T6 Organic Chem Flashcards
hydrocarbons
compound containing only carbon and hydrogen
saturated
containing only single bonds
unsaturated
containing one or more multiple bonds
displayed formula
shows every atom and bond separately
structural formula
all atoms joined to a singular carbon are grouped
skeletal formula
only shows bonds between carbon atoms
molecular formula
shows numbers of each atom, not structure
empirical formula
molecular formula with each atom in its simplest whole-number ratio
functional group
an atom or group of atoms in a molecule that is responsible for its chemical reactions.
homologous series
family of compounds with the same functional group, differing by CH2.
they have similar chemical/physical properties displaying gradation.
alkane general formula
CnH2n+2
alkene general formula
CnH2n
halogenoalkane general formula
CnH2n+1X
alcohol general formula
CnH2n+1OH
structural isomers
compounds with the same molecular formula but differing structural formula
chain isomers
structural isomers with different carbon chains.
similar chemical properties but different physical.
position isomers
molecules with the same functional group attached in a different position on the same carbon chain
different physical/chemical properties
stereoisomerism
compounds with the same structural formula but with the atoms/groups arranged differently in 3 dimensions.
geometric isomers
compounds containing a CC double bond with atoms or groups attached at different positions.
bond angles shown on geometric isomers
at 120 degrees
trans
when the 2 Carbon groups are on opposite sides to one another.
cis
when the 2 carbon groups are on the same side to one another.
why do geometric isomers only occur at double bonds?
because the CC double bond presence restricts rotation so groups attached can’t move around
process of E/Z notation
- ) work out names of both isomers
- ) use priority rules as to which of 2 atoms on left of C=C has the higher priority (higher having a greater atomic number)
- ) copy on the right
- ) are they in the cis or trans positions?
E notation
equivalent of trans notation for non-carbons
Z notation
equivalent of cis notation for non-carbons
3 main processes used to convert crude oil into fuels
cracking
reforming
fractional distillation
fractional distillation
crude oil heated in furnace and passed into fractionating column in which there’s a temp gradient (hot at bottom and cooler at top), passing through column via a series of bubble caps, condensing at different heights, depending on bp.
larger molecules at bottom and smaller at top
cracking
hydrocarbons are passed over a heated catalyst (e.g zeolite/ aluminium oxide) causing them to break down.
why does reforming take place
as straight chains burn less efficiently than cyclic compounds so reforming occurs to convert straight chains into cyclic compounds
process of reforming
heating w a catalyst (eg. platinum)
complete combustion word equation
alkane + oxygen»_space; carbon dioxide + water
incomplete combustion word equation
alkane + oxygen»_space; carbon + carbon dioxide + water + carbon monoxide
what’s released in incomplete combustion?
soot
carbon monoxide (toxic replacement of oxygen in blood, colourless/odourless)
unburned hydrocarbons
how is sulfur dioxide formed?
effects on environment?
during alkane combustion, sulfur impurities react with oxygen in the air to form SO2 and further react in air to form sulfur trioxide.
both are acidic oxides and so dissolve in water to form sulphurous/ sulfuric acid.
nitrogen oxide formation
only under v high temps, nitrogen reacts in the air to form nitrogen oxides
these dissolve to form nitrous/nitric acid
catalytic converters
use metal meshes (eg, platinum, rhodium, palladium) to remove pollutants.
reactions that take place in catalytic converters
oxidation of carbon monoxide (2CO+O2»2CO2)
oxidation of unburned HC
Removal of nitrogen impurities
disadvantage of catalytic converter
poor at sulfur impurity removal so must be removed before is burnt
why do we need alternative fuels?
depletion of natural resources
global warming
biofuel
fuel obtained from living matter (that hasn’t died recently)
biodiesel
a fuel formed from vegetable oils obtained from plants
bioalcohol
fuels formed from plant matter, often using enzymes/bacteria.
facts to consider in use of alternative fuels
carbon neutrality
manufacture/transport
yield
land use
disadvantages/advantages of bioethanol/biodiesel
much land required that could be used to grow food
low yield (increasing?)
no exploration/drill costs, rather extraction and transport costs are high
more carbon neutrality
evaluate natural gas use
no land needed
high yield
high drilling cost, low processing and transport cost
bad for environment
relative reactivity of alkanes
relatively unreactive as is just made up of C and H joined by single bonds
substitution reaction
when an atom/group is replaced by another atom/group
mechanism
sequence of steps in an overall reaction showing electrons involved in the formation/breaking of bonds.
INITIATION in chlorination of methane
chlorine molecule is split apart and each chlorine takes one electron from the pair to form 2 chlorine radicals.
homolytic fission
the breaking of a covalent bond where each of the bonding electrons leaves with one species, forming a radical.
radical
a species with an unpaired electron
initiation step
the formation of radicals, usually as a result of bond breaking caused by UV radiation
under what conditions does the chlorination of methane occur in?
v high temp conditions or using UV radiation
propagation
the two steps that, when repeated many times, convert the starting materials into the products of a reaction
propagation step in chlorination of methane
v reactive radicals collide w methane molecules and react by removing a hydrogen atom
Cl+CH4»HCl+CH3
methyl radical can further react with chlorine molecules
CH3+Cl2»CH3Cl+Cl
termination
when a molecule is formed from 2 radicals.
examples of termination reactions in chlorination of methane
Cl+Cl»Cl2
Cl+CH3»CH3Cl
CH3+CH3»C2H6
why is chlorination of methane ineffective in industrial use?
has a low yield and products must be separated.
alkenes double bond effect on reaction
makes them more reactive than alkanes so can be used in useful reactions.
sigma bonds
covalent bonds formed when electron orbitals overlap axially
bonding in alkenes
double bond uses a pi bond and sigma bond
how are pi bonds formed in alkenes
the 2 sigma bonds surrounding the 2 carbon atoms in the C=C as each carbon has one electron in a p orbital not used in bond formation. p orbitals parallel to one another result in 2 regions of negative charge above and below the sigma bond forming a pi bond.
pi bond
covalent bonds formed when electron orbitals overlap sideways.
why are alkenes more reactive?
the pi bond spreads the electrons further from the carbon atoms so that they are more available for reactions
what happens to the bonds when alkenes react in addition reactions?
sigma bond remains unchanged in reactions while the pi bond is used to form new bonds with an attacking molecule to form a saturated product.
sigma is more stable and stronger as electrons are less readily available to react.
how to test for presence of a C=C double bond
place in bromine water, if it decolorises then a C=C double bond is present
hydrogenation
the addition of hydrogen to an alkene
catalyst in hydrogenation of alkenes
nickel and requires heat
how are addition reactions used in margarine manufacture
unsaturated vegetable oils react with hydrogen, so they then thicken.
halogenation
reaction between alkenes and halogens to form halogenoalkanes
hydration
addition of water/steam
how are alkenes hydrated?
heat alkene with steam and run over a catalyst of phosphoric acid
hydrogen halide addition
forms a halogenoalkane
diol oxidation
addition of oxygen and water to an alkene to form a diol with 2 hydroxyl groups. oxygen atom comes from air while water molecule gives H2O
conditions for diol oxidation
potassium manganate used in acidic condition (sulfuric acid).
what happens to potassium manganate in the presence of alkenes
changes from purple to colourless
curly arrows
start from a bond/lone pair and move to an atom
electrophile
a species that is attracted to a region of high electron density
how do hydrogen halides act as electrophiles
slight positive end of the HX is attracted to the electrons in the pi bond in the C=C, as is electronegative
heterolytic fission
the breaking of a covalent bond so that both bonding electrons are taken by one atom
electrophilic addition
reaction in which two molecules form one molecule and the attacking molecule is an electrophile.
carbocation
positive ion in which the charge is shown on a carbon atom
first step of electrophilic addition
HBr bonding electrons are given to the Br atom (so is negative ion) and the Hydrogen joins to the alkene, forming a carbocation.
second step of electrophilic addition
2 oppositely charged ions attract each other and react to form new covalent bond
process of electrophilic addition of halogens
Br2 forms a slightly positive/negative end and so positive end is attracted to surrounding electrons in the pi bond, forming a carbocation which then reacts with the remaining ion
what do unsymmetrical molecules form in electrophilic addition?
a major and minor product
how does the number of alkyl groups attached to the carbocation affect the amount produced
more alkyl groups spread the positive charge more so it is more stable, therefore more product is formed
property of alkyl groups
electron-releasing
how to name a polymer
stick ‘poly’ in front of the alkene name
reasons for increased polymer use
can be manufactured easily on large scale in variety of shapes/colors
lightweight
unreactive
cheap and disposable
3 main ways of using polymer waste
recycling
incineration
chemical feedstock
recycling
sorting (as mixtures of polymers are ineffective) via hand (inefficient/tedious)
processing (chopping waste into small pieces and washing)
incineration
takes in waste and converts into heat energy for homes/factories/electricity
waste ends up as gas (polluting)
chemical feedstock
chemical reaction use
biodegradable
broken down by microbes in the environment.
requires land for plant material
cant be incinerated, recycled or used as feedstock
difference between homolytic and heterolytic fission
both breaking of a covalent bonds but homolytic fission transfers electron to both species so that two of the same species are formed but heterolytic transfers both electrons to one atom, forming two different species
typical energy of a UV photon
300 kj/mol
steps of propagation reactant and product relations
product in step one is reactant in step two and product in step two is reactant in step 1
problem w radical substitution
end up w a mixture of products
meaning more energy must be used to separate them
aromatic compounds
contain benzene rings
zeolite catalyst
hydrated aluminosilicate
thermal cracking
takes places at high temp and pressure (1000 degrees and up to 70atm), producing many alkenes
catalytic cracking
uses zeolite catalyst at a slight pressure and high temperature, producing aromatic hydrocarbons and motor fuels
cuts cost and speeds up reaction
why is cracking done
greater demand for motor fuels, petrochemicals and polymers
products from reforming
cycloalkanes, arenes, aromatic compounds, branched alkanes
CC double bond shape (120 degrees)
trigonal planar (120 degrees)
