Question

Name the following compounds according to IUPAC system of nomenclature: (i) \(\mathrm{CH}_{3} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CHO}\) (ii) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}\left(\mathrm{C}_{2} \mathrm{H}_{5}\right) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl}\) (iii) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCHO}\) (iv) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COCH}_{3}\) (v) \(\mathrm{CH}_{3} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{COCH}_{3}\) (vi) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2} \mathrm{COOH}\) (vii) \(\mathrm{OHCC}_{6} \mathrm{H}_{4}\) CHO \(-p\)

Short answer

(i) 2-methylpentanal, (ii) 6-chloro-4-ethylhexan-3-one, (iii) but-2-enal, (iv) pentane-2,4-dione, (v) 4,4-dimethylpentan-2-one, (vi) 2,2-dimethylpentanoic acid, (vii) para-phthalaldehyde or 1,4-benzenedicarbaldehyde.

Step-by-step solution

Identify Functional Groups (i)

The compound is \(\mathrm{CH}_{3} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CHO}\). It contains an aldehyde group (\(\mathrm{-CHO}\)), which is the primary functional group.

Longest Carbon Chain (i)

Determine the longest carbon chain containing the aldehyde group. Here, it is 5 carbons long, corresponding to 'pentane'.

Naming Alkyl Groups (i)

Identify alkyl groups: there's a methyl group on the second carbon.

Combine to Name (i)

Combine the parts: the name is 2-methylpentanal.

Identify Functional Groups (ii)

The compound \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}\left(\mathrm{C}_{2} \mathrm{H}_{5}\right) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl}\) contains a ketone (\(\mathrm{-CO-}\)) as the primary functional group.

Longest Carbon Chain (ii)

Find the longest chain containing the ketone: it has 6 carbons, for the base name 'hexanone'.

Naming Alkyl and Other Groups (ii)

Identify substituents: an ethyl group on the 4th carbon and a chlorine on the 6th carbon.

Combine to Name (ii)

Combine the parts: the name is 6-chloro-4-ethylhexan-3-one.

Identify Functional Groups (iii)

For \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCHO}\), there is an aldehyde and a double bond, prioritizing aldehyde as the main functional group.

Longest Carbon Chain (iii)

The chain is 4 carbons long, indicating 'butanal' as the base name.

Naming Unsaturated Bonds (iii)

Identify the double bond at carbon 2: it changes the name to 'but-2-enal'.

Combine to Name (iii)

Combine the parts: the name is but-2-enal.

Identify Functional Groups (iv)

In \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COCH}_{3}\), the ketone functional groups takes precedence.

Longest Carbon Chain (iv)

A 5-carbon chain contains both ketones, giving 'pentane' the base name.

Indicate Ketone Positions (iv)

Ketone groups are located on carbons 2 and 4.

Combine to Name (iv)

Combine the parts for the name: pentane-2,4-dione.

Identify Functional Groups (v)

\(\mathrm{CH}_{3} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{COCH}_{3}\) includes a ketone group.

Longest Carbon Chain (v)

The longest chain with the ketone is 6 carbons long, yielding 'hexanone'.

Naming Alkyl Groups (v)

Identify methyl groups on carbons 2 and 4.

Combine to Name (v)

The complete name is 4,4-dimethylpentan-2-one.

Identify Functional Groups (vi)

The compound \((\mathrm{CH}_{3})_{3} \mathrm{CCH}_{2} \mathrm{COOH}\) is carboxylic acid.

Longest Carbon Chain (vi)

The longest chain including \(\mathrm{COOH}\) is 5 carbons long, indicating 'pentanoic acid'.

Naming Alkyl Groups (vi)

A trimethyl group on carbon 2.

Combine to Name (vi)

The assembled name is 2,2-dimethylpentanoic acid.

Identify Functional Groups (vii)

For \(\mathrm{OHCC}_{6} \mathrm{H}_{4}\) CHO \(-p\), we have a dicarboxylic benzene compound.

Designate Positions of Functional Groups (vii)

It's a benzene ring with aldehyde groups in a para position.

Combine to Name (vii)

The full name is para-phthalaldehyde or 1,4-benzenedicarbaldehyde.

Key concepts

Aldehyde Naming

When it comes to naming aldehydes under IUPAC nomenclature, it's important to identify the presence of the aldehyde functional group, denoted as \( \text{-CHO} \). Aldehydes take priority over other functional groups in naming.

To find the name of the aldehyde compound, start with the following steps:

• Identify the longest continuous carbon chain that includes the \( \text{-CHO} \) group. This chain will determine the base name of the aldehyde.
• The name of the longest chain is derived from the parent alkane by replacing the ending '-e' with '-al'. For instance, if there are five carbons in the longest chain, the base name will be 'pentanal'.
• Note any substituents, such as alkyl groups, attached to the main chain, and their respective carbon positions.
• Construct the full name by combining these elements. For example, a methyl group on the second carbon of a five-carbon aldehyde would result in "2-methylpentanal."

The aldehyde group is always located at the end of the chain, hence it is always positioned as carbon 1, and is typically understood even if not explicitly numbered.

Ketone Naming

Ketones feature the \( \text{-CO-} \) functional group. Unlike aldehydes, ketones can appear in mid-chain positions, so identifying their location is key.

To name a ketone under IUPAC guidelines:

• Determine the longest continuous carbon chain the ketone function is integrated into. This will establish the base name.
• The parent name of the chain is altered from alkane '-e' to '-one'. If there are six carbons in the chain, the basic name would be 'hexanone'.
• Number the chain from the end nearest the ketone group to give it the lowest position number.
• Include the position numbers for the ketone groups. For example, a five-carbon chain with ketones at carbons 2 and 4 would be named 'pentane-2,4-dione'.
• Add any other substituents by name and position in front of the main structure name. For instance, '3-methylhexan-2-one' denotes a methyl group on carbon 3 of a hexane chain with the ketone group at the second carbon.

This methodology ensures the correct name by capturing all structural features of the compound.

Longest Carbon Chain

Finding the longest carbon chain in a compound is crucial, as it forms the backbone of the compound's name.

Follow these steps to ensure accurate identification:

• Examine the entire molecular structure to identify the longest continuous chain of carbon atoms, which is inclusive of all significant functional groups.
• When there's a choice of chains of equal length, select the one that includes the maximum number of functional groups.
• Once this chain is identified, it sets the primary backbone from which numbering should start, ensuring the lowest possible numbers are given to the functional groups or multiple bonds.
• This step is crucial in ensuring the base name of the compound accurately reflects its longest carbon chain, forming the foundation for further naming steps.

Ensuring the longest chain is rightly identified avoids errors and inaccuracies in determining the compound's complete name.

Functional Groups Identification

Identifying functional groups in a compound is a vital step in the nomenclature process.

Here's how to systematically identify them:

• Look for specific groups that are known to characterize certain functional types, such as \( \text{-CHO} \) for aldehydes, \( \text{-COOH} \) for carboxylic acids, or \( \text{-CO-} \) for ketones.
• Identify and prioritize these groups by their relative precedence when naming (e.g., carboxylic acids typically take precedence over ketones).
• Use these identified groups to direct the numbering of the carbon chain, ensuring functional groups receive the lowest possible numbers while considering other substituents.
• This identification allows for the structuring of the compound’s name in hierarchical order, ensuring all relevant structural features are accounted for in the full IUPAC name.

Recognizing these groups correctly is crucial for deciding how to apply further naming conventions within the IUPAC system.