CIE Nov 2015 v2 Paper 4 Q6

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PMT Boron forms many useful compounds. 10 (a) The compound diborane, B2H6, can be used as a rocket fuel. It can be prepared by the reaction of boron trifluoride, BF3, with sodium borohydride, NaBH4. Balance this equation. BF3 + NaBH4B2H6 + NaBF4 [1] (b) Primary and secondary alcohols can be formed by the reaction of carbonyl compounds with NaBH4, which is a source of hydride ions, H. Complete the mechanism for the reaction of butanone with hydride ions, H, and draw the intermediate in the box. Include all necessary curly arrows and relevant dipoles. H H3C step 1 CH2CH3 H+ H3C OH CH2CH3 intermediate [3] (c) Borane, BH3, is used to synthesise alcohols from alkenes. The reaction occurs in two steps. The BH2 group from BH3 bonds to the least substituted carbon atom of the double bond, and the remaining H from BH3 bonds to the other carbon. CH3 C CH3 CH3 step 1 + BH3 CH3 CH3 CH3 [O] BH2 CH3 OH CH3 CH3 (i) Suggest the type of reaction in step 1.[1]UCLES 2015 9701/42/O/N/15<br /> (ii) The diol Y can be prepared by the same method. 11 H3C CH3 OH CH3 OH CH3 Draw the structure of the diene which could be used to prepare diol Y. PMT [1] (d) Benzene, C6H6, and borazine, B3N3H6, have planar, cyclic structures. (i) Describe the structure of and bonding in benzene, C6H6.[3] (ii) In borazine, B3N3H6, the boron and nitrogen atoms alternate around the ring. Each ring atom has a single hydrogen atom bonded to it. All boron-nitrogen bonds in borazine are 0.144 nm in length, whereas in simple compounds BN and B=N bond lengths are 0.154 nm and 0.136 nm respectively. Suggest and draw the structure of borazine.UCLES 2015 9701/42/O/N/15 [1] [Total: 10] [Turn over<br />

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