Question

IUPAC names of alcohols are derived by changing the suffix of the parent alkane from \(e\) to \(-\alpha\). \- The chain is numbered from the direction that gives the carbon bearing the - OH the lower number. \- In compounds containing other functional groups of higher precedence, the presence of - OH is indicated by the porefix hvdroxy-

Short answer

Answer: In naming alcohols using IUPAC nomenclature, first, replace the suffix 'e' of the parent alkane with '-ol'. Then, number the carbon chain so that the carbon bearing the -OH group gets the lower number. In the presence of other functional groups having higher precedence in naming, use the prefix 'hydroxy-' to indicate the -OH group, and assign numbering according to the higher priority functional groups.

Step-by-step solution

Replacing the suffix of parent alkane with \(-\alpha\)

When naming alcohols using IUPAC nomenclature, replace the suffix 'e' of the parent alkane with '-ol'. For example, if the parent alkane is methane, the alcohol derived from it will be named methanol.

Numbering the carbon chain

To number the carbon chain, the chain is numbered in such a way that the carbon bearing the -OH group gets the lower number. For example, in the alcohol derived from propane, if the -OH group is present on the first carbon, it is named as 1-propanol. If the -OH group is on the second carbon, it is named as 2-propanol.

Using the prefix 'hydroxy-'

In cases where the alcohol molecule contains other functional groups having higher precedence in naming (such as carboxylic acids, aldehydes, etc.), the presence of the -OH group is indicated by using the prefix 'hydroxy-'. Numbering should be assigned to ensure that other higher priority functional groups get the lowest numbers. For example, if there is an alcohol group and a carboxyl group in a molecule, we name it as 'hydroxy-(alkane)carboxylic acid', with numbering assigned according to the functional groups' priority.

Key concepts

Alkane to Alcohol Suffix Change

When converting the name of an alkane to an alcohol in IUPAC nomenclature, a simple yet crucial modification is made. The ending 'e' of the parent alkane's name is replaced with the suffix '-ol'. This indicates the presence of a hydroxyl (-OH) functional group in the structure of the molecule, transforming the hydrocarbon into an alcohol.

For instance, consider the simplest alkane, methane. By replacing the 'e' with '-ol', we obtain 'methanol', the name of the alcohol form. Ethane becomes ethanol, and so on. This rule applies no matter the length or complexity of the carbon chain; the terminal 'e' of the alkane name consistently changes to '-ol' to signal the presence of an alcohol group.

Numbering Carbon Chain in Alcohols

Correctly numbering the carbon chain in an alcohol is critical for specifying the position of the hydroxyl group. The carbon atoms in the chain are numbered starting from the end nearest to the -OH group. This ensures that the -OH group receives the lowest possible number in the alcohol's name, which is essential for unambiguous identification.

For example, if you have a three-carbon alkane, propane, and the -OH group is on the first carbon, the correct IUPAC name is 1-propanol. If the -OH is on the second carbon, the name becomes 2-propanol. This numbering system ensures clarity, especially for alcohols with longer carbon chains, where multiple hydroxyl groups may be present, or the position of the group can significantly affect the molecule's properties.

Hydroxy- Prefix in Functional Group Naming

In cases where an alcohol contains other functional groups that have precedence over the hydroxyl in IUPAC nomenclature, we use the prefix 'hydroxy-' to denote the presence of the -OH group. This is common in multifunctional compounds, where the -OH group is not the primary characteristic being named.

For example, if a molecule contains both an alcohol and a carboxylic acid group, the acid takes naming priority. Here, the name will reflect the acid as the parent structure, such as in 'hydroxyethanoic acid', where the 'hydroxy-' prefix indicates the presence of the alcohol group. Numbering of the compound gives the lowest possible numbers to the highest priority groups, ensuring that the name precisely reflects the structure of the molecule.