# Mind Map Reaction of Alkene: Branches and a Worked Example

Canonical: https://sakura5.app/blog/mind-map-reaction-of-alkene/  
Published: 2026-11-12  
Author: the Sakura5 team · 7 min read  
Updated: 2026-11-12  
Publisher: Sakura5 (https://sakura5.app) · support@sakura5.app

> **TL;DR:** A mind map of alkene reactions, branch by branch: hydrogenation, halogenation, HBr, hydration, oxidation, polymerisation, plus a worked propene example.

![Mind Map Reaction of Alkene: Branches and a Worked Example](https://sakura5.app/img/blog/inline/mind-map-reaction-of-alkene-1.jpg)

A mind map of the reactions of an alkene puts the C=C double bond in the centre and runs one branch for each thing that bond can do: add hydrogen, add a halogen, add a hydrogen halide, add water, get oxidised, or join with other alkenes into a polymer. Nearly every exam question on alkenes is one of those branches, because the reactivity of an alkene comes from a single feature — the electron-rich pi bond that sits above and below the carbon–carbon axis.

That is exactly why a map beats a page of equations. A reaction list shows you six unrelated facts. A map shows that five of the six are the same move — an addition across the double bond — with a different reagent each time, and that the sixth, oxidation, is the odd one out. Once you see that, you stop memorising and start predicting.

Below: why the usual lists fail, what goes on each branch, how to build the map step by step, a worked example using propene, the edge cases examiners love, and a short FAQ.

## Why a list of alkene reactions does not stick

Most revision sheets give you something like: ethene + H2 gives ethane, ethene + Br2 gives 1,2-dibromoethane, ethene + HBr gives bromoethane. Each line looks new. Each line gets its own slot in memory, and under exam pressure the slots blur.

The second problem is that lists hide conditions. Hydrogenation needs a nickel catalyst and heat. Hydration needs steam and a phosphoric acid catalyst. Bromine water needs nothing at all, which is why it works as a test. Conditions are marks, and a flat list puts them in the same grey type as everything else.

The third problem is that lists hide the one rule that matters for unsymmetrical alkenes: which carbon the hydrogen ends up on. That rule is a node in a map, attached to the right branch. In a list it is a footnote you skip.

## What goes on a mind map of the reactions of an alkene

Keep the first ring to six branches. Everything else hangs one level down.

- **Hydrogenation.** Alkene + H2 gives an alkane. Conditions: nickel catalyst, around 150 °C. Use: hardening vegetable oils.
- **Halogenation.** Alkene + Br2 (or Cl2) gives a 1,2-dihaloalkane. Room temperature. The orange-to-colourless change of bromine water is the standard test for a double bond.
- **Hydrohalogenation.** Alkene + HBr or HCl gives a haloalkane. For an unsymmetrical alkene, the major product follows Markovnikov’s rule.
- **Hydration.** Alkene + steam gives an alcohol. Conditions: phosphoric acid catalyst on silica, high temperature and pressure. This is how ethanol is made industrially from ethene.
- **Oxidation.** Cold, dilute, acidified or alkaline potassium manganate(VII) turns the alkene into a diol and the purple solution goes colourless or brown. Stronger conditions can cleave the double bond.
- **Polymerisation.** Many alkene molecules join by addition to give a long chain, such as poly(ethene) or poly(propene).

Under hydrohalogenation, add one more node: the hydrogen goes to the carbon that already has more hydrogens, and the halogen goes to the other. For background on all of these, the [Wikipedia article on alkenes](https://en.wikipedia.org/wiki/Alkene) covers each reaction class with mechanisms.

## How to build the map, step by step

Twenty minutes is enough on paper. The order matters more than the colours.

### 1. Draw the double bond first

Write “alkene, C=C” in the centre and add one short node: “pi bond = electron-rich, attacked by electrophiles.” Every branch will refer back to this, so it earns the middle of the page.

### 2. Add the six reaction branches

Label each branch with the reagent, not the product. Reagents are what you must recall; products you can then work out. Hydrogen, bromine, hydrogen bromide, steam, permanganate, and “itself” for polymerisation.

### 3. Hang conditions and observations underneath

One child node for conditions, one for what you see or make. For bromine water the child is “orange to colourless.” For hydration it is “H3PO4, steam, high pressure.”

### 4. Mark the shared pattern

Colour the four addition branches the same and draw a loop labelled “C=C becomes C–C, two new atoms added.” Oxidation and polymerisation get different colours, because they are different stories.

### 5. Test it from memory

Cover the map, redraw it, and compare. Gaps show up as blank branches. This is the same retrieval idea behind [revising with flashcards and mind maps together](https://sakura5.app/blog/how-to-revise-for-exams-using-flashcards-and-mind-maps/).

If you would rather not start from a blank page, [MindMap AI](https://sakura5.app/mindmapai/) lets you type “reactions of alkenes” or paste your class notes and get a draft map you can then edit, prune and add your own conditions to. Editing a draft is faster than drawing one, and you still do the thinking in step 4.

## A worked example: the reactions of propene

Take propene, CH3CH=CH2, and put it in the centre. Propene is the right choice because it is unsymmetrical, so it tests the Markovnikov node that ethene never does.

![A worked example: the reactions of propene — mind map reaction of alkene](https://sakura5.app/img/blog/inline/mind-map-reaction-of-alkene-2.jpg)

*Take propene, CH 3 CH=CH 2 , and put it in the centre.*

Branch by branch, with 1 mole of propene each time:

- **H2, Ni, heat:** propane, CH3CH2CH3. One product, no ambiguity.
- **Br2, room temperature:** 1,2-dibromopropane, CH3CHBrCH2Br. Bromine water goes from orange to colourless.
- **HBr:** the hydrogen goes to the CH2 end, which already has two hydrogens, and the bromine goes to the middle carbon. Major product: 2-bromopropane, CH3CHBrCH3. The minor product is 1-bromopropane.
- **Steam, H3PO4:** by the same rule, propan-2-ol, CH3CH(OH)CH3, is the major product.
- **Cold dilute KMnO4:** propane-1,2-diol, CH3CH(OH)CH2OH.
- **Polymerisation:** poly(propene), a chain with a CH3 side group on every second carbon.

Count what the map did here. Six reactions, but the HBr and steam rows share one rule, and the H2 and Br2 rows are just symmetrical additions. In practice you recall three ideas plus the conditions, not six equations.

## Edge cases that cost marks

Examiners go after the same few spots every year. Give each its own warning node on the map.

![Edge cases that cost marks — mind map reaction of alkene](https://sakura5.app/img/blog/inline/mind-map-reaction-of-alkene-3.jpg)

*Examiners go after the same few spots every year.*

- **Bromine water versus bromine in solvent.** Bromine water can also give a bromohydrin product, with an OH group on one carbon. Check what your syllabus expects before you write 1,2-dibromo in every answer.
- **Alkanes do not decolourise bromine water in the dark.** That is the point of the test. Alkanes need UV light and react by a different mechanism.
- **Symmetrical alkenes.** Ethene and but-2-ene have no major and minor product from HBr, so Markovnikov is irrelevant. Do not invent one.
- **Conditions that sound similar.** Hydrogenation uses a solid nickel catalyst. Hydration uses an acid catalyst. Swapping them loses the mark even when the product is right.
- **Oxidation strength.** Cold dilute permanganate gives a diol. Hot concentrated acidified permanganate breaks the C=C bond into smaller molecules. Check which your course asks for.

The same habit — tagging each fact with the condition that makes it true — is what makes a projectile map work in physics, as in our [mind map of projectile motion](https://sakura5.app/blog/mind-map-projectile-motion/). The subject changes; the structure does not.

When you have the map, keep it small enough to redraw in five minutes. A map you can reproduce from memory is one you know. For a quick draft to start from, [open MindMap AI](https://sakura5.app/mindmapai/), generate the alkene map, then delete anything you cannot explain.

## FAQ

**What are the main reactions of alkenes?**

The main reactions are all driven by the C=C double bond: hydrogenation to an alkane, halogenation with bromine or chlorine, addition of hydrogen halides, hydration with steam to form an alcohol, oxidation with potassium manganate(VII), and addition polymerisation. Four of these are addition reactions across the same bond.

**How do I test for an alkene?**

Shake the sample with bromine water. An alkene decolourises it from orange to colourless within moments, at room temperature and without light. A saturated alkane leaves the orange colour in place. Cold dilute acidified potassium manganate(VII) turning from purple to colourless also indicates a double bond.

**What is Markovnikov’s rule in a mind map?**

Put it as a child node under hydrohalogenation and hydration: when a hydrogen halide or water adds to an unsymmetrical alkene, the hydrogen attaches to the carbon that already has more hydrogens. So propene plus HBr gives mainly 2-bromopropane. It does not apply to symmetrical alkenes.

**Can I make the mind map with an app?**

Yes. In [MindMap AI](https://sakura5.app/mindmapai/) you can enter a topic or paste notes, get a draft map, and edit the branches. Treat the draft as a starting point and check every reagent and condition against your textbook, because exam marks depend on the exact wording.

About the app: [MindMap AI: Mind Map Maker](https://sakura5.app/mindmapai/) · App Store: https://sakura5.app/go/mindmapai?from=/blog/mind-map-reaction-of-alkene/