A, C₂H₄, is evidently ethene CH₂=CH₂.. This reacts with hydrogen bromide in the gas phase to give bromoethane, B, CH₃CH₂Br. With aqueous sodium hydroxide solution bromoethane gives ethanol, C, CH₃CH₂OH.

Ethanol is oxidised by acidified potassium dichromate solution to give successively D, which since it reacts with both 2,4-dinitrophenylhydrazine and ammoniacal silver nitrate is a carbonyl compound and an aldehyde. D is ethanal, CH₃CHO. Ethanal is oxidised further to E, ethanoic acid, CH₃COOH.

Magnesium, dry ether and a halogenoalkane signifies the Grignard reaction. Bromoethane B gives F, CH₃CH₂MgBr, ethylmagnesium bromide. Grignard reagents react with carbonyl compounds in a nucleophilic addition reaction to give alcohols. With aldehydes apart from methanal (which yields a primary alcohol) the product is a secondary alcohol. G, C₄H₁₀O, is therefore butan-2-ol, CH₃CH₂CH(OH)CH₃. Oxidation of secondary alcohols with acidified potassium dichromate solution gives ketones, so H is CH₃CH₂COCH₃, butanone. This will also react with the Grignard reagent F; ketones give tertiary alcohols in this reaction, so that I is 3-methylpentan-3-ol, (CH₃CH₂)₂C(OH)CH₃. I, like all tertiary alcohols, is not oxidised by acidified potassium dichromate solution.

The reaction of ethene, A, with bromine in the presence of sodium chloride is a straightforward electrophilic addition. The electrophile is Br^d+ from the polarisation of the bromine molecule by the C=C bond. The resulting carbocation is then attacked by the negative ions present in the mixture. There are two; attack by Br ^- gives J, BrCH₂CH₂Br, 1,2-dibromoethane. Attack by Cl ^- from the sodium chloride gives K, BrCH₂CH₂Cl, 1-bromo-2-chloroethane. No C₂H₄Cl₂ is formed because there is no possibility of a Cl^d+ species being generated.

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