SUMMARY OF ORGANIC MECHANISMS FOR UNIT 2

Mechanisms you need to know for the examMechanism Homologous

seriesFormulae of reagents

Conditions

free radical substitution

Alkanes Cl2 uv

electrophilic additionAlkenes

Br2

HBrH2SO4

All room temp

nucleophilic substitution

Haloalkanes OH-

CN-

NH3

Warm aqWarm ethanolExcess NH3

eliminationHaloalkanes

OH- Concentrated OH- alcoholic

-Remember: 1. All curly arrows must start from a lone pair or the middle of a bond. 2. The lone pair must be shown 3. All free radicals must be shown clearly with a dot

1. free radical substitution

Initiation:

UV

Propagation:

+ CH3Cl

Termination

Further propagation with excess chlorine:

1

2. Electophilic addition

a) with hydrogen bromide

b) with bromine

c) with sulphuric acid

2

3. nucleophilic substitution

a) with hydroxide ions (dilute aqueous)

b) with cyanide ions

c) with ammonia

4. elimination (Base elimination)

potassium hydroxide concentrated alcoholic

3

New molecule which mechanism?Think, Pair Share : Your team has been given a list of molecules. For each decide what type of attacking species in generated by the reagent, which type of mechanism and thus give the name of the mechanism. You can use the table on P1 to cheat.

Organic molecule reagent Attacking species nucleophile, electrophile Free radical

TypeSubstitutionAdditionElimination

Name of mechanism

OH-

Dilute sodium hydroxide warm

HBr

Cl2 in UV light

H2SO4

NH3 (ammonia in excess)

:CN-

HCN (hydrogen cyanide)

4

C HCH2

H

ICH3

Concentrated potassium hydroxide in ethanol

:CN-

HCN (hydrogen cyanide)

In UV light

OH-

Dilute sodium hydroxide warm

HBr

Concentrated potassium hydroxide in ethanol

OH-

Dilute sodium hydroxide warm

5

OH-

Dilute sodium hydroxide warm

HBr

NH3 (ammonia in excess)

HBr

NH3 (ammonia in excess)

Br2

HBr

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Correct the mistakes that this student has made on the following mechanisms

1. Methane with chlorine in the presence of UV lightStep 1

Step 2

Step 3

2. Bromobutane with aqueous sodium hydroxide (Na+ is a spectator ion)

3. But-2-ene with bromine at room temperature

4. Bromoethane with ammonia in excess heated in a sealed tube

5. 2-bromopropane heated with concentrated potassium hydroxide in ethanol (remember K+ is a spectator ion)7

6. But-1-ene with hydrogen bromide at room temperature

7. 2- bromobut-2-ene with aqueous dilute sodium hydroxide

8. Propane with bromine in uv light (excess bromine)

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9. 2-bromobut-2-ene with hydrogen bromide

1. 2- bromobut-2-ene with hydrogen cyanide (use CN- ions)

2. 2-bromoethanol warmed with aqueous sodium hydroxide (remember Na+ is a spectator ion)

3. Propene and concentrated sulfuric acid

4. 2-bromo-2-methylbutane heated with concentrated potassium hydroxide in ethanol (remember K+ is a spectator ion)

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The OH- ion is behaving as a base. A H+ donor

The CN- ion is behaving as a nucleophile. A species which attacks electron rich areas

Design a mechanismYou have been given the names of some organic compounds their reagents and conditions below.Draw out the structure of the organic molecule, decide on the attacking species (nucleophile, electrophile or free radical) then come up with a mechanism. You can use pages 13 to cheat

1. Methane with chlorine in the presence of UV light2. Bromoethane with cyanide ions in ethanol3. But-2-ene with bromine at room temperature4. Bromoethane with ammonia in excess heated in a sealed tube5. Bromoethane with aqueous, dilute sodium hydroxide6. 2-bromopropane heated with concentrated potassium hydroxide in ethanol (remember K+ is a spectator ion)7. But-1 ene with hydrogen bromide at room temperature8. 2- bromobut-2-ene with aqueous dilute sodium hydroxide9. Propane with bromine in uv light (excess bromine)10. 2-bromobut-2-ene with hydrogen bromide11. 2- bromobut-2-ene with hydrogen cyanide (use CN- ions)12. 2-bromoethanol warmed with aqueous sodium hydroxide (remember Na+ is a spectator ion)13. Propene and concentrated sulfuric acid14. 2,2 dimethyl propane with chlorine in the presence of UV light15. 2-bromo-2-methyl butane heated with concentrated potassium hydroxide in ethanol (remember K+ is a

spectator ion)

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