Organic chemistry B

Chapter 13

Aliphatic cyclic compoundsAlicyclic compounds

By Prof. Dr.Adel M. Awadallah

Islamic University of Gaza

• Cycloalkanes: Nomenclature

Cyclopropane Cyclobutane Cyclopentane Cyclohexane

OH

OH CH3

Br

OH

OH

Bicyclo[2.2.1]heptane Bicyclo[2.2.2]octaneBicyclo[2.1.1]hexane

Bicyclo[2.2.2]octa-2-ene Tricyclo[2.2.2.02,6]octaneTricyclo[2.2.1.02,6]heptane

Cyclopentanol 1,3-Cyclopentadiene 3-Ethylcyclopentene

2-Cyclohexenol 1-Bromo-3-methylcyclohexane 1,3-Cyclohexanediol

Norbornane

1 2

3

45

6

7

Industrial source

Preparation

Reactionssimilar to that of alkanes (free radical substitution) ,

Reactionsalkenes (addition or cleavage of the double bond)

Ring Strain in Cyclopropane• Average heat of composition per CH2 = 157.4 Kcal / mol• Ring strain in cyclopropane = 27.6 Kcal/mol• Ring strain in cyclobutane = 26.3 Kcal/mol

Ring Strain in Cyclopropane

• Eclipsing (torsional) strain: • Strain resulting from deviation

from the staggered arrangement

• Bond-Angle Strain:• Strain resulting from deviation

from the normal bond angle (tetrahedral 109.5)

Addition to cyclopropane

Addition to cyclopropaneCyclobutane undergoes hydrogenation under vigorous conditions

Relieve of torsional strain in cyclobutanePuckered structure (butterfly)

Relieve of torsional strain in cyclopentaneEnvelope (half chair) structure

• Conformations of Cyclohexane

CH3H

CH3

H

flip

Chair conformation

Boat conformation

axial

equatorial

flip

5% 95%

flip

0% 100%

methylcyclohexanetert-butylcyclohexane

Conformations of cyclohexane

Twist boat is more stable than the boat conformation

1,2 + 1,4 Trans diaxial or diequatorial1,3 cis diaxial or diequatorial

Example