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 °

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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 °

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