Question

One molc of a symmetrical alkene on ozonolysis gives two moles of an aldehydc having molccular mass \(44 u\). The alkene is (1) cthenc (2) propene (3) 1-butenc (4) 2 -butenc

Short answer

2-butene

Step-by-step solution

Understand Ozonolysis

Ozonolysis is a reaction where an alkene breaks down when treated with ozone \((O_3)\). It typically results in the formation of two carbonyl compounds.

Determine the Product

According to the problem, ozonolysis of one mole of the alkene gives two moles of an aldehyde with molecular mass \(44 u\).

Identify the Aldehyde

A known aldehyde with molecular mass \(44 u\) is ethanol (acetaldehyde), which has a molecular formula of \((CH_3CHO)\).

Deduce the Alkene

Since two moles of ethanol \((CH_3CHO)\) are produced, the original alkene must be symmetrical. Each aldehyde fragment \((CH_3CHO)\) comes from splitting the alkene at the double bond.

Verify the Alkene

The symmetrical alkene that splits to form two moles of ethanol is \((CH_3CH=CH_3)\), which corresponds to 2-butene.

Key concepts

alkene reaction mechanisms

Alkenes are a class of hydrocarbons that contain a carbon-carbon double bond. This double bond is the site of many interesting chemical reactions. One such reaction is ozonolysis.
Ozonolysis involves the reaction of an alkene with ozone (O_3) to break the carbon-carbon double bond. This reaction typically occurs in two stages.

• The first stage forms an unstable intermediate called a molozonide.
• The molozonide quickly rearranges to give a more stable ozonide.
• Finally, the ozonide is reduced (often by a mild reducing agent like zinc or dimethyl sulfide) to yield carbonyl compounds.

In summary, ozonolysis is a very effective method for breaking the double bond in alkenes, resulting in the formation of oxygen-containing products like aldehydes or ketones. This reaction mechanism is crucial for breaking down complex organic molecules into simpler fragments.

carbonyl compounds formation

In many organic reactions, the formation of carbonyl compounds is a significant outcome. When we talk about carbonyl compounds, we refer to molecules with a C=O group, such as aldehydes and ketones.
During ozonolysis, the double bond of the alkene is broken and replaced with two C=O groups. Here’s what happens step-by-step:

• The ozone molecule attaches to the double bond to form a cyclic intermediate.
• This intermediate breaks down to yield an ozonide.
• The ozonide then breaks apart in the presence of a reducing agent, resulting in two carbonyl compounds.

This process usually involves simple, symmetrical alkenes that produce identical carbonyl fragments. For instance, ozonolysis of 2-butene results in the formation of two molecules of the same aldehyde, acetaldehyde (CH_3CHO).
Understanding carbonyl compounds' formation is crucial because it helps in identifying the original alkene from its ozonolysis products.

symmetrical alkenes

Symmetrical alkenes are those alkenes where the groups attached to either side of the double bond are identical. This symmetry plays a role in their reactivity and the types of products they form in reactions like ozonolysis.
When a symmetrical alkene undergoes ozonolysis, each fragment from the double bond splitting will be identical. For example, in the given exercise, ozonolysis of 2-butene yields two molecules of acetaldehyde (CH_3CHO). This indicates that the original alkene was symmetrical.

• Another example could be ethene (C_2H_4), which would yield two molecules of formaldehyde (HCHO) on ozonolysis.
• Similarly, a larger symmetric alkene like hex-3-ene would also produce identical carbonyl compounds on ozonolysis.

Symmetry simplifies the analysis of olefin-derived products, helping us trace back the original structure of the alkene from the ozonolysis-derived carbonyl compounds.