3.3.3.1 Nucleophilic substitution
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Which one has a higher boiling point: 2-iodoheptane and 3-iodo-2,3-dimethylpentane?
2-iodoheptane because of the increased tesselation
What is a nucleophile?
Reagents that attack and form bonds with positively or partially positively charged carbon atoms Negatively charged ion or atom Lone pair of electrons Lone pair is situated on the electronegative atom E.g. NH3, OH, CN
What is the process of substitution?
A nucleophile replaces the halogen in a halogenoalkane They move to the partially positive charged carbon atom
Are halogenoalkanes soluble?
Not in water so ethanol can act as a solvent
What occurs when halogenoalkanes are added to aqueous sodium/potassium hydroxide?
Nucleophilic substitution OH ion is the nucleophile Happens slowly at room temperature Halogenoalkanes do not mix with water so ethanol can be used as a solvent Hydrolysis reaction Alcohol formed Rate of reaction depends on the strength of the carbon halogen bond: C-F > C-I
What occurs when halogenoalkanes are warmed with an aqueous alcoholic solution of potassium cyanide?
Nitriles are formed Nucleophile is the CN ion CN group is counted as part of the root, CH3CH2CN is propanenitrile, not ethanenitrile
What occurs when halogenoalkanes are added to concentrated ammonia?
Amine is produced R-X + 2NH3 = RNH2 + NH4X
How do you draw a nucleophilic substitution reaction with mechanisms?
See card First arrow points from the nucleophile to the positively charged carbon atom 2nd arrow points from the carbon - X bond to the X atom
What is a nucleophilic substitution reaction?
A reaction where a halogenoalkane reacts with a nucleophile The rate of the reaction depends on the strength of the carbon halogen bond: C - F > C - Cl etc When cyanide is involved, the carbon is counted as part of the chain
What’s the difference in conditions between a substitution and elimination reaction in halogenoalkanes?
Substitution: cold OH- ion in water, forms an alcohol Elimination: hot OH- in ethanol, forms an alkene Primary halogenoalkanes mainly react by substitution Tertiary halogenoalkanes mainly react by elimination Secondary can react by both
What are the conditions for the reaction between halogenoalkanes and aqueous sodium or potassium hydroxide?
Occurs very slowly at room temperature Warm the mixture to speed it up Halogenoalkanes do not mix with water so dissolve in ethanol
What are the conditions for the reaction between halogenoalkanes and potassium cyanide?
Needs to be warmed