SCAN0019 - (‘9’ 7 r09 o H OW An Hm e H2C=C—C=CH2...

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Unformatted text preview: (‘9’ 7 r09 o H OW An Hm e H2C=C—C=CH2 + H—Cl ‘r—_¥_ HZC—g—(H‘.=CH2 <—> HzT—fi—"g—CHz H \ 1 H .0 x (922. @ +cr CI HZC‘J—?—E=CH2 Hzf—fi=fi—(|:H2 H Cl H This reaction is general for conjugated polyenes, but the ratio of products depends on the polyene, nucleophile, and sometimes temperature. Consider the following reactions: 80 ”C St Br [(1:12 ., A? .1. (V ' H 2 4 H 31 9;, 1 9% N Jim;— 1,2 addition product 1,4 addition product 1 3 Br Br 4o 0;; (k5? + N ‘ mo~ '- H worn» H 56% 1,2 addition product 1,4 addition product It can also be shown that th 1,2-addition produc can be converted to the more stable: 1,4-addition i product in the presence of HBr at °C. H- Br N 40°C H This represents a case of kinetic vs. thermodynamic control. - kinetic control: The product that forms fastest is favored. Kinetic control generally occurs at lower temperatures. - hermodynamic control: The most stable product is the major product. Thermodynamic control generally occurs at higher temperature. Since the 1,2-addition product is formed at low temperature, it is most likely the kinetic product. The 1,4-addition product is the thermodynamic product. ...
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