Question

State Saytzeff's Rule.

Answer 1

Saytzeff’s Rule is also known as Zaitsev’s rule, Saytzev’s rule or Z – rule. Alexander Zaitsev, a Russian Chemist, analysed different elimination reactions and finalized a general pattern in the resulting alkenes. Based on his conclusion, Zaitsev stated that stable alkene is made or generated when the removal of hydrogen from β-carbon has a less number of hydrogen substituents.

Complete answer:
Saytzeff’s Rule comes into the picture, during elimination reactions. The most substituted product will considerably be the most stable and most preferred one. This rule does not generalize about all the product stereochemistry, but only the regiochemistry of the elimination reaction. Some alkyl halides elimination reaction and alcohol will result in different alkenes and Saytzeff’s Rule is important to predict the major product. The major and minor products are predicted based on the number of alkyl groups attached to the alkene. If more than one elimination product can be formed, then the most substituted alkene is the most stable product or can also be called as the major product.
$C{H_2} = CHR < RCH = CHR < {R_2}C = CHR < {R_2}C = C{R_2}$
For Example, 1) When Butanol will experience dehydration, it provides two products 1 – Butene (minor product) and 2 – Butene (major product). This is dehydration of Alcohol.
2) When 2 – bromobutane experiences a dehydrohalogenation reaction it will give two products 1 – butene and 2 – butene. Out of these two, 2 – Butene is a major product because it is highly substituted and more stable. This is known as the dehydrohalogenation reaction.

Note: Saytzeff’s rule depicts or suggests the regioselectivity of the olefin (alkene), formed by the elimination reaction of 2o or 3o alkyl halides. During the elimination reaction proton is separated from the carbon atom having less number of substituents. The forming olefin is known as the Saytzeff’s product.