Return to Contents Chapter 3: Conformations of Alkanes and Cycloalkanes  Ch 3 contents

Cycloalkanes

The structures of some of the smaller cycloalkanes are shown below with the planar structures for contrast. In each case, manipulate the JMOL images to look for the deviation from planarity and the effect this has on the eclipsing interactions of adjacent H atoms and C-C bonds. In order to be able to compare the strain in each member of the cycloalkane series, the heat of combustion per methylene (i.e. -CH2-) is also given. The smaller this number is the less ring strain there is.
 
C3H6

CYCLOPROPANE
ΔHc / CH2 = -697 kJ/mol
(-166.6 kcal/mol)





 
C4H8

CYCLOBUTANE
ΔHc / CH2 = -681 kJ/mol
(-
162.7 kcal/mol)

planar
most stable structure

 
C5H10

CYCLOPENTANE
ΔHc / CH2 = -658 kJ/mol
(-
157.3 kcal/mol)

planar
most stable structure

 


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© Dr. Ian Hunt, Department of Chemistry University of Calgary