mechanism of haloalkanes Flashcards
what is the general idea on how haloalkanes are formed?
when you mix haloalkanes and halogens in the present of uv light
why do halogens do not react with alkanes in the dark
It requires UV light to form halogens into free radicals which are free to act as nucleophiles in a reaction.
What are the steps in a chain reaction
initiation, propagation. and termination.
Initiation
• The first step is initiation, this reaction is breaking the Cl-Cl bond to form two chlorine atoms.
hetolytic fission
when one compoment takes both electrons of the covalently bonded molecule forms ions
homolytic fission
both elements take an electron. radicals
why does the c–h bond does not break in present of UV light
bond in the alkanes needs more energy to break than is
available in ultraviolet radiation, so this bond does not break.
how many steps does propagation has
2
first step of propagation
The chlorine free radical takes a hydrogen atom from methane
ch3 radical
hcl molecule
second step of prorogation
The methyl free radical is also very reactive and reacts with a chlorine molecule.
ch3cl and cl radical
termination of haloalkane synthesis
either
two chlorine radicals
two methyl radicals
methyl and chlorine radical
other products of progation
Dichloromethane may be made at the propagation stage, if a chlorine radical reacts with some chloromethane that has already formed.
why can haloalkane isomers may be formed with longer chain isomers
because the Cl• can replace any of the hydrogen atoms.
why are chain reactions not ideal
it creates a mixture of products
why are CFCS important
chloronurorocarbons (CFCs) in the stratosphere are
destroying the ozone layer.
what is the ozone layer
a layer that has 03
How do CFCS destroy the atmosphere
in present of uv light in atmosphere it forms cl radicals these radicals react with oxygen to form 03 and catalyes the breakdown of the ozone layer
why is the destruction of the ozone layer an issue
if uv is not absorbed by ozone layer it will absorb the earth and life on earth. this could lead to;
damage dna - cancer
kill plantlon etc which destroys food chain
CFCS purposes
coolants in fridges
polymers
propellants
general haloalkane formula
2n+1 and halogen
example of haloalkane
1,1,1,2-tetrachloroethane
bond polarity of haloalkanes
This bond is polar.
because halogens are more electronegative than carbon. This means that it attracts the shared electrons more so it becomes more electron dense and delta negative than the carbon
why are haloalkanes INSOLUBLE in water
- they can’t form hydrogen bonds,
and the energy required to break hydrogen bonds in water is higher than the energy released when new bonds between the haloalkane and water are formed
boiling point of haloalkanes
increases down the periodic table
increases as chain gets longer
increases down periodic table
electron number increases. This means that the van der waal forces are stronger so more energy is required to break the bonds
chain length
more electrons
more surface for van der waals forces to act on.
why is c-f bonds strongest and least reactive
f is the smallest atom.
less shielding.
closer to nucleus
requires more energy to break bond
what is nucleophile
a reagant with two lone pair electrons that donates the lone pair of electron and forms a bond with a partially postively charge carbon.
nucleophiles that I learnt about
the hydroxide ion. -:oH
• ammonia, :NH3
• the cyanide ion, -:CN.
name of mechanism
nucleophilic substitutions
they replace the halogen on haloalkane
what does curly arrow mean
electrons are being donated
what are electrons attracted to
partially postive carbon
what is a radical
highly reactive species with one single unpaired electron.
photochemical reaction
a reaction that is initiation by absorbing light energy
chain reaction
when products yield initiated more reacts to form more products
