Interpret the ozonolysis result

Ozonolysis cleaves the double bond of an alkene to give carbonyl compounds.

The question says:

• the alkene is symmetrical
• 1 mole of alkene gives 2 moles of the same aldehyde
• the aldehyde has molecular mass 44 u

Identify the aldehyde of molar mass 44 u

For an aldehyde, possible simple formula:

$\text{HCHO}$

Molecular mass of methanal:

$12 + 2(1) + 16 = 30$

For ethanal:

$\text{CH}_3\text{CHO} = \text{C}_2\text{H}_4\text{O}$

Molecular mass:

$2(12) + 4(1) + 16 = 24 + 4 + 16 = 44$

So the aldehyde is ethanal.

Find the symmetrical alkene that gives two ethanal molecules on ozonolysis

To produce two identical molecules of ethanal, the alkene must be:

$\text{CH}_3-\text{CH}=\text{CH}-\text{CH}_3$

which is 2-butene.

Ozonolysis reaction:

$\text{CH}_3-\text{CH}=\text{CH}-\text{CH}_3 \xrightarrow[\text{}]{\text{O}_3} 2\,\text{CH}_3\text{CHO}$

Check the options

• A: propene $\text{CH}_3-\text{CH}=\text{CH}_2$ Gives methanal + ethanal, not two identical aldehydes.

• B: 1-butene $\text{CH}_2=\text{CH}-\text{CH}_2-\text{CH}_3$ Gives methanal + propanal, not two identical aldehydes.

• C: 2-butene $\text{CH}_3-\text{CH}=\text{CH}-\text{CH}_3$ Gives two moles of ethanal. Correct.

• D: ethene $\text{CH}_2=\text{CH}_2$ Gives two moles of methanal (molar mass 30), not 44.

Final answer

The alkene is 2-butene.