Posted by: Mark Foreman | February 5, 2012

Alkyls and alkenes

Dear Reader,

For those of you who are new to organic chemistry I imagine you have lots of new names and words which you need to come to terms with. One person recently asked me about the difference between alkyl and alkene.

The alkanes are saturated hydrocarbons which are made up of sp3 carbons linked to each other and bonded to hydrogen atoms. The alkanes all have the formula CxH2x+2. Except for methane (CH4) which is a single carbon atom bonded to four hydrogen atoms. All the bonds in an alkane are sigma (σ) bonds.

The alkanes can be thought of as alkyl hydrides, the term alkyl means a carbon group with the formula (CxH2x+1). By forming a sigma bond to an alkyl group a stable compound can be formed.

Alkyl halide = Haloalkane (eg C2H5I)

Alkyl hydroxide = Alcohol (eg C2H5OH)

Alkyl alkoxide = Ether (eg C2H5OC2H5)

The alkenes are a family of hydrocarbons which all have at least two sp2 carbons, they have the formula (CxH2x). These alkenes have at least one pi (π) bond in addition to the sigma bonds. The defining thing about the alkenes is the carbon carbon double bond which they all have. The pi bond is responsible for the vast majority of the chemistry of the alkenes.

The old name for the alkanes was paraffins which means little affinity, the alkanes have very little reactivity other than the free radical reactions with halogens and oxygen. While the alkenes have plenty of chemistry in which the alkene group does things. When doing organic chemistry it is best to look for the functional group, typically this is involved in almost all reactions.


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