Final answer:
Two protons are diastereotopic if their substitution results in diastereomers, and enantiotopic if their substitution yields enantiomers. Using molecular models to visualize these changes can help determine the relationship between the protons. Enantiomers are non-superimposable mirror images, whereas diastereomers are not.
Step-by-step explanation:
To determine if two protons are diastereotopic or enantiotopic, one must understand the concepts of chirality and symmetry within molecules. Enantiotopic protons are protons that, when one is replaced with a different substituent, convert a molecule into one of two enantiomers. Conversely, diastereotopic protons are protons that, when one is substituted, result in diastereomers but not enantiomers. A practical approach is to use a molecular model or computational chemistry software to visualize the molecule and the effects of substituting each of the protons in question. If substituting one proton gives rise to enantiomers, they are enantiotopic. If the result is diastereomers, the protons are diastereotopic. Remember that enantiomers only differ in the three-dimensional placement of atoms and are non-superimposable mirror images, while diastereomers differ at one or more stereocenters but are not mirror images. For example, glucose has several chiral carbons, and the last optically active carbon defines the D and L enantiomers. In 1,2-dimethylcyclopropane, changing one methyl group from trans to cis configuration results in diastereomers, not enantiomers, because the altered molecule is not a mirror image of the original.