Paper 2 Last Minute
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Why are tertiary carbocations more stable than secondary carbocations
Suggest a suitable reagent for hydrolysis of proteins
Concentrated HCl
Why can 2 liquids be separated by a separating funnel?
1 is insoluble OR they are immiscible (don’t mix to form a homogenous solution)
1,6-Diaminohexane can also be formed in a two-stage synthesis starting from 1,4-dibromobutane. Suggest the reagent and a condition for each stage in this alternative synthesis. Stage 1 reagent and condition Stage 2 reagent and condition
Stage 1 reagent and condition KCN, aqueous alcohol Stage 2 reagent and condition H2, Ni
Explain why 3-aminopentane is a stronger base than ammonia.
in 3-amino pentane. Lone pair on N more available and accepts H+ better. because alkyl group gives greater inductive effect High electron density
The student dried this cyclohexene by adding a few lumps of anhydrous calcium chloride and allowing the mixture to stand. Give one observation that the student made to confirm that the cyclohexene was dry.
Liquid goes clear / not cloudy
Suggest why it was necessary to use two different solvents.
Some of the amino acids did not separate/dissolve with the first/either solvent OR Some amino acids have the same Rf value or have the same affinity with the first/either solvent
The dicarboxylic acid in question 10.1 and the isomers of C6H14O2 in Questions 10.3 and 10.4 all have a relative molecular mass of 118 State why the dicarboxylic acid can be distinguished from the two diols by high resolution mass spectrometry using electrospray ionisation.
The precise (relative molecular) masses are different or wtte
Explain how carbon dioxide causes global warming. [1 mark]
C=O Bonds in CO2 absorb infrared radiation (of 2350 cm-1) IR radiation emitted by the earth does not escape (from the atmosphere) OR This energy is transferred to other molecules in the atmosphere by collisions (so all atmosphere is warmed)
Explain why NaBH4 reduces 2-methylbutanal but has no reaction with 2-methylbut-1-ene.
H- ion / nucleophile is attracted to delta +C M4 electron rich C=C M5 H- ion / nucleophile is repelled by C=C OR C=C only attacked by/reacts with electrophiles
State in general terms what determines the distance travelled by a spot in TLC. [1 mark]
solubility in moving phase and retention by stationary phase
Deduce the relative polarities of the 1,2-dinitrobenzene and 1,4-dinitrobenzene Explain why 1,4-dinitrobenzene has the greater Rf value.
Less/non polar is) more attracted to / more soluble in (non-polar) solvent / mobile phase
Amines E, F and G are weak bases. Explain the difference in base strength of the three amines and give the order of increasing base strength.
lone pair on N (atom) E N (next to ring): (lp) delocalised into ring lp) less available (to donate to or to accept a H+) F or G: N (next to alkyl): (positive) inductive effect/electrons (lp) more available (to donate to or to accept a H+)
Explain why the reaction produces a racemic mixture.
planar carbonyl group Attack from either side With equal probability OR produces equal amounts (of the two isomers/enantiomers)
Will methyl bromide or methyl chloride have a higher chemical shift
Methyl chloride Proton attached to a more electronegative atom Stronger inductive effect
What makes a step the rate-determining step?
If all reactants in the step are the only ones in the rate equation
Acid hydrolysis
1️⃣ Ester Hydrolysis (Acidic Conditions) Reaction: Ester + Water → Carboxylic acid + Alcohol Catalyst: Dilute HCl or H₂SO₄ (heat under reflux) Example: CH₃COOCH₃ + H₂O ⇌ CH₃COOH + CH₃OH ➡ This is reversible, forms equilibrium. 2️⃣ Amide Hydrolysis (Acidic Conditions) Reaction: Amide + Water → Carboxylic acid + Ammonium salt Catalyst: Dilute acid (HCl), heated Example: CH₃CONH₂ + H₂O + HCl → CH₃COOH + NH₄Cl ➡ Forms a carboxylic acid and ammonium salt. 3️⃣ Polymers Polyesters and polyamides can be hydrolysed under acidic conditions. Polyester → dicarboxylic acid + diol Polyamide → dicarboxylic acid + ammonium salt of diamine 💡 Tips In acid hydrolysis, the carboxylic acid is always regenerated. Base hydrolysis gives carboxylate salt instead.
Difference between saponification and biodiesel production
🔥 Saponification (Base Hydrolysis of Esters) Reaction: Triglyceride + 3 NaOH → Glycerol + 3 Soap molecules (sodium salts of fatty acids) Done with hot aqueous NaOH Soap = sodium salt of long-chain carboxylic acid Glycerol is a useful by-product (hydrogen bonding, soluble) 🛢️ Biodiesel Production Reaction: Triglyceride + 3 Methanol ⇌ Glycerol + 3 Methyl esters (biodiesel) Catalyst: KOH or NaOH (acts as a base, not acid) Methyl esters = biodiesel Glycerol is also formed as a by-product Why it matters: Renewable source of fuel Cleaner burning Less sulfur (so fewer sulfur dioxide emissions)
Benzene vs cyclohexa-1,3,5-triene
Benzene Very stable, 152kJ mol-1 more stable than expected Doesn’t do electrophilic addition C-C bond lengths are intermediate length