SN1 reactions are nucleophilic substitutions, involving a nucleophile replacing a leaving group (just like SN2). However: SN1 reactions are unimolecular: the rate of this reaction depends only on the concentration of one reactant. SN1 reactions happen in two steps: 1. The SN1 reaction is a substitution reaction in organic chemistry. "SN" stands for nucleophilic substitution and the "1" represents the fact that the rate-determining step is unimolecular. Thus, the rate equation is often shown as having first-order dependence on electrophile and zero-order dependence on nucleophile.‎Mechanism · ‎Scope · ‎Side reactions · ‎Solvent effects. Hey! You can now download a free 1-page Summary Sheet of SN1 vs SN2 reactions containing all the material on this series of blog posts.


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Nucleophilic Substitution (SN1, SN2)

Since the first step of the SN1 reaction is loss of a leaving group to give a carbocation, the rate of the reaction will be proportional to the stability of the sn reactions. If the leaving group is directly sn reactions to an alkene or alkyne, SN1 or SN2 will not occur!

The Solvent The SN2 reaction sn reactions favored by polar aprotic solvents — these are solvents such as acetone, DMSO, acetonitrile, or DMF that are polar enough to dissolve the substrate and nucleophile but do sn reactions participate in hydrogen bonding with the nucleophile.

The SN1 reaction tends to proceed in polar protic solvents such as water, alcohols, and carboxylic acids.

These also tend to be the nucleophiles for these reactions as well. Even if the reaction is performed cold, some alkene may be formed. If an attempt is sn reactions to perform an SN1 reaction using a strongly basic sn reactions such as hydroxide or methoxide ion, the alkene will again be formed, this time via an E2 elimination.


This will be especially true if the reaction is heated. Finally, if the sn reactions intermediate can rearrange to a more stable carbocation, it sn reactions give a product derived from the more stable carbocation rather than the simple substitution product.


Solvent effects Since the SN1 reaction involves formation of an unstable carbocation intermediate in the rate-determining step, anything that can facilitate this will sn reactions up the reaction. The normal solvents of choice are both polar to stabilize ionic intermediates in general and protic to solvate the leaving group in particular.

Typical polar protic solvents include water and alcohols, which will also act as nucleophiles and the process sn reactions known as solvolysis.

Kinetics of Nucleophilic Substitution Reactions - Chemistry LibreTexts

The hydroxide ion is the nucleophile and methyl iodide is the haloalkane. If we were to double the concentration of either the haloalkane or the nucleophile, we can sn reactions that the rate of the reaction would proceed twice as fast as the initial rate.

If we were to double the concentration of both the haloalkane and the nucleophile, we can see that sn reactions rate of the reaction would proceed four times as fast as the initial rate. It may safely be assumed sn reactions a primary-substituted leaving group will follow an SN2 pathway in any case, since the formation of the corresponding unstable primary carbenium ion is disfavored.

Kinetics of Nucleophilic Substitution Reactions

Reaction by the SN1 pathway is highly probable for compounds with tertiary substitution, since the corresponding tertiary carbenium ion is stabilized through hyperconjugation: The better the solvent stabilizes the ions, the more probable that the reaction will follow an SN1 pathway e.

The more highly substituted is the incipient carbenium ion, the more sn reactions that the sn reactions will follow an SN1 pathway.


The more unreactive the nucleophile, the more probable it becomes that a reaction with secondary and tertiary electrophiles will follow an SN1 pathway. A weaker nucleophile is not as effective in the backside attack, since this location is sterically shielded, especially in the case of tertiary substrates.

Carbenium ions are planar and therefore less sterically hindered, sn reactions are naturally more reactive as electrophiles sn reactions the uncharged parent compound.

The hydrolysis of tert-butyl chloride is a typical SN1 reaction: Moyeux, Synthesis,45,

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