Chapter 15 - Haloalkanes Flashcards
What is a haloalkane?
A compound containing the elements carbon, hydrogen and at least one halogen
What is a nucleophile?
An atom or group of atoms that is attracted to an electron deficient carbon bond, where it donates a pair of electrons to form a new covalent bond
What type of reaction occurs when a haloalkane reacts with a nucleophile?
Substitution
What is hydrolysis?
A chemical reaction involving water or an aqueous solution of a hydroxide that causes the breaking of a bond in a molecule. This results in the molecule being split into 2 parts
What happens in the hydrolysis of a haloalkane?
The nucleophile (OH-) approaches the carbon atom attached to the halogen. This minimises repulsion between the nucleophile and delta negative halogen atom. A lone pair of electrons of the OH- ion is attracted and donated to the delta positive carbon atom. A new bond is formed between the oxygen atom of the OH ion and carbon atom. The carbon-halogen bond breaks by heterolytic fission, and the new organic product is an alcohol - a halide ion is also formed.
How can haloalkanes be converted to alcohols?
Using aqueous sodium hydroxide.
The reaction is very slow at room temp, so the mixture is heated under reflux to gain a good yield of product.
What does the rate of hydrolysis in haloalkanes depend on?
The strength of the carbon-halogen bond in the haloalkane
Which is the weakest carbon-halogen bond and why?
C-I is the weakest as less energy is required to break it (it is less ionic)
What is the relationship between the rate of hydrolysis and strength of carbon-halogen bond?
The rate of hydrolysis increases as the strength of the carbon-halogen bond decreases
Why do tertiary haloalkanes hydrolyse faster than primary ones?
The tertiary carbocation is much more stable than that of the primary
How can we prove the difference in rate of hydrolysis between haloalkanes?
Add ethanol solvent to test tubes with different haloalkanes, and then add silver nitrate.
1-chlorobutane - white precipitate forms very slowly
1-bromobutane - cream precipitate forms faster than chlorobutane but slower than iodobutane
1-iodobutane - yellow precipitate forms rapidly
Why is a carbon-halogen bond polar?
Halogen atoms are more electronegative than carbon atoms. The electrons in the C-Hal bond are more attracted to the halogen making the bond polar
What are organohalogen compounds?
Molecules that contain at least one halogen atom joined to a carbon chain
What are organohalogens used for?
General solvents, dry cleaning solvents, making polymers, flame retardents, refridgerants
Where is the ozone layer found?
At the outer edge of the stratosphere. at a height that varies from about 10-40km above the Earth’s surface
