ORGANIC CHEM BUNDLE >BI<
ORGANIC CHEM BUNDLE >BI<
10th Edition
ISBN: 9781260719567
Author: Carey
Publisher: MCG
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Textbook Question
Chapter 8, Problem 25P

How many alkenes yield 2,2,3,4,4-pentamethylpentane on catalytic hydrogenation?

How many yield 2,3-dimethylbutane?

How many yield methylcyclobutane?

Expert Solution & Answer
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Interpretation Introduction

Interpretation:

The number of alkenes which are required to produce the given alkanes on catalytic hydrogenation is to be determined.

Concept introduction:

On catalytic hydrogenation, alkenes get converted to the corresponding alkanes with the same number of carbon atoms.

In hydrogenation reaction, one hydrogen atom gets attached to each of the double bonded carbon atoms.

To accelerate the rate of hydrogenation, the metal catalyst provides an alternative pathway involving low activation energy steps.

The alkane that is formed contains two hydrogen atoms more than the corresponding alkene and these two hydrogen atoms are added on the adjacent carbon atoms in the alkene.

Answer to Problem 25P

Solution:

a) Only one alkene can produce 2,2,3,4,4-pentamethylpentane upon catalytic hydrogenation.

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  1

b) Two alkenes can produce 2,3-dimethylbutane upon catalytic hydrogenation.

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  2 ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  3

c) Three alkenes can produce methylcyclobutane upon catalytic hydrogenation.

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  4 ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  5 ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  6

Explanation of Solution

a) The structure of 2,2,3,4,4-pentamethylpentane is shown below:

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  7

Hydrogenation of alkenes adds one hydrogen atom on each carbon atom of the double bonded carbon atoms. So in the alkane, these two carbon atoms (previously double bonded) should be attached to at least one hydrogen atom each.

In 2,2,3,4,4-pentamethylpentane, the C3 carbon atom is attached to a hydrogen atom. It has an adjacent methyl group. So in the structure of the alkene, the double bond must be present between these two carbon atoms.

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  8

The alkane structure is symmetric, and carbon atoms 2 and 4 do not have any hydrogen atoms attached. Thus, there is no other pair of adjacent carbon atoms having one hydrogen atom attached to each. This means there cannot be any other alkene structure which would produce 2,2,3,4,4-pentamethylpentane upon catalytic hydrogenation.

b) The structure of 2,3-dimethylbutane is shown below:

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  9

The hydrogen of alkenes adds one hydrogen atom on each carbon atom of the double bonded carbon atoms. So in the alkane, these two carbon atoms (previously double bonded) should be attached to at least one hydrogen atom each.

In 2,3-dimethylbutane, the C2 and C3 carbon atoms are attached to one hydrogen atom each. So in the structure of the alkene, the double bond could be present between these two carbon atoms.

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  10

The C1 and C2 carbon atoms are also attached to at least one hydrogen atom each. So in the structure of the alkene, the double bond could be present between these two carbon atoms.

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  11

The alkane structure is symmetric, and the carbon atoms 2 and 3 are attached to two methyl groups each. This means there cannot be any other alkene structure which would produce 2,3-dimethylbutane upon catalytic hydrogenation.

Hence, two alkenes can produce 2,3-dimethylbutane upon catalytic hydrogenation.

c) The structure of methylcyclobutane is shown below:

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  12

The hydrogen of alkenes adds one hydrogen atom on each carbon atom of the double bonded carbon atoms. So in the alkane, these two carbon atoms (previously double bonded) should be attached to one at least one hydrogen atom each.

In methylcyclobutane, the C1 carbon atom is attached to a hydrogen atom. It has an adjacent methyl group. So in the structure of the alkene, the double bond could be present between these two carbon atoms.

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  13

The C1 and C2 carbon atoms are also attached to at least one hydrogen atom each. So in the structure of the alkene, the double bond could be present between these two carbon atoms.

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  14

The C2 and C3 carbon atoms are attached to one hydrogen atom each. So in the structure of the alkene, the double bond could be present between these two carbon atoms.

ORGANIC CHEM BUNDLE >BI<, Chapter 8, Problem 25P , additional homework tip  15

The alkane structure is symmetric. This means, there cannot be any other distinct alkene structure which would produce methylcyclobutane upon catalytic hydrogenation.

Hence, three alkenes can produce methylcyclobutane upon catalytic hydrogenation.

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Chapter 8 Solutions

ORGANIC CHEM BUNDLE >BI<

Ch. 8.7 - You can calculate the equilibrium constant for the...Ch. 8.7 - Does the presence or absence of a catalyst such as...Ch. 8.7 - The gas phase reaction of ethanol with hydrogen...Ch. 8.8 - Prob. 14PCh. 8.8 - Hydroborationoxidation of -pinene, like its...Ch. 8.10 - Arrange the compounds 2-methyl-1-butene,...Ch. 8.10 - Give the structure of the product formed when each...Ch. 8.11 - Prob. 18PCh. 8.11 - Prob. 19PCh. 8.12 - Prob. 20PCh. 8.12 - Prob. 21PCh. 8.13 - Prob. 22PCh. 8.14 - Prob. 23PCh. 8.14 - Prob. 24PCh. 8 - How many alkenes yield...Ch. 8 - Prob. 26PCh. 8 - Catalytic hydrogenation of...Ch. 8 - Prob. 28PCh. 8 - Prob. 29PCh. 8 - Prob. 30PCh. 8 - Prob. 31PCh. 8 - A single epoxide was isolated in 7984% yield in...Ch. 8 - Prob. 33PCh. 8 - Prob. 34PCh. 8 - On catalytic hydrogenation over a rhodium...Ch. 8 - Prob. 36PCh. 8 - Prob. 37PCh. 8 - Prob. 38PCh. 8 - Prob. 39PCh. 8 - 1-Butene has a higher heat of hydrogenation than...Ch. 8 - Match the following alkenes with the appropriate...Ch. 8 - The heats of reaction were measured for addition...Ch. 8 - Complete the following table by adding + and -...Ch. 8 - Match the heats of hydrogenation (107 kJ/mol,...Ch. 8 - The iodination of ethylene at 25 C is...Ch. 8 - Specify reagents suitable for converting...Ch. 8 - (a) Which primary alcohol of molecular formula...Ch. 8 - Identify compounds A and B in the retrosynthesis...Ch. 8 - Identify compounds A and B in the retrosynthesis...Ch. 8 - Prob. 50PCh. 8 - On being heated with a solution of sodium ethoxide...Ch. 8 - Compound A (C7H15Br) is not a primary alkyl...Ch. 8 - Prob. 53PCh. 8 - Prob. 54PCh. 8 - A mixture of three alkenes (A, B, and C) was...Ch. 8 - Reaction of 3,3-dimethyl-1-butene with hydrogen...Ch. 8 - Dehydration of 2,2,3,4,4-pentamethyl-3-pentanol...Ch. 8 - Prob. 58PCh. 8 - East Indian sandalwood oil contains a hydrocarbon...Ch. 8 - Prob. 60PCh. 8 - Prob. 61PCh. 8 - Prob. 62PCh. 8 - Prob. 63PCh. 8 - Prob. 64PCh. 8 - On the basis of the mechanism of acid-catalyzed...Ch. 8 - As a method for the preparation of alkenes, a...Ch. 8 - Which of the following is the most reasonable...Ch. 8 - Prob. 68PCh. 8 - Oxymercuration Concerns about mercurys toxicity...Ch. 8 - Prob. 70DSPCh. 8 - Prob. 71DSPCh. 8 - Prob. 72DSPCh. 8 - Prob. 73DSPCh. 8 - Oxymercuration Concerns about mercurys toxicity...
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