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Sn2vSn1 - Sn2 Less substituted is better why Sterics We...

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Sn2 Less substituted is better, why? Sterics We learned that Sn2 must occur via “back attack.” Therefore, the more carbons that are in the ‘back’ the harder time it will have to actually move in and interact with the biggest lobe ( ) of the electrophile. Here when we compare a 3° Alkyl halide (on the left) with a 1° Alkyl halide we see why its so hard for the Nucleophile OH to interact with it. Sterics are to blame in this case and they seem to be the overriding factor. Therefore we can conclude, generally, that the more substituted the electrophile carbon is the less favorable Sn2 becomes. Br C H D O - H sigma * C‐BR O - sp 3 H H H Br C C C H H H H H H H H H O - H sigma * C‐BR O - sp 3
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Sn1 Unlike in Sn2, an electronic effect (instead of a steric one) seems to be the overriding factor in Sn1. Another way of saying this is that the added stabilization of the extra methyl groups seem to be the most important factor. This means that the more substituted the electrophile carbon is, the more favorable and Sn1 mechanism becomes. Below, we see a diagram that shows one of the three methyl
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