AS Organic Flashcards
define empirical formula
the formula that shows the simplest whole number ratio of atoms of each element in a compound
define molecular formula
the formula that shows the actual number of atoms of each element in a compound
define general formula
members of the same homologous series have the same general formula
define structural formula
the formula that shows the arrangement of atoms within a molecule
define displayed formula
the formula that shows all bonds b/w atoms of each element in a molecule
define skeletal formula
the formula that does not show c-h bonds
each vertex represents a carbon atom bonded to the max # of hydrogen atoms
what are the characteristics of a homologous series?
same functional group
same general formula
similar chemical properties
trend in physical properties
differ by ch2
what are the iupac nomenclature rules?
name is based around the longest carbon chain which contains the functional group
functional group is indicated by prefix or suffix
position of functional group is given by a # - from the end that gives the lowest #
where there are 2 or more of the same groups, di-, tri-, tetra- etc. are used
if there is more than one functional group, the groups are in alphabetical order & #s are separated by commas
#s only included if needed
what are the prefixes/suffixes for as functional groups?
alkanes: -ane
alkenes: -ene
alcohols: -ol, hydroxy-
haloalkanes: fluoro-, chloro-, bromo-, iodo-
aldehydes: -al
ketones: -one, oxo-
carboxylic acids: -oic acid
nitriles: -nitrile
amines: -amine, amino-
ethers: alkoxy-, -ether
what are the functional groups of:
alkenes
alcohols
haloalkanes
aldehydes
ketones
carboxylic acids
nitriles
amines
ethers?
see table in organic nomenclature booklet
what are reaction mechanisms?
explains the steps of the reactions of organic compounds
what is the formation of a covalent bond shown by?
a curly arrow that starts from a lone electron pair or from another covalent bond
what is the breaking of a covalent bond shown by?
a curly arrow starting from the bond
what are isomers?
molecules with the same molecular formula, but different arrangement of atoms
what are structural isomers?
molecules with same molecular formula, but different structural arrangement of atoms (structural, displayed or skeletal formula)
includes chain, position & functional group isomers (can overlap)
what are chain isomers?
molecules with same molecular formula, but different carbon chain branches
what are position isomers?
molecules with same molecular formula, but the functional group is on a different carbon atom
what are functional group isomers?
molecules with same molecular formula, but different functional group
what are the pairs of homologous series that can be functional group isomers?
- alcohol & ether
- aldehyde & ketone
- alkenes & cycloalkanes
- carboxylic acids & esters
what are alkanes?
homologous series of saturated hydrocarbons with the general formula CnH2n+2
very unreactive
what is the trend in boiling points in alkanes?
the longer the carbon chain, the higher the boiling point
bc more e-s so stronger vdw b/w molecules (only have vdw)
for alkanes that are isomers, the more branched the carbon chain, the lower the boiling point
bc molecules cannot pack as closely together so weaker vdw b/w molecules
what is petroleum?
mixture containing mainly alkanes that can be separated by fractional distillation
what is crude oil?
mixture of hydrocarbons, mainly alkanes
how is crude oil formed?
slow decay of marine animals and plants over millions of years, under heat & pressure & anaerobic conditions
describe the process of fractional distillation of crude oil
- crude oil is vaporised & passed into a fractionating tower
- that is hotter at the bottom
- hydrocarbons condense at different heights according to their different boiling points
- as the vapour rises, it cools
- shorter/smaller hydrocarbons have lower boiling points so condense nearer the top
the fractions contain hydrocarbons with similar boiling points
what is the order of heights of fractions & their uses?
refinery gases - domestic gas
gasoline - car fuel
kerosene - jet fuel
diesel - fuel for cars, lorries etc. w diesel engines
fuel oil - fuel for ships
bitumen - tarmac for roads
what does cracking involve?
breaking c-c bonds in alkanes
why is cracking useful?
cracking breaks up long chain, less useful alkanes, of which there are an excess for the demand, into more useful shorter alkanes (fuels) & alkenes (to make polymers), of which there are not enough to satisfy the demand
what are the products of & conditions for thermal cracking?
products: alkenes
high temp: 900C
high pressure: 70atm
no catalyst
what are the products of & conditions for catalytic cracking?
products: motor fuels (branched alkanes, cyclic alkanes, aromatics)
high temp: 450C
slight pressure: 1-2atm
catalyst: zeolite
alkanes are used as fuels
what is formed in complete combustion of alkanes & why is it harmful?
plentiful supply of O2
hydrocarbon + O2 —> CO2 + H2O
CO2 is a greenhouse gas that contributes to global warming
what is formed in incomplete combustion of alkanes?
insufficient supply of O2
hydrocarbon + O2 —> CO + H2O
hydrocarbon + O2 —> C (soot) + H2O
what pollutants does the internal combustion engine (incomplete combustion) produce & why are they harmful?
NOx - nitrogen reacts with oxygen in air because of the high temperatures in car engines
e.g. NO2 - toxic, asthma attacks, forms HNO3 which reacts with water & oxygen to form acid rain
CO - toxic, binds to haemoglobin in blood which reduces the body’s carrying capacity for O2
C - toxic, respiratory irritant
unburnt hydrocarbons - wastes fuel
what does combustion of substances containing sulfur impurities lead to?
SO2 - forms acid rain & causes air pollution
how are gaseous pollutants from internal combustion engines removed?
catalytic converters
flue gas desulfurisation
what is the function of catalytic converters & how do they work?
function: to reduce the emission of CO & NO by allowing them to react together to make harmless products & remove unburnt hydrocarbons
structure of machine: ceramic coated with platinum, palladium or rhodium
honeycomb structure with large surface area for increased rate of reaction
what are the equations of the reactions that happen inside a catalytic converter (with state symbols)?
2CO(g) + 2NO (g) —> 2CO2 (g) + N2(g)
C8H18(g)(petrol) + 25NO(g) —> 8CO2(g) + 12 1/2N2(g) + 9H2O(g)
how does flue gas desulfurisation work?
when in combustion reaction:
SO2 + H2O —> H2SO3 (calcium sulphite)
H2SO3 + 1/2O2 —> H2SO4
desulfurisation uses calcium oxide or calcium carbonate to form calcium sulfate (CaSO4)
dry: CaO(s) + SO2(g) –> CaSO3(g)
CaCO3(g) + SO2(g) –> CaSO3(g) + CO2(g)
how do gases affect global warming?
in troposphere, several gases absorb infrared radiation & re-radiates it in all directions, which increases the temperature inside the atmosphere
what are the steps in the free-radical substitution mechanism?
alkanes react with halogens in the presence of uv light to form halogenoalkanes (haloalkanes)
1. initiation - 1 reaction
2. propagation - 2 reactions
3. termination - 3 reactions (only use 2)
see notes
what happens in initiation?
halogen breaks down (in the presence of uv) to form 2 free-radicals
what happens in propagation?
a hydrogen is replaced by a halogen atom & .Cl radical is reformed by:
1. free-radical reacts to form a alkyl free-radical
2. free-radical reforms
free-radical is acting as a catalyst
what happens in termination?
2 free-radicals combine, forming a covalent bond & a stable compound, which ends the chain reaction
what is further substitution & when does it occur?
more than one H atom is replaced by a halogen atom
if halogen is in excess
presence of uv
what are the equations for further substitution?
see sheet
why does nucleophilic substitution happen?
the C-halogen bond is polar/has a dipole
define nucleophile
species that donates a lone pair of e-s
what are the conditions for nucleophilic substitution?
warm, aqueous
with what nucleophiles do haloalkanes undergo nucleophilic substitution?
OH-, CN-, NH3
what are the conditions for nucleophilic substitution with nitriles?
alcoholic/ethanolic, KCN reagent
heat under reflux
draw mechanisms for nucleophilic substitution
see notes
describe & explain how the C-halogen bond enthalpy affects the rate of elimination reaction
C-F highest bond energy
least reactive
as bond enthalpy increases, rate of reaction decreases
shared pair of e-s in covalent bond is closer to & more strongly attracted to the halogen nucleus so the bond requires more energy to be broken
what haloalkanes can nucleophilic substitution happen in?
only primary & secondary
draw mechanisms for elimination with OH-
see notes
what are the conditions for elimination?
hot, ethanolic, high concentration of hydroxide, heat under reflux
how does the nucleophile act in elimination?
as a base & accepts a proton, removing a hydrogen atom from the molecule
what haloalkanes can elimination happen in?
only secondary & tertiary
what are the roles of OH- in elimination?
nucleophile - donates a lone pair of e-s
base - accepts a proton
what is ozone & why is it beneficial?
O3 that naturally forms in the atmosphere
absorbs uv radiation
how are chlorine atoms formed in the atmosphere?
when uv radiation causes C-Cl bonds in CFCs (chlorofluorocarbons) to break, forming chlorine free radicals
what do chlorine atoms do in the atmosphere?
catalyse the decomposition of ozone & contribute to the hole in the ozone layer
what did results of research by different groups in the scientific community provide?
evidence for legislation to ban the use of CFCs as solvents & refrigerants
chemists have now developed alternative chlorine-free compounds.
what are the equations for the formation of ozone?
see notes
what are the equations (initiation & propagation) for the depletion of ozone?
see notes
what is the solution to the depletion of ozone?
use hydrogen fluorocarbons instead
CFCs unreactive
HFCs more reactive so might not reach the stratosphere
C-F bond too strong for UV to break
why is a hole in the ozone layer forming?
the decomposition of ozone is faster than ozone formation
what are alkenes?
unsaturated hydrocarbons
contain at least 1 c=c double bond
describe the c=c
electron dense
define stereoisomer
substances with the same molecular formula & structural formula but different 3d arrangement of atoms in space
what is the difference b/w e & z isomers?
e: highest priority groups on different sides
z: highest priority groups are on the same side
why does stereoisomerism occur?
no free rotation around the planar c=c double bond
how do alkenes react?
addition reactions
what type of reaction is alkenes + HBr, H2SO4 & Br2?
electrophilic addition
define electrophile
species attracted to the double bond
e- pair acceptors
+ve ions or polar species
how is bromine used to test for unsaturation?
add bromine water to alkene
shake
bromine is added across the c=c to form colourless dibromoalkane
by electrophilic addition
what are the major & minor products in addition reactions (of unsymmetrical alkanes)?
higher % of major product formed than minor product
why are there major & minor products?
carbocations with 3 structure are more stable than 2 structure, which is more stable than 1 structure
because they have more e- donating alkyl groups
outline the mechanism for electrophilic addition of HBr
see notes
outline the mechanism for electrophilic addition of H2SO4
see notes
outline the mechanism for electrophilic addition of Br2
see notes
what are the conditions for electrophilic addition?
room temp.
outline the mechanism for elimination of halogenoalkanes
see booklet
what are the reagents & conditions for elimination?
hydroxide ions e.g. KOH
ethanolic
heat under reflux
define polymer
long chain molecules formed by monomers joining together
define monomer
small, individual molecules that are repeated/joined together to form a polymer
define addition polymers
formed from alkenes & substituted alkenes
c=c double bonds open up & join together
what are the intermolecular forces of polyalkenes?
polyalkenes are often non-polar so VDW only
the longer the polymer & the closer the polymer chains, the stronger the VDW
polyalkenes made up of long, straight chains are strong & rigid vs short, branched chains are weaker & flexible
describe the reactivity of addition polymers & why
unreactive
saturated
no c=c double bond
& non-polar C-C chain
knowledge & understanding of the production & properties of polymers has developed over time
what is PVC & its uses?
poly(chloroethene)
rigid PVC: drainpipes, window frames
plasticised PVC: cable insulation, clothing
what are plasticisers?
small molecules, often esters, that are added to polymers to change their properties
they get in b/w chains of polymers & let chains slide over each other so the polymer becomes more flexible
they stop covalent bonds or intermolecular forces forming b/w chains
what is the repeating unit of a polymer
opened bond
brackets
2 Cs across
what is the structure of a polymer
opened bond
brackets
2Cs across
n
why are addition polymers unreactive?
main C chain is non-polar bc only contains c-c single bonds
why is there an attraction b/w c=c & Br2?
c=c is electron dense
Br2 is polar/has an induced dipole
attraction b/w c=c & delta + Br atom
in electrophilic addition to form an alcohol, water is added to the hydrogen sulfate to reform H2SO4, leaving an alcohol
H2SO4 is a catalyst
what are the 2 methods for producing alcohols?
hydration of alkenes (reacting with steam) using an acid catalyst = hydrolysis
ethanol produced by fermentation of glucose
what are the conditions needed for direct hydration of ethene?
350C
60-70atm
conc. phosphoric acid catalyst
what is the raw material for direct hydration of ethene & what is its source?
raw materials: ethene
source: thermal cracking larger alkanes from petroleum
is direct hydration of ethene renewable? explain
non-renewable
finite resources based on crude oil
what type of process is direct hydration of ethene?
continuous
products removed constantly
stream of reactants passed continuously over catalyst
= more efficient
what is the cost, purity & rate of direct hydration of ethene?
more expensive
pure/high % yield - nearly 100% ethanol
faster (minutes)
what are the conditions needed for fermentation of glucose?
35C
zymase (yeast) catalyst
anaerobic - absence of O2
(1 atm - not on ms)
what are the raw materials for fermentation & what are their sources?
raw materials: glucose, zymase
source: glucose from sugar cane/plant material, zymase from yeast
is fermentation of glucose renewable?
renewable
ethanol used as a biofuel
plant material can be regrown
what type of process is fermentation of glucose?
batch
reactants allowed to react for a fixed time
then process is repeated
what is the cost, purity (how separated)& rate of fermentation of glucose?
cheaper
impure/low % yield - majority is H2O - ethanol separated by fractional distillation
slower (days)
what are the advantages & disadvantages of batch vs continuous processes?
batch:
cost-effective, better quality control
but higher setup cost, slower, higher energy input
continuous:
faster, lower energy input
inflexible, expensive resources (machinery)
define biofuel
fuel derived from living matter
what are the equations for fermentation of glucose & direct hydration of ethene?
see notes
define carbon neutral
an activity which has no net CO2 emissions to the atmosphere
(same amount of CO2 released into atmosphere as taken in)
what are the equations that show fermentation of glucose is carbon neutral?
see notes
photosynthesis makes glucose & uses up CO2
fermentation & combustion of ethanol releases CO2
why is fermentation not actually carbon neutral?
other processes involved in the production of ethanol by fermentation that release CO2:
fuel for machinery (to heat to 35C) & transport
what is the mechanism for the formation of ethanol from ethene & steam with presence of acid catalyst?
see notes
be able to do for any alcohol from the alkene
what are primary alcohols oxidised to & by what oxidation agent?
aldehydes (obtained by distillation), which are further oxidised to carboxylic acids (obtained by reflux)
oxidising agent is acidified potassium dichromate orange –> green
when is water produced in oxidation of alcohols?
1y alcohol –> aldehyde
NOT aldehyde –> carboxylic acid
1y alcohol –> carboxylic acid
2y alcohol –> ketone
what are secondary alcohols oxidised to?
ketones
oxidising agent is potassium dichromate orange –> green
distillation (or reflux)
what are tertiary alcohols oxidised to?
not easily oxidised
describe the oxidation of ethanol, including the IMFs b/w each species
primary alcohol
ethanol is oxidised to ethanal, which is further oxidised to ethanoic acid
oxidising agent is acidified potassium dichromate - colour change orange –> green
IMFs: ethanol - hydrogen bonds
ethanal - dipole-dipole (so lowest bp)
ethanoic acid: hydrogen bonds
ethanol –> ethanal = distillation
ethanol –> ethanoic acid = reflux
what are the equations for the oxidation of ethanol?
see notes
describe the process of reflux
vertical condenser
heat reactants –> vapour
vapour continually condenses in condenser
what is the chemical test for aldehydes?
add Fehling’s solution
heat in hot water bath
blue solution –> red precipitate
Tollen’s reagent forms a silver mirror
add silver nitrate
add dilute sodium hydroxide - light brown precipitate forms
add dilute ammonia solution until brown precipitate just dissolved
what is the chemical test for carboxylic acids?
add small amount of Mg
produces gentle bubbles of H2 - slow rate bc weak acid
what is the chemical test for alkenes?
add bromine water & shake
orange –> colourless
tests for presence of c=c double bond
forms dibromoalkane
how are alkenes formed from alcohols?
elimination reactions
dehydration
acid catalyst - conc. sulfuric or phosphoric acid
what can alkenes formed by dehydration be used for?
making addition polymers without using monomers derived from crude oil
what is the mechanism for the dehydration of alcohols?
see notes
what is the test-tube test for alkenes?
add bromine water
shake
positive result: solution turns from orange to colourless
what are the test-tube tests for aldehydes?
Tollen’s reagent:
add to solution being tested & warm gently
positive result: colourless solution –> silver mirror
Fehling’s reagent:
add Fehling’s solution to solution being tested
heat in hot water bath
positive result: blue solution turns to brick red ppt
what is the test-tube test for alcohols?
add acidified potassium dichromate
positive result: for 1 & 2 alcohols, solution will turn from orange to green
3 alcohols remain orange
what is the test-tube test for carboxylic acids?
either add a small amount of Mg
positive result: bubbles of H2
or
add sodium carbonate
positive result: bubbles of CO2 - bubble through limewater & solution turns from colourless to white cloudy
what is mass spectrometry used for?
% abundance of isotopes
high resolution can determine the molecular formula of a compound
how does high resolution ms work?
elements contain different isotopes with different masses so Ar will not be a whole number
what is the first species formed in ms?
molecular ion - has a +ve charge & a radical
on the spectra graph, what shows the Mr?
peak with greatest m/z value
what is the % abundance of each Cl & Br isotope?
35Cl = 75%
37Cl = 25%
79Br = 50%
81Br = 50%
practise identifying compounds by high res. ms
see notes booklet
how does infrared spectroscopy work?
bonds in a molecule absorb ir radiation at characteristic wave numbers
all bonds vibrate at a characteristic frequency
fingerprint region 2 marker
look at fingerprint region <1500
find exact match with known spectrum/
look at database of the known compound & find exact match
what are the labels for the spectra axes for ir spectroscopy?
x = wave number
y = transmittance
functional group signals
above 1500
what are the shapes & positions of characteristic peaks?
see notes sheet
compound with a bigger bp…
means more interference of C-H bond
why does methane act as a greenhouse gas?
methane absorbs infrared radiation
