Conclusions Suitable Conditions for Observation of Specific MW Effects

Conclusions Suitable Conditions for Observation of Specific MW Effects 

We have proposed in this review a rationalization of microwave effects in organic synthesis based on the effect of the medium and on mechanistic considerations. The most suitable conditions in which there is any chance of checking specific not purely thermal effects are  

Polar mechanisms via polar transition states. If the polarity of a system is enhanced from the ground state to the transition state, acceleration can result from an increase in material-wave interactions during the course of the reaction. The most frequently encountered examples are unimolecular or bimolecu-lar reactions between neutral molecules (because dipoles are developed in the TS) and anionic reactions of tight ion-pairs, i.e. involving charge-localized anions (leading to ionic dissociation in the TS). 

Slower reacting systems, necessitating a high energy of activation and consequently with late product-like transition states along the reaction coordinates, in agreement with the Hammond postulate. 

Nonpolar solvents or, even better, solvent-free conditions (green chemistry) to avoid that microwave effects will be masked or limited by solvent effects. 

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