haloalkanes chp 15 Flashcards
what are haloalkanes
haloalkanes are compounds containing the elements carbon, hydrogen, and at least 1 halogen
how would you go about naming a haloalkane
-when naming haloalkanes, a prefix is added to the name of the longest chain to indicate of the halogen
-when 2 or more halogens are present in a structure they are listed in alphabetical order
explain the chemistry behind the reactivity of haloalkanes
- have polar carbon-halogen bond.
- carbon atom has a slightly positive charge and can attract species containing lone electron pairs
what is a nucleophile
A nucleophile is an atom or group of atoms that is attracted to an electron deficient carbon atom, where it donates a pair of electrons to form a new covalent bond
gives some examples of nucleophiles
hydroxide ions (OH-)
water molecules (H2O)
ammonia molecules (NH3)
what type of reaction is it when haloalkanes and nucleophiles react
nucleophilic substitution
what is a substitution reaction
substitution is a reaction in which 1 atom or group of atoms is replaced by another atom of group of atoms
define hydrolysis reactions
- chemical reaction involving water/aqueous solution of a hydroxide
^results in breaking of bonds in a molecule.
molecule split hence lysis
what occurs in the hydrolysis of a haloalkane
in the hydrolysis of a haloalkane, the halogen atom is replaced by an -OH group
- what is the product of the hydrolysis of a haloalkane
- draw reaction mechanism
- what conditions are used
- alcohol product
- heated under reflux with aq NaOH reagent
explain what happens to the carbon-halogen bond during a hydrolysis reaction
in hydrolysis, the carbon-halogen bond is broken and the -OH group replaces the halogen in the haloalkane
what does the rate of hydrolysis of a haloalkane depend on
The rate of hydrolysis depends upon the strength of the carbon-halogen bond in the haloalkane
explain the trend in reactivity of carbon-halogen bonds
less energy is required to break the C-I bond than other carbon-halogen bonds
-iodoalkanes react faster than bromoalkanes
-bromoalkanes react faster than chloroalkanes
-fluoroalkanes are unreactive as a large quantity of energy is required to break the C-F bond
how do you measure the rate of hydrolysis of primary haloalkanes
for example 1-chlorobutane, 1-bromobutane, 1-iodibutane
1)set up 3 test tubes, each with 1cm^3 of ethanol and 2 drops of the primary haloalkane
2)stand the test tubes in a water bath at 60 °C
3)place a test tube containg 0.1 mol dm^-3 silver nitrate in the water bath and allow all tubes to reach a constant temperature
4)Add 1cm^3 of the silver nitrate quickly to each of the test tubes. immediately start a stop-clock
5)observe the test tube for 5 minutes and record the time taken for the precipitate to form
similar to halogen test
whats the difference between the primary, secondary and tertiary haloalkanes
follows the same rules as primary, secondary and tertiary alcohols
what are organohalogen compounds
organohalogen compounds are molecules that contain at least 1 halogen atom joined to a carbon chain
what is the Ozone layer made up of and what is its purpose
- tiny fraction of the ozone layer is ozone
- absorbs most biologically damaging ultraviolet radiation (UV-B) from suns rays.
how is ozone made in the ozone layer
- high energy UV breaks oxygen molecules into oxygen radicals
- O2 –> 2O*
- O2 + O* <–> O3
* = radical
Are CFCs reactive
- CFCs are very stable and therefore unreactive
- but are broken up by UV radiation
What does CFC stand for
chloroflurocarbons
what are common uses for CFCs
CFCs and HCFCs were the most common compounds used as refrigerants, in air-conditioning units and as aerosol propellants
how do CFCs deplete the ozone layer
- once in stratosphere UV breaks carbon halide bond (homolitic fission)
- forms halogen radical
- breaks ozone into oxygen
draw the mechanism for ozone break down
initiation CF2Cl2 –> CF2Cl* + Cl*
prop 1 Cl* + O3 –> ClO* + O2
prop 2 ClO* + O –> Cl* + O2
overall O3 + O –> 2O2
what Is photodissociation
- process of breaking down a molecule using through the absoption of electromagnetic radiation or photons
what other radicals can catalyse the breakdown of ozone
nitrogen oxide radicals are formed naturally during lighting strikes and also as a result of aircraft travel in the stratosphere
