Organic Chemistry
9th Edition
ISBN: 9781305080485
Author: John E. McMurry
Publisher: Cengage Learning
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Question
Chapter 4.4, Problem 10P
Interpretation Introduction
Interpretation:
The conformation of cyclopentane is to be analysed considering the structure to be planar and the torsional strain is to be calculated.
Concept introduction:
Cyclopentane was predicted by Baeyer to be nearly strain-free, but it actually has total strain energy of 26 kJ/mol. planar cyclopentane has practically no angle strain, it has a large torsional strain. Cyclopentane therefore twists to adopt a puckered, nonplanar conformation that strikes a balance between increased angle strain and decreased torsional strain. Four of the cyclopentane carbon atoms are in approximately the same plane, with the fifth carbon atom bent out of the plane. Most of the hydrogens are nearly staggered with respect to their neighbours.
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5. Assume that the types of strain in the rotation about the C1-C2 bond in 1,2-dibromopropane have the
following values.
•Torsional strain = 20 kJ/mol
•Steric strain between two Br substituents gauche = 13 kJ/mol
•Steric strain between two Br substituents eclipsed = 16 kJ/mol
•Steric strain between Br and CH3 substituents gauche = 8 kJ/mol
•Steric strain between Br and CH3 substituents eclipsed
(a) Perform a conformational analysis about the C1-C2 bond, analogous to the diagram in Figures 4-4 and 4-7
(Karty). Draw a full rotational energy profile (add E values in kJ/mol on y-axis) drawing each eclipsed and
staggered conformation as Newmann projections i.e. 60° rotations for complete rotation about the C1-C2 bond.
= 10 kJ/mol.
E
(kJ/mol)
0°
360 °
Estimate the heat released when ethene(CH2=CH2) reacts with HBr to giveCH3CH2Br. Bond enthalpies areC-H : 412 kJ/mol; C-C : 348 kJ/mol;C=C : 612 kJ/mol; C-Br : 276 kJ/mol;Br-Br : 193 kJ/mol; H-Br : 366 kJ/mol.
Choose the correct answer:1. 1036 kJ/mol2. 58 kJ/mol3. 424 kJ/mol4. 200 kJ/mol5. 470 kJ/mol
Given the following:
(i) The barrier to rotation about the C-C bond in ethane is 12 kJ/mol
(ii) The barrier to rotation about the C-C bond in 1-bromoethane is 15
kJ/mol
What is the total strain energy associated with an H Br eclipsing
interaction in 1-bromoethane?
Select one:
O A. 9 kJ/mol
O B. 7 kJ/mol
O C. 22 kJ/mol
Chapter 4 Solutions
Organic Chemistry
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