IMG_0001_NEW_0011

IMG_0001_NEW_0011 - _ O more freedom in products + br...

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Hydrogenation of l-butene: H Consider only the strength of different bonds in starting materials and product: Slarting material product 2TSkcaVmol AHo : 278 -292: -14 kcaVmol C-C bond (90 kcaVmol) C-H bond (101 kcal/mol) C-H bond (101 kcaVmol) 292kcaUmol if AH" is (-) than the reaction is exothermic if AH" is (+) than the reaction is endothermic ASo : entropy : freedom of movement in a system (decrease freedom (e.g. restrict movement) than you decrease entropy) AS' : freedom of movement in products - freedom of movement in starting materials examples: 1. one molecule becomes two molecules C:C bond (174 kcal/mol) H-H bond (104 kcaVmol) 9H. E1 orSxl 9Hs H3c-fBr .-----.-.------ H3c--l @ CHs CHs 2. frryo molecules react to form one molecule
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Unformatted text preview: _ O more freedom in products + br therefore AS" would be (+) H.H z\/ ----------------morefreedom in starting material therefore AS" would be (-) NOTE: as temperature increase the AS" factor for determining AG" becomes more important Consider this: in the reaction of secondary alkyl halide with a nucleophile where the reaction may precede via either an SNl or SN2 process. Syl has more freedom in transition structure while SN2 has less (2 molecules are coming together in TS)! Therefore AS'would favor SN1. With this in mind, another way to select for SN2 wouldle-to-ea*qr-outlhe reaction at low temperaturet so that AS'is less important or, to [email protected]_ temperatures!...
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This note was uploaded on 12/27/2011 for the course CHEM 282 taught by Professor Nabylmerbouh during the Fall '10 term at Simon Fraser.

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