The Geminal Effect

When two functional groups are borne by the same atom, they interact to cause either stabilization or destabilization. This is the geminal effect.20 If the substituents are both strong o-acceptors and n-donors [for example a gem-dimethoxy-C(OMe)2-], a stabilization occurs.21 This is easy to understand. Oxygen, being electronegative, is a o-acceptor and o co is low in energy and is 71-donor thanks to its lone pair. Therefore, we have here a double anomeric effect ... 

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