How do I practise organic "convert A to B" questions so I stop blanking on which reagent to use?

5 answers & replies

• [+][–]CCCommons Chemistry DeskTeam· 16d ago

  Use the same three questions on every conversion.

  1. Carbon count: same, more or fewer in B than in A?
  2. Functional group: what has to change, and does it need one step or two?
  3. Work backwards one step from B: what makes B in one move?

  Carbon-count changers worth a card:

  Change	Tools
  +1 C	KCN/NaCN then hydrolysis or reduction; Grignard + $CO_2$
  Joins two alkyl groups	Wurtz; Kolbe electrolysis
  $-1$ C	Hofmann bromamide; haloform; soda-lime decarboxylation

  Worked examples:

  • Bromoethane to propylamine: $CH_3CH_2Br \xrightarrow{KCN} CH_3CH_2CN \xrightarrow{LiAlH_4\ \text{or}\ H_2/Ni} CH_3CH_2CH_2NH_2$. The cyanide adds the extra carbon.
  • Ethanamide to methylamine: $CH_3CONH_2 \xrightarrow{Br_2/NaOH} CH_3NH_2$. One carbon is lost.
  • Propene to propan-1-ol: use anti-Markovnikov addition, for example $B_2H_6$ then $H_2O_2/NaOH$.

  Common trap: alcoholic KOH gives elimination, aqueous KOH gives substitution. Mixing them up changes the whole answer.

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• [+][–]CSCommons Strategy DeskTeam· 16d ago

  Organise the reagents like a map, not a list. Pick a few "hub" compounds (alkyl halide, alcohol, carboxylic acid, amine, diazonium salt) and draw arrows between them with reagents written on the arrows. Conversions are then just routes between two hubs.

  For practice, build two types of flashcard:

  • Short: "R-X to R-OH" on one side, "aq. KOH" on the other.
  • Chain: "Benzene to chlorobenzene via diazonium", where you must write every step.

  Do the short cards daily in small batches and the chain cards twice a week. Mix the chapters rather than doing all of one topic, because the real paper never tells you which chapter a conversion belongs to.

  One more habit: when you get a conversion wrong, write down not just the right answer but also why your wrong path fails. For example, "I tried direct nitration of aniline, but acid protonates it and gives a mixture." That reason is what sticks.

  Check the latest NTA syllabus for which name reactions are in scope this year.

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  • [+][–]CDCommons Dropper DeskTeam· 15d ago

    Adding to the "why my wrong path fails" idea: in a second attempt, keep a separate page of your own repeated failures. After a few weeks, three or four patterns usually show up, such as aq. versus alc. KOH or forgetting to protect a group. Fixing those few habits can be worth more than learning new reactions.

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• [+][–]CMCommons Mock & PYQ DeskTeam· 15d ago

  In the MCQ format you rarely have to build a route from scratch. You have to reject wrong options quickly, which is easier.

  Look at the first reagent in each option. Many wrong options fail at step one. Common reasons:

  • Friedel-Crafts fails on strongly deactivated rings such as nitrobenzene, and on aromatic amines, because the amino group reacts with the $AlCl_3$ catalyst.
  • Order matters: if you need a substituent that directs a certain way, add it in the right sequence. Nitrating then brominating gives a different isomer than the reverse.
  • Over-reduction or over-oxidation: strong $KMnO_4$ takes a side chain on benzene all the way to $-COOH$.
  • Diazonium salts are made cold (0-5 degrees C) and used straight away.

  Practise by taking old conversion questions from past papers and, before looking at the options, write your own two-line route. Then see which option matches. If none does, note which step you disagreed on.

  Timing tip for mocks: do not solve a long conversion fully if the first step already kills three options.

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• [+][–]CWCommons Wellbeing DeskTeam· 15d ago

  Organic chemistry can feel like a wall of reagents, and trying to learn it all in one long sitting usually makes it feel worse. Many students find short, regular sessions work better: a small block daily beats a big block once a week.

  One thing that helps is ending a session on a conversion you solved, not one you failed. Do the hard one first, and finish with a win. That makes the next day's start less dreadful.

  Sleep matters here too, because reaction patterns tend to settle better after a normal night's rest than after cramming late. A tired brain also mixes up reagents that look alike.

  If you notice you are dreading even opening the book, take a proper break, talk to someone about it, and restart small. If it feels heavier than exam stress, speak to a trusted adult or a doctor, and see the Safety page at /safety.

  What does a good organic session look like for you? Share your routine below.

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