0243Pb79an-09.cwk (WP)

0243Pb79an-09.cwk - "forcing conditions" Br Br Br H Br – HBr Br Toluene can form three possible ions Two are better stabilized by

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Answers to Problem 79, Chemistry 0243 - 2009 The first reasonable step is formation of either a bromonium ion or the corresponding open carbocation (in fact it s the open one - look at the resonance stabilization). 1 "forcing conditions" Br Br Br Br (+) (+) or The reaction doesn t go on to add bromide - the structure of the product tells you that (and we didn t ask why). To make bromobenzene, a proton must be lost - it is just a garden- variety E1 step most easily written from the open ion, but possible from both intermediates shown above.
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Unformatted text preview: "forcing conditions" Br Br Br (+) (+) H Br – HBr Br + Toluene can form three possible ions. Two are better stabilized by resonance than the third (note the tertiary carbocation in A and B , but not C ), and the transition states leading to them will profit energetically from that stabilization. However there are steric problems in B , and the major product is the 1,4-isomer (called para). A C B CH 3 CH 3 CH 3 CH 3 Br Br Br 2 CH 3 CH 3 CH 3 Br Br Br (+) (+) (+) (+) (+) (+) tertiary tertiary...
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This note was uploaded on 03/02/2010 for the course CHEM orgo taught by Professor Jones during the Fall '10 term at NYU.

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