Predict reactions of molecules with several groups
Use the target group and stated conditions to predict the change, retained groups and likely products.
AS Level; Cambridge International Chemistry 9701, syllabus for 2028–2030. Synthetic routes use reactions in this syllabus; reagent hazards are not practical instructions. Written practice is self-checked
Before you begin
- Use the functional-group reactions, reagents and conditions from Topics 13–20. Check connectivity and carbon count at each step.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What should you check first when a multi-group molecule reacts?
What you will learn
- Predict a reaction from functional-group evidence
- Use conditions to select among possible transformations
- State which other groups remain in the molecule
Choose the reaction from the group and conditions
A molecule with several functional groups may have more than one possible reaction, but the question's reagent and conditions identify the transformation to apply. Oxidising a primary alcohol under reflux can lead to a carboxylic acid; distillation can collect the aldehyde intermediate. A nitrile hydrolysis route converts –CN into –COOH.
For an alkene, hydrogenation, addition of steam, halogen addition and oxidation produce different products. Read the reagent and conditions before drawing the product rather than relying on the substrate name alone.
Preserve what the reaction does not change
Track the whole structure through each step. Change only the bonds or groups involved in the stated reaction and keep the remaining carbon skeleton and functional groups unless a later step acts on them.
A product can therefore contain more than one group. After each proposed step, check atom balance where an equation is requested, group identity, carbon count and whether a new stereochemical or isomer issue is explicitly in scope.
Pause and explain
During nitrile hydrolysis, what happens to the nitrile carbon?
Worked example
Predict the product when CH₃CH₂C≡N is hydrolysed with dilute alkali and then acidified.
Show the worked solution
- Hydrolysis transforms the nitrile group.
- The nitrile carbon becomes the carboxyl carbon.
- Acidification converts carboxylate to –COOH.
Answer Propanoic acid, CH₃CH₂COOH.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Predict the product after 2-hydroxypropanenitrile is hydrolysed and the mixture is acidified.
Give me a hint
Change –CN into –COOH and retain the existing –OH group.
Compare my reasoning
- The nitrile carbon becomes the carboxyl carbon.
- The secondary hydroxy group remains on carbon 2.
- Name the three-carbon product.
2-hydroxypropanoic acid, CH₃CH(OH)COOH.
Look for these in your work
- Nitrile converted
- Existing OH retained
- Correct product named
A primary alcohol is oxidised under reflux with acidified dichromate. What product class is expected, and which carbon skeleton feature should be checked?
Give me a hint
Reflux allows the primary-alcohol oxidation to continue beyond the aldehyde.
Compare my reasoning
- A primary alcohol can oxidise through an aldehyde.
- Under reflux the acid is the target product.
- Retain the original carbon count.
A carboxylic acid is expected, with the same carbon count as the starting primary alcohol.
Look for these in your work
- Product class correct
- Reflux interpreted
- Carbon skeleton retained
An alkene is treated with hydrogen and a nickel catalyst with heat. Predict the type of change and state what happens to any –Cl substituent elsewhere in the molecule.
Give me a hint
Hydrogenation targets the C=C bond; check whether the chlorine is part of that bond or a separate substituent.
Compare my reasoning
- The alkene becomes a saturated C–C bond.
- Hydrogen adds across the double bond.
- A separate C–Cl group is retained unless conditions target it.
The C=C is hydrogenated to C–C. A separate C–Cl substituent remains in the product; the reaction does not replace it.
Look for these in your work
- Alkene reaction identified
- Hydrogen addition described
- Unchanged group retained
Common mistakes
- Changing a group not targeted by the reagent
- Ignoring a required acidification step
- Dropping the nitrile carbon
- Choosing a product before checking the reaction conditions
What can you explain now?
What should you check first when a multi-group molecule reacts?
Compare with the explanation
The reagent and conditions
They select which syllabus reaction occurs.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do reagents, conditions and unaffected groups help you predict a product from a molecule with several functional groups?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.