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Nomenclature of Alcohols

Alcohols are one of the most important functional groups in organic chemistry. Alcohols are a good source of reagents for synthesis reactions. The ability to identify alcohols is important especially when looking at IR and NMR spectra. The alcohol signal is very easy to spot on IR graphs, because they have a strong signal near the 3200 cm-1 region.

Introduction

The following is list of some common primary alcohols based on the IUPAC naming system.

 

Name

Molecular Formula

Methanol (methyl alcohol)

CH3OH

Ethanol (ethyl alcohol)

C2H­­­­5OH

Propanol

C3H7OH

Butanol

C4H9OH

Pentanol

C5H11OH

Hexanol

C6H13OH

Heptanol

C7H15OH

Octanol

C8H17OH

Rules for naming the alcohols

  1. Find the longest chain containing the hydroxy group (OH). If there is a chain with more carbons than the one containing the OH group it will be named as a subsitutent.
  2. Place the OH on the lowest possible number for the chain. With the exception of carbonyl groups such as ketones and aldehydes, the alcohol or hydroxy groups have first priority for naming.
  3. When naming a cyclic structure, the -OH is assumed to be on the first carbon unless the carbonyl group is present, in which case the later will get priority at the first carbon.
  4. When multiple -OH groups are on the cyclic structure, number the carbons on which the -OH groups reside.
  5. Remove the final e from the parent alkane chain and add -ol. When multiple alcohols are present use di, tri, et.c before the ol, after the parent name. ex. 2,3-hexandiol. If a carbonyl group is present, the -OH group is named with the prefix "hydroxy," with the carbonyl group attached to the parent chain name so that it ends with -al or -one.

Examples

Ethane: CH3CH3 ----->Ethanol:   (the alcohol found in beer, wine and other consumed sprits)

Secondary alcohol:  2-propanol

Other functional groups on an alcohol:  3-bromo-2-pentanol

Cyclic alcohol (two -OH groups):  cyclohexan-1,4-diol

Other functional group on the cyclic structure:  3-hexeneol (the alkene is in bold and indicated by numbering the carbon closest to the alcohol)

A complex alcohol:  4-ethyl-3hexanol (the parent chain is in red and the substituent is in blue)

References

  • Thurlow, K.J.. Chemical Nomenclature. Netherlands: Kluwer Academic Publishers, 1998.

Problems

Name the following alchols:

1.

Contributors

  • Abhiram Kondajji (UCD)