Describe the differences between the anti-Markovnikov and Markovnikov addition.

The anti-Markovnikov and Markovnikov additions differ in the way the hydrogen atom is added to the carbon-carbon double bond.

In a Markovnikov addition, the hydrogen atom is added to the carbon atom with the most hydrogen atoms already attached. This is due to the electrophilic addition mechanism, where the positively charged hydrogen ion is attracted to the negatively charged carbon atom. The other carbon atom in the double bond receives the other atom or group.

On the other hand, in an anti-Markovnikov addition, the hydrogen atom is added to the carbon atom with the least hydrogen atoms attached. This is due to the radical addition mechanism, where the hydrogen atom is added to the carbon atom with the most available electrons. The other carbon atom in the double bond receives the other atom or group.

The anti-Markovnikov addition is usually achieved through the use of radical initiators, such as peroxides, which generate free radicals that add to the double bond. This type of addition is important in the synthesis of alcohols, where the anti-Markovnikov product is desired.

In contrast, the Markovnikov addition is more commonly observed in electrophilic addition reactions, such as the addition of hydrogen halides to alkenes. This type of addition is important in the synthesis of alkyl halides, where the Markovnikov product is desired.

A-Level Chemistry Tutor Summary: In essence, Markovnikov addition means the hydrogen attaches to the carbon with more hydrogens in an alkene bond, following an electrophilic addition mechanism. Conversely, anti-Markovnikov addition sees hydrogen going to the less hydrogen-rich carbon, via a radical addition mechanism, often initiated by peroxides. While Markovnikov's rule helps in making alkyl halides, anti-Markovnikov is key for synthesising alcohols.