Mechanisms - Halogenoalkanes Flashcards
What is a nucleophile?
electron pair donor
Which ion is considered a better nucleophile due to its full formal negative charge?
Hydroxide ion (OH-).
What is the difference in charge between a hydroxide ion and water?
Hydroxide ion has a full formal negative charge, while water only carries a partial negative charge.
List three typical nucleophiles.
- Hydroxide ion (OH-)
- Cyanide ion (CN-)
- Ammonia (NH3)
What characterizes a nucleophilic substitution reaction?
A nucleophile attacks a carbon atom carrying a partial positive charge.
In a nucleophilic substitution reaction, what is replaced by the nucleophile?
An atom that has a partial negative charge.
Why do halogenoalkanes undergo nucleophilic substitution reactions?
Due to the polar C-X bond, where X is a halogen, caused by large differences in electronegativity between the carbon and halogen atom.
What causes the polar bond in halogenoalkanes?
Large differences in electronegativity between the carbon and halogen atom.
True or False: A nucleophile always has a negative charge.
False.
Fill in the blank: A nucleophile is attracted to _______ charged species.
positively.
What is the general mechanism for nucleophilic substitution?
Nucleophilic substitution involves a nucleophile (Nu) attacking a carbon atom bonded to a leaving group (X), resulting in the substitution of X with Nu.
What is the nucleophilic substitution reaction of bromoethane with aqueous alkali?
Bromoethane reacts with aqueous alkali (e.g. NaOH) to form ethanol.
CH3CH2Br + OH- → CH3CH2OH + Br-
What is the nucleophilic substitution reaction with cyanide ions?
forms nitriles
for example, bromoethane reacts with ethanolic potassium cyanide to form propanenitrile
What is the product of the nucleophilic substitution of bromoethane with KCN?
The product is propanenitrile.
CH3CH2Br + CN- → CH3CH2CN + Br-
What effect does the nucleophilic substitution of halogenoalkanes with KCN have on the carbon chain?
It adds an extra carbon atom to the carbon chain.
What can chemists use this reaction for?
To make a compound with one more carbon than the best available organic starting material.
What is the nucleophile in the nucleophilic substitution reaction with ammonia?
Ammonia (NH₃) is the nucleophile.
What is the typical solvent used in the reaction with halogenoalkane?
An ethanolic solution of excess ammonia.
What is the product of the reaction between bromoethane and excess ethanolic ammonia?
The product is ethylamine.
What is the reaction equation for bromoethane and ammonia?
C₂H₅Br + NH₃ → C₂H₅NH₂ + HBr
What are the conditions for nucleophilic substitution reactions with NaOH?
Aqueous and warm.
What are the conditions for nucleophilic substitution reactions with KCN?
Ethanolic and warm.
What are the conditions for nucleophilic substitution reactions with NH₃?
Ethanolic, warm, and in a sealed container.
What is an example of a reaction involving 2-chloropropane?
2-chloropropane can react with ammonia under specified conditions.
