in this particular problem i am going over the protection of alcohols ( in this

Question

in this particular problem i am going over the protection of alcohols ( in this case its R-O-H) and i used triethylamine to deprotonate the alcohol and chlorotrimethyl silyl ether to protect it. I know this goes through the sn2 or sn2 like reaction once the alcohol group becomes the neucleophile and forms a partial bond intermediate with the silicone and chlorine before it kicks off the chlorine but what i dont understand is why it can do this as a 3rd degree silicon atom where as a 3rd degree carbon cannot.

Explanation / Answer

Silicon is bigger than carbon in size, which allows it to form a stable transition state in an SN2 reaction without having a considerabke steric crowding problem. In a transition state five bonds are connected to the same atom of silicon. This is not possible in case of a tertiary carbon compound, where steric hindrance prohibits entry of nucleophile from backside and thus SN2 mechanism does not occur.

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