Question

The olefin which on ozonolysis gives \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO}\) and \(\mathrm{CH}_{3} \mathrm{CHO}\) is (1) 1 -butene (2) 2 -butene (3) 1-pentene (4) 2-pentenc

Short answer

The olefin is 2-pentene.

Step-by-step solution

- Understand the ozonolysis products

The products of ozonolysis given are \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CHO}\) (propionaldehyde) and \(\mathrm{CH}_{3}\mathrm{CHO}\) (acetaldehyde). This means the double bond in the olefin splits and oxygen atoms are inserted.

- Determine the original structure

Ozonolysis splits a double bond in an olefin and forms carbonyl compounds. Propionaldehyde (3 carbons) and acetaldehyde (2 carbons) indicate the original double bond was between the second and third carbon atoms of a 5-carbon chain.

- Identify appropriate olefin

The olefin must be a 5-carbon chain with a double bond between the second and third carbon atoms, which corresponds to 2-pentene.

Key concepts

ozonolysis mechanism

Ozonolysis is a chemical reaction wherein an olefin (alkene) reacts with ozone \(\text{O}_3\). This process cleaves the double bond and transforms the alkene into carbonyl compounds, typically aldehydes or ketones. The mechanism begins with ozone attaching to the double bond, forming a molozonide intermediate. This unstable molecule quickly rearranges to form a more stable ozonide.
The ozonide can then be broken down further by reducing agents like zinc in acetic acid or dimethyl sulfide, yielding the final carbonyl compounds.
Ozonolysis is valuable for determining the position of double bonds in organic molecules and for synthesizing aldehydes and ketones from alkenes.

olefins

Olefins, also known as alkenes, are hydrocarbons containing at least one carbon-carbon double bond. The general formula for alkenes is \(\text{C}_n\text{H}_{2n}\).
They are unsaturated hydrocarbons, meaning they have fewer hydrogen atoms attached to their carbon skeleton compared to alkanes. This double bond can participate in a variety of chemical reactions, including ozonolysis.
In our problem, we're dealing with 2-pentene, an olefin with five carbon atoms and a double bond between the second and third carbon atoms. This double bond is crucial for the formation of the carbonyl compounds obtained from ozonolysis.

carbonyl compounds

Carbonyl compounds contain a carbon-oxygen double bond. Two primary types are aldehydes and ketones.

• Aldehydes have the structure \(\text{R}-\text{CHO}\), where \(\text{R}\) is a hydrocarbon group or hydrogen.
• Ketones have the structure \(\text{R}-\text{CO}-\text{R'}\), where \(\text{R}\) and \(\text{R'}\) are hydrocarbon groups.

In our case, ozonolysis produces two aldehydes: propionaldehyde (\(\text{CH}_3\text{CH}_2\text{CHO}\)) and acetaldehyde (\(\text{CH}_3\text{CHO}\)).
These compounds result from the cleavage of a double bond in 2-pentene.

organic reaction pathways

Organic reaction pathways refer to the series of steps and intermediate stages leading from reactants to products in a chemical reaction. Each pathway involves various possible transitions and intermediates.
For ozonolysis, the pathway involves several stages:

• Initial addition of ozone to the double bond, forming a molozonide.
• This intermediate rearranges into an ozonide.
• The ozonide then breaks down to produce carbonyl compounds.

Understanding these pathways helps predict product formation. For example, we used the ozonolysis pathway to deduce that 2-pentene must be the starting olefin to produce propionaldehyde and acetaldehyde as the final products.