 The move towards a fully spatial interpretation was advanced by the simultaneous postulation in 1874 of a tetrahedral structure for the orientation of carbon’s four bonds by Jacobus van ’t Hoff (1852–1911) and Joseph Achille Le Bel (1847–1930) to account for optical isomerism (see Figure 4 and section 2.2). When carbon atoms are bonded to four different constituents, they cannot be superimposed on their mirror images, just as your left and right hands cannot be. This gives rise to two possible configurations of chiral molecules, thus providing for a distinction between distinct substances whose physical and chemical properties are the same except for their ability to rotate plane polarized light in different directions. 