ChemistryChapter 16: Hydrocarbons
Electrophilic Addition (ethene School)
Ethene + Br2: the C=C attacks Br2, a bromonium / stepwise school picture, product 1,2-dibromoethane.
Learning objectives
- Explain electrophilic addition (ethene school) in simple chemical language.
- Connect 1. br2 and h2 with 2. hbr and steam using equations, observations, or trends where needed.
- Answer a short Federal Board question with the correct terms and a clear reason.
Definition
Ethene + Br2: the C=C attacks Br2, a bromonium / stepwise school picture, product 1,2-dibromoethane. Br2 water decolourises (orange to colourless) — the alkene test. HBr adds (Markovnikov named: H to the carbon that already has more H, if unsymmetric). H2 / Ni: hydrogenation to alkane (named). Steam / acid: ethanol from ethene (industrial name, not a plant). Meaning: the double bond is a nucleophilic cloud; the reagent is the electrophile. Electrophile attacks pi bond; carbocation intermediate then nucleophile adds — Markovnikov for HX. Show curly arrows on addition mechanisms; Markovnikov reasoning must precede the product structure.
Mathematical form
C=C attacks Br2
C=C alkane does not (no C
Important terms
- ELECTROPHILIC ADDITION (ETHENE SCHOOL)
- Ethene + Br2: the C=C attacks Br2, a bromonium / stepwise school picture, product 1,2-dibromoethane.
- 1. Br2 AND H2
- Organic solvent or water: still addition.
- 2. HBr AND STEAM
- Unsymmetric alkene: two possible products; major follows Markovnikov named.
Relationship
- C=C attacks E+
Overview
Test, then unsymmetric add:
Br2 AND H2
Organic solvent or water: still addition. Ni, Pt, or Pd named as hydrogenation catalysts (names). Vegetable-oil hardening named as a slogan, not a factory SOP. Ethene + Br2 -> 1,2-dibromoethane; + H2O (catalyst) -> ethanol industrial route named.
Examples Orange -> colourless · H2 / Ni named · Count: one Br2 per C=C
HBr AND STEAM
Unsymmetric alkene: two possible products; major follows Markovnikov named. Ethene + H2O (acid) -> ethanol named. Cold dilute KMnO4: diol, purple fade (named mild ox). Mechanism arrows: pi electrons attack E+, then Nu- attacks carbocation.
Examples Propene + HBr named · Ethene hydration named · KMnO4 diol named
WHAT — ELECTROPHILIC ADDITION (ETHENE SCHOOL)
Ethene + Br2: the C=C attacks Br2, a bromonium / stepwise school picture, product 1,2-dibromoethane. Br2 water decolourises (orange to colourless) — the alkene test. HBr adds (Markovnikov named: H to the carbon that already has more H, if unsymmetric). H2 / Ni: hydrogenation to alkane (named). Steam / acid: ethanol from ethene (industrial name, not a plant). Meaning: the double bond is a nucleophilic cloud; the reagent is the electrophile. Electrophile attacks pi bond; carbocation intermediate then nucleophile adds — Markovnikov for HX. Show curly arrows on addition mechanisms; Markovnikov reasoning must precede the product structure.
WHY — Why this topic matters
ELECTROPHILIC ADDITION (ETHENE SCHOOL) is an independent FBISE learning unit because students must use its definitions, conditions, equations, or trends separately in explanations and calculations.
HOW — How it works
Br2 AND H2: Organic solvent or water: still addition. Ni, Pt, or Pd named as hydrogenation catalysts (names). Vegetable-oil hardening named as a slogan, not a factory SOP. Ethene + Br2 -> 1,2-dibromoethane; + H2O (catalyst) -> ethanol industrial route named. Examples: Orange -> colourless; H2 / Ni named; Count: one Br2 per C=C. HBr AND STEAM: Unsymmetric alkene: two possible products; major follows Markovnikov named. Ethene + H2O (acid) -> ethanol named. Cold dilute KMnO4: diol, purple fade (named mild ox). Mechanism arrows: pi electrons attack E+, then Nu- attacks carbocation. Examples: Propene + HBr named; Ethene hydration named; KMnO4 diol named. Exam Br2 test: alkene decolourises Br2 water addition across C=C alkane does not (no C=C)
In simple words
School addition. No industrial hydration-plant design.
Key points
- C=C attacks E+
- Br2 water test
- decolourise Br2
- H to richer H carbon
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Electrophilic Addition (ethene School)
Sticky Notes · Quick Revision
Core Idea
- Ethene + Br2: the C=C attacks Br2, a bromonium / stepwise school picture, product 1,2-dibromoethane. Br2 water decolourises (orange to colourless) — the alkene test. HBr adds (Markovnikov named: H to the carbon that already has more H, if unsymmetric). H2 / Ni: hydrogenation to alkane (named). Steam / acid: ethanol from ethene (industrial name, not a plant). Meaning: the double bond is a nucleophilic cloud; the reagent is the electrophile. Electrophile attacks pi bond; carbocation intermediate then nucleophile adds — Markovnikov for HX. Show curly arrows on addition mechanisms; Markovnikov reasoning must precede the product structure.
1. Br2 AND H2
- Organic solvent or water: still addition. Ni, Pt, or Pd named as hydrogenation catalysts (names). Vegetable-oil hardening named as a slogan, not a factory SOP. Ethene + Br2 -> 1,2-dibromoethane; + H2O (catalyst) -> ethanol industrial route named.
- Orange -> colourless
- H2 / Ni named
- Count: one Br2 per C=C
2. HBr AND STEAM
- Unsymmetric alkene: two possible products; major follows Markovnikov named. Ethene + H2O (acid) -> ethanol named. Cold dilute KMnO4: diol, purple fade (named mild ox). Mechanism arrows: pi electrons attack E+, then Nu- attacks carbocation.
- Propene + HBr named
- Ethene hydration named
- KMnO4 diol named
Exam Example
- Exam Br2 test:
- alkene decolourises Br2 water
- addition across C=C
- alkane does not (no C=C)
Common Misconceptions
- Do not confuse 1. Br2 AND H2 with 2. HBr AND STEAM; state the difference before giving an example.
- Writing only “C=C attacks E+” is not enough. Explain what it means in a complete sentence.
FBISE Exam Check
- Explain electrophilic addition (ethene school), compare its two main parts, and include the correct chemical evidence.
- School addition. No industrial hydration-plant design.
60-second revision
- Ethene + Br2: the C=C attacks Br2, a bromonium / stepwise school picture, product 1,2-dibromoethane.
- 1. Br2 AND H2: Organic solvent or water: still addition.
- 2. HBr AND STEAM: Unsymmetric alkene: two possible products; major follows Markovnikov named.
- Exam reminder: Exam Br2 test: alkene decolourises Br2 water addition across C=C alkane does not (no C=C)
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