explain the styzeffs rule with suitable example.
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Answer:
Saytzeff’s Rule is also called Zaitsev’s rule, Saytzev’s rule or Z-rule. A Russian Chemist Alexander Zaitsev analysed different elimination reactions and observed a general pattern in the resulting alkenes. Based on this analysis, Zaitsev stated that stable alkene is formed when the removal of hydrogen from β-carbon has a low number of hydrogen substituents.
During elimination reactions, Saytzeff’s Rule comes into the picture. The most substituted product would be the most stable and most preferred one. This rule does not generalize about the product stereochemistry, but only the regiochemistry of the elimination reaction.Examples:
1. Dehydrohalogenation of 2-Bromobutane
When 2-bromobutane undergoes a dehydrohalogenation reaction it gives two products 1-butene and 2-butene. Out of these two, 2-Butene is a major product since it is highly substituted and more stable.
During elimination reactions, Saytzeff’s Rule comes into the picture. The most substituted product would be the most stable and most preferred one. This rule does not generalize about the product stereochemistry, but only the regiochemistry of the elimination reaction.
Important concept behind Saytzeff’s Rule:
If more than one elimination product is possible, the most substituted alkene is the most stable product (major product).
CH2 = CHR < RCH = CHR < R2C = CHR < R2 C = CR2
Mono < di < Tri < tetra
Examples:
1. Dehydrohalogenation of 2-Bromobutane
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Dehydrohalogenation of 2-Bromobutane
When 2-bromobutane undergoes a dehydrohalogenation reaction it gives two products 1-butene and 2-butene. Out of these two, 2-Butene is a major product since it is highly substituted and more stable.
2. Dehydration of alcohols
When Butanol undergoes dehydration, it gives two products 1-Butene (minor product) and 2-Butene (major product).