Haloalkanes and Haloarenes — Chemistry STD 12 Science — Question

→ In the year 1937, Edward Davies Hughes at Sir Christopher Ingold proposed a mechanis for an SN² reaction.
→ The reaction between CHCl₃ and hydroxide in to yield methanol and chloride ion follows second order kinetics.
→ The rate depends upon the concentration of both the reactants.
→ Rate = K [CH₃CI]¹ [OH]¹

→ The incoming nucleophile interacts with alkyl halide causing the carbon-halide bond to break and a new bond is formed between carbon and attacking nucleophile.
→ Here it is C-O bond formed between C and -OH. These two processes take place simultaneously in a single step and no intermediate is formed.
→ As the reaction progresses and the bond between the incoming nucleophile and the carbon atom starts forming, the bond between carbon atom and leaving group weakens.
→ As this happens, the three carbon-hydrogen bonds of the substrate start moving away from the attacking nucleophile.
→ In transition state all the three C-H bonds are in the same plane and the attacking and leaving nucleophiles are partially attached to the carbon.
→ As the attacking nucleophile approaches closer to the carbon, C-H bonds still keep on moving in the same direction till the attacking nucleophile attaches to carbon and leaving group leaves the carbon.
→ As a result configuration is inverted, this process is called inversion of configuration.
→ In the transition state, the carbon atom is simultaneously bonded to incoming nucleophile and the outgoing leaving group.
→ Such structures are unstable and cannot be isolated. Thus, in the transition state, carbon is simultaneously bonded to five atoms.