Module 4: Core organic chemistry Flashcards
what is general formula?
an algerbraic formula that can describe any member of a family of compounds
what is empirical formula?
the simplest whole ratio number of atoms of each elements in a compound
what is molecular formula?
the actual number of atoms of each element in a molecule
what is structural formula?
shows the arrangement of atoms carbon by carbon
what is skeletal formula?
shows the bonds of the carbon skeleton only, with any functional groups
what is the displayed formula?
shows how all the atoms are arranged, and all the bonds between them
Give the prefix or suffix and a example of the group alkanes?
- ane
- propane
Give the prefix or suffix and a example of the group branched alkanes?
- alkyl (-yl)
- methylpropane
Give the prefix or suffix and a example of the group alkenes?
- ene
- propene
Give the prefix or suffix and a example of the group haloalkanes?
- chloro
- bromo
- iodo
- chloroethene
Give the prefix or suffix and a example of the group alcohols?
- ol
- ethanol
Give the prefix or suffix and a example of the group aldehydes?
- al
- ethanal
Give the prefix or suffix and a example of the group ketones?
- one
- propanone
Give the prefix or suffix and a example of the group cycloalkanes?
- cyclo..ane
- cyclohexane
Give the prefix or suffix and a example of the group carboxylic acids?
- oic.. acid
- ethanoic acid
Give the prefix or suffix and a example of the group esters?
- alkyl… annotate
- methyl propanoate
what are alkanes?
they have the general formula CnH2n+2
- they are saturated and all the carbon-carbon bonds are single
what is a alkane molecule like?
- Each carbon has four pairs of bonding electrons around it. they all equally repel each other, so the molecule forms a tetrahedral shape around each carbon, the angle is 109.5 degrees
describe the structure of an alkane?
- they have covalent bonds inside the molecules, between the molecules there are induced dipole-dipole interactions (AKA London forces) which hold them all together
what does it mean the longer the alkane chain?
the stronger the induced dipole-dipole interactions. this is because there is more surface contact and more electrons to interact.
- as they get longer, it takes more energy to overcome the induced dipole-dipole interactions, and the boiling point rises
what does a branched chain have?
it has a lower boiling point than its straight chain isomer.
- they cant pack closely together and they have smaller molecular surface areas so the induced dipole-dipole interactions are reduced
what happens when you oxidise alkanes?
you can get carbon dioxide and water which is a combustion reaction, longer alkanes release heaps more energy per mole as they have more bonds to react which is why they make good fuels
what do combustion reactions happen between?
they occur between gases, so liquid alkanes have to be vaporised first. smaller alkanes turn into gases more easily as they’re more volatile and so they burn easier too
when are two molecules isomers of one another?
if they have the same molecular formula but the atoms are arranged differently
what are chain isomers?
the carbon skeleton can be arranged differently eg as a straight chain or branched in different ways
what are positional isomers?
the skeleton and functional group could be the same, only with the functional group attached to a different carbon atom. they also have different physical properties and the chemical properties might differ too
what are functional group isomers?
where the same atoms can be arranged into different functional groups. they have very different physical and chemical properties
what is bond fission?
where a covalent bond is broken, there are two types. homolytic fission and heterolytic fission
what is heterolyctic fission?
where the bond breaks unevenly with one of the bonded atoms receiving both electrons from the bonded pair. two different substances are formed from this, a positively charged cation (X+) and a negatively charged anion (Y-).
- X .-. Y -> X+ + Y-
what is homolytic fission?
where the bond breaks evenly and each bonding atom receives one electron from the bonded pair. two electrically uncharged radicals are formed. Radicals are particles that have an unpaired electron. they’re shown in mechanisms by a big dot next to the MF, the dot represents the unpaired electron. because of the unpaired electron, radicals are v reactive
- X .-. Y -> X. + Y.
how do alkanes react with halogens?
in photochemical reactions, they are started light - this reaction require UV light
- a hydrogen is substituted by chlorine or bromine. its called Free radical substitution reaction
what are two problems with free radical substitution reactions?
- if you’re trying to make a particular product is that you don’t only get the product you want you get a mixture
- free radical substitution can take place at any point along the carbon chain, so a mixture of isomers can be formed
what happens in the reaction of making chloromethane?
if there is too much chlorine in the reaction, some of the hydrogen atoms on the chloromethane molecule will be swapped for Cl atoms. instead the propogation reaction make dichloromethane
- Cl. + CH3Cl -> .CH2Cl + HCl
- .CH2Cl + Cl2 -> CH2Cl2 + Cl.
what’s the best way of reducing the chance of by-products?
to have an excess of methane which means there’s greater chance of a chlorine radical colliding only with a methane molecule and not a chloromethane molecule
what are CFCs?
chlorofluorocarbons are well known halogens, where the hydrogens are replaced with halogens. they contain chlorine, fluorine and carbon only.
- they are stable, volatile, non-flammable and non toxic
what and how is ozone (03) formed?
- ozone is found in the upper atmosphere and acts as a chemical sunscreen, it absorbs a lot of the UV radiation which can cause sunburn and skin cancer
- its formed naturally when an oxygen molecule is broken down into two free radicals by UV radiation, the free radicals attack other oxygen radicals forming ozone
- O2 (UV0 –> O + O –> O2 + O –> O3
when did scientists discover ozone?
- in the 1970s and 80s, they discovered the ozone layer above Antarctica and the artic was getting thinner. these ‘holes’ in the ozone layer are bad as they allow more harmful UV radiation to reach earth
how are ‘holes’ formed?
- they are formed as CFCs in the upper atmosphere absorb UV radiation and split to form chlorine free radicals. these free radicals catalyse the destruction of the ozone as they destroy ozone molecules and are then regenerated to destroy more ozone molecules.
what happens in the first part of the reaction of CF2Cl2?
- CF2Cl2 (g) uv –> .CF2Cl (g) + Cl. (g)
- chlorine free radicals, Cl. are formed when the C-Cl bonds in CFCs are broken down by the UV radiation
what happens in the second part of the reaction of CF2Cl2?
- these free radicals are catalysts, they react with ozone to form an intermediate (ClO.) and an oxygen molecule
- Cl. (g) + O3 (g) -> O2 (g) + ClO. (g)
- ClO. (g) + O* (g) -> O3 (g) + Cl. (g)^
- the o radical comes from the breakdown of oxygen by UV radiation
^ the cl radical is regenerated & attacks another ozone molecule
what is the overall equation of the reaction of CF2Cl2?
O3 (g) + O (g) –> 2O2 (g) and Cl. is the catalyst
what are NO. free radicals?
they are from nitrogen oxides which are produced by car aircraft engines, NO. free radicals affect the ozone layer same as Cl. radicals
how can a reaction of Cl. or NO. be represented?
using R, where in both cases the free radicals act as catalysts for the destruction of the ozone
- R + O3 –> RO + O2
- RO + O –> R + O2
overall equation is O3 + O -> 2O2
what did scientists discover in the 1970s?
- that CFCs were causing damage to the ozone layer although there were advantages to their use they couldn’t outweigh the environmental problems, so they were banned
what’s the Montreal protocol of 1989?
- it was an international treaty to phase out the use of CFCs and other ozone-destroying haloalkanes by the year 2000. there were a few permitted uses eg medical inhalers and submarines
what are HCFCs and HFCs?
hydrochlorofluorocarbons and hydrochlorocarbons are being used as temporary alternatives to CFCs, HCFCs are still harmful but their effect is smaller. HFCs are also broken down but don’t contain chlorine so don’t damage the ozone layer
what are the other two alternatives to CFCs?
- hydrocarbons are being used but they are greenhouse gases
- most aerosols have been replaced with pump spraying systems or use nitrogen as the propellent
- in industrial fridges and freezers they use ammonia as the coolant gas and CO2 is used to make foamed polymers
what is a haloalkane?
its an alkane with at least one hydrogen atom in place of a hydrogen atom
- halogens are generally much more electronegative than carbon, so the carbon-hydrogen is polar
what is delta positive carbon? a nucleophile?
- its electron deficient, this means that it can be attacked by a nucleophile.
- a nucleophile is an electron pair donor. it could be negative ion or an atom with a lone pair of electrons. it donates an electron pair to somewhere without enough electrons
give examples of nucleophiles?
- OH-, CN-, and NH3 are all nucleophiles which will react haloalkanes. water’s a nucleophile too, but it reacts slowly
what is nucleophilic substitution reaction?
- where haloalkanes can be hydrolysed to alcohols.
eg. sodium hydroxide or potassium hydroxide
R-X + OH- –> (OH-/H2O/ reflux) R-OH + X-
describe nucleophilic substitution reaction with bromoethane?
- you use a warm aqueous alkali
- OH- is the nucleophilic which provides a pair of electrons for the C delta positive
- the C-Br bond breaks heterolytically - both electrons from the bond are taken by Br-
- Br- falls off as OH- bonds to the carbon
describe nucleophilic substitution reaction with water?
- water molecule is a weak nucleophile, but it will substitute for the halogen
- you get an alcohol produced again GE:
- R-X + H2) –> R-OH + H+ + X-
with bromoethane: - CH3CH2Br + H2O –. C2H5OH + H+ + Br-
what determines how quickly haloalkanes are hydrolysed?
- their bond enthalpy
- weaker carbon-hydrogen bonds break more easily so they react faster
what about fluoroalkanes and iodoalkanes?
- fluoroalkanes have the strongest bonds so they are the slowest at hydrolysing
- iodoalkanes have the weakest bonds so they hydrolyse the fastest
what are alkenes?
they have the general formula CnH2n. they all have at least one c=c double bond
- molecules with c=c double bonds are unsaturated as they can make more bonds with extra atoms in addition reactions
what is a sigma bond?
- it is formed when two s orbitals overlap, the two s orbitals overlap in a straight line which gives the highest electron density between the two nuclei.
- this is a single covalent bond
what does the high electron density in sigma bonds mean?
- the high electron density between the nuclei means there is a strong electrostatic attraction between the nuclei and the shared pair of electrons. this means that the sigma bonds have a high bond enthalpy - they’re the strongest type of covalent bond
what is a pi bond?
- its formed by the sideways overlap of two adjacent p orbitals. its got two parts to it - one above and one below the molecular axis. this is because the p-orbitals which overlap are dumb-bell shaped
why are pi bonds weaker than sigma bonds?
- pi bonds are weaker as the electron density is spread out above and below the nuclei. this means that the electrostatic attraction between the nuclei and the shared pair of electrons is weaker, so the pi bonds have a relatively low bond enthalpy
what do alkanes only contain?
- they only contain c-c and c-h bonds which have a high bond enthalpy and so are difficult to break. the bonds are also non-polar so they don’t attract nucleophiles or electrophiles so they don’t react easily
why are alkenes more reactive?
- they have a c=c bond which contains both a sigma bond and a pi bond
- the double bond contains four electrons so it has a high electron density and the pi bond also sticks out above and below the rest of the molecule. these two factors mean the pi bond is likely to be attacked by electrophiles
how does the low bond enthalpy of the pi bond contribute to the reactivity of alkenes?
- because the double bonds are so reactive, alkenes are handy starting point for making organic compounds and for making petrochemicals
what are stereoisomers?
- they have the same structural formula but a different arrangement in space. they occur when the two double bonded carbon atoms have two different atoms or groups attached to the,
what is the z isomer?
- has the same groups either both above or both below the double bond
what is the e-isomer?
- has the same groups positioned across the double bond
why cant atoms in a c=c double bond rotate?
- its because of the way the p orbitals overlap to form a pi bond. double bonds are actually rigid, they don’t bend much. the restricted rotation around the c=c double bond is what causes alkenes to form stereoisomers
what does ‘cis’ mean?
- means the same groups are on the same side of the double bond
what does ‘trans’ mean?
- means the same groups are on the opposite sides of the double bond
- if the carbon atoms both have totally different groups attached to them, the cis-trans naming system doesn’t work
what are electrophiles?
- they are electron pair donors, they are partially charged ions like H+, NO2+ and polar molecules since the delta + atom is attracted to places with lots of e.
what happens in an electrophilic addition reaction?
- the alkene double bond opens up and atoms are added to the carbon atoms. it happens as the double bond has got lots of electrons and are easily attacked by electrophiles
give an example of an adding hydrogen to C=C bonds to produce alkanes? 1
- ethene will react with hydrogen gas in an addition reaction to produce ethene. it needs a nickel catalyst and temperature of 150 degrees
- H2C=CH2 + H2 –> CH3CH3
what happens when halogens react with alkenes? 2
- they form dihaloalkanes
- the halogens are added across the double bond and each of the carbon atoms end up bonded to the halogen atom -> electrophilic addition reaction
describe the mechanism of bromine to make 1,2 dibromoethane? (2)
- the double bond repels the electrons in Br2, polarising the Br-Br bond
- heterolytic fission of Br2. the closer the Br gives up the bonding electron to the other Br and bonds to the C atom
- you get a postively charged carbocation
- the Br- then bonds to the other C atom, forming 1,2 dibromoethane
how do you use bromine water to test for carbon double bonds?
- when you shake an alkene with orange bromine water, the solution quickly decolourises. this is because bromine is added across the double bond to form a colourless dibromoalkane
give an example of alcohols being made by steam hydration? 3
- alkenes can be hydrolysed by steam at 300 degrees and a pressure of 60-70atm, it needs a solid phosphoric(V) acid catalyst
- eg ethanol from ethene
H3C=CH2 (g) + H20 (g) CH3CH2OH (g)
give an example of alkenes undergoing addition reactions with hydrogen halides? 4
- they form haloalkanes
eg ethene and HBr
H2C=CH2 + HBr –> CHBrCH3
what happens when you add hydrogen halides to unsymmetrical alkenes? 5
- they form two possible products
- the amount of each product depends on how stable the carbocation formed in the middle of the reaction is
- carbocations with more alkyl groups are more stable as the alkyl groups feed electrons towards the positive charge. the more stable carbocation is likely to form
what is Markownikoff’s rule?
- the major product from addition of a hydrogen halide (HX) to an unsymmetrical alkene is one where the hydrogen adds to the carbon with the most hydrogen already attached
whats the carbocation order from least to most?
- primary carbocation with one alkyl group
- secondary carbocation with two alkyl groups
- tertiary carbocation with three alkyl groups
what are polymers and monomers?
- the double bonds in alkenes can open up and join together to make long chains called polymers
- the individual small alkenes are called monomers
what are synthetic polymers?
- they are widespread and unreactive which means food doesn’t react with the PTFE coating on pans etc
- however this lack of reactivity means most polymers aren’t biodegradable and so they’re difficult to dispose of
what is landfill and when is it used?
- it is a option for dealing with waste plastics, it is generally used when the plastic is:
1. difficult to separate from other waste
2. not in sufficient quantities to make separation financially worthwhile
3. too difficult technically to recycle
how can we recycle plastics?
- many plastics are made from non-renewable oil fractions so after sorting the plastics
1. some plastics can be recycled by melting and remoulding them
2. some plastics can be cracked into monomers and can be used as organic feedstock to make plastics
what happens when plastic can’t be recycled?
- waste plastics can be burned and the heat used to generate electricity
- this process needs to be controlled to reduce toxic gases. waste gases from the combustion are passed through scrubbers which can neutralise gases such as HCl by allowing them to react with a base
what are biodegradable polymers?
- they decompose quickly in certain conditions as organisms can digest them. they can be made from renewable raw materials such as starch or oil fractions but they are more expensive than non-biodegradable equivalents
what is the problem with biodegradable polymers?
- these polymers need the right conditions before the will decompose. you couldn’t put them in landfill and expect them to perish away as there is a lack of O2 and moisture under all that compressed soil
- you’d need to put them on a big compost heap which means that you need to collect and separate the biodegradable polymers, from the non-biodegradable plastics
what are the uses to biodegradable polymers?
- plastic sheeting used to protect plants from the frost can be made from poly(ethene) with starch grains embedded in it. in time the starch is broken down by microorganisms and the remaining poly(ethene) crumbles into dust.
- there is no need to collect and dispose of the old sheeting
what have scientists started to develop?
- photodegradable polymers which decompose when exposed to sunlight
What are alcohols?
They have the general formula CnH2n+1 OH. Its primary, secondary and tertiary depending on which carbon the -OH group is bonded to
- they are generally polar molecules due to the electronegative hydroxyl groups which pulls the e in the C-OH bond away from the carbon atom
- they have a low votality
How are hydrogen bonds formed with alcohols?
The electronegative oxygen in the polar hydroxyl group draws attention away from the hydrogen, giving it a slightly positive charge which can attract the lone pairs on an oxygen from a neighbouring molecule, forming H bonds
What happens when you mix an alcohol with water?
Hydrogen bonds between -OH and H2O, if its a small alcohol, hydrogen bonding lets it mix freely with water - its soluble
- in larger alcohols, most of the molecule is a non polar carbon chain, son there’s less attraction for the polar H2O molecules. So as alcohols incease in size, their solubility in water decreases
what happens in free radical substitution reactions?
- H atoms on alkanes or haloalkanes are replaced by halogen atoms
- for every H atom replaced by a halogen F/Cl etc, one molecule of F2/Cl2 etc is used and one molecule of HF/ HCl is released
what happens at initiation reactions?
- when exposed to UV light, a molecule of halogen breaks apart into two halogen atom free radicals (F., Cl.). the UV light provides the energy to break the covalent bond between two halogen atoms
eg F2 -> 2F.
what happens at propagation reactions?
- (molecule + radical -> molecule + radical)
- for every H that is replaced, there is one pair of propagation reactions
- the alkane/haloalkane reacts with the halogen radicals which removes an H atom from the alkane/haloalkane this produces HF, HCl etc
- the C based radical reacts with F2,Cl2 etc to put an atom of F/Cl onto the bases radical which produces another halogen free radical.
what happens at termination?
- (2 radicals -> molecule)
- if two free radicals collide, they will form a molecule and stop the chain reaction. any two free radicals involved could collide
what happens in a nucleophilic substitution reaction?
- the halogen atom is replaced by another atom/group
- this is because the halogen atom is more electronegative than carbon atoms and so the C of the C-halogen bond is delta positive
describe nucleophilic substitution reaction with NaOH?
- warm, aqueous NaOH is needed, the halogen atom is replaced by the OH group
- R–X + NaOH -> R–OH + NaX
describe nucleophilic substitution reaction with KCN?
- ethanolic, warm KCN is needed, the halogen atom is replaced by the CN group
- R–X + KCN -> R–CN + KX
describe nucleophilic substitution reaction with NH3?
- excess concentrated ammonia dissolved in ethanol at pressure in concealed container is needed,
1. the first molecule of NH3: halogen atom is replaced by NH2 group.
2. second molecule of NH3: leads to the formation of NH4X - R–X + 2NH3 -. R–NH2 + NH4X
how do combustion reactions occur with alcohols?
- when alcohols are burned with a pale blue flame to form CO2 and H2O
- you can use the oxidising agent acidified dichromate (VI) (Cr2O72-/H+) to mildly oxidise alcohols
what are primary alcohols oxidised too?
- aldehydes and then to carboxylic acids
what are secondary alcohols oxidised too?
- ketones only
- refluxing a secondary alcohol with acidified dichromate (VI) will give a ketone, but ketones can’t be oxidised easily so even prolonged refluxing wont produce anything more
what are tertiary alcohols oxidised to?
- they are not oxidised, they dont react with acidified potassium dichromate (VI) so the solution stays orange.
- the only way to oxidise tertiary alcohols is by burning them , the orange dichromate ion is reduced to the green chromium (III) ion Cr3+
what do aldehydes and ketones have?
- aldehydes have a hydrogen and alkyl group attached to the carbonyl carbon atom
- ketones have two alkyl groups attached to the carbonyl carbon atom
aldehydes and ketones have the functional group C=O and general formula CnH2nO
how do you form an aldehyde?
- you need to get it out of the oxidising solution as soon as it is formed, you can do this by gently heating excess primary alcohol with a controlled amount of oxidising agent in distillation apparatus, so the aldehyde (which boils at a lower temp than the alcohol) is distilled off immediately
how do you form a carboxylic acid?
- the alcohol has to be vigorously oxidised. the alcohol is mixed with excess oxidising agent and heated under reflux
what is an homologoes series?
a family of ompounds with similar chemical properties whose members differ by a -CH2 group
what is aliphatic?
carbon atoms are joined to each other in straight or branched chains
what is alicyclic?
carbon atoms are joined to each other in ring (cyclic structures)
what is aromatic?
some or all of the carbon atoms are found in a benzene ring
