Question

Write the structural formula of an aldehyde that is structural isomer of acetone.

Short answer

Propanal (\(CH_3CH_2CHO\)) is a structural isomer of acetone.

Step-by-step solution

Understand the Structure of Acetone

Acetone is a simple ketone with the chemical formula \(C_3H_6O\). Its structure consists of a central carbonyl group (C=O) with a methyl group (CH₃) attached on either side, forming the structure: \(CH_3COCH_3\).

Identify the Need for a Structural Isomer

A structural isomer of acetone must have the same molecular formula, \(C_3H_6O\), but with a different connectivity of atoms, specifically forming an aldehyde rather than a ketone.

Write the Aldehyde Structure

In an aldehyde, the carbonyl group (C=O) is located at the end of the carbon chain. To make a structural isomer of acetone in the form of an aldehyde, place the carbonyl group at the terminal position with two carbon groups bonded. Thus, the structure is: \(CH_3CH_2CHO\) (propanal).

Verify the Isomerism

Check that both acetone (\(CH_3COCH_3\)) and propanal (\(CH_3CH_2CHO\)) have the same molecular formula (\(C_3H_6O\)) but their structural arrangements differ, confirming they are structural isomers.

Key concepts

Aldehydes

Aldehydes are organic compounds characterized by the presence of a carbonyl group at the end of a carbon chain. This carbonyl group consists of a carbon atom double-bonded to an oxygen atom. In aldehydes, the carbonyl group is bonded to at least one hydrogen atom and another carbon-containing group. This unique position distinguishes aldehydes from other carbonyl-containing compounds.

Some key features of aldehydes include:

• They usually have a pleasant or fruity smell.
• The general formula for aldehydes is RCHO, where R can be any alkyl or aryl group.
• Their reactivity is due to the highly polar nature of the carbonyl group, making them easily involved in various chemical reactions.

In structural isomerism, aldehydes can have the same molecular formula as other compounds like ketones, but differ in the position of the carbonyl group, resulting in different properties.

Ketones

Ketones are a type of organic compound belonging to the carbonyl group family, where the carbonyl group is situated between two carbon atoms. This internal position of the carbonyl group differentiates ketones from aldehydes.

Exploring ketones further, we find:

• The general structure of ketones is denoted as RCOR', where R and R' represent hydrocarbon chains or rings.
• Ketones have a variety of fragrances and are often found in sugars and hormones.
• They are typically less reactive than aldehydes due to the surrounding carbon groups providing stabilizing effects.

The differing structural setups between ketones and aldehydes, despite having identical molecular formulas, give rise to their classification as structural isomers.

Carbonyl Group

The carbonyl group is a fundamental functional group in organic chemistry, consisting of a carbon atom double-bonded to an oxygen atom (C=O). Its presence is the defining feature of carbonyl-containing compounds such as aldehydes, ketones, carboxylic acids, and esters.

The carbonyl group is significant because:

• It is highly polar, making compounds containing them quite reactive.
• The polar nature of the carbon-oxygen bond allows carbonyl groups to participate in various kinds of chemical reactions, like nucleophilic addition.
• This group influences boiling points and solubility because of its strong dipole moment.

Understanding where the carbonyl group is located in a molecule helps in naming, identifying types of compounds, and determining their possible reactions.

Molecular Formula

A molecular formula represents the actual number of atoms of each element in a molecule. It gives a simple snapshot of the compound's composition but does not show the arrangement of atoms.

Consider these aspects of molecular formulas:

• It is crucial in identifying structural isomers, as they have the same molecular formula but different structures.
• The formula can be derived from empirical formulas and provides insight into the larger molecule's potential structure.
• Molecular formulas are essential in chemical equations and calculations to ensure the conservation of mass.

By analyzing molecular formulas, chemists can predict and deduce potential isomers, like converting the formula for acetone to form an aldehyde, employing the same set of atoms.