Microwave absorption is not very touchy about individual atoms, ions nor even molecules.
You probably use microwaves at few GHz, for instance 2.45GHz, and heat liquids, don't you? Then absorption results from imperfect conduction and from sluggish polarization. Ions permit conduction losses, polarized molecules permit dielectric losses. So while an alkane would absorb little, you can expect useable absorption from any aqueous solution.
In addition, ovens (I suppose the chemistry microwave heaters differ little) are designed electrically to deliver heat to watery objects over a wide range of conductivity. Too little absorption doesn't happen with water, even pure, and too much absorption results only in heat being superficial.
In a liquid and for few GHz, resonances play no role. The time between shocks is much shorter than the microwave's half-period, so resonances observed in gases at very low pressure are flattened out by the shocks.
So in a kitchen oven, the microwaves are not selective and give just heat to the complete item, nothing subtle acting on specifiic atoms no ions. Would that be very different for chemical reactions?