AS organic

name the 6 ways organic compounds can be represented:

• empirical formula

• molecular formula

• general formula

• structural formula

• displayed formula

• skeletal formula

what is the empirical formula of a compound?

formula that gives the simplest ratio of atoms of each element in a compound

what is the molecular formula of a compound?

formula which gives the actual number of atoms of each element in one molecule

what is the general formula of a compound?

formula which shows the number of atoms of each element in a substance which has n carbon atoms

what is the structural formula of a compound?

formula which shows how the atoms are joined together in a molecule

what is the displayed formula of a compound?

formula which shows all bonds and atoms in a molecule

(does not show accurate bond angles)

what is the skeletal formula of a compound?

simplified displayed formula:

• H atoms not shown (unless part of a functional group)

• C atoms represented by corners

• double bonds shown

• other atoms shown

what is a homologous series?

a series of compounds containing the same functional group

what are the characteristics of a homologous series?

• same general formulae

• same functional group

• each subsequent compound differs by a CH₂ unit, forming next homologue in series

give the IUPAC rules for nomenclature:

• find and number longest C chain to determine stem name (e.g. but-)

• identify key functional group (e.g. -oic acid)

• add side chains in alphabetical order and w/ correct numbers (indicating which C atom side chains are on), adding multipliers if necessary (e.g. 3-chloro, 2,2-dimethyl)

• → 3-chloro-2,2-dimethylbutanoicacid

• (molecules that contain rings have the prefix cyclo-)

what is the functional group of a molecule?

the part of a molecule that determines how it reacts and is the same across the homologous series

what is a structural isomer?

a molecule w/ the same molecular formula but different structural formulae

what are the 3 types of structural isomer?

• functional group isomers

• chain isomers

• position isomers

what is a functional group isomer? give an example:

• structural isomers w/ same molecular formula but different functional groups

• e.g. ethanoic acid and methylmethanoate

what is a chain isomer? give an example:

• structural isomers w/ same molecular formula but different carbon chain arrangements

• e.g. butane and methylpropane

what is a position isomer?

• structural isomers w/ same molecular formula but different position of functional group

• e.g. 1-chlorobutane and 2-chlorobutane

what is a stereoisomer?

molecules that have the same molecular formula but a different arrangement of the atoms in space

when does E/Z / geometric isomerism occur?

• when you have restricted rotation about the planar C=C

• (both atoms of C=C must have 2 or more different functional groups)

does this but-2-ene display E or Z isomerism? why?

E (entgegen) as the functional groups are opposite each other

does this but-2-ene display E or Z isomerism? why?

Z (zusammen) as the functional groups are together

explain the Cahn-Ingold Prelog (CIP) rules:

• we look at the atomic numbers of the atoms directly connected to the C=C and give them a ‘priority’

• highest values opposite = E

• highest values together = Z

what is geometric isomerism?

• compounds/molecules w/ the same structural formula

• but atoms/bonds/groups arranged differently in space

what is stereoisomerism? give 2 examples:

compounds/molecules w/ the same molecular and same structural formula but a different arrangement of atoms in space:

• geometric isomerism

• optical isomerism

what are structural isomers? give 3 examples:

compounds/molecules with the same molecular formula but a different structural formula:

• chain isomerism

• position isomerism

• functional group isomerism

what are the 3 types of structural isomerism?

• chain isomer

• position isomer

• functional group isomer

whata chain isomer?

compounds/molecules w/ the same functional group and molecular formula but a different arrangement of the carbon chain

what is a position isomer?

compounds/molecules w/ the same molecular formula and carbon chain but w/ the functional group in a different place

what are functional group isomers?

compounds/molecules w/ the same no. of atoms but arranged to form a diff functional group

why does E-Z isomerism occur?

restricted rotation around the C=C double bond

give the 2 types of E/Z isomers:

• Z isomer (zusammen) = higher priority groups are on the same side of the C=C double bond

• E isomer (entgegen) = higher priority groups are on opposite sides of the C=C double bond

summarise the CIP priority rules:

C w/ the groups w/ the highest atomic number = highest priority

what are alkanes?

homologous series of saturated hydrocarbons w/ the general formula C_nH_2n+2

how reactive are alkanes?

very unreactive, but do burn and react w/ halogens (to form haloalkanes)

what is a homologous series?

family of compounds:

• same general formula

• similar chemical properties

• each member differs by the addition of a CH₂ group and a gradual change in physical properties

how does bpt change as the C chain gets longer?

• longer C chain = higher bpt

• as more e^-

• so stronger VDWs between molecules

• which require more energy to break

how does bpt change w/ increase in branching?

• more branching = lower bpt

• as molecules do not pack as close together

• so weaker VDWs between molecules

• which require less energy to break

how does viscosity change as the C chain gets longer?

viscosity increases (can be found by residue in fractional distillation)

how does flammability change as the C chain gets longer?

flammability decreases

how does the flame change as the C chain gets longer?

flame gets dirtier (clean → smoky flame)

what can the products of combustion be?

complete: CO₂ + H₂O

incomplete: CO + H₂O or C + H₂O

which pollutants does an internal combustion engine produce?

NO_x, CO, C and unburned hydrocarbons

what is the function of a catalytic converter?

removes toxic gaseous pollutants from internal combustion engines and converts them into less harmful substances (e.g. CO₂, water vapour, N)

how is CO₂ formed in the atmosphere? what potential problems may this cause?

• complete combustion of C in fuel

• greenhouse gas causing global warming

how is CO formed in the atmosphere? what potential problems may this cause?

• incomplete combustion of C in fuel

• toxic

how is C formed in the atmosphere? what potential problems may this cause?

• incomplete combustion of C in fuel

• blackens buildings, global dimming

how is SO₂ formed in the atmosphere? what potential problems may this cause?

• combustion of S in fuel (through fuel impurities)

• acid rain, air pollution

how are NO and NO₂ formed in the atmosphere? what potential problems may this cause?

• reaction of N₂ in air w/ O₂ in air at very high temperatures (e.g. engines/furnaces)

• acid rain

what potential problems may unburned fuel cause?

fuel waste, harmful greenhouse gas

how can we reduce SO₂ emissions?

flue gas desulfurisation:

• powdered CaO or CaCO₃ mixed w/ water to make an alkaline slurry

• when flue gases mix w/ alkaline slurry, acidic SO₂ gas reacts w/ calcium compounds to form CaSO₃, which is harmless

describe the process of fractional distillation:

• crude oil vaporised

• vapour passed into a column - hot at bottom and cool at top (temp gradient)

• as the vapour rises it cools

• molecules condense at different fractions as they have different bpts

• larger the molecules, the lower down the column they condense

what is thermal decomposition? give an example:

breaking down compounds by heating into simpler compounds - e.g. cracking

what is cracking?

breaking up large, less useful hydrocarbons into smaller, more useful hydrocarbons (thermal decomposition of alkanes)

why do we crack?

• petroleum fractions w/ shorter C chains are in higher demand than larger fractions

• longer hydrocarbons are cracked to make use of XS larger hydrocarbons and supply demand for shorter ones

• products are more valuable than the starting materials

give a use of shorter alkanes:

fuels

give a use of alkenes:

making plastics

describe the conditions and products of thermal cracking:

• high temp (900^oC)

• high pressure (70 atm)

• no catalyst

• produces alkenes

describe the conditions and products of catalytic cracking:

• high temperature (450^oC), but lower than thermal cracking

• slight pressure (1-2 atm)

• zeolite catalyst

• produces motor fuels, aromatic hydrocarbons, cyclic hydrocarbons and branched alkanes

what is a haloalkane?

an alkane where at least 1 H atom has been replaced w/ a halogen atom

what is the product of free rad sub?

haloalkanes

what is a mechanism?

process showing the step by step movement of e^- as reactants are converted into products

what does a single headed curly arrow represent?

movement of a single e^-

what does a double headed curly arrow represent?

movement of an e^- pair

what is a free radical?

a molecule w/ an odd no. of e^- and so an unpaired e^-

how reactive are free radicals?

very reactive!

name the steps of free rad sub:

1. initiation

2. propagation

3. termination

give the overall eqn for the reaction of methane w/ chlorine:

CH₄ + Cl₂ → CH₃Cl + HCl

describe and give the eqn for the initiation step of free rad sub of the reaction of methane w/ chlorine:

• UV light breaks Cl molecules into free radicals by providing the E to break the Cl-Cl bond

• Cl : Cl → . Cl + . Cl

which side are the radicals on in initiation?

RHS

describe and give the eqn for the propagation step of free rad sub of the reaction of methane w/ chlorine:

• Cl radicals react w/ alkanes in a chain reaction where the Cl radical acts as a catalyst

• for each H replaced, there is a pair of propagation steps

• . Cl + CH₄ → HCl + . CH₃

• . CH₃ + Cl₂ → CH₃Cl + . Cl

which side are the radicals on in propagation?

both sides

describe and give the eqns for the termination step of free rad sub of the reaction of methane w/ chlorine:

• when any 2 free radicals meet, they react to form a molecule w/ no unpaired e^-, stopping the chain reaction

• . Cl + .Cl → Cl₂

• OR . Cl + . CH₃ → CH₃Cl

• OR . CH₃ + . CH₃ → C₂H₆

what is an alkene?

an unsaturated hydrocarbon - C=C double bond is an area of high e^- density

what is a polymer?

long chain molecule made from lots of small molecules (monomers) joined together

what is a monomer?

small molecules that join together to make polymers

what is addition polymerisation?

formation of long chain molecules from lots of small molecules joining together w/ no other products

draw the monomer structure of poly(ethene):

draw the polymer structure of poly(ethene):

draw the repeating unit of poly(ethene) and name the bonds at either end of the repeating unit:

trailing bonds

how do we name addition polymers?

poly(name of alkene)

what are addition polymers formed from?

alkenes and substituted alkenes

describe the properties of addition polymers:

• unreactive

• chains usually non-polar so held together by VDWs

• the longer the polymer chains are/the closer together the chains can get, the stronger the VDWs between the chains will be

• polyalkenes made up of long, straight chains → strong and rigid

• polyalkenes made up of short, branched chains → weaker and flexible

what is poly(chloroethene)/PVC and what can it be used for?

• polymer of chloroethene

• has long, closely packed polymer chains - hard, but brittle at room temp

• rigid PVC - drainpipes and window frames

how can we modify PVC’s properties?

• by adding a plasticiser - pushes polymer chains apart, reducing strength of VDWs

• this means the polymer can slide around more, making it easier to bend

• plasticised PVC - electric cable insulation, flooring tiles, clothes

what is an electrophile?

e^- deficient species which will accept a pair of e^-

what is a carbocation?

+vely charged C atom w/ only 3 bonds, making it unstable

what does electrophilic addition involve? what does it form?

alkene → dihaloalkane

draw out the electrophilic addition mechanism between HBr and propene (for both the major and minor product):

draw out the electrophilic addition mechanism between Br₂ and ethene:

draw out the electrophilic addition mechanism between H₂SO₄ and ethene and state the conditions:

give the order of carbocation stability - why is this the case?

• tertiary carbocations have the most stability as they have the greatest +ve inductive effect as they have the most alkyl/C groups

• as they push e^- density towards the carbocation and stabilise the +ve charge

• the more alkyl groups, the more stable

what is a primary carbocation?

carbocation w/ only 1 alkyl group

what is a secondary carbocation?

carbocation w/ 2 alkyl groups

what is a tertiary carbocation?

carbocation w/ 3 alkyl groups

why may a product of electrophilic addition display optical isomerism?

• electrophilic addition involving an alkene w/ one of the Hs substituted for a different functional group e.g. CN + HX

• product is a haloalkane w/ one of the Hs subbed for the other functional group

• one of the carbocations may form a product w/ a chiral C

• optical as C+ on carbocation planar so can be attacked from above or below

there is a very low yield of butan-1-ol from but-1-ene in this manufacturing process - explain why (2)

• formed from less stable carbocation

• formed from 1^o rather than 2^o carbocation

order the C-Br, C-I and C-Cl bonds in order of strength:

(strongest to weakest) C-Cl, C-Br, C-I

what are the 2 factors affecting bond strength? which one is more significant?

• polarity

• bond enthalpy (more significant)

explain why the C-halogen bond enthalpy influences the RoR:

• C-halogen bonds get weaker down the group due to the increased size of the halogen atom

• the further apart the atoms are in size, the higher the bond enthalpy

• this means the C-F bond is strongest, meaning fluoroalkanes undergo nuc sub reactions more slowly than other alkanes

how is bond enthalpy affecting bond strength more significantly seen in the periodic table?

• reactivity decreases down the group

• if polarity were more significant, reactivity would increase down the group as the C-F would be predicted to be more reactive as the difference in electronegativity is the greatest

give the molecular formula for ozone:

O₃