Question

Draw structures of the following compounds. \(\begin{array}{ll}{\text { a. butanone }} & {\text { c. hexanoic acid }} \\\ {\text { b. propanal }} & {\text { d. heptanoamide }}\end{array}\)

Short answer

The structures of the given compounds are as follows: a. Butanone: \(\mathrm{CH_3 - CH_2 - C = O \ - CH_3}\) b. Propanal: \(\mathrm{CH_3 - CH_2 - CHO}\) c. Hexanoic acid: \(\mathrm{CH_3 - CH_2 - CH_2 - CH_2 - CH_2 - COOH}\) d. Heptanoamide: \(\mathrm{CH_3 - CH_2 - CH_2 - CH_2 - CH_2 - CH_2 - CONH_2}\)

Step-by-step solution

a. Butanone

Butanone contains 4 carbon atoms, and as a ketone, also possesses a carbonyl group (C=O) in between two carbon atoms. The structure of butanone can be drawn as follows: \[ \mathrm{CH_3 - CH_2 - C = O \ - CH_3} \]

b. Propanal

Propanal contains 3 carbon atoms, and as an aldehyde, it has a carbonyl group (C=O) at the terminal position. The structure of propanal can be drawn as follows: \[ \mathrm{CH_3 - CH_2 - CHO} \]

c. Hexanoic acid

Hexanoic acid contains 6 carbon atoms, and as a carboxylic acid, it has a carboxyl group (-COOH) at the terminal position. The structure of hexanoic acid can be drawn as follows: \[ \mathrm{CH_3 - CH_2 - CH_2 - CH_2 - CH_2 - COOH} \]

d. Heptanoamide

Heptanoamide contains 7 carbon atoms, and as an amide, it has an amide group (-CONH2) at the terminal position. The structure of heptanoamide can be drawn as follows: \[ \mathrm{CH_3 - CH_2 - CH_2 - CH_2 - CH_2 - CH_2 - CONH_2} \]

Key concepts

Butanone Structure

Butanone, also known as methyl ethyl ketone (MEK), is an organic compound with a relatively simple structure. It is identified by its four-carbon backbone with a carbonyl group (C=O) located at the second carbon atom. This positioning makes it a ketone, as the carbonyl group is not at the end but rather flanked by carbon atoms.

The structure of butanone is represented by the molecular formula \( C_{4}H_{8}O \) which translates into a written structure as \( CH_{3} - CH_{2} - C = O - CH_{3} \). It is important for students to recognize the \( C = O \) group characterizing the ketone functional group, and understand its placement within the carbon chain. The simplicity of butanone’s structure provides a great learning foundation for recognizing ketone compounds in organic chemistry.

Propanal Structure

Propanal is a three-carbon aldehyde, distinguishable by its \( C_{3}H_{6}O \) molecular formula. The carbonyl group (C=O) in aldehydes such as propanal is located at one of the terminal ends of the carbon chain, positioning it as the first carbon atom in the structure.

Its structure is illustrated as \( CH_{3} - CH_{2} - CHO \), showing clearly the terminal \( CHO \) functional group. This is a critical aspect because it defines the substance as an aldehyde. Understanding the specific location of this group is essential for identifying and differentiating aldehydes from other functional groups in organic chemistry.

Hexanoic Acid Structure

Hexanoic acid falls within the category of carboxylic acids, featuring a six-carbon chain and a carboxyl group \( -COOH \) at one end. It is often written out based on its molecular formula \( C_{6}H_{12}O_{2} \) and has the structural representation of \( CH_{3} - (CH_{2})_{4} - COOH \).

The \( -(CH_{2})_{4}- \) indicates a repetition of the \( CH_{2} \) unit four times in the chain, which is a convenient notation for a longer carbon chain. Recognizing the carboxyl group with the acidic hydrogen (\( -OH \) bonded to the carbonyl \( C = O \) group) is pivotal for students to accurately identify carboxylic acids from other organic compounds.

Heptanoamide Structure

Heptanoamide pertains to the class of amides and its structure is indicated by its seven-carbon framework, with an amide group \( -CONH_{2} \) at the terminus. Its structural formula is usually written as \( CH_{3} - (CH_{2})_{5} - CONH_{2} \), derived from its molecular formula \( C_{7}H_{15}NO \).

The repeating five \( CH_{2} \) units between the initial \( CH_{3} \) and the final amide group are summarized as \( (CH_{2})_{5} \), whereas the placement of the \( -CONH_{2} \) group at the end of the chain is a distinctive feature for amides. By recognizing these structural details, students can differentiate amides from other functional groups and understand the nature of amide compounds in organic chemistry.