exam specific answers (aldehydes and ketones)
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explain why NaBH4 reduces 2-methylbutanal but has no reaction with 2-methylbut-1-ene. (3)
• nucleophile is attracted to partially positive carbon in aldehyde • alkene contains electron rich C=C bond • nucleophile is repelled by C=C
explain how the structure of ethanal leads to the formation of two isomers. (2)
• ethanal is planar around the carbonyl group • there is an equal chance of attack from each side
describe how you would distinguish between separate samples of the two stereoisomers of 2-hydroxyhexanenitrile. (2)
• plane polarised light • enantiomers would rotate light in opposite directions
suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH. (1)
it dissolves both the oil and KOH (mutual solvent)
suggest why the reaction between water and ethanal is slower than the reaction between water and chloroethanal. (3)
• C in C=O of ethanal is less partially positive • because the CH3 attached to it has a positive inductive effect (electron donating) • so higher Ea
by considering the mechanism of this reaction, explain why the product formed is optically inactive. (3)
• planar C=O bond • attack equally likely from either side • racemic mixture formed
state the relationship between two chiral molecules with the same structural formula. (1)
non super-imposable mirror images