---
title: "Electrophilic Addition Revisited: Bridged Ions and Stereospecificity"
description: "Markovnikov's rule was a result to memorise. Once cations can be ranked, the rule becomes a prediction, and the cases where a bridged intermediate forms explain outcomes the rule alone cannot."
canonical: https://lightmysky.com/learn/science/electrophilic-addition-revisited-bridged-ions-and-stereospecificity-mt_sbsBxFJyZy
source: https://lightmysky.com/learn/science/electrophilic-addition-revisited-bridged-ions-and-stereospecificity-mt_sbsBxFJyZy.md
retrieved: 2026-09-12
---

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# Electrophilic Addition Revisited: Bridged Ions and Stereospecificity

Markovnikov's rule was a result to memorise. Once cations can be ranked, the rule becomes a prediction, and the cases where a bridged intermediate forms explain outcomes the rule alone cannot.

Subject: Science · Area: Chemistry · Ages 19 to 21
Page: https://lightmysky.com/learn/science/electrophilic-addition-revisited-bridged-ions-and-stereospecificity-mt_sbsBxFJyZy

## Ready when they can

- Derives the Markovnikov outcome from the relative stability of the two possible cations
- Draws a bromonium ion and uses it to explain anti addition across a double bond
- Predicts the stereochemistry of halohydrin formation, including which carbon the hydroxyl lands on
- Explains an anti-Markovnikov outcome by identifying the different intermediate involved

## Lesson: Bridges over the double bond

Alkenes are electron rich, so electrophiles attack them first. Protonation of the double bond creates a carbocation, and the proton adds to whichever end gives the stabler cation. The nucleophile then captures that cation. So the new hydrogen lands on the less substituted carbon and the nucleophile on the more substituted one. That is the whole content of Markovnikov's rule, turned from memory into prediction.

Bromine refuses the open cation. The second bromine atom stays bound and bridges both carbons as a three membered bromonium ring with the charge shared. The bridge blocks one face and forbids rearrangement. The nucleophile must open the ring from the back, so the two new groups finish trans to each other in strict anti addition.

**Example.** Treat cyclohexene with bromine water and two selectivities combine. Bromine supplies the bridge, water supplies the nucleophile that opens it. Water attacks the more substituted end of the ring, where more partial positive charge sits. So bromine lands on the less substituted carbon and the hydroxyl on the more substituted one, trans to each other.

**Tip.** Learn the exception that proves the pattern. Peroxides with HBr give anti-Markovnikov addition because a bromine radical adds first, making the most stable carbon radical. The intermediate is a radical, not a cation, so bromine finishes on the less substituted carbon. Spot rearranged skeletons as fingerprints of open cations, since bridged ions cannot shift.

**Recap.** Cations predict Markovnikov, bridges enforce anti addition, and radicals flip the regiochemistry.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Carbocations: Stability, Rearrangement and Neighbouring Groups](https://lightmysky.com/learn/science/carbocations-stability-rearrangement-and-neighbouring-groups-mt_0r1d2u30PE)
- [Electrophilic Addition to Alkenes](https://lightmysky.com/learn/science/electrophilic-addition-to-alkenes-mt_1RB5nj8zR8)
- [Substitution Against Elimination: Predicting the Major Product](https://lightmysky.com/learn/science/substitution-against-elimination-predicting-the-major-product-mt_6WyFC9kQuu)

## Opens up

- [Hydroboration, Oxidation and Cleavage of Alkenes and Alkynes](https://lightmysky.com/learn/science/hydroboration-oxidation-and-cleavage-of-alkenes-and-alkynes-mt_Ny7vC57rqc)