A concerted substitution
Predict firstShould OH⁻ approach the bromine, or the carbon bonded to it?
Understand the spatial relation between concerted bond making, bond breaking, and backside attack.
Prerequisites: The nucleophile supplies a bonding electron pair; the leaving group takes the original bonding pair with it.Locate the reaction center
Predict firstShould OH⁻ approach the bromine, or the carbon bonded to it?
The oxygen end of the nucleophile donates its electron pair to the carbon. In CH₃Br the electrons of the C–Br bond finally leave with the departing Br. All position changes here are driven by a teaching reaction coordinate.
How to observe
- Watch the nucleophile attack from the side opposite the leaving group
- Pause at the transition state and inspect the two partial bonds and the three in-plane hydrogens
- Compare the umbrella inversion between the reactant and the product
Model notes
A qualitative reaction path for OH⁻ and CH₃Br forming CH₃OH and Br⁻. The horizontal progress is a reaction coordinate, not real time or a computed minimum-energy path; dashed lines mark partial bonds. The three hydrogens of the methyl group are identical, so this example gives no distinguishable R/S enantiomers even though the geometry inverts.