The acceleration of a reaction that occurs when reactive groups are constrained in a productive orientation, either intermolecularly, as on an enzyme surface, or intramolecularly as in a model compound. Depending upon which aspect of this phenomenon is being emphasized, the physical bringing together of the components or some special feature of their association, it has been referred to variously as antichimaeric assistance, approximation, catalytic configuration, the Circe effect, coupling between conformational fluctuations, directed proton transfer, electric field effect, electrostatic stabilization, FARCE (freezing at the reactive centres of enzymes), gas-phase analogy, group transfer hydration, oribital steering, propinquity effect, proximity effect, rotamer distribution, stereoelectronic control, stereopopulation control, substrate anchoring, togetherness, torsional stress and virbrational activation.