Question

Write the IUPAC names of the following ketones and aldehydes. Wherever possible, give also common names. (i) \(\mathrm{CH}_{3} \mathrm{CO}\left(\mathrm{CH}_{2}\right)_{4} \mathrm{CH}_{3}\) (ii) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHBrCH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CHO}\) (iii) \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{5} \mathrm{CHO}\) (iv) \(\mathrm{Ph}-\mathrm{CH}=\mathrm{CH}-\mathrm{CHO}\) (v) O=CC1CCCC1 (vi) PhCOPh

Short answer

(i) 2-Hexanone; (ii) 5-Methyl-3-bromohexanal; (iii) Hexanal; (iv) Cinnamaldehyde; (v) Cyclohexanone; (vi) Benzophenone.

Step-by-step solution

Identify the parent chain and functional group

For each compound, first, identify the longest carbon chain that includes the functional group (ketone or aldehyde). In the case of aldehydes, the carbonyl carbon is always at the end, while ketones have the carbonyl group within the chain.

Compound (i): Assigning IUPAC name

The longest chain is 6 carbons. The compound is a ketone, and with the carbonyl at C-2, the parent name is hexanone. Therefore, the IUPAC name is 2-hexanone. The common name is methyl n-butyl ketone.

Compound (ii): Determine substituents and numbering

The longest chain is 6 carbons with the aldehyde group at the end. The substituents are a bromine (Br) and a methyl group (CH₃). Assign locants lowest numbers: bromine at C-3 and methyl at C-5. IUPAC name is 5-methyl-3-bromohexanal.

Compound (iii): Naming a straight chain aldehyde

The longest chain consists of 6 carbons, ending in an aldehyde. The IUPAC name for this compound is hexanal. Common name is caproaldehyde.

Compound (iv): Naming conjugated aldehyde with a phenyl group

The aldehyde is attached to a phenyl group through a 2-carbon chain. This is a conjugated system due to the C=C bond. The IUPAC name is cinnamaldehyde.

Compound (v): Cyclohexanone identification

The structure provided is a cyclohexanone, where the carbonyl group is bonded to a cyclohexane ring. The IUPAC name is cyclohexanone.

Compound (vi): Naming diphenyl ketone

The compound is symmetrical with two phenyl groups attached to the carbonyl carbon. This gives us the IUPAC name benzophenone, which is also the common name.

Key concepts

Ketones

Ketones are a type of organic compound characterized by having a carbonyl group (1C=O) bonded to two carbon atoms. This group is always positioned somewhere within the carbon chain, distinguishing ketones from aldehydes. In IUPAC nomenclature, ketones are named by identifying the longest carbon chain that includes the carbonyl group, ensuring the carbonyl carbon gets the lowest possible number. For example, in the compound

• (i)
  60CH
  63CO(
  62CH
  62)
  64CH
  63

The carbonyl is at C-2, hence it is named "2-hexanone." Ketones often have common names based on the alkyl groups attached to the carbonyl carbon, such as methyl n-butyl ketone.
Ketones play a significant role in many biological processes and industrial applications, from solvents to hormone synthesis.

Aldehydes

Aldehydes are organic compounds that have a carbonyl group at the end of a carbon chain, bonded to at least one hydrogen atom. This structure can be easily identified since the carbonyl group is always terminal. In terms of IUPAC naming, the suffix '-al' is used, and the carbon in the carbonyl group usually counts as carbon number one. For instance:

• (ii)
  60CH
  63CH
  62CHBrCH
  62CH(
  63CH
  63)CHO

In this compound, the aldehyde group is at the end, with bromine and a methyl group as substituents. It's called "5-methyl-3-bromohexanal."
Another example is when only the carbon chain extends from the aldehyde such as in (iii), which is called "hexanal," with its common name being caproaldehyde.
Aldehydes are crucial in organic chemistry for reactions like oxidation and are building blocks in the synthesis of many compounds.

Organic Chemistry

Organic chemistry is the branch of chemistry that studies the structure, properties, composition, reactions, and synthesis of carbon-based compounds. This area of chemistry is foundational to a wide range of topics including biochemistry, materials science, and medicinal chemistry.
In the context of naming organic compounds, understanding the structure and functional groups present in a molecule is vital. For instance, in compound (iv)

• Ph-CH=CH-CHO (cinnamaldehyde),

It involves knowing about the conjugation of double bonds (C=C) within a phenyl group, which requires comprehension of hybridization and resonance in organic molecules.
Understanding these principles aids chemists in predicting reactions and designing new compounds.

Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties, influencing the behavior and reactivity of the molecule. They are the sites of chemical reactivity. In organic chemistry, identifying these groups is key to predicting the chemical behavior of organic compounds.
The carbonyl group is a central functional group in both ketones and aldehydes:

• In ketones, this group (
  61C=O) is bonded to two carbons.
• In aldehydes, it is bonded to at least one hydrogen, always terminal in the chain.

Other examples in the original exercise include the phenyl group (Ph) in benzophenone or diphenyl ketone (

• (vi) PhCOPh).

Each functional group affects the compound's polarity, solubility, and the type of reactions it can undergo, making it a critical aspect of organic chemistry.