Advices For Studying Organic Chemistry

1. Cyclohexane has the lowest heat of combustion per CH 2 group (658.7 kJ
   mol–1).⇒ the same as unbranched alkanes (having no ring strain) ⇒ cyclohexane
   has no ring strain.


2. Cycloporpane has the greatest heat of combustion per CH 2 group (697 kJ mol–1)
   ⇒ cycloporpane has the greatest ring strain (115 kJ mol–1) ⇒ cyclopropane
   contains the greatest amount of potential energy per CH 2 group.

1. The more ring strain a molecule possesses, the more potential energy it has
   and the less stable it is.

3. Cyclobutane has the second largest heat of combustion per CH 2 group (686.0 kJ
   mol–1) ⇒ cyclobutane has the second largest ring strain (109 kJ mol–1).


4. Cyclopentane and cycloheptane have about the same modest amount of ring
   strain (27 kJ mol–1).

4.11 THE ORIGIN OF RING STRAIN IN CYCLOPROPANE AND

CYCLOBUTANE: ANGLE STRAIN AND TORSIONAL STRAIN

1. The carbon atoms of alkanes are sp^3 hybridized ⇒ the bond angle is 109.5°.
   
   
   1. The internal angle of cyclopropane is 60° and departs from the ideal value by a
      very large amout — by 49.5°.
   
   
   
   

C

CC

H H

H

H H

H

60 o

C

CC

HH

HH HH

H

H

H H

H

H

1.510 A

1.089 A

H

H

H

H

CH 2

115 o

(a) (b) (c)
Figure 4.10 (a) Orbital overlap in the carbon-carbon bonds of cyclopropane cannot