3.1.2 reaction mechanisms

mechanisms are used to show the reactions of organic compounds.

a double headed curly arrow indicates the movement of a pair of electrons

• this shows bond making and bond breaking (covalent and dative)

the arrow starts where the electrons come from, which could be:

• from a covalent bond

• from a lone pair

the arrow points to where the electrons are going, which could be:

• to another atom to become an extra lone pair

• between 2 atoms to become a bond between them

• to a single bond to form a double bond

example mechanism - the formation of a covalent bond:

• curly arrow starts from a lone electron pair or from another covalent bond

example mechanism - the breaking of a covalent bond:

• curly arrow starts from the bond that is being broken

electrons gained = -ve ion, must lose electrons to be neutral

electrons lost = +ve ion, must gain electrons to be neutral

free radical: an uncharged molecule or atom with an unpaired valence electron

in free-radical mechanisms:

• the unpaired electron in a radical is represented by a dot

• the use of curly arrows is not required