Organic Chemistry III: Aldehydes, Ketones, and Carboxylic Acids - SS2 Chemistry Past Questions and Answers - page 2

Nomenclature rules for aldehydes and ketones follow the general principles of organic compound naming established by the International Union of Pure and Applied Chemistry (IUPAC). The key nomenclature rules for aldehydes and ketones include:

1.    Identify the parent chain: The parent chain is the longest continuous carbon chain containing the carbonyl group (C=O).

2.    Number the carbon atoms: Assign numbers to the carbon atoms in the parent chain to locate the position of the carbonyl group.

3.    Name the substituents: Substituents are groups or atoms attached to the parent chain. They are named as prefixes, indicating the type and number of substituents present.

4.    Indicate the carbonyl group: The carbonyl group is named as a suffix (-al for aldehydes and -one for ketones) and is assigned the lowest possible number to maintain the lowest possible numbering sequence.

5.    Use proper punctuation and word order: Commas, hyphens, and proper word order are used to ensure clarity in the compound's name.

Systematic naming is important as it allows chemists to convey the structure and composition of aldehydes and ketones accurately. It provides a common language that facilitates communication and ensures clarity in chemical discussions and literature. Examples of nomenclature application for aldehydes and ketones include:

●     Methanal (CH2O): The parent chain contains one carbon atom, and the compound is named methanal.

2-Propanone (C3H6O): The parent chain is a three-carbon chain, and the carbon

Aldehydes and ketones are organic compounds that contain a carbonyl group (C=O). They exhibit distinct properties and characteristics compared to other functional groups. Some key features of aldehydes and ketones include:

1.    Boiling Points: Aldehydes and ketones generally have lower boiling points compared to alcohols and carboxylic acids of similar molecular weight. This is because aldehydes and ketones do not form intermolecular hydrogen bonds like alcohols and carboxylic acids do.

2.    Solubility: Aldehydes and ketones are soluble in organic solvents but have limited solubility in water. Their solubility decreases with increasing carbon chain length.

3.    Reactivity: Aldehydes are more reactive than ketones due to the presence of a hydrogen atom attached to the carbonyl carbon. The reactivity of aldehydes and ketones is mainly focused on the carbonyl group, which can undergo various reactions, including nucleophilic addition, oxidation, and reduction.

4.    Oxidation: Aldehydes can be oxidised to form carboxylic acids. Ketones, on the other hand, are resistant to oxidation under normal conditions.

Examples illustrating the properties of aldehydes and ketones include the boiling point difference between formaldehyde (CH2O) and propanone (C3H6O), where formaldehyde has a lower boiling point due to its smaller size. Additionally, the reactivity difference can be observed in the oxidation of ethanol (CH3CH2OH) to acetaldehyde (CH3CHO), which is further oxidised to acetic acid (CH3COOH).

Addition of oxygen to a compound