Heterolytic nucleophilic addition and addition/elimination:carnonylcompounds withhydrogen cyanide0CN=8310-038一NCNCHOOVRL0=20CN=&Dcatalyst regeneratedStage 1Initial attack is by the lone pair of a nucleophile on an electrondeficient carbon atom. The hydrogen cyanide is not a goodnucleophile, because it does not have a prominent lone pair. But thecyanideion does.The positive reactive site on the carbon atom is due to the electronwithdrawing or inductive effect of the more electronegative oxygenatombondedtoit.The carbon atom is unsaturated. As the lone pair from the nucleophilemoves in, the pair between the carbon and the oxygen moves ontothe oxygen at the same time. This movement of π electrons is called amesomeric(介的)shift and is theheterolyticbreaking of the元bond
11 Heterolytic nucleophilic addition and addition/elimination:carnonyl compounds with hydrogen cyanide Stage 1 • Initial attack is by the lone pair of a nucleophile on an electron deficient carbon atom. The hydrogen cyanide is not a good nucleophile, because it does not have a prominent lone pair. But the cyanide ion does. • The positive reactive site on the carbon atom is due to the electron withdrawing or inductive effect of the more electronegative oxygen atom bonded to it. • The carbon atom is unsaturated. As the lone pair from the nucleophile moves in, the p pair between the carbon and the oxygen moves onto the oxygen at the same time. This movement of p electrons is called a mesomeric(中介的) shift and is the heterolytic breaking of the p bond
Heterolytic nucleophilic addition and addition/elimination:carnonylcompounds with hydrogen cyanide00CN=830-038NCNCHOAHROAEMNRY0=ZCN=&Dcatalyst regeneratedStage 2The intermediate made has a four bonded carbon atom.This is the usualbonding for carbon and so the energy of the intermediate is low. A lowactivation energy means a fast reaction.5福If there is a good leaving group joinedNCto the carbon, the lone pair on thethisisanaddition/eliminationoxygen may move back between the9oxygen and carbon making the bond9again as the leaving group moves away.NC
12 Heterolytic nucleophilic addition and addition/elimination:carnonyl compounds with hydrogen cyanide Stage 2 The intermediate made has a four bonded carbon atom. This is the usual bonding for carbon and so the energy of the intermediate is low. A low activation energy means a fast reaction. If there is a good leaving group joined to the carbon, the lone pair on the oxygen may move back between the oxygen and carbon making the p bond again as the leaving group moves away