Question

125% Zoom T Insert HE Table T Text View Chart Shape Media Comment Collaborate Format Document Text Body Question 2 (Parts A-C, 20 points): Use the energy diagrams shown below to answer parts A and B. Style Layout More Font Transition state Transition state - Products Arial ..... ............ Regular 12 pt Reactants Energy Energy Character Styles None* Reactants Products Alignment Reaction coordinate (a) Highly exothermic reaction Reaction coordinate (b) Highly endothermic reaction T oke A) Does the structure of the transition state in the endothermic reaction resemble that of the reactants or the products? Spacing 10 - Single Bullets & Lists None B) Which energy diagram best represents the rate determining step of free radical bromination (Brz, light) of butane: the one on the left or the one on the right? C) Will the major product of free radical bromination (Brz. light) of butane be: achiral. racemic, or a single enantiomer?

Answer 1

A) According to the Hammond's Postulate, the structure of the transition state resembles the the structure of that compound(reactant or product), which is closer in energy to the transition state.

Therefore, in the endothermic reaction the structure of the transition state resembles the structure of the products.

B)

Hence, the energy diagram on the right, best represents the rate determining step of free radical bromination of butane.

Free radical bromination of butane: step is the The rate determining propagation step — CH₃ CH₂ CH₂ CH3 Br Br CH₂ CH₂ CH₂ CH2 + HBP since H-Br bond energy is less than the C-H bond energy, this step is an endothermic step.

C)

Hence, the major product forms with a racemic mixture of both the enantiomers.

Since the rate determing sep is endo- thermic , the reaction rate is slow . Thus the reaction is more selective as we know, less reactive reactions are more selective]. Phones Therefore, the radical generated in major amount, is the most stable one i.e. CH₃CH2 CH₂ CH3 Br CH₂-CH-CH₂-CH3 or, CH3-CH2-CH-CH3 (both are the same) Now the radical generated, is planar and Br can add from either face of the plane , resulting in racemic Box products. H é CH₂ CH2-ad . 9 8 ) CH-CH2-CNH, + CH₃ CH2 H CH₂

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