Question

What are: Hammond Postulate, Markovnikov’s rule and Can-Ingold-Prelog rule?

Answer 1

According to Hammond Postulate, the transition state of reaction resembles either reactants or products to which it is closer in energy. In an endothermic reaction, it is closer to products in energy. In the case of exothermic reaction, it is closer to reactants in energy.

Markovnikov’s rule states that negative part of the addendum (adding molecule) gets attached to that carbon atom which possesses lesser number of hydrogen atoms and positive part of the addendum (adding molecule) gets attached to that carbon atom which possesses more number of hydrogen atoms.

R, S nomenclature of chiral carbons is assigned based on the Chan-Ingold-Prelog rule.

According to Chan-Ingold-Prelog rule, assign priorities for the attached atoms/groups based on atomic number of attached atom. If first attached atom is same proceed in the chain till the point of difference is obtained. After assigning the priority, keep the least priority atom/group below the plane, if the priority order is clock-wise the configuration R and if it is anti-clockwise, the configuration is S.