SN1 and SN2 Reaction of Haloalkanes

A haloalkane’s structure determines whether it will hydrolyze or not. Primary haloalkanes are often hydrolyzed using an SN2 mechanism, while secondary and third-generation secondary haloalkanes are typically hydrolyzed using an SN1 mechanism for tertiary haloalkanes or tertiary alkyl halides. There are two types of reactions involving haloalkanes, referred to as the SN1 and SN2 reactions.

SN1 Reaction  chemical reaction 

The SN1 reaction is a nucleophilic substitution reaction that occurs in a single molecule. A two-step reaction is required. In the first stage, the carbon-halogen bond is broken heterolytically, with the halogen maintaining the pair of electrons that it had previously shared with the carbon. This is accomplished in the second step by a fast reaction between the nucleophile and the carbocation that was produced in the first stage.

This reaction takes place in polar protic solvents such as water, alcohol, acetic acid, and other similar substances. In this case, the reaction is governed by first-order kinetics. As a result, this is referred to as substitution nucleophilic unimolecular substitution. This reaction occurs in two stages, which are explained in greater detail below.

Step-1

Because of the presence of a nucleophile, the link between carbon and halogen is broken, resulting in the creation of a carbocation between the two elements.

It is the most time-consuming and reversible stage since it requires a significant amount of energy to completely dissolve the connection.

The bond is broken by solvation of the molecule in a protic solvent, which is why this step is the most time-consuming of the entire process.

The rate of reaction is solely dependent on the haloalkane and not on the nucleophile.

Step-2

The nucleophile attacks the carbocation that was produced in step 1, resulting in the formation of the new compound.

Because the development of a carbocation is the rate-determining step in the reaction, the greater the stability of the production of an intermediate carbocation, the greater the ease with which the compound can undergo substitution nucleophilic unimolecular or SN1 reaction.

Because of the great stability of 3 degree carbocations, 3 degree alkyl halides undergo the SN1 reaction fairly quickly in the case of alkyl halides.

As a result, the allylic and benzylic halides exhibit a high degree of reactivity toward the SN1 reaction.

SN2 Reaction chemical reaction

This reaction has second order kinetics, and the rate of reaction is dependent on both the haloalkane and the nucleophile that is participating in the process. So-called substitution nucleophilic bimolecular reaction is the term used to describe this reaction. In this reaction, the nucleophile attacks the positively charged carbon, and the halogen is expelled from the group as a result of the attack.

It is a simple one-step reaction to the situation. Both the creation of carbocation and the expulsion of halogen occur at the same time in nature. For the first time since the SN1 mechanism has been identified in this process, the inversion of configuration has been observed. Because this reaction necessitates the proximity of the nucleophile to the carbon atom that bears the leaving group, the presence of bulky substituents on or near the carbon atom has a significant inhibitory influence on the reaction.

As a result, in contrast to the SN1 reaction mechanism, this is favoured primarily by primary carbon, followed by secondary carbon, and last tertiary carbon. A number of factors influence the outcome of a nucleophilic substitution process. Some of the most critical considerations are as follows.

• The influence of the solvent

• The influence of the substrate’s structural characteristics

• The nucleophile has an effect.

• The ramifications of leaving the group

Conclusion

SN1 and SN2 are summarised in this section.This leads us to the conclusion that SN1 and SN2 are two different types of nucleophilic substitution reactions.

A nucleophile is an atom or molecule with a high concentration of electrons. It can appear in the form of an anion at times, and it can also appear in the form of a compound or atom that has at least one lone pair of electrons at other times.

In contrast to a nucleophile, an electrophile is a substance that attracts electrons. An electrophile is a chemical species that has a positive charge attached to it. The nucleophile is a chemical compound or atom that attacks the positively charged region of a compound or atom.

A nucleophilic substitution reaction is a type of reaction in which one negatively charged functional group or atom is replaced by another negatively charged functional group or atom in a process.

SN1 is a unimolecular reaction, but SN2 is a bimolecular reaction, as seen in the diagram.SN1 is composed of two steps. SN2 consists of a single stage.

There is a moment in SN1 where carbocation begins to form. The anion, or negatively charged atoms or compounds, is subsequently attracted to the carbocation by the electrostatic force. There is only a transition stage in SN2 and no generation of intermediates during the reaction.

 This article demonstrates that a weaker nucleophile can be displaced by a stronger nucleophile when the two react together.