Chad shows how to identify the type of isomerism between two molecules if any. They may be different compounds, identical, constitutional isomers, enantiomers, or diastereomers. The first question to ask is whether two molecules even have the same bond connectivity as this will help determine between constitutional isomers and stereoisomers. If two molecule do not have the same bond connectivity, they are either constitutional isomers or not even isomers at all. If two molecules have the same bond connectivity, they are either identical, enantiomers, or diastereomers (i.e. identical or stereoisomers).

Chad demonstrates that in some cases the pair of molecules may be drawn in such a way that the visual comparison is all that is needed to identify the type of isomerism. In other cases, a visual comparison may be problematic, and he shows that assigning R and S to chiral centers can help to distinguish between structures that have the same bond connectivity. In such cases, if the two molecules have all the same absolute configurations (same assignments of R and S), then they are identical. If they are chiral and have all the opposite absolute configurations, they are enantiomers. Finally, if they have some chiral centers in the same configuration and some in opposite configuration, then they are diastereomers.

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00:00 Lesson Introduction
01:01 Problem #1 - Identical, Enantiomers, or Diastereomers?
03:28 Problem #2 - Identical, Enantiomers, or Diastereomers?
05:49 Problem #3 - Identical, Enantiomers, or Diastereomers?
08:44 Problem #4 - Meso Compound - Identical?
10:04 Problem #5 - Identical, Enantiomers, or Diastereomers with Fischer Projections

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