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Structure and Nomenclature

ALKANES and
CYCLOALKANES
consist exclusively of carbon and hydrogen. These are molecules lacking functional groups.

Video: Endless carbon chains: alkanes▶ Watch the video on YouTube
Video: Linear (n-butane) and branched (methylpropane) structures of C₄H₁₀▶ Watch the video on YouTube

Isomerism is a very important phenomenon in Organic Chemistry. With just a few carbons one can form a large number of different compounds. A good exercise is to draw the 18 possible alkane isomers with eight carbon atoms. Do you dare? And do not forget stereoisomers!

Isomers of alkanes with four to seven carbons and number of isomers by number of carbons

In the language of Organic Chemistry it is usual to distinguish certain positions in a carbon chain:

Carbon types by substitution (primary, secondary, tertiary, quaternary) and stereocentre in 2,2,4-trimethylhexane

A carbon bonded to only one other carbon is called PRIMARY.

A carbon bonded to two other carbons is called SECONDARY.

To three, TERTIARY.

And finally to four, QUATERNARY.

And do not forget to look for stereocentres!

Chains CANNOT be branched without limit:

Steric limit of isomerism: 3,3-di-tert-butyl-2,2,4,4-tetramethylpentane is impossible

STERIC HINDRANCE is the consequence of atoms occupying space. If we keep replacing H atoms with CH3 groups, a point is reached where there is no room left and the molecule is impossible.