Alcohols

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Alcohols are organic compounds that have the general formula; CnH2n+1OH. They are often recognised by the -OH group attached to the first carbon.

Contents

Naming Alcohols

Alcohols have the ending -ol, however when naming alcohols with more than one -OH there is now hydroxy added, between the number of the position of the extra -OH and then ending is now -anoic acid.If there are more than one -OH groups, then di, tri and tetra are used. Numbers are used between the stem and the -ol to show where the position of the -OH is in the compound.

Alcohol Structures

There are 3 different types of alcohol structures. There is the primary structure, the secondary structure and the tertiary structure. The primary structure has one alkyl group attached to the carbon, that holds the -OH group these alcohols are normally named; Methanol, Ethanol, Propanol, Butanol etc.The secondary structure has two alkyl groups attached to the carbon, that is holding the -OH group and the tertiary structure has three alkyl groups attached to the carbon, holding the -OH group. The secondary and the tertiary alcohols are named using numbers between the stem and -ol to show where the -OH group is. An example of a secondary alcohol is - Butan-2-ol and an example of a tertiary alcohol is - 2-methyl butane-2-ol.

Reactions

Primary and secondary alcohols undergo oxidation. Primary alcohols with the addition of potassium dichromate(VI) and dilute sulphuric acid, is converted to an aldehyde which has the ending -CHO, when you warm it gently, this can then be distilled. Primary alcohols can then be further oxidised by using excess potassium dichromate(VI) and distilled sulphuric acid using heat under reflux and can be converted into a carboxylic acid which has the ending -COOH. In order to test that an acid is produced, sodium carbonate is added which will cause some fizzing and the production of carbon dioxide ( C02). Secondary alcohols can also be oxidised using acidified potassium dichromate(I), this will change the secondary alcohol into a ketone, when you heat under reflux,ketones have the ending -one.These reactions always produce water.Tertiary alcohols cannot undergo oxidation using potassium dichromate(VI), as the carbon holding the -OH group has no hydrogen bonded to it. As well as being oxidised alcohols can also be dehydrated and be made into alkenes using concentrated sulphuric acid and warming it under reflux. Primary alcohols produce one product whilst secondary and tertiary alcohols produce two products that are E/Z isomers of the alkene made from the original alcohol[1].

References

  1. Neil Goalby. 3.5 Alcohols. ( Online ); Citied 2017 December 5th. Available from: https://chemrevise.files.wordpress.com/2016/08/3-5-revision-guide-alcohols.pdf
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