haloalkanes chp 15

Question 1

what are haloalkanes

Answer 1

haloalkanes are compounds containing the elements carbon, hydrogen, and at least 1 halogen

Question 2

how would you go about naming a haloalkane

Answer 2

-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

Question 3

explain the chemistry behind the reactivity of haloalkanes

Answer 3

• have polar carbon-halogen bond.
• carbon atom has a slightly positive charge and can attract species containing lone electron pairs

Question 4

what is a nucleophile

Answer 4

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

Question 5

gives some examples of nucleophiles

Answer 5

hydroxide ions (OH-)
water molecules (H2O)
ammonia molecules (NH3)

Question 6

what type of reaction is it when haloalkanes and nucleophiles react

Answer 6

nucleophilic substitution

Question 7

what is a substitution reaction

Answer 7

substitution is a reaction in which 1 atom or group of atoms is replaced by another atom of group of atoms

Question 8

define hydrolysis reactions

Answer 8

• chemical reaction involving water/aqueous solution of a hydroxide
  ^results in breaking of bonds in a molecule.

molecule split hence lysis

Question 9

what occurs in the hydrolysis of a haloalkane

Answer 9

in the hydrolysis of a haloalkane, the halogen atom is replaced by an -OH group

Question 10

• what is the product of the hydrolysis of a haloalkane
• draw reaction mechanism
• what conditions are used

Answer 10

• alcohol product
• heated under reflux with aq NaOH reagent

Question 11

explain what happens to the carbon-halogen bond during a hydrolysis reaction

Answer 11

in hydrolysis, the carbon-halogen bond is broken and the -OH group replaces the halogen in the haloalkane

Question 12

what does the rate of hydrolysis of a haloalkane depend on

Answer 12

The rate of hydrolysis depends upon the strength of the carbon-halogen bond in the haloalkane

Question 13

explain the trend in reactivity of carbon-halogen bonds

Answer 13

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

Question 14

how do you measure the rate of hydrolysis of primary haloalkanes

for example 1-chlorobutane, 1-bromobutane, 1-iodibutane

Answer 14

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

Question 15

whats the difference between the primary, secondary and tertiary haloalkanes

Answer 15

follows the same rules as primary, secondary and tertiary alcohols

Question 16

what are organohalogen compounds

Answer 16

organohalogen compounds are molecules that contain at least 1 halogen atom joined to a carbon chain

Question 17

what is the Ozone layer made up of and what is its purpose

Answer 17

• tiny fraction of the ozone layer is ozone
• absorbs most biologically damaging ultraviolet radiation (UV-B) from suns rays.

Question 18

how is ozone made in the ozone layer

Answer 18

• high energy UV breaks oxygen molecules into oxygen radicals
• O2 –> 2O*
• O2 + O* <–> O3

* = radical

Question 19

Are CFCs reactive

Answer 19

• CFCs are very stable and therefore unreactive
• but are broken up by UV radiation

Question 20

What does CFC stand for

Answer 20

chloroflurocarbons

Question 21

what are common uses for CFCs

Answer 21

CFCs and HCFCs were the most common compounds used as refrigerants, in air-conditioning units and as aerosol propellants

Question 22

how do CFCs deplete the ozone layer

Answer 22

• once in stratosphere UV breaks carbon halide bond (homolitic fission)
• forms halogen radical
• breaks ozone into oxygen

Question 23

draw the mechanism for ozone break down

Answer 23

initiation CF2Cl2 –> CF2Cl* + Cl*

prop 1 Cl* + O3 –> ClO* + O2

prop 2 ClO* + O –> Cl* + O2

overall O3 + O –> 2O2

Question 24

what Is photodissociation

Answer 24

• process of breaking down a molecule using through the absoption of electromagnetic radiation or photons

Question 25

what other radicals can catalyse the breakdown of ozone

Answer 25

nitrogen oxide radicals are formed naturally during lighting strikes and also as a result of aircraft travel in the stratosphere