Nucleophilic substitution in halogenoalkanes Flashcards
What is a nucleophile?
A nucleophile is a reagent that attacks and forms bonds with positively or partially positively charged carbon atoms
What are the four key characteristics of a nucleophile?
- It is a negatively charged ion or an atom with a δ- charge
- Contains a lone pair of electrons
- The lone pair is found on an electronegative atom
- Can donate electrons to form a covalent bond
What are the three common nucleophiles in organic chemistry?
Hydroxide ion - :OH-
Ammonia - :NH3
Cyanide ion - :CN-
What type of reaction do nucleophiles undergo with halogenoalkanes?
Nucleophilic substitution, where the nucleophile replaces the halogen atom in a halogenoalkane
What is a reaction mechanism?
A reaction mechanism describes the step by step process by which reactant are converted into products, often involving short lived intermediates
Where does the curly arrow start when a nucleophile attacks?
The arrow starts at the lone pair of the nucleophile and moves towards the partially positive carbon (C+)
What do curly arrows represent in organic reaction mechanisms?
Curly arrows show the movement of electron pairs during a reaction
What determines the rate of nucleophilic substitution in halogenoalkanes?
The rate depends on the C-X bond strength, the weaker bonds break more easily, making substitution faster
What happens to the C-X bond during nucleophilic substitution?
A curly arrow shows the electron pair in the C-X bond moving to the halogen, forming a halide ion (X-), which is the leaving group
Why are fluoro - compounds unreactive in nucleophilic substitution?
The C-F bond is very strong, so it is difficult to break, making fluoro - compounds unreactive
How does reactivity change down Group 7 in nucleophilic substitution?
Reactivity increases down the group as the C-X bond strength decreases
What is the suitable reagent and condition needed for a nucleophilic substitution reaction with a hydroxide ion? (-OH)
Suitable reagent = Aqueous sodium or potassium (NaOH/KOH)
Conditions needed = being heated under reflux
When an alkyl halide (halogenoalkane) undergoes nucleophilic substitution with hydroxide, what is formed?
When an alkyl halide undergoes nucleophilic substitution with hydroxide, an alcohol is formed
Why is ethanol used as a reagent for the nucleophilic substitution reaction with a hydroxide ion?
Ethanol is used as a solvent because both the halogenoalkane and aqueous sodium/potassium can mix
What is the suitable reagent and condition needed fr a nucleophilic substitution reaction with a hydroxide ion? (-CN)
Suitable reagent = potassium cyanide
Conditions needed = being heated under reflux in ethanol
When an alkyl halide (halogenoalkane) undergoes nucleophilic substitution with cyanide, what is formed?
When an alkyl halide undergoes nucleophilic substitution with cyanide, a nitrile is formed
When naming a nitrile what bond takes the most priority?
When naming a nitrile , carbon - nitrogen triple bond is the most important bond before anything else
What is the suitable reagent and condition needed for a nucleophilic substitution reaction with ammonia ? (-NH3)
There seems to be no “suitable reagent”
Conditions needed = This reaction needs to be done in excess ethanolic ammonia, with it being under high pressure
When an alkyl halide (halogenoalkane) undergoes nucleophilic substitution with ammonia, what is formed?
When an alkyl halide undergoes nucleophilic substitution with ammonia, an amine is formed
Draw the full mechanisms for a hydroxide ion reacting with an alkyl halide:
1/ 2-iodo-3-methylbutane reacts with aqueous sodium
2/ bromocyclohexane reacts with aqueous potassium
Draw the full mechanisms for a cyanide ion reacting with an alkyl halide:
1/ chloroethane reacts with potassium cyanide
2/ 2-bromopropane reacts with potassium cyanide
Draw the full mechanisms for a cyanide ion reacting with an alkyl halide:
1/ bromoethane reacts with ammonia
2/ 2-chloro-3methylbutane reacts with ammonia
Draw the mechanisms for a hydroxide ion reacting with an alkyl halide:
1/ propanol
2/ cyclohexanol
Draw the mechanisms for a cyanide ion reacting with an alkyl halide:
1/ propanenitrile
2/ 2-methylpropane nitrile
Draw the mechanisms for a cyanide ion reacting with an alkyl halide:
1/ methylamine
2/ 2-methylbutylamine
