What a learner can do afterwards
- Explains what a planar intermediate does to the stereochemistry of a product and why
- Distinguishes a stereospecific reaction from a stereoselective one with an example of each
- Uses an observed inversion at a stereocentre to argue for a backside attack
- States what partial racemisation with net inversion suggests about competing pathways
1 · Read
The stereochemical outcome is the strongest ordinary evidence about how a reaction happened. A flat intermediate invites attack from both faces and delivers a racemic mix. Read the products and the hidden pathway reveals itself. Start every analysis by asking what shape the intermediate must have had.
A concerted backside attack flips the centre cleanly, like an umbrella in wind. Clean inversion at one centre therefore argues for that route. Learn the vocabulary precisely. Stereospecific maps each starting geometry to one product, while stereoselective merely prefers one product among options.
A single enantiomer of substrate gives an almost racemic product. The flat intermediate explains the scrambling, since both faces were open. But a small net inversion remains, which points to a second pathway running alongside. The verdict is competing pathways, mostly backside attack with some planar intermediate leaking racemic product.
Match each outcome to its cause. Full racemisation means a planar intermediate. Clean inversion means backside attack. Partial racemisation with net inversion means both routes at once. Never argue from speed or colour when the stereochemistry already testifies.
Inversion, retention and scrambling each point at a different geometry at the moment of reaction.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.