3. Chemical stability: coupling chemical reactivity and structural relaxation

In addition to physical stability, the crystalline state generally ensures high chemical stability of a compound. The amorphous state, on the other hand, can be a source of chemical instability. This is well demonstrated, for example, in a quantitative nuclear magnetic resonance study ( ¹³ C NMR – CPMAS spectrum evolution) of the mutarotation reaction of dry lactose . When anhydrous crystalline α-isomeric lactose (αL) is heated to melting (≈ 200°C), no mutarotation from α to β form is observed. After melting, however, chemical changes occur rapidly. The situation is very different if the lactose is initially in the amorphous...