Block 042: Organic Chemistry Naming Alcohols

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1 Sophomore Chemistry Block 042: Organic Chemistry Naming Alcohols Page 1 Block 042: Organic Chemistry Naming Alcohols What do you think of when you think of alcohol? NAME: Cliff and Norm from Cheers The How I Met Your Mother gang Barney from The Simpsons You probably think of ethanol, the compound that people consume. However, you may be surprised to learn that ethanol is only one of the many types of alcohol that exist. H OH H C C H H H The structural formula for ethanol. Four residents of Quahog, RI, enjoying the consumption of ethanol. You probably have used rubbing alcohol, otherwise known as propan-2-ol. The structure of propan-2-ol is seen below on the right. Alcohols, or alkanols, have the general formula R OH, and are characterized by the presence of a hydroxyl group, OH. Alcohols are structurally similar to water, but with one of the hydrogens replaced by an alkyl group. H OH H H C C C H H H H The structural formula for propan-2-ol.

2 Sophomore Chemistry Block 042: Organic Chemistry Naming Alcohols Page 2 In the naming rules, the hydroxyl group in alcohols is indicated by the ending ol after the name of the carbon chain that the OH is attached to. Of course, you will have to remember the names of the unsubstituted carbon chains that the hydroxyl group is attached to: 1 = methane 3 = propane 5 = pentane 7 = heptane 2 = ethane 4 = butane 6 = hexane 8 = octane The location of the hydroxyl group on the carbon chain is indicated by placing the appropriate number just before the ol ending. Consider the following examples of some simple straight-chain alcohols. H O H H OH H H H H C C C C C C C H H H H H OH is on the second carbon from the left pentan-2-ol OH is on the fourth carbon in the chain heptan-4-ol Remember that the numbering can go from left-to-right or right-to-left, depending on the location of the hydroxyl group. The correct name will have the lowest possible numbering. H H H H O OH H H H H OH is on the first carbon if you number from the right pentan-1-ol OH is on the second carbon if you number from the right hexan-2-ol Use the same logic to name the following alcohol molecules. H H OH H H Alcohol name:

3 Sophomore Chemistry Block 042: Organic Chemistry Naming Alcohols Page 3 H OH H Alcohol name: H H OH H H H Alcohol name: H H H OH H Alcohol name: H C C C C H H H H H H H H OH Alcohol name: H C C C C H H H H H H H O H Alcohol name:

4 Sophomore Chemistry Block 042: Organic Chemistry Naming Alcohols Page 4 When there are alkyl substituents (other carbon groups) attached to an alcohol, they are named in the same way that alkyl substituents are named on non-alcoholic molecules. A prefix (meth-, eth-, prop-) is chosen for the substituent based on its length. A yl is added to the prefix. Therefore, a substituent that is one carbon in length is methyl, a substituent that is two carbons in length is ethyl, and so on. Also, if there are two methyl attachments, it is called dimethyl. Three methyl attachments would be called trimethyl. As you would expect, the locations of the carbon attachments must also be numbered. However, the numbering is always based on the location of the alcoholic OH group. The alcohol functional group has higher priority than the alkyl substituents, and the numbering has to reflect this. Consider the following examples: H H H OH H H CH 3 H Alcohol name: 7-methyloctan-4-ol The OH is on the fourth carbon in the chain. Therefore, the base name of the alcohol is octan-4-ol. The numbering is based on the location of the alcoholic OH group, and continues through the chain. The methyl attachment is on the seventh carbon in the chain. Thus, the name of the entire molecule is 7-methyloctan-4-ol. H CH 3 H H OH Alcohol name: 4-methylpentan-1-ol The OH is on the first carbon if you number from the right. The base alcohol is therefore called pentan-1-ol. That numbering continues through the chain, from right to left. Therefore, the methyl attachment is on the fourth carbon in the chain. Thus, the name of the entire molecule is 4-methylpentan-1-ol. H OH CH 3 CH 3 H H Alcohol name: H H CH 3 H H H 3,3,4-trimethylhexan-2-ol The OH is attached to the second carbon on a chain of six. Thus, the base alcohol name is hexan-2-ol. The numbering continues from left to right. There are three methyl groups, attached on carbons 3, 3, and 4. Therefore, the name of the entire molecule is 3,3,4-trimethylhexan-2-ol.

5 Sophomore Chemistry Block 042: Organic Chemistry Naming Alcohols Page 5 Use the same logic to name the following molecules: H OH H CH 3 H H Alcohol name: H H H CH 3 H H H H OH H H Alcohol name: H H CH 3 H H H CH 3 H OH H Alcohol name: H OH H Alcohol name: H C C C H H CH 3 H OH H CH 3 H H H Alcohol name: H H CH 3 H H H