A hypothesis is advanced for a mechanism by which ultrasound could help to activate chemical reactions, even in the absence of cavitation. It is suggested that the compression phase of an acoustic wave could produce transient solid-like structures within the solution. These structures would result in an "ordering effect" of the molecules in which electrical charges could develop. Such electrical charges could facilitate electron movement from one molecule to another triggering therefore chemical reactions. Such reactions could occur even in the absence of cavitation especially if the solvent or reagents employed show piezoelectric/electrostriction properties. Similar transient ordering effects could be induced by the shockwave accompanying bubble collapse and these would help to explain some of the anomalous effects observed in sonochemistry under cavitation.
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