Markovnikov Rule:
The Markovnikov rule, also known as the Markovnikov's rule or Markownikoff's rule, is a principle in organic chemistry that predicts the outcome of addition reactions of alkenes or alkynes. It states that when a hydrogen halide or water is added to an unsymmetrical alkene or alkyne, the hydrogen atom of the reagent adds to the carbon atom with fewer hydrogen atoms, while the halide or hydroxyl group adds to the carbon atom with more hydrogen atoms.

Explanation:
The Markovnikov rule is based on the stability of carbocations. Carbocations are positively charged carbon species that are formed as intermediates during addition reactions. According to the rule, the more stable the carbocation intermediate, the more likely it is to form.

When a hydrogen halide or water is added to an unsymmetrical alkene or alkyne, the hydrogen atom adds to the carbon atom with fewer hydrogen atoms. This is because the carbon atom with fewer hydrogen atoms is electron-deficient and can stabilize the positive charge of the carbocation more effectively. On the other hand, the halide or hydroxyl group adds to the carbon atom with more hydrogen atoms, which is electron-rich and can better accommodate the negative charge.

Anti-Markovnikov Rule:
The anti-Markovnikov rule, also known as the anti-Markownikoff's rule, is a modification of the Markovnikov rule. It states that in the presence of certain reagents, such as peroxides, the addition of hydrogen halides or water to unsymmetrical alkenes or alkynes follows a different pattern. In this case, the hydrogen atom adds to the carbon atom with more hydrogen atoms, while the halide or hydroxyl group adds to the carbon atom with fewer hydrogen atoms.

Explanation:
The anti-Markovnikov rule is observed when the addition reaction proceeds via a radical mechanism instead of a carbocation intermediate. In the presence of peroxides, the hydrogen atom from the reagent initially abstracts a hydrogen atom from the alkene or alkyne, forming a radical species. This radical can then add to the alkene or alkyne in a different manner compared to the Markovnikov addition.

The anti-Markovnikov addition occurs because the radical intermediate is less stable compared to the carbocation intermediate. By adding the hydrogen atom to the carbon atom with more hydrogen atoms, the overall stability of the radical intermediate is increased. The halide or hydroxyl group then adds to the carbon atom with fewer hydrogen atoms.

Summary:
- The Markovnikov rule predicts that in the addition of hydrogen halides or water to unsymmetrical alkenes or alkynes, the hydrogen atom adds to the carbon atom with fewer hydrogen atoms, while the halide or hydroxyl group adds to the carbon atom with more hydrogen atoms.
- The rule is based on the stability of carbocation intermediates, with the more stable carbocation being favored.
- The anti-Markovnikov rule is a modification of the Markovnikov rule and is observed when the addition reaction proceeds via a radical mechanism.
- In the anti-Markovnikov addition, the hydrogen atom adds to the carbon atom with more hydrogen atoms, while the halide