Alkanes and cycloalkanes

DEFINITION

Key Notes

Alkanes

Alkanes are organic molecules consisting solely of carbon and hydrogen atoms linked by single σ bonds. All the carbon atoms are tetrahedral and sp³ hybridized. Alkanes are stable molecules and unreactive to most chemical reagents. They have the general formula C_nH_2n2

Cycloalkanes

Cycloalkanes are cyclic alkane structures. They have the general formula C_nH_2n. Most cycloalkanes are unreactive to chemical reagents. However, three- and four-membered rings are reactive due to ring strain and behave like alkenes.

Alkanes

Alkanes are organic molecules with the general formula C_nH_2n2, which consist of carbon and hydrogen atoms linked together by C–C and C–H single bonds. They are often referred to as saturated hydrocarbons – saturated because all the bonds are single bonds, hydrocarbons because the only atoms present are carbon and hydrogen. All the carbon atoms in an alkane are sp³ hybridized and tetrahedral in shape. The C–C and C–H bonds are strong σ bonds, and so alkanes are unreactive to most chemical reagents.

Alkanes  are  sometimes  referred  to  as  straight  chain  or  acyclic  alkanes  to distinguish them from cycloalkanes or alicyclic compounds.

Cycloalkanes

Cycloalkanes are cyclic alkanes (alicyclic compounds) having the general formula C_nH_2n where the carbon atoms have been linked together to form a ring. All sizes of ring are possible. However, the most commonly encountered cycloalkane in organic chemistry is the six-membered ring (cyclohexane). Most cycloalkanes are unreactive to chemical reagents. However, small three- and four-membered rings are reactive and behave like alkenes. Such cyclic structures are highly strained since it is impossible for the carbon atoms to adopt their preferred tetrahedral shape.