3.3.3.1 Nucleophilic substitution Flashcards
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
