Chapter 15 - Haloakanes Flashcards
(28 cards)
What are haloalkanes?
Compounds containing hydrogen, carbon and at least one halogen atom
When two or more halogens are present in a haloalkane, how do you name it?
Put the two halogens in alphabetical order
How do you name haloalkanes?
Add the suitable prefix onto the name of the longest chain
What is a nucleophile?
An electron pair donor
Why are haloalkanes polar?
The carbon-halogen bond is polar. The halogen generally has a much higher electronegativity than carbon, so the electrons are pulled slightly towards the halogen and the carbon is left with a slight positive charge
Give three examples of nucleophiles
Hydroxide ions, :OH-
Water molecules, H2O:
Ammonia molecules, :NH3
What happens when a nucleophile is attracted to a carbon?
It donated electrons to form a new covalent bond
Why are nucleophiles attracted to carbon?
The carbon-halogen bond is polar, so carbon is left with a slight positive charge
What happens when a nucleophile reacts with a haloalkane?
The nucleophile replaces the halogen in a substitution reaction
What is nucleophilic substitution?
When a nucleophile replaces a halogen in a haloalkane
What happens when a haloalkane is hydrolysed?
An alcohol is formed
Describe the nucleophilic substitution reaction to make an alcohol from a haloalkane
1) The nucleophile (OH- in this case) approaches the slightly positively charged carbon
2) The direction of the attack of this nucleophile reduces the repulsion between the negatively charged hydrogen atom and the OH- ion
3) The lone pair of electrons on the nucleophile is donated to the carbon atom
4) A new bond forms between the carbon and the oxygen of the OH- ion
5) The carbon-halogen bond breaks by heterolytic fission
6) An alcohol and halide ion are formed
Why is the reaction different when water is used as a nucleophile?
It is much slower but will eventually get the same result
Which bond in the haloalkane is broken during hydrolysis?
The carbon-halogen bond
What does the rate of hydrolysis in haloalkanes rely upon?
The strength of the carbon-halogen bond
Which haloalkanes have the weakest bonds and so react fastest?
Iodoalkanes
Which haloalkanes have the strongest bonds and so react the slowest?
Fluoroalkanes
Will primary, secondary or tertiary haloalkanes react fastest?
Tertiary
Why do tertiary haloalkanes react fastest?
The tertiary haloalkane is much more stable than the primary one and reacts with a two-step mechanism
What reaction would you conduct to measure the rate of hydrolysis of the haloalkanes?
1) 1 cm³ of ethanol + two drops of haloalkanes
2) stand in 60 C of water
3) place test tube with 0.1 moldm silver nitrate
4) add 1 cm³ of silver nitrate quickly to each of the test tubes
5) observe the test tubes for five minutes and record the time taken to form a precipitate
Hydrolysis of 1-chlorobutane observation?
White precipitate forms very slowly
Hydrolysis of 1-bromobutane observation?
A cream precipitate forms faster that 1-chlorobutane but slower than 1-iodobutane
Hydrolysis of 1-iodobutane observation?
A yellow precipitate forms rapidly
What is the conclusion of the hydrolysis of haloalkanes?
Rate of hydrolysis increase as the strength of the carbon-halogen bond decreases
