Isomers of Butane

Butane and Methylpropane are isomers.

Similarity

Organic Compound	Butane	2-Methylpropane
displayed formula / full structural formula
molecular formula	$C_4{H}_{10}$	$C_4{H}_{10}$

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Differences

They have different arrangements of atoms. Thus, they have different structural formulae

Organic Compound	Butane	2-Methylpropane
Structural Formula	$C{H}_{3}C{H}_{2}C{H}_{2}C{H}_3$	$C{H}_{3}CH(C{H}_3)C{H}_3$
Arrangement of atoms	straight chain butane → because all carbon atoms are joined up in a row to form the carbon chain	branched chain butane → because only 3 carbon atoms made up the carbon chain - one of the carbon atom is part of the side chain. - has a branch or a side chain, $-C{H}_3-$
Different physical properties due to different structural formula	- higher boiling point of $-0.5°C$ as it has larger molecular size than 2-methypropane - more energy required to overcome the greater amount of weak intermolecular forces of attraction between the butane molecules to boil this substance	- lower boiling point of $-11.7°C$ as it has smaller molecular size than butane - less energy required to overcome the lesser amount of weak intermolecular forces of attraction between the 2-methylpropaoen molecules to boil this substance.

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Side chain is an alkyl group → which is formed by removing a hydrogen atom from an alkane molecule. In this case → methyl group forms the side chain in methylpropane. Branched chain alkanes → can also have longer side chains, such as an ethyl group ($-C_2{H}_5$)

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Sample

are these compounds isomers? explain? (2m)

• yes, butane and 2 methylpropane are isomers AND both compounds have the same molecular formula of $C_4{H}_{1}0$
• they have different structural formula as butane is a straight chain alkane but 2-methylpropane is a branched chain alkane

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