Noah Vinter
Alcohols are organic compounds with a hydroxyl (OH) functional group on an aliphatic carbon atom. The presence of other substituents in alcohol is indicated by their names and numerical positions, with the hydroxyl group taking the lowest possible number. The generic IUPAC name for alcohol is alkanols, and they are represented in reactions by the general formula R-OH. Alcohols can be classified as primary, secondary, or tertiary, depending on the number of alkyl substituents attached to the carbon bonded to the OH group. The common system of naming is often used when the alcohol only contains a few carbons. In this system, the hydroxyl group is treated as if it is attached to a single substituent, with the word alcohol added to the end of the name.
| Characteristics | Values |
|---|---|
| Generic IUPAC name for alcohol | Alkanols |
| General formula | R-OH or ROH |
| Longest continuous chain | The hydroxyl group is directly attached |
| Parent alkane name | Ends with -ol |
| Locant | Indicates the position of the hydroxyl group |
| Cyclic alcohol | Ring is numbered clockwise or counterclockwise |
| Polyhydroxy alcohols | Suffixes: -diol and -triol |
| Classification | Primary, secondary, or tertiary |
| Carbon atom in tertiary alcohol | Attached to three other carbon atoms |
| General formula for tertiary alcohol | R3COH |
| Ethers | Compounds containing the functional group –O– |
| Common name for ethers | Two branches connected to oxygen atom, followed by "ether" |
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What You'll Learn
The hydroxyl group
The generic IUPAC name for alcohol is alkanols, and they are represented in reactions by the general formula R-OH. When giving alcohol IUPAC substitutive names, the following procedure should be followed:
- Select the longest continuous chain to which the hydroxyl group is directly attached.
- Change the name of the alkane corresponding to the chain by dropping the final -e and adding the suffix -ol.
- Number the longest continuous carbon chain to give the carbon atom bearing the hydroxyl group the lowest number.
- Indicate the position of the hydroxyl group by using this number as a locant.
- Indicate the position of any other substituents as a prefix by using the numbers corresponding to their positions along the carbon chain as locants.
For mono-functional alcohols, a common naming system consists of naming the alkyl group followed by the word "alcohol." Alcohols may also be classified as primary, secondary, or tertiary, in the same manner as alkyl halides. When the hydroxyl functional group is present with a function of higher nomenclature priority, it must be cited and located by the prefix "hydroxy" and an appropriate number. For example, lactic acid has the IUPAC name 2-hydroxypropanoic acid.
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The position of the OH group
When naming an alcohol, the position of the OH group is crucial. The OH group, also known as the hydroxyl group, is the functional group of all alcohols and is represented by the formula ROH, where R is an alkyl group.
The International Union of Pure and Applied Chemistry (IUPAC) has established a set of rules for naming alcohols, which involve indicating the position of the hydroxyl group. The first step is to identify the longest continuous chain (LCC) of carbon atoms containing the OH group. This chain serves as the parent compound, and the alcohol's name is derived from it. The chain is then numbered, starting from the end closest to the OH group, giving it the lowest possible number. This number is used as a locant to indicate the position of the OH group in the alcohol's name.
For example, let's consider the alcohol with the formula CH3CH2OH, which is known as ethanol. The longest continuous chain containing the OH group is two carbon atoms long (CH3-CH2). The chain is numbered from the end closest to the OH group, so the OH group is at position 2. Therefore, the name of this alcohol is ethyl-2-ol, indicating that the hydroxyl group is on the second carbon atom in the chain.
Additionally, when naming cyclic alcohols, the carbon atom bearing the OH group is typically designated as C1, but the number "1" is usually omitted from the name. For example, the cyclic alcohol with the formula C3H5OH is named cyclopropanol, without specifying the position of the OH group.
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The common naming system
Alcohols are organic compounds with a hydroxyl (OH) functional group on an aliphatic carbon atom. The common system of naming is often used when the alcohol only contains a few carbon atoms. In this system, the hydroxyl group (-OH) is treated as if it is attached to a single substituent, with the word "alcohol" added at the end (Name of the substituent + Alcohol). For example, ethyl alcohol, or ethanol, is CH3CH2OH. Some simple alcohols are given their own generic names, such as ethylene glycol or glycerol.
The generic IUPAC name for alcohol is alkanols, and they are represented in reactions by the general formula R-OH. The presence of other substituents in alcohol is indicated by their names and numerical positions, always keeping the lowest possible number for the hydroxyl group. To give an alcohol its IUPAC substitutive name, follow this procedure:
- Select the longest continuous chain to which the hydroxyl group is directly attached.
- Change the name of the alkane corresponding to the chain by dropping the final -e and adding the suffix -ol.
- Number the longest continuous carbon chain so as to give the carbon atom bearing the hydroxyl group the lower number.
- Indicate the position of the hydroxyl group by using this number as a locant.
- Indicate the position of another substituent as a prefix by using the numbers corresponding to their positions along the carbon chain as locants.
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The IUPAC naming system
The generic IUPAC name for alcohol is alkanols, and they are represented in reactions by the general formula R-OH. The presence of other substituents in alcohol is indicated by their names and numerical positions, with the hydroxyl group (OH) receiving the lowest number possible. To name an alcohol with an oxygen substituent using the IUPAC system, the following steps should be followed:
Firstly, select the longest continuous chain of carbon atoms to which the hydroxyl group is directly attached. This chain will serve as the basis for the name of the alcohol. Then, change the name of the alkane corresponding to the chain by dropping the final "-e" and adding the suffix "-ol". This suffix indicates the presence of an alcohol functional group.
Number the carbon atoms in the selected chain so that the carbon atom bearing the hydroxyl group receives the lowest number. This number will be used as a locant to indicate the position of the hydroxyl group. If there are other substituents present, their positions can be indicated as prefixes by using the numbers corresponding to their positions along the carbon chain as locants. It is important to ensure that the hydroxyl group always receives the lowest possible number among the substituents.
Additionally, if the OH group is connected to a chiral center, the absolute configuration should be included at the beginning of the name. When naming cyclic alcohols, start numbering the ring from the carbon atom connected to the OH group. This rule typically assigns the OH group to C1, so the "1" may be omitted from the name. When other groups are present on the ring, it is numbered clockwise or counterclockwise, depending on which direction gives the next substituent a lower number.
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Primary, secondary, tertiary alcohols
Alcohols are classified as primary, secondary, or tertiary. This classification is based on how the -OH group is positioned on the chain of carbon atoms. The generic IUPAC name for alcohol is alkanols, and they are represented in reactions by the general formula R-OH. The presence of other substituents in alcohol is indicated by their names and numerical positions, always keeping the lowest possible number for the hydroxyl group.
In a primary (1°) alcohol, the carbon atom that carries the -OH group is attached to only one alkyl group. Examples of primary alcohols include methanol (propanol) and ethanol. The complexity of the alkyl chain is unrelated to the classification of any alcohol considered primary. Methanol, CH3OH, is counted as a primary alcohol, even though there are no alkyl groups attached to the -OH carbon atom.
In a secondary (2°) alcohol, the carbon atom with the -OH group attached is directly joined to two alkyl groups, which may be identical or different in structure.
Tertiary (3°) alcohols feature a hydroxyl group attached to the carbon atom, which is connected to three alkyl groups. The presence of the -OH group in tertiary alcohols allows them to form hydrogen bonds with neighbouring atoms. Examples of tertiary alcohols include those with three alkyl groups attached to the -OH carbon atom.
When naming alcohols, the following procedure should be followed:
- Select the longest continuous chain to which the hydroxyl group is directly attached.
- Change the name of the alkane corresponding to the chain by dropping the final -e and adding the suffix -ol.
- Number the longest continuous carbon chain to give the carbon atom bearing the hydroxyl group the lower number.
- Indicate the position of the hydroxyl group by using this number as a locant.
- Indicate the position of another substituent as a prefix by using the numbers corresponding to their positions along the carbon chain as locants.
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