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Organic Chemistry
Alkanes
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Cards (20)
general formula of alkane - C
n
H
2n+2
Alkanes and cycloalkanes are
saturated
hydrocarbons because they contain no
double
bonds / maximum number of
hydrogen
atoms
Hydrocarbons are usually obtained from
fractional
distillation
of
crude
oil
Fractions - molecules with similar number of
carbon
atoms in their chains
They are separated due to the difference in their boiling temperature
Reforming -
processing
of
straight
chain hydrocarbon into
branched-chain
alkanes and
cyclic
hydrocarbons for efficient
combustion
Pollutants
carbon
monoxide
(toxic - reduce
capacity
of oxygen in RBC)
oxides of
nitrogen
(acid rain)
oxides of
sulfur
(acid rain - H2SO4)
unburnt
hydrocarbons
carbon
particulates
Are formed during
combustion
of alkane fuels
Catalytic converter uses a rhodium catalyst
absorbs, reacts, desorbs
turns
2NO
->
N2
+
O2
turns
2CO
+
O2
->
2CO2
turns
2NO2
->
N2
+
2O2
Acid rain consequences
damage to
aquatic
life in lakes / rivers
damage to
crops
and forests
damage to
buildings
/ structures made of
marble
or limestone
Fractions - molecules with similar number of
carbon
atoms in their chainsThey are separated due to the difference in their
boiling
temperature
Alternative fuels
biofuels
release fewer and less harmful products (but release CO2 = greenhouse gas = contributes to climate change)
ethanol
is an example of a biofuel - carbon neutral (crops need to be grown, fermented for ethanol) + low
percentage
yield
however sustainable - and
renewable
so wont run out
A radical
species with an
unpaired
electron
and is represented in mechanisms by a
single
dot
formed by
homolytic
fission
of a
covalent
bond
Free radical substitution with Halogens (UV LIGHT)
CH4
+
Cl2
->
CH3Cl
+
HCl
Free radical substitution (initiation propogation termination)
UV
radiation causes
homolytic
fission
Cl2 -> 2Cl*
Free radical substitution PROPAGATION
Cl* +
CH4
-> *
CH3
+
HCl
*CH3 +
Cl2
->
CH3Cl
+
Cl
*
Free radical substitution (termination)
*CH3 + *CH3 -> C2H6
Cl*
+
Cl*
->
Cl2
*CH3 + Cl* -> CH3CL
Free Radical Substitution is not
efficient
difficult to
control
excess
halogen
present
mixture of
products
needs to be
fractionally
distilled - costly
Boiling vs melting point of alkanes
(boiling)
as the number of carbon atoms
increases
, the number of electrons
increases
, the strength of
London
forces
increases
, and boiling temperature
increases
(melting)
EVEN NUMBER CARBON vs ODD NUMBER CARBON
even-numbered chains pack together more
efficiently
- the melting point is higher
Alkanes are
insoluble
in water
no
hydrogen
bonding possible
Alkanes are soluble in
non
polar
solvent
Octane
rating or octane number is a
standard
measure
of the
performance
of an engine or aviation fuel.
HIgher the octane number, the more
compressible
the fuel can withstand before
combustion
Why do branched chains have lower boiling points
branched chains have
lower
surface
area
so the London forces are
weaker