chapter 13 - halogenoalkanes Flashcards
How do you classify primary tertiary and secondary haloalkanes
One primed - one R group. (3- number of hydrogens) =1
Two primed - 2 R groups. (3 - number of hydrogens) = 2
Three primed - 3 R groups. (3 - number of hydrogens) = 3
what are features of high boiling points in haloalkanes
Larger molecule, stronger Vanderwaals forces between molecules
Longer carbon chain/straight carbon chain [More points of contact with adjacent molecules and more vanderwaals forces]
What is and define a free radical
They are a highly reactive species containing an unpaired electron. They attack/form a bond with anything it collides with.
What is an electrophile
An electrophile is attracted to electron rich areas [double bonds] and it is a positive element it self. eg the H on H-Br.
What is a nucleophile
A nucleophile is attracted to electron deficient areas, It contains a lone pair of electrons and it is usually a negative ion, except for NH3. it is an electron pair donor and is negative itself
What are the conditions for sodium hydroxide (NaOH) in nucleophilic substitution
warm (aq)
What are the conditions for KCN in nucleophilic substitution.
reflux KCN solution in ethanol.
reflux- heated strongly
water and ethanol mixture
What are the conditions for ammonia (NH3) in nucleophilic substitution
Heat access NH3 in ethanol in a sealed tube under high pressure
dissolved in ethanol
heated in reflux
How do you maximize base elimination over nucleophilic substitution.
3/2 primed haloalkane
high temperature and the presence of ethanol
OH will act as a base in this case.
where do the arrows go in nucleophillic substitution in KCN and NaOH
middle of the lone pair to the carbon with halogen attached
from middle of the carbon halogen bond to the halogen
halogen is left as a product
OH / CN will act as a nucleophile
where do the arrows go in nucleophillic substitution with ammonia
middle of lone pair on NH3 to carbon with halogen attached.
second ammonia molecule- middle of lone pair to a hydrogen attached to the nitrogen. make sure the nitrogen has a positive charge.
products are NH4+ and the halogen
what is base elimination
when the OH- ion brings about elimination of HBr to form an alkene. OH becomes a proton acceptor.
where do the arrows go in base elimination
arrow from the middle of the lone pair of the OH- to a hydrogen which is attached to a carbon next to the carbon halogen
an arrow from the CH bond to the CC bond.
an arrow from the C halogen bond onto the halogen.
products are water and the halogen. H2O and :Br-
what occurs in the free radical substitution stage of initiation.
UV light is enough energy to break the bond between Cl2 or C-Cl to form a Cl radical or 2Cl radicals. radicals are highly reactive. there is not enough energy to break the CH bond.
what is the termination stage in free radical substitution.
when two radicals combine together to form a molecule.
the major product is when two different radicals combine.
the minor product is when two of the same radical combine together
how do you name amine groups
(NH2)
if there is an amine group on carbon 2 and the longest chain is 5 carbons. this would be called 2-amino-pentane
and if there are other groups you would just name them normally. eg 2-amino-3-methyl pentane
give an example of free radical substitution
Cl2 = 2Cl. (UV light)
Cl. + CH3Cl = HCl + .CH2Cl
.CH2Cl + Cl2 = .Cl + CH2Cl2
.Cl + .CH2Cl = CH2Cl2 (major)
.CH2Cl + .CH2Cl = C2H4Cl2 (minor)
naming nitriles
if there was a chain of 4 carbons and there was a CN nitrile group on carbon 4. you would include the carbon from the CN into the carbon chain. making it pentanenitrile.
what is the charge on oxygen if it forms only 1 bond
Negative
What is the charge on oxygen if it forms three bonds
Positive
what does ozone do O3
absorbs UV radiation
what do CFCs do (Chlorofluorocarbons]
Chlorofluorocarbons also absorb UV radiation breaking down carbon halogen bonds to form free radicals that can cause Ozone depelation
What are the uses of chlorofluorocarbons [CFC]
They are propellants in aerosols
Used as dry cleaning solvent
They are used for degreasing circuit boards
Used as refrigerants
And they are very unreactive therefore they reach the ozone layer before decomposing.
How is an ozone hole formed
Caused by a chain reaction as CFCs break down ozone in the atmosphere. UV radiation in the upper atmosphere has enough energy to break C-Cl bonds in CFCs to produce a Chlorine radicals.
How is ozone depletion prevented
CFCs are replaced with HCFCs these contain no chlorine therefore this will not lead to Chlorine radicals being formed. therefore no ozone depletion.
How does nitrogen cause the breakdown of the ozone layer
Nitrogen reacts with oxygen in the atmosphere at high temperatures to produce nitrogen oxides these can cause ozone depletion. This is mainly produced from planes in the aviation industry and nitrogen oxide acts as a catalyst.
NO + O3 = NO2 + O2
O3 = O2 + .O
.O + NO2 = NO + O2
nitrogen oxide is a catalyst as it is not used up.
What is the equation for ozone depletion
CFCs = .Cl
O3 + .Cl = O2 + .OCl
.OCl + O3 = 2O2 + .Cl
overall equation. 2O3 = 3O2
