Question

Which of the following compounds are ketones? (a) \(\mathrm{CH}_{3} \mathrm{CHO}\) (b) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\) (d) \(\mathrm{HCHO}\)

Short answer

Only compounds (b) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) and (c) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\) are ketones.

Step-by-step solution

Analyzing Compound (a) \(\mathrm{CH}_{3} \mathrm{CHO}\)

Here, the carbonyl group (C=O) is at the end of the chain so it's an aldehyde, not a ketone. Therefore, compound (a) is not a ketone.

Analyzing Compound (b) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\)

In this compound, the carbonyl group (C=O) is positioned between two carbon atoms (CH3 on either side). According to the definition, this is a ketone. Therefore, compound (b) is a ketone.

Analyzing Compound (c) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\)

Similarly to compound (b), the carbonyl group in compound (c) is also placed between two carbon atoms. Hence, compound (c) is also a ketone.

Analyzing Compound (d) \(\mathrm{HCHO}\)

There is only one carbon atom in this compound, and the carbonyl group is at the end of the chain meaning this compound is an aldehyde, not a ketone. Therefore, compound (d) is not a ketone.

Key concepts

Understanding the Carbonyl Group

The carbonyl group is a defining feature in many organic compounds and plays a pivotal role in determining their chemical properties. This group consists of a carbon atom double-bonded to an oxygen atom, represented as \(\text{C=O}\). The presence of this double bond makes the carbonyl group highly reactive and involved in various chemical reactions.
Understanding its structure is essential because it influences how the compound behaves chemically. It's commonly found in two major types of compounds: ketones and aldehydes. In simple terms:

• Ketones have the carbonyl group in the middle of the carbon chain.
• Aldehydes have the carbonyl group at the end of the carbon chain.

Identifying the positioning of the carbonyl group is crucial in recognizing whether an organic compound is a ketone or an aldehyde. This knowledge aids in predicting the reactivity and interactions of the compound.

What are Aldehydes?

Aldehydes are a class of organic compounds that contain a carbonyl group at the end of the carbon chain. This positioning is distinctive because the carbon of the carbonyl group is also bonded to at least one hydrogen atom. In chemical notation, aldehydes can be represented as \(\text{RCHO}\), where "R" stands for any carbon-containing group. Common examples include and acetaldehyde \(\text{CH}_3\text{CHO}\).
These compounds are recognized for their distinct fragrances and are often found in natural sources like essential oils and flavorings. Aldehydes also serve as vital intermediates in synthetic chemistry, aiding in the formation of various complex molecules. This makes them crucial in both industrial applications and biological processes, contributing significantly to numerous chemical reactions.

Introduction to Organic Compounds

Organic compounds are primarily made of carbon atoms and form the basis of all life on Earth. They're characterized by carbon atoms forming stable bonds with hydrogen, oxygen, nitrogen, and other elements. This versatility allows for numerous structures and functions, facilitating the vast diversity seen in organic chemistry.
Organic compounds are classified into groups based on functional groups like alcohols, acids, ketones, and aldehydes. Each group has distinct chemical properties and reactivity. For example:

• Alcohols contain hydroxyl groups \(\text{-OH}\).
• Acids feature carboxyl groups \(\text{-COOH}\).
• Ketones include carbonyl groups \(\text{C=O}\), but unlike aldehydes, these are surrounded by carbon atoms on both sides.

This classification is fundamental for understanding and predicting the behavior of organic compounds in chemical reactions, providing a framework for studying and utilizing these molecules efficiently.