Question

(a) Bromination of 2-methylpropane gives a mixture of brominated products. Compound B, with the formula C4H8Br2, was isolated from the mixture. (i) Draw and name the possible isomers of C4H2Br2 that could be formed from 2-methylpropane. [3 marks] (ii) The 'H NMR spectrum of compound B is shown below. Integral = 3 Integral = 1 6 4 0 (ppm) Identify which of the isomers you drew in part i) corresponds to this spectrum. You should clearly explain your reasoning, using information from the data sheet to support your answer and indicated why you disregarded the other isomers. You should include discussion of the presence or absence of splitting patterns in your answer. [3 marks] (b) Compound C is another product formed during the bromination of 2- methylpropane, which has the formula C4H9Br. Compound C undergoes a nucleophilic substitution reaction with sodium hydroxide. Kinetic data for this reaction are given in the table below. [Compound C] [NaOH) Relative rate I mol dm3 1 mol dm3 of reaction 0.5 0.5 0.75 0.5 1.5 0.75 0.75 1.5 Process the kinetic data to identify the rate equation for the reaction and deduce the structure of Compound C, fully explaining your reasoning. Your answer should be accompanied by a drawing of the rate determining step of the reaction, including any relevant curly arrows. [4 marks] 1

Answer 1

CH3 CH3 Bromination Br H3C CH3 CH3 Br Br + CH3 H3C CH3 1,2-dibromo-2-methylpropane 2-bromo-2-methylpropane M. F = C4H8Br2 M. F = C4H9Br Compound B Compound C 2-methylpropane

(a) i) Ther is no Isomers possible of C4H2Br2 due to No chiral center. but the positional isomer is as follows Br CH3 Br CH3 Br Br CH3 CH3

(ii) The 'H NMR spectrum of compound B is shown below. a Integral = 3 CH3 Br Br CH3 - two -CH3 (s, 6H) a Singlet Integral = 1 |-CH2- (s, 2H) b Singlet 6 4 2 (ppm)

b)

Compound C undergoes nucleophilic substitution reaction with NaOH. Leaving group SN? Reaction (Bimolecular Reaction) Transition state Na+ (-) OH H3C CH3 CH3 ...11 CH3 Backside attack H3C Br Br C OH OH + NaBr H3Cm CH3 CH3 C4H9Br Substrate (Compound C) Electrophilic centre H3C tert-Butyl alcohol Partial bonds Rate Determining Step (RDS)

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