Markownikoff’s Rule

“When a hydrogen halide reacts with an unsymmetrical alkene the hydrogen of the hydrogen halide attaches itself to the carbon of the alkene bearing the larger number of hydrogens and smaller number of carbons" Markownikoff’s Rule

Addition of HBr to propene CH 3 CH=CH 2 : H–Br can add in two different ways Two products are possible: CH 3 CH 2 –CH 2 Br H–BrBr–H Contains more H atoms CH 3 CH=CH 2 CH 3 CHBr–CH 3 Minor productMajor product Addition reactions of unsymmetrical alkenes

Primary carbocation One C joined to C + Secondary carbocation Two C joined to C + Minor product Major product It’s all controlled by carbocations

Primary carbocation One carbon chains attached to C + Secondary carbocation: Two carbon chains attached to C + Tertiary carbocation: Three carbon chains attached to C + Most stable Least stable Types of carbocation

Electron-donating ability of alkyl groups. Each alkyl group pushes electrons towards C+ charge of carbocation. Positive charge is spread over alkyl groups The more alkyl groups attached to the C + The more the positive charge is spread out The greater the stability of the carbocation Primary Secondary Tertiary Reasons for carbocation stability Most stable Least stable