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The reaction map

Covers AS91391

Why this page exists

Almost every question in this paper asks you to move from one functional group to another.
There are only about fifteen conversions in the whole standard, and they fit on a single diagram.
Learn this map and you can answer a synthesis question you have never seen before.

The conversions, by starting material

From an alkene

$+\,\text{HX}$ → haloalkane
$+\,\text{H}_2\text{O}/\text{H}^+$ → alcohol

From a haloalkane

$\text{NaOH}(aq)$ or $\text{KOH}(aq)$ , warm → alcohol (substitution)
KOH in alcohol, heat → alkene (elimination)
conc $\text{NH}_3$ , heat in a sealed tube → primary amine

From an alcohol

conc HCl, HBr or $\text{SOCl}_2$ → haloalkane
conc $\text{H}_2\text{SO}_4$ , heat → alkene (elimination)
$\text{MnO}_4^-/\text{H}^+$ or $\text{Cr}_2\text{O}_7^{2-}/\text{H}^+$ → aldehyde, ketone or carboxylic acid
carboxylic acid / conc $\text{H}_2\text{SO}_4$ → ester

From an aldehyde or ketone

$\text{MnO}_4^-/\text{H}^+$ or $\text{Cr}_2\text{O}_7^{2-}/\text{H}^+$ , reflux → carboxylic acid (aldehyde only)
$\text{NaBH}_4$ → back to the alcohol

From a carboxylic acid

$\text{SOCl}_2$ → acyl chloride
alcohol / conc $\text{H}_2\text{SO}_4$ → ester

From an acyl chloride

alcohol → ester
conc $\text{NH}_3$ or a primary amine → amide

Back to the acid

an ester or an amide $+\,\text{H}_2\text{O}/\text{H}^+$ or $\text{H}_2\text{O}/\text{OH}^-$ → hydrolysis

Three patterns worth noticing

Alcohols are the hub. Almost every route passes through an alcohol, so if you are stuck in a synthesis, ask how to get to one.
Oxidation goes one way, reduction comes back. Alcohol → aldehyde → acid climbs the ladder; $\text{NaBH}_4$ comes back down one rung.
Every acid derivative hydrolyses back to the acid. Esters, amides and acyl chlorides all return to $-\text{COOH}$ with water.

The conditions are half the answer

Two pairs of reactions use almost the same reagent and give completely different products:

Reagent	Conditions	Reaction	Product
KOH	aqueous, warm	substitution	alcohol
KOH	in alcohol, heat	elimination	alkene
oxidant	distil off	partial oxidation	aldehyde
oxidant	reflux	full oxidation	carboxylic acid

Writing "KOH" or "oxidise" without the conditions cannot score, because the marker cannot tell which reaction you mean.

Tips and Tricks

Redraw this map from memory at the start of every revision session. It takes three minutes and it is the single highest-value thing you can memorise for this paper.

Always give the reagent and the conditions. " $\text{Cr}_2\text{O}_7^{2-}/\text{H}^+$ " is incomplete; " $\text{Cr}_2\text{O}_7^{2-}/\text{H}^+$ , heated under reflux" tells the marker you mean the carboxylic acid.

When a question asks you to convert A into B and you cannot see the route, work backwards from B. Ask what makes B, then what makes that, until you reach A. Backwards is usually easier because most groups have only one or two ways in.

Do not invent reagents. The standard's list is closed — if the reagent you want is not on this page, the route you are imagining is not the one being examined.

Check whether a conversion needs more than one step. Turning an alcohol into an amide takes three: oxidise to the acid, convert to the acyl chloride, then react with ammonia.

Worked ExampleReading a route off the map

Give the reagents and conditions needed for each of the following single-step conversions.

(a) propan-1-ol → 1-chloropropane (b) propan-1-ol → propene (c) propanal → propan-1-ol (d) propanoic acid → propanoyl chloride

(a) propan-1-ol → 1-chloropropane

The –OH group is being replaced by a chlorine, so this is a substitution starting from an alcohol.

The map gives two reagents that do this: concentrated hydrochloric acid, or thionyl chloride.

(b) propan-1-ol → propene

An alcohol is becoming an alkene, so a molecule of water is being removed — this is an elimination.

From an alcohol, the eliminating reagent is concentrated sulfuric acid, and heat is required.

(c) propanal → propan-1-ol

An aldehyde is becoming a primary alcohol, so we are moving down the oxidation ladder. That is a reduction.

The only reducing agent in the standard is sodium borohydride.

(d) propanoic acid → propanoyl chloride

The –OH of the acid is being replaced by a chlorine, giving an acyl chloride.