<P> An example of a reaction proceeding in a S 1 fashion is the synthesis of 2, 5 - dichloro - 2, 5 - dimethylhexane from the corresponding diol with concentrated hydrochloric acid: </P> <P> As the alpha and beta substitutions increase with respect to leaving groups the reaction is diverted from S 2 to S 1 . </P> <P> The carbocation intermediate is formed in the reaction's rate determining step is an sp hybridized carbon with trigonal planar molecular geometry . This allows two different avenues for the nucleophilic attack, one on either side of the planar molecule . If neither avenue is preferentially favored, these two avenues occur equally, yielding a racemic mixture of enantiomers if the reaction takes place at a stereocenter . This is illustrated below in the S 1 reaction of S - 3 - chloro - 3 - methylhexane with an iodide ion, which yields a racemic mixture of 3 - iodo - 3 - methylhexane: </P> <P> However, an excess of one stereoisomer can be observed, as the leaving group can remain in proximity to the carbocation intermediate for a short time and block nucleophilic attack . This stands in contrast to the S 2 mechanism, which is a stereospecific mechanism where stereochemistry is always inverted as the nucleophile comes in from the rear side of the leaving group . </P>

Draw the structure of the intermediate of the sn1 process