Chapter 2 : Alkanes

Cycloalkanes

Another type of molecule containing only sp³ hybridised C and H atoms connected by s bonds is possible with a ring of 3 or more C atoms.  These are the cycloalkanes which are fairly common in the world of organic chemistry, both man-made and natural.

Nomenclature:
Functional group prefix = cyclo- (review)

Physical Properties:
Like alkanes, the low polarity of all the bonds in cycloalkanes means that the only intermolecular forces between molecules of cycloalkanes are the very weak induced dipole - induced dipole forces, also known as van der Waals forces which are easily overcome.  As a result, compared to other functional groups, but like alkanes, cycloakanes tend to have low melting and boiling points.

Structure:
They have a generic formula of C_nH_2n, (note: there 2 less H atoms compared to the analogous alkane).
The C3 to C6 cycloalkanes are shown below in a variety of representations.

Cyclopropane C3H6
Cyclobutane C4H8
Cyclopentane C5H10
Cyclohexane C6H12

• Very similar reactivity to the closely related alkanes which have the same types of bonds.
• Since C and H atoms have very similar electronegativities, both the C-H and C-C bonds are non-polar.
• As a result, cycloalkanes, like alkanes, are not a very reactive functional group

© Dr. Ian Hunt, Department of Chemistry