Consider the difference in the rate between the following two second-order substitution reactions.

Reaction 1: The reaction of bromoethane and iodide ion to produce iodoethane and bromide ion is second order: that is, the rate of the reaction depends on the concentrations of both bromoethane and iodide ion:

Rate = k[CH3CH2Br][I-] mol L-1 s-1

Reaction 2: The reaction of l-bromo-2,2-dimethylpropane (neopentyl bromide) with iodide ion to produce neopentyl iodide and bromide ion is more than 10,000 times slower than the reaction of bromoethane with iodide ion

Rate = k[neopentyl bromide][I-] mol L -1s-1

(a) Formulate each reaction by using bond-line structural drawings in your reaction scheme.

(b) Identify the reactive site of the starting haloalkane as primary, secondary, or tertiary.

(c) Discuss how the reaction might take place; that is, how the species would have to interact in order for the reaction to proceed. Remember that, because the reaction is second order, both reagents must be present in the transition state. Use your model kit to help you visualize the trajectory of approach of the iodide ion toward the bromoalkane that enables the simultaneous iodide bond making and bromide bond breaking required by the second-order kinetics of these two reactions. Of all the possibilities, which one best explains the experimentally determined difference in rate between the reactions?

(d) Use hashed-wedged line structures to make a three-dimensional drawing of the trajectory on which you agree.