question_answer

"The addition of unsymmetrical reagents to unsymmetrical 'alkenes occurs in such a way that the negative part of the addendum goes to that carbon atom of the double bond which carries lesser number of hydrogen atoms" is called by :

A) Saytzeff rule     

B) Markownikoff's rule

C) Kharasch effect               

D) Anti-Saytzeff rule

Correct Answer: B

Solution :

The Markownikoffs rule : During the addition across unsymmetrical double bond the negative part of the adding molecule attaches itself to the carbon atom Carrying less number of hydrogen atoms. As \[{{\text{3}}^{\text{o}}}\] and \[{{2}^{\text{o}}}\] carbocation are more stable than \[{{1}^{\text{o}}}\] carbocation hence the addition through path I is favoured which is in accordance with Markownikoffs rule. Kharasch effect or peroxide effect: In the presence of organic peroxides such as benzoyl peroxide (addition on alkenes give the product against the Markownikoffs rule. \[C{{H}_{3}}CH=C{{H}_{2}}+HBr\xrightarrow{Peroxide}C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}Br\] Saytzeff rule: During dehydrohalogenation of alkyl halide, the hydrogen atom is removed from that carbon atom which has lesser number of carbon atoms and more number of alkyi groups attached to it i.e., to form more alkylated alkene