How do amines act as bases, what is a chiral centre, and how do condensation polymers form?
Amines and their basicity and preparation, amino acids and the amide link, optical isomerism and chirality, condensation polymers (polyesters and polyamides), carbon-carbon bond formation using nitriles, and multi-step organic synthesis.
An OCR H432 module 6 answer on nitrogen compounds and polymers: amine basicity and preparation, amino acids and the amide link, optical isomerism, condensation polymers (polyesters and polyamides), carbon-carbon bond formation with nitriles, and organic synthesis.
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What this topic is asking
OCR specification points across 6.2 want you to explain the basicity and preparation of amines, describe amino acids and the amide link, explain optical isomerism and identify chiral centres, describe condensation polymers (polyesters and polyamides), use nitriles to form carbon-carbon bonds, and plan multi-step syntheses. This is the nitrogen chemistry and the polymer and synthesis strands that round off the organic course.
Amines
Amino acids and chirality
Condensation polymers
Carbon-carbon bond formation and synthesis
Examples in context
Example 1. Nylon and polyester fabrics. Nylon (a polyamide) and PET (a polyester) are condensation polymers whose hydrolysable links allow chemical recycling back to monomers, unlike addition polymers such as poly(ethene), a direct consequence of the polar links formed here.
Example 2. Drug chirality and thalidomide. Many drugs have a chiral centre, and the two enantiomers can behave very differently in the body; the thalidomide tragedy showed why pharmaceutical chemists must control which optical isomer is made.
Try this
Q1. Explain why an amine acts as a base. [2 marks]
- Cue. The nitrogen atom has a lone pair of electrons that can accept a proton ().
Q2. State the two types of monomer that react to form a polyamide. [2 marks]
- Cue. A diamine and a dicarboxylic acid (or a diacyl chloride).
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20204 marks(a) Explain why amines act as bases. (b) Describe how ethylamine can be made from bromoethane, giving the reagents and conditions. (c) Describe how a primary amine can be made by reducing a nitrile.Show worked answer →
(a) The nitrogen atom has a lone pair of electrons that can accept a proton (), so an amine acts as a Bronsted-Lowry base (1).
(b) Heat bromoethane with excess ethanolic ammonia in a sealed tube; nucleophilic substitution gives ethylamine (1)(1).
(c) Reduce the nitrile with lithium tetrahydridoaluminate () in dry ether (or with and a nickel catalyst) to give the primary amine (1).
Markers reward the lone pair accepting a proton, the haloalkane-plus-ammonia route, and the reduction of a nitrile with a named reducing agent.
OCR 20224 marksHexanedioic acid reacts with 1,6-diaminohexane to form a polymer. (a) Name the type of polymerisation and the polymer class. (b) Draw the repeat unit and name the small molecule eliminated. (c) State why this polymer can be hydrolysed but poly(ethene) cannot.Show worked answer →
(a) Condensation polymerisation; the polymer is a polyamide (nylon) (1).
(b) The repeat unit contains an amide link joining the two monomer units (drawn with continuation bonds and ); the small molecule eliminated is water (1)(1).
(c) The polyamide has polar amide (or ester-type) links that can be broken by hydrolysis, whereas poly(ethene) is an addition polymer with only unreactive carbon-carbon and carbon-hydrogen bonds (1).
Markers reward the polymerisation type and polyamide class, the repeat unit with an amide link and water eliminated, and the hydrolysable-link reason.
Related dot points
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An OCR H432 module 4 answer on haloalkanes: the polar carbon-halogen bond, nucleophilic substitution with hydroxide, cyanide and ammonia, the hydrolysis-rate trend with bond enthalpy, elimination to alkenes, and CFCs and ozone depletion.
Sources & how we know this
- OCR A-Level Chemistry A (H432) specification — OCR (2015)