Question

In SN² reactions , the sequence of bond breaking and bond formation is as follows _________________. *
bond breaking is followed by formation
bond formation is followed by breaking
bond breaking and formation take place simultaneously
bond breaking and formation take place randomly

Answer 1

Answer:

Bond breaking and formation take place simultaneously.

Some more points about SN² rxn:

Order of SN² rxn is 2.

Stereochemistry of the molecule changes.

Reactivity order towards SN² is 1°>2°>3°.

Answer 2

Bond breaking and a new bond formation occur simultaneously in a $S_{N} 2$ reaction.

• $S_{N} 2$ reaction is a nucleophilic substitution reaction that follows second-order kinetics.
• The rate-determining step in the reaction is the formation of the transition state, where two reactants are involved. So it is a second-order reaction.
• A leaving group is replaced by a nucleophile, forming the desired product. The attack of nucleophiles occurs from the backside of the carbon with leaving group, forming a transition state.
• So less crowded carbons favor $S_{N} 2$ reactions. the order of reactivity towards the $S_{N} 2$ mechanism is 3°<2°<1°<methyl carbon.
• Examples of a reaction involving $S_{N} 2$ mechanism include the formation of alcohols from alkyl halides.
• The general reaction mechanism is shown in the given attachment.