general formula of alkenes
CnH2n
whats special about alkenes
c=c (carbon-carbon double bond)
restricts rotation of groups attached (therefore E/Z isomers)
how many electrons does the c=c contain and what do we think of it as
4 electrons
electron dense
so has potential to attract d+ or positive ions
so is reactive
electrophiles are
species looking for a pair of electrons (eg H+)
induced dipole of Br2 by c=c
electron dense c=c ‘pushes’ electron density in Br2 from one side to another causing a temporary dipole
structure of the carbocation
positively charged ion. when the reaction is occurring the Br can attach onto carbon 1,2,3…..
primary secondary and tertiary structures
- how to identify
find the special bit (in our case the positive charge)
find the carbon it is related to
find how many carbons this carbon is attached to (1=primary, 2=secondary…)
primary secondary and tertiary structures
- which is least stable
primary
primary secondary and tertiary structures
- which is most stable
tertiary
electrophilic addition of H2SO4 to alkenes
- type of reaction
- what type of h2so4 is used
- what can happen to the product
- very exothermic
- conc h2so4 is used
- product can be converted into alcohol by addition of water (H2SO4 is reformed so has acted as a catalyst
test for c=c
add orange Br2 water –> decolourises
polymer defintion
large molecule made up of lots of repeating units called monomers
how to modify plastics
add plasticisers
they are small molecules that can get in between the chain of polymer, force them apart and allow them to slide over each other
poly(chloroethane) is also known as…
PVC
two types of poly(ethene)
LOPE
HOPE
when do you get LOPE poly(ethene)
high pressure high temperature produces branch chain polymers which don't pack well molecules are flexible uses - plastic bags, electric cables
when do you get HOPE poly(ethene)
just over room temp and pressure
less branching so more closely packed
molecules are inflexible
uses - crates, bottles, buckets
environmental issues with poly(ethene)
made from crude oil thereofre non-renewable
inert as non-polar
non biodegradable
high melting point as strong vdw between molecules
alcohol functional group
O-H
two ways to produce ethanol
direct hydration
fermentation
comparing direct hydration and fermentation
- rate of reaction
DH vs fermentation
fast vs slow
comparing direct hydration and fermentation
- cost
DH vs fermentation
expensive vs cheap
comparing direct hydration and fermentation
- manpower
DH vs fermentation
low vs high
comparing direct hydration and fermentation
- purity
DH vs fermentation
pure vs impure
comparing direct hydration and fermentation
- type of process
DH vs fermentation
continuous vs batch
comparing direct hydration and fermentation
- environmental impact
DH vs fermentation
non-renewable (ethene from crude oil) vs renewable (sugar cane)
direct hydration equation
h2c=ch2 + H2o ——–> h3c-ch2-o-h
H3PO4
type of mechanism to make alcohol
electrophilic addition
see hard copy cards
fermentation equation
c6h12o6 ——> 2c2h5oh +2co2
conditions for fermentation
yeast
zymase
35 degrees
absence of air
what alcohol content does fermentation produce and why
up to 15%, because any greater and yeast is killed
what can fermentation alcohol be used for (other than to drink)
biofuel = renewable
why are biofuels considered carbon neutral
plus equations
a carbon neutral substance takes in as much CO2 as it produces
+6 6CO2 + 6H2O —> C6H12O6 + 6O2 (photosynthesis)
+4 C6H12O6 —–> 2C2H5OH +2CO2 (fermentation)
+0 2x C2H5OH + 3O2 —> 2CO2 + 3H2O (fuel is burnt)
why is considering biofuels as carbon neutral too simplistic
co2 will be released at many other points
extraction of glucose
fermentation (must heat to 35)
transporting raw materials
oxidation of alcohols
- oxidising agent (what happens to the oxidising agent and what can we see)
K2Cr2O7 /HCl acidified potassium dichromate it gets reduced species that gets reduced.... (K+ is a spectator ion) Cr2O7^2- orange
Cr^3+ green
primary alcohol is oxidised…
twice
primary –>….—>….
primary –>aldehyde—>carboxylic acid
secondary –> …
secondary –>ketone
tertiary–>…
not possible
no reaction
to make an aldehyde we use which method
distillation
to make a carboxylic acid we use which method
reflux
why do we use different methods to collect aldehydes and carboxylic acids
carboxylic acid = hydrogen bonding = high bp
aldehyde = permanent dipole forces = lower bp
so have to re-condense the aldehyde to make a carboxylic acid
testing for aldehydes and ketones
tollens reagent
aldehyde = silver mirror
ketone = NVC
testing for alcohols
add a very small piece of sodium
if gently fizzes then alcohol, if violent, water or carboxylic acid
another way to test for aldehydes (not tollens reagent)
Fehlings solution (blue) –> brick red precipitate
haloalkane test
warm then add silver nitrate
white prcipitate - chloroalkane slowest
cream precipitate - bromoalkane
yellow precipitate - iodoalkane fastest
carboxylic acid test
add sodium hydrogencarbonate
bubbles = carboxylic acid
catalyst and conditions for dehydration of alcohols
Al2O3
600 degrees c
conc H2SO4