Question

Draw the line structures and provide common names for the following ketones: (a) 1-Phenylpropanone (b) 2 -Methylpentan-3-one (c) \(1-\) Cyclohexyl- 3,3 -dimethylbutan-2-one

Short answer

(a) Desmethyl ketone, (b) Methyl sec-butyl ketone, (c) Cyclohexyl tert-butyl ketone.

Step-by-step solution

Understanding 1-Phenylpropanone

Start by identifying the components: 'phenyl' indicates a benzene ring is present; 'propanone' suggests a three-carbon ketone. The ketone’s carbonyl group (C=O) is on the first carbon after the 'phenyl'. Draw a benzene ring, and connect it to a three-carbon chain with the carbonyl on the first carbon: C6H5-C(=O)-CH2-CH3.

Identifying 2-Methylpentan-3-one Structure

Begin by breaking down the name: '2-methyl' indicates a methyl group (CH3) on the second carbon; 'pentan-3-one' means a five-carbon chain with a ketone group (C=O) on the third carbon. Draw a carbon skeleton: C5 (pentane), place CH3 at C2, and C=O at C3. Complete the structure as: CH3-CH(CH3)-C(=O)-CH2-CH3.

Breaking Down 1-Cyclohexyl-3,3-dimethylbutan-2-one

Divide the name: '1-cyclohexyl' indicates a cyclohexane (hexagonal ring of 6 carbons) attached to the main chain; '3,3-dimethylbutan-2-one' is a four-carbon chain with two methyl groups at C3 and a ketone at C2. The cyclohexane attaches at the first carbon. Sketch it as: C6H11-CH2-C(=O)-CH(CH3)2.

Drawing Line Structures

For each compound, convert the carbon skeleton and its substituents into line structures. (a) Draw a line from the benzene ring, representing a three-carbon chain with a ketone. (b) Create a line structure for a five-carbon chain with a branching methyl at C2 and a ketone at C3. (c) Draw the cyclohexyl group attached to a carbon chain with branching dimethyls and a ketone at the second carbon.

Providing Common Names

Use common names for each compound based on its structure. (a) 1-Phenylpropanone's common name is 'Desmethyl ketone'. (b) 2-Methylpentan-3-one's common name is 'Methyl sec-butyl ketone'. (c) 1-Cyclohexyl-3,3-dimethylbutan-2-one's common name could be 'Cyclohexyl tert-butyl ketone', highlighting its bulky groups.

Key concepts

Chemical Nomenclature

Chemical nomenclature is a systematic way of naming chemical substances. In organic chemistry, this process is guided by the International Union of Pure and Applied Chemistry (IUPAC) rules. These rules help ensure that each chemical compound has a unique name, making it easier for chemists to communicate.

When naming ketones, the suffix "-one" is used. This suffix indicates the presence of a carbonyl group (C=O) in the compound. The position of the carbonyl group affects the ketone's name. For instance:

• In "1-phenylpropanone," "1-" suggests that the carbonyl group is attached to the first carbon, with "phenyl" indicating the presence of a benzene ring.
• "2-Methylpentan-3-one" signifies a five-carbon chain with a methyl group at the second carbon and a ketone at the third.

The IUPAC name also reveals the compound's structure, helping chemists draw and understand complex molecules.

Organic Chemistry

Organic chemistry is the study of carbon-containing compounds and their properties, structures, and reactions. The versatility of carbon allows it to form a vast diversity of compounds, making organic chemistry a broad and diverse field.

In the context of ketones:

• Carbon forms the backbone of the molecules often seen as chains or rings in ketones. For example, the benzene ring in 1-Phenylpropanone is a classic feature in organic chemistry.
• The presence of the carbonyl group (C=O) in ketones is crucial as it defines their reactivity and interactions with other compounds.

Organic chemistry principles guide the synthesis and analysis of ketones, providing insights into their utilization in various chemical reactions and applications.

Functional Groups

Functional groups are specific groups of atoms within molecules that dictate how the compounds react. In organic chemistry, they are the key players in determining the characteristics and reactivity of molecules.

For ketones, the key functional group is the carbonyl group (C=O). This group:

• Is found in the middle of the carbon chain, as opposed to aldehydes, where it's at the end.
• Influences the compound's polarity, affecting solubility and boiling points.
• Acts as a site for chemical reactions, such as nucleophilic additions.

The type of functional groups present in a molecule, such as the carbonyl in ketones, is essential in predicting the behavior and transformation of the molecule in chemical reactions.