the+sn1+mechanism

The first substitution reaction we will investigate is called "SN1", which stands for __s__ubstitution, __n__ucleophilic, 1st order. In essence, all this reaction does is functional group swapping, where one functional group (a good leaving group) is replaced by another (a good nucleophile).

Here is an overview of the SN1 reaction mechanism:

Notice the details:
 * The leaving group is X, and undergoes heterolysis in the first step (called "leaving group dissociation);
 * The positively charged carbon that is produced in step //a// is called a __carbocation__ and is of major importance in SN1 reactions;
 * In step //b// the nucleophile (Nu) bonds (heterogenesis) to the carbocation.

This two-step process occurs in //every single SN1 reaction// and must be shown if a mechanism is needed.

Here is a specific example of an SN1 reaction, without the mechanism:



The leaving group in the reaction is Br, since it is no longer part of the parent molecule in the product. The nucleophile is the cyanide ion (CN-) and is provided to you over the reaction arrow (a common feature). Notice it takes the place of the bromide (hence 'substitution'!).

Here is a video explaining the process:

media type="youtube" key="JmcVgE2WKBE" height="315" width="560"

Watch this [|animation of the SN1 mechanism] for more insight. This [|slide show] may help, too.