Sodium Cyanide (NaCN) followed by a dilute acid (H₂SO₄/HCl).

1. Safety: HCN is a toxic gas and is therefore dangerous/difficult to work with.

2. Reaction Rate: HCN is a weak acid and dissociates very poorly (HCN ⇌ H⁺ + CN⁻). This means there is a very low concentration of the nucleophile (CN⁻) available, making the reaction extremely slow.

HCN is not a nucleophile because it does not have a lone pair on the carbon.

The carbonyl carbon is partially positive (δ+) due to the electronegative oxygen atom, making it susceptible to attack by a lone pair of electrons (nucleophile). Additionally, the pi (π) bond between the carbon and oxygen is relatively weak/high energy and breaks easily.

2-hydroxy-2-methylpropanenitrile

The product molecule does not have a chiral centre. The central carbon is attached to two identical methyl groups (-CH₃), so it is achiral and does not rotate plane polarised light.

The carbonyl group in propanal is trigonal planar. The nucleophile (CN⁻) can attack the carbonyl carbon from either above or below the plane with equal probability.

This produces a racemic mixture (equal amounts of both enantiomers). As the two enantiomers rotate plane polarised light in opposite directions by the same amount, the effects cancel out.

NaBH₄ (Sodium Borohydride) dissolved in ethanol (or aqueous ethanol).

Butanone is trigonal planar around the carbonyl group. The hydride ion (from BH₄⁻) can attack from above or below the plane with equal probability, producing equal amounts of both enantiomers (a racemic mixture).

Both molecules are ketones. Ketones cannot be oxidised by mild oxidising agents like Tollens’ reagent, so neither molecule will produce a visible change (no silver mirror for either).

As ketones, neither butanone nor propanone can be oxidised by acidified potassium dichromate. Both solutions would remain orange (no reaction).

• Butanone produces 2-hydroxy-2-methylbutanenitrile. This is chiral but forms a racemic mixture, so it is optically inactive.
• Propanone produces 2-hydroxy-2-methylpropanenitrile. This is achiral (has two methyl groups), so it is optically inactive.

Since neither product rotates plane polarised light, they cannot be distinguished by this method.

High Resolution Mass Spectrometry

They have different molecular masses (Propanone Mr = 58.0, Butanone Mr = 72.1). The molecular ion peaks will be at different m/z values.