iodination is  -55 kJ/mol

Step 3 of 3

Chapter 4, Problem 57SP is Solved
Textbook: Organic Chemistry
Edition: 8
Author: L.G. Wade Jr
ISBN: 9780321768414

Since the solution to 57SP from 4 chapter was answered, more than 742 students have viewed the full step-by-step answer. The answer to “Iodination of alkanes using iodine (I2) is usually an unfavorable reaction. (See 4-17, for example.) Tetraiodomethane (CI4) can be used as the iodine source for iodination, in the presence of a free-radical initiator such as hydrogen peroxide. Propose a mechanism (involving mildly exothermic propagation steps) for the following proposed reaction. Calculate the value of for each of the steps in your proposed mechanism. The following bond-dissociation energies may be helpful: (a) Using the BDEs in Table 4-2 (p. 143), compute the value of ?H° for each step in the iodination of methane.Reference: 4-17:(b) Compute the overall value of ?H° for iodination.(c) Suggest two reasons why iodine does not react well with methane.” is broken down into a number of easy to follow steps, and 112 words. Organic Chemistry was written by and is associated to the ISBN: 9780321768414. This textbook survival guide was created for the textbook: Organic Chemistry, edition: 8. The full step-by-step solution to problem: 57SP from chapter: 4 was answered by , our top Chemistry solution expert on 05/06/17, 06:41PM. This full solution covers the following key subjects: Iodination, iodine, proposed, steps, reaction. This expansive textbook survival guide covers 25 chapters, and 1336 solutions.

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