Allylic organom tallics e d ch 3 ch2 li h 2c c ch 3 o

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Unformatted text preview: CH2 Li H 2C C CH 3 O RC H H 2C C OH CH 2 C HR CH 3 + Li CH 3 Alte rnativepre paration: allylic Grignard re nts age Br + Mg M gBr Weshall e ncounte ne r utral analogs of allylic anions: CH2 X isoe ctronic to le X : : X = OR, S NR2 R, Conjugated Double Bonds Conjugated What about CCCC CCCC ? Nom nclature C e : is/trans; E/Z. Re w C vie hapte 11 r Nom S tability: He of hydroge ats nation (kcal m -1) ol ΔH˚ C 3(C 2)3C C 2 HHHH + H2 + 2 H2 1,5-He xadie ne -30.3 -60.5 But: 1,3-Butadie ne + 2 H2 -57.1 Re sonancee rgy of butadie ~ 3.5 ne ne Structure Fast Fast S re hort lativeto an alkane C Csinglebond ― (1.54 Å). Orbitals Orbitals Antibonding Bonding C onjugation stabilize the odynam s rm ically, but it also incre s re ase activity, for e plein e ctrophilic additions (re w C xam le vie hapte 12). r (re Markovnikov addition with a twist: Fast CH CH + HC l Re ason: I nte e rm diatecation is also stabilize d Re 1,2-Addition 1,2-Addition (“kine tic”) (“kine C l - - 1,4-Addition C 1,4-Addition l (“the odynam rm ic”) (“the C l Te inal alke le stable rm ne ss Te than inte t han rnal CH + cis C l More stable HC lAddnF11 CH Less stable Kinetic vs Thermodynamic Control Kinetic We r contributor ake S tronge contributor r Extended Conjugation Extended + HBr Quitere active e n , ve Quitere though t hough stabilize by d conjugation conjugation CH 3 CH 3 Br Thre products e CH 3 Cation also stabilize by conjugation d The odynam stability doe not always rm ic s The e qual lack...
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This note was uploaded on 09/04/2010 for the course CHEM 10966 taught by Professor Vollhardt during the Spring '10 term at University of California, Berkeley.

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