4. Answer ALL parts of this question. a) This part of the question concerns the determination of reaction mechanisms. 1) What is the hydrogen/deuterium primary kinetic isotope effect (KIE), as used in determining reaction mechanisms? ii) Consider the base-promoted mono-bromination of acetone (shown below). The rate of reaction is found to be independent of the concentration of bromine. To determine the rate determining step for the reaction, a substitution of hydrogen for deuterium can be made, as shown, and the KIE determined to be 6.1. Explain the significance of this value and hence propose a reaction mechanism to explain this observation. Welch Bez HC CH, base ; CHE = 6.1 Br2 ko CD: base D C CD,Br [12 marks] b) This question concerns radical reactions i) Using the radical polymerisation of ethene as an example, illustrate what is meant by a radical chain reaction (a full mechanism is required). ii) In each of the three molecules (2-4) below, rank the different labelled hydrogen atoms by their increasing case to be abstracted by a radical. Ha Hb Hb Ha " (2) H (3) (4)