What's the difference between alkanes and alkenes, and what's an example of each?

2 Answers
Mar 18, 2018

See below.

Explanation:

Alkenes are saturated hydrocarbons and contain only single bonds. Alkenes are unsaturated hydrocarbons and contain one carbon to carbon double bond.

Alkanes: methane ethane propane

Alkenes: ethenen propene; butene

Mar 18, 2018

A very useful expedient in these problems is to assess the the so-called #"degree of unsaturation..."#

Explanation:

An #"saturated organic compound"# has formula #C_nH_(2n+2)#. That is EVERY CARBON atom in the chain has three or two hydrogens. Methane, the simplest alkane, has 4 hydrogens, but higher alkanes fulfil the criterion. Each degree of unsaturation REDUCES the hydrogen count by 2, and corresponds to a RING JUNCTION or an olefinic bond. When oxygen appears in the formula, we assess the degree of unsaturation directly (and of course a degree of unsaturation could correspond to #C=O#). Halogens count for #1*H#; we subtract #NH# from the formula if nitrogen is present.

And thus #HC-=CH# has 2 degrees of unsaturation, it is an alkyne.

And #H_3C-CH_3# has 0 degrees of unsaturation.....an alkane.

And #H_2C=CH_2# has 1 degree of unsaturation.....an olefin, or alkene.

And #H_3C-CH_2NH_2-=C_2H_6#...no degrees of unsaturation.

And #C_3H_8# has 0 degrees of unsaturation.....an alkane.

So to your answer your question....an alkane has the maximum number of hydrogens, and is saturated with respect to hydrogen content....#CH_4#, #C_2H_6#, #C_3H_8#, #C_4H_10#...

And alkenes or olefins have ONE degree of unsaturation given the presence of the #C=C# bond .. consider, ethylene, propylene etc. #H_2C=CH_2#, #H_3C-CH=CH_2#....