OCR A Jun 2013 Paper 2 Q4 (with explained solutions) |

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OCR A Jun 2013 Paper 2 Q4

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Iodine monobromide, IBr, has a permanent dipole. Alkenes react with IBr in a similar way to the reactions of alkenes with HBr. (a) Propene reacts with IBr to make two possible organic products. One of these products is 2-bromo-1-iodopropane. (i) Using the curly arrow model, complete the mechanism to make 2-bromo-1-iodopropane. CH3 (cid:44) + Br(cid:44) CH3 Br (ii) What is the name of this mechanism?[1] (iii) Draw the structure of the other possible organic product of the reaction of propene with IBr. [3] [1]OCR 2013 Turn over<br />
(b) Methane reacts with IBr to form many products. 10 Two of these products are iodomethane and hydrogen bromide. (i) Suggest the essential condition needed for this reaction.[1] (ii) The mechanism of the reaction involves three steps, one of which is called termination. Describe the mechanism of the reaction that forms iodomethane and hydrogen bromide. Include in your answer:the name of the mechanism the names for the other two steps of the mechanism equations for these two steps of the mechanism the type of bond fission one equation for a termination step. Your answer should link the named steps to the relevant equations.OCR 2013<br />
11[7] [Total: 13]OCR 2013 Turn over<br />

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F322/01 Mark Scheme June 2013 Marks Guidance Curly arrow must start from bond and go to correct atom DO NOT ALLOW partial charges on carboncarbon double bond DO NOT ALLOW + on carbon atom The positive charge must be associated with the carbon atom and not with a bond Make certain the carbonium ion includes the iodine atom Curly arrow must come from any lone pair or the negative sign of the bromide ion The lone pair on the bromide ion does not need to be shown ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) eg CH2BrCHICH3 IGNORE any name given Question 4 (a) Answer (i) correct curly arrow from double bond to iodine atom and curly arrow from the IBr bond to the bromine atom (cid:57) correct carbonium ion OR correct carbocation (cid:57) correct curly arrow from bromide ion to the (positive) carbon (cid:57) H CH3 CH3 +Br (ii) Electrophilic addition (cid:57) (iii) Br CH3 (cid:57) Br 16<br />
F322/01 Mark Scheme June 2013 Question (b) (i) Ultraviolet OR UV (cid:57) Answer (ii) (free) radical substitution (cid:57) (Initiation step) IBr (cid:198) Br + I (cid:57) homolytic fission (cid:57) (Propagation steps) Br + CH4 (cid:198) HBr + CH3 (cid:57) CH3 + IBr (cid:198) CH3I + Br (cid:57) (Termination steps) I + CH3 (cid:198) CH3I OR Br + Br (cid:198) Br2 OR I + I (cid:198) I2 OR Br + CH3 (cid:198) CH3Br OR CH3 + CH3 (cid:198) C2H6 OR I + Br (cid:198) IBr (cid:57) QWC propagation linked to correct equations Br + CH4 (cid:198) HBr + CH3 CH3 + IBr (cid:198) CH3I + Br AND initiation linked to correct equation IBr (cid:198) Br + I (cid:57) Guidance ALLOW high temperature OR 300 oC IGNORE light/radiation DO NOT ALLOW any catalyst Use the SEEN annotation on page 11 if blank or no credit can be given IGNORE any state symbols in equations Radicals do NOT need a single dot IGNORE dots DO NOT ALLOW homolytical fission Heterolytic anywhere in the answer contradicts this mark IGNORE I + CH4 (cid:198) HI + CH3 IGNORE CH3 + IBr (cid:198) CH3Br + I DO NOT ALLOW equations with H OR any other incorrect equation (i.e. not one of the four propagation steps shown) ALLOW any other suitable termination steps DO NOT ALLOW termination steps with H QWC can only be given if marking points 2, 4 and 5 have been awarded Marks Total 13 17<br />

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