Organic Chemistry II
Notes for every section, eight new exam-style questions with full worked solutions, and online recall cards for your review days. Nothing here is copied from the book.
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17.1 Chirality and optical isomers
A chiral centre is a carbon atom bonded to four different atoms or groups.
Optical isomers (enantiomers) are non-superimposable mirror images of each other.
To draw a pair, sketch the chiral carbon with its four groups in 3D (two in the plane, one wedge, one dash), then draw the mirror image beside it.
Spot chiral centres by checking each sp3 carbon: CH3CH(OH)CH2CH3 has one (H, OH, CH3, C2H5). A carbon with two identical groups, such as two CH3, is not chiral.
Check yourself: Does propan-2-ol have a chiral centre?
No; C2 carries two identical CH3 groups
17.2 Optical activity and racemic mixtures
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17.3 Optical activity as evidence for SN1 and SN2
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17.4 Aldehydes and ketones: structure and physical properties
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17.5 Oxidation: telling aldehydes from ketones
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17.6 Reduction with lithium tetrahydridoaluminate
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17.7 Nucleophilic addition of HCN
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17.8 2,4-DNPH: a test for C=O and a way to identify it
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17.9 Iodine in alkali, and putting the tests together
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17.10 Carboxylic acids: structure and physical properties
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17.11 Making carboxylic acids
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17.12 Reactions of carboxylic acids
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17.13 Acyl chlorides
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17.14 Esters and their hydrolysis
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17.15 Polyesters
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17.16 Putting it together: the reaction map
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Extra worked questions
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All 8 worked solutions are free for members. The first one is open to everyone.
Finding a chiral centre
Butan-2-ol is CH3CH(OH)CH2CH3. Identify its chiral centre and explain why it is chiral.
Try it first, then show the worked solution
| Identify | Carbon 2, which carries the OH | 1 |
|---|---|---|
| Explain | It is bonded to four different groups: H, OH, CH3 and C2H5 | 1 |
Answer: C2 is chiral: four different groups.
Examiner tip: List all four groups. That list is the evidence the examiner wants.
Reducing with LiAlH<sub>4</sub>
Propanone and propanoic acid are each reduced with LiAlH4 in dry ether. Name each product and write an equation for propanoic acid using [H].
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Ethanal and cyanide
Ethanal reacts with KCN followed by dilute acid. Name the product, outline the mechanism, and explain why the product is not optically active.
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Three carbonyl compounds
Three bottles contain butanal, butanone and 2-methylpropanal. Describe tests to identify all three.
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Two ways to hydrolyse an ester
Ethyl propanoate is hydrolysed (a) with dilute acid and (b) with sodium hydroxide solution. Give the products of each and explain why (b) is usually preferred.
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Four reactions of ethanoyl chloride
Name the organic product when ethanoyl chloride reacts with (a) water, (b) ethanol, (c) ammonia and (d) methylamine.
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Is it S<sub>N</sub>1 or S<sub>N</sub>2?
A single enantiomer of 2-bromobutane is hydrolysed with aqueous sodium hydroxide. Explain how measuring the optical activity of the butan-2-ol formed would show which mechanism occurred.
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Mechanism: ethanoyl chloride and ethanol
Describe the mechanism for the reaction of ethanoyl chloride with ethanol. Name the mechanism and the organic product.
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Video walkthroughs
Narrated walkthroughs of exam-style questions from this topic of the book, showing where each mark comes from. Try the question first, then watch. Captions are available in the player.
Chiral centres and optical isomers
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Hydrogen cyanide adds to butanone
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Identifying a ketone from tests
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Bromoethane to propanoic acid
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Polyesters and biodegradability
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Recall cards
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