Concept: Ozonolysis of Alkenes

Ozonolysis is a reaction where an alkene is cleaved by ozone (O₃) to form carbonyl compounds (aldehydes or ketones). The type of carbonyl compound produced depends on the substituents attached to the carbon atoms of the double bond.

Step-by-Step Explanation:

Step 1: Analyze the Given Alkene Structure

The reactant is 2,3-dimethylbut-2-ene. Its structure is:

$C H 3 - C (C H 3) = C (C H 3) - C H 3$

This is a symmetrical alkene with identical substituents on both carbons of the double bond.

Step 2: Apply Ozonolysis Cleavage Rule

In ozonolysis, the carbon-carbon double bond is broken. Each carbon of the original double bond becomes a carbon in a carbonyl group (C=O).

If a carbon was bonded to two hydrogen atoms (i.e., it was =CH₂), it becomes formaldehyde (H₂C=O).
If a carbon was bonded to one hydrogen and one alkyl group (i.e., it was =CHR), it becomes an aldehyde (RHC=O).
If a carbon was bonded to two alkyl groups (i.e., it was =CR₂), it becomes a ketone (R₂C=O).

Step 3: Determine the Products for 2,3-dimethylbut-2-ene

Let's label the double bond carbons as C₁ and C₂.

C₁ is part of these groups: CH₃- and (CH₃)-. Therefore, it has two alkyl substituents (it is =CR₂ type).

C₂ is part of these groups: (CH₃)- and -CH₃. Therefore, it also has two alkyl substituents (it is =CR₂ type).

Since both carbons are of the =CR₂ type, the ozonolysis of this symmetrical alkene will produce two identical ketone molecules.

Each ketone will be acetone: (CH₃)₂C=O.

The reaction is: 2,3-dimethylbut-2-ene + O₃ → 2 CH₃-CO-CH₃

Step 4: Identify the Final Product from the Options

We are looking for the structure of acetone: CH₃-CO-CH₃.

Comparing the given options, the correct final product is the second image, which shows the structure of acetone (propanone).

Final Answer: The final product is acetone, $C H 3 - C (= O) - C H 3$ , which corresponds to the second option.

Related Topics

Alkenes: Unsaturated hydrocarbons containing carbon-carbon double bonds.
Carbonyl Compounds: Organic compounds containing a carbonyl functional group (C=O), such as aldehydes and ketones.
Oxidative Cleavage Reactions: Reactions that break carbon-carbon double or triple bonds and oxidize the carbons, e.g., ozonolysis and KMnO₄ cleavage.

Key Formulae and Theory

General Ozonolysis Reaction:

Alkene + O₃ → Carbonyl compounds

The reaction is typically followed by a "work-up" with a reducing agent like Zn/AcOH or dimethyl sulfide (CH₃)₂S to convert intermediate ozonides to the final carbonyl products.

Predicting Products:

Replace the double bond C=C with two C=O bonds. The oxygen atoms come from the ozone.

$R 2 C = C R 2' \to R 2 C = O + O = C R 2'$