topic 18 Flashcards
what is benzene and its formula
- benzene is a cyclic planar molecule
- has the formula C6H6
describe the structure of benzene
- carbon has 4 valent e-
- each carbon is bonded to 2 other carbons and one hydrogen
- the final lone e- is in a p-orbital which sticks out above and below the planar ring
- the lone electrons in the p-orbital combine to form a delocalised ring of e-
why are all of the C-C bonds in benzene the same length
- because of the delocalised e- structure all of the C-C bonds are the same bond length
- in between the length of the single and double bond
what is the length of the C-C bonds in benzene
139pm
what is the length of a single and double bond
single- 154pm
double- 133pm
draw kekules model of benzene
what did august kekule think the structure of benzene was
he thought that there was alternating double and single bonds
draw the delocalised model of benzene
explain the delocalised model of benzene
- sigma bonds form due to head on overlap of atomic orbitals
- the p orbitals on each carbon atom overlap sideways to form a ring of pi bonds
- the delocalised pi bonds are made up of two ring shaped clouds of e- → one above and below the plane of 6 carbon atoms
how can the stability of benzene be measured
stability of benzene measured by comparing the enthalpy change of hydrogenation in benzene and cyclohexa-1,3,5-triene
what proves the delocalised system and disproves kekules model
benzene is more stable than the theoretical alternative cyclohexa-1,3,5-triene (which is kekules alternating single and double bond model)
if kekules model was correct
bromine water should decolourise but doesnt when added to benzene
benzene should undergo addition
thermochemical evidence
therefore kekules model is incorrect
what is enthalpy change of hydrogenation
when one mole of unsaturated compound is converted to saturated compound
how can enthalpy change of hydrogenation be used to prove the stability of benzene
- if we hydrogenate cyclohexene which has 1 double bond→ has an enthalpy change of -120kj mol-1
- if benzene has 3 double bonds → would expect an enthalpy change of hydrogenation of -360kj mol-1
- 3 x -120
however when measuring the experimental value for enthalpy change of hydrogenation for benzene it is -208kjmol-1
- 3 x -120
why does benzenes enthalpy change of hydrogenation suggest that benzene is more stable than cyclohexa-1,3,5-triene
- this means that more energy is needed to break bonds in benzene than cyclohexa-1,3,5-triene
- suggests that benzene is more stable than the theoretical cyclohexa-1,3,5-triene which has 3 double bonds
why is benzene thought to be more stable than cyclohexa-1,3,5-triene
due to delocalised e- ring
what is the combustion reaction equation for benzene
- benzene is a hydrocarbon
- readily burns in oxygen
- produces carbon dioxide and water if burned completely
what is observed when benzene in burnt in oxygen and why
- in reality carbon doesnt burn completely as theres not enough oxygen in the air
- results in a lot of unreacted carbon → soot
- so a yellow sooty flame is observed when benzene is burnt in oxygen
what reaction do alkenes undergo
alkenes have a double bond and undergo electrophilic addition
requires a nickel catalyst and 150C
why do alkenes undergo electrophilic addition
electrophile is attracted to high e- density in double bond
what is the colour change observed when bromine water is added to alkenes
colour change from orange to colourless due to formation of dibromoalkane
describe the electrophilic addition reaction between electrophiles and alkenes
- bromine attracted to high e- density in double bond
- Br2 is polarised as the e- in the double bond repels the e- in Br2 when it approaches the alkene → induced charge
- electron pair in the double bond is attracted to the slightly positive bromine + forms a bond
- breaks the Br-Br bond
- carbocation intermediate formed
- Br- attracted to slight positive carbon
- forms dibromoalkane
what are arenes
arenes are aromatic hydrocarbons that contain a benzene ring in their structure
what are the 2 ways of naming arenes
for some compounds we add benzene at the end
or phenyl can be used (names as if phenyl is a functional group -C6H5)
if theres more than one group attached to benzene → number the carbons to show where the groups are
what reaction do arenes undergo
electrophilic substitution
hydrogen/functional group on benzene ring is substituted for the electrophile
why is benzene attractive to electrophiles
benzene has a high electron density due to its delocalised ring of e- which is attractive to electrophiles
why doesnt benzene undergo electrophilic addition
benzene is stable unlike traditional alkenes they dont undergo electrophilic addition reactions as this would disrupt the stable ring of e- in benzene
what are the 4 main mechanisms that arenes/benzene undergo
- Freidel- crafts acylation
- friedel- crafts alkylation
- halogenation reaction
- nitration reaction
draw the general halogenation reaction of benzene
positive in the ring has to be shown next to the carbon where the halogen has been added
use of AlCL3 halogen carrier
halogens are diatomic so halogen carrier accepts pair of e- from the halogen to create an electrophile (R+)
why is a strong positive electrophile needed in the electrophilic substitution reaction with benzene
- positive (NOT SLIGHT POSITIVE) charge on the electrophile needed which is highly reactive
- to break the benzene ring as benzene rings are stable molecules
describe the electrophilic substitution reaction with benzene
- electrons go to the positive electrophile
- the electrophile joins to the benzene ring
- the delocalised e- in the ring are attracted to the carbocation
- 2e- from the ring move to form a bond → this breaks the ring and a positive charge is formed
- the e- in the C-H bond move to neutralise the positive charge and reform the ring and hydrogen is substituted
how can a strong electrophile be created
in the Friedel-crafts acylation or alkylation → have to react an acyl chloride or halogenoalkane with the halogen carrier to create strong positive electrophile
- halogen carriers are typically aluminium halides, iron and iron halide such as AlCl3 -> acts as a catalyst
give two uses of benzene
benzene is widely used in pharmaceuticals and dye stuffs
what can the friedel-crafts reaction help solve
the Friedel-crafts reaction can help solve the problem of benzene being difficult to react due to its stability
how does the friedel crafts reaction work
Charles Friedel and James craft came up with a reaction where an acyl group (RCO-) or alkyl group (R-) is added onto a benzene molecule making benzene weaker and easier to modify further to make useful products
draw the general mechanism for the formation of the strong electrophile in the friedel-crafts acylation reaction
describe the mechanism for the formation of the strong electrophile in the friedel-crafts acylation reaction
- AlCl3 accepts a pair of e- away from the acyl group
accepts 2e- from chlorine on acyl chloride - as a result the polarisation increases and a carbocation is formed
so the carbon with the =O joins onto benzene
under what conditions is a phenyl ketone produced in the friedel-crafts acylation
- done under reflux and a dry ether solvent
- if done without reflux itll evaporate to the atmosphere
draw the general mechanism for the formation of a less stable phenylketone in friedel-crafts acylation reaction
describe the mechanism for the formation of a less stable phenylketone in friedel-crafts acylation reaction
- the delocalised e- are attracted to the carbocation → 2 e- move to form a bond which breaks the ring
- positive charge develops
- acyl group added onto the benzene ring
- the negative AlCl4- is then attracted to the positively charged ring
- one of the chlorine atoms breaks away to form a bond with the hydrogen which breaks away to form HCL
- the e- in the C-H bond move to neutralise the positive charge and reform the ring
what are the products of the friedel-crafts acylation reaction
HCL
AlCl3
phenylketone
draw the mechanism to make a strong electrophile in the friedel-crafts alkylation reaction
explain the mechanism used to make a strong electrophile in the friedel-crafts alkylation reaction
- electrons from the bond go to the halogen from the halogenoalkane
- AlCl3 hydrogen carrier accepts a pair of e- from the halogen
- results in the formation of a carbocation
- stronger electrophile (R+) is produced which can react with benzene
what conditions are needed for the production of a less stable alkylbenzene in the friedel crafts alkylation reaction
need to react it with benzene to make a less stable alkylbenzene under reflux and dry ether solvent:
draw the mechanism for the production of a less stable alkylbenzene using a strong electrophile in the friedel-crafts alkylation reaction
describe the mechanism for the production of a less stable alkylbenzene using a strong electrophile in the friedel-crafts alkylation reaction
- the delocalised e- are attracted to the carbocation → 2 e- move to form a bond which breaks the ring
- positive charge develops
- electrophile adds on
- halogen carrier (AlCl4-) is attracted to the positively charged ring
- one of the chlorine atoms break away to form a bond with hydrogen to form HCL
- the electrons in the C-H bond move to neutralise the positive charge and reform the ring
- AlCl3 reformed
what are the products of friedel-crafts alkylation
alkylbenzene
HCl
AlCl3
draw the mechanism for how an alcohol based group can be added to a benzene ring
describe the mechanism for how an alcohol based group can be added to a benzene ring to form a benzyl alcohol
- if we use an electrophile that contains an alkyl chain with OAlCl3- → can be used to add an alcohol based group to a benzene ring
- halogen carrier isnt separated → is joined onto the alcohol group
- the electrons from the O-AlCl3- bond go to the oxygen
- then the e- from the oxygen go to the hydrogen → bond forms between oxygen and hydrogen (OH) group
- the electrons from the C-H bond move to the delocalised e- ring → reforms the ring
why does the mechanism for producing a benzyl alcohol work similarly to the friedel-crafts reaction
as the oxygen in the group has a lone pair of e- → allows it to act as a nucleophile
what does nitrating benzene allow us to do
allows us to make dyes for clothes and explosives
write the equation for how the powerful electrophile is made for the nitration of benzene
must memorize
describe how the powerful electrophile is made in the nitration of benzene
- react conc. sulfuric acid with conc. nitric acid
- halogen carriers not used
- nitric acid accepts a proton → acts as a base
- sulfuric acid donates a proton → acts as a base
- H2NO3+ formed decomposes to form the electrophile which is NO2+ (nitronium ion)
what is the equation for the decomposition of H2NO3+
draw the mechanism for the production of nitrobenzene using the strong electrophile
describe the mechanism for the production of nitrobenzene using the strong electrophile
- the nitronium ion is attacked by the benzene ring forming an unstable positively charged ring
- e- in the C-H bond move to reform the delocalised e- ring
- nitrobenzene is formed and a H+ is formed
- H+ reacts with HSO4- formed previously to make H2SO4 → catalyst reformed
what temperature does the nitration of benzene have to be done
below 55C
why does the nitration of benzene have to be carried out below 55C
- reaction has to be done below 55C to ensure a single NO2 substitution
- a temp above this will result in multiple substitutions
- reaction done in ice bath as this reaction generates a lot of heat
what is a phenol + draw an example
phenols have an -OH group attached to a benzene ring
which carbon in the benzene ring is carbon 1
wherever the OH group is → thats carbon 1 so we number the other groups from this
why are phenols more reactive than benzene
phenols are more reactive than benzene due to the electron density being higher in the ring
why are electrophilic substitution reactions more likely to occur with phenol than with benzene
electrophilic substitution reactions are more likely to occur with phenol than with benzene due to the -OH group and orbital overlap
- the e- in the p-orbital of the oxygen overlaps with the delocalised ring structure
- so the e- in the p-orbital of oxygen are partially delocalised into the pi-system
- the electron density increases within the ring structure → so is more susceptible to attack from the electrophiles
what is aspirin and how is it made
- is an ester
- made by reacting ethanoic anhydride or ethanoyl chloride and salicyclic acid
draw the equation for the production of aspirin using displayed formula
why is ethanoic anhydride used instead of ethanoyl chloride in industry
- its safer as its less corrosive
- doesnt produce harmful HCl gas
- cheaper
- doesnt react vigorously with water so its safer
why are phenols weak acids
phenols partially dissociate → so theyre weak acids
what do phenols produce when they dissociate
to form phenoxide ion and H+ ion
what do phenols react with alkalis to form
phenols react with alkalis to form salt and water
draw the reaction of phenol with NaOH and name the products
draw the reaction of phenol with bromine and name the products formed
what happens when phenol reacts with bromine
observe decolourisation of bromine water
- as the OH is an electron donating group substitution occurs a carbon 2,4 and 6 → product is 2,4,6-tribromophenol
- OH pushes e- into the benzene ring
what are the properties of 2,4,6-tribromophenol
smells of antiseptic and is insoluble in water
what do phenols react with to produce nitrophenols
dilute nitric acid
what do phenols react with dilute nitric acid to produce
two isomers produced 2-nitrophenol and 4-nitrophenol
why are two isomers produced in the reaction of phenol with dilute nitric acid
as OH is an electron donating group which is why substitution occurs on carbon 2 and 4
draw the two isomers produced in the reaction of phenol with dilute nitric acid
what is amine
- an amine is derived from ammonia molecules
- they all contain a nitrogen atom where hydrogens are replaced with an organic group (e.g an alkyl group)
what are the different types of amines
primary, secondary, tertiary and quaternary
what is a primary amine- draw an example
- primary amine- only has one methyl/ organic group attached
- methyl group replaces hydrogen
what is a secondary amine- draw an example
secondary amine - 2 methyl/organic group attached
what is a tertiary amine- draw an example
tertiary amine- 3 methyl/organic groups attached
what is a quaternary amine - draw an example
- quaternary ion - 4 organic/methyl groups
- nitrogen can only bond 3 times but there are 4 bonds in this so nitrogen has a positive charge → is a salt
what are non aromatic amines known as
are known as aliphatic amines
what is an aromatic amine- draw an example
a primary amine but one of the hydrogens are substituted with an (organic) benzene ring
what are the two ways of making aliphatic amines
- by reacting a halogenoalkane with excess ammonia
- reducing a nitrile
draw the mechanism for the production of a primary amine by reacting a halogenoalkane with excess ammonia
describe the mechanism for the production of a primary amine by reacting a halogenoalkane with excess ammonia
- ammonia is a nucleophile so it attacks the delta positive carbon
- forms a bond with carbon and halogen (chlorine) is removed
- an intermediate is formed (alkylammonium salt) with a positive nitrogen and a Cl- ion
- second ammonia molecule gives up a lone pair of e- to hydrogen→ Hydrogen breaks away from the salt
- then the electrons from the N-H bond to neutralise the positive charge of the nitrogen
- a primary amine and ammonium chloride salt is produced
why are two molecules of ammonia (excess) needed to produce a primary amine by reacting a halogenoalkane with it
- one ammonia molecule acts as a nucleophile
- the other ammonia molecule acts as a base (accepts a proton)
what is the downside of producing a primary amine by reacting a halogenoalkane with excess ammonia
- this reaction carries on to produce secondary, tertiary and quaternary salts to → impure product
- this happens because primary amines still have a lone pair of e- on the nitrogen so also acts as a nucleophile
- the amine can react with any remaining halogenoalkanes to produce a secondary amine and then react further to make tertiary and quaternary salts
write the equation for the cheapest way to produce a primary amine by reducing a nitrile and state its conditions
using a nickel catalyst and hydrogen gas
high temp and pressure
what is catalytic hydrogenation
this reaction is called catalytic hydrogenation → this reaction produces primary amines only so a pure product is made
write the equation for the most expensive way to produce a primary amine by reducing a nitrile and state its conditions
using a strong reducing agent (LiAlH4) and dilute acid
reducing agent dissolved in non-aqueous solvent such as dry ether
why is the method for reducing nitriles using LiAlH4 expensive
- this method is more expensive than using hydrogen gas and a nickel or platinum catalyst
- this is because LiAlH4 is expensive → so isnt used in industry
how are aromatic amines made
they are made by reducing nitro compounds such as nitrobenzene
recall the method for producing aromatic amines by reducing nitrobenzene
1) heat nitrobenzene under reflux with conc. HCL and tin to form a salt such as C6H5NH3+CL-
2)the salt produced in step 1 is reacted with an alkali such as NaOH to produce an aromatic amine e.g phenylamine
draw the equation for producing aromatic amines by reducing nitrobenzene and state the conditions
- tin acts as a catalyst
- done under reflux as youre using volatile substances
why are amines able to act as a base
they have a lone pair of e- that allow them to accept protons and act as a base
how would a proton bond to an amine- draw this reaction
- a proton bonds to an amine via a dative covalent bond
- both electrons in the bond originate from the lone pair on nitrogen
what does the strength of a base depend on
strength of base dependant on the availability of the lone pair of e- on the nitrogen
what does the electron density/availability of the lone pair on nitrogen depend on
- availability/electron density on the nitrogen depends on the type of group attached to the nitrogen
- the higher the electron density the more readily available the electrons are
what is the order of base strength of amines from weakest to strongest
aromatic amines → ammonia → primary aliphatic amines
why are aromatic mines the weakest base out of the amines?
- benzene → e- withdrawing group so it pulls e- away from nitrogen and into the benzene ring structure
- electron density at nitrogen reduced → lone pair availability reduced
- therefore aromatic amines are less basic
why is ammonia neither the strongest nor the weakest base (in the middle) out of the amines
- ammonia has no groups which are withdrawing/pushing electrons in
- so ammonia has its e- centrally based in the nitrogen
why are primary aliphatic amines the strongest base out of the amines
- alkyl groups are electron pushing groups → push e- towards nitrogen
- electron density at nitrogen increases → so lone pair availability is increased
- therefore primary aliphatic amines are more basic
- amines are also nucleophiles as well
why are amines soluble
- amines can hydrogen bond with water
- so some has the ability to dissolve in water → to form alkaline solutions
- the lone pair of e- on the nitrogen can form hydrogen bonds with the hydrogen bonds on water molecules
the lone pair on oxygen can also form hydrogen bonds with the hydrogen on the amine
draw an image of a primary amine hydrogen bonded to water
why are amines able to hydrogen bond to other
why does solubility of amines decrease with increasing chain length
- if the amine is large enough then the london forces between the non-polar hydrocarbon chain will be stronger than the hydrogen bonding between the nitrogen and H on water molecules
- this means larger amines wont dissolve
how do amines react with copper complex ions and how is the copper complex formed
- amines can react with copper complex ions → form a deep blue solution
- copper complex formed by dissolving copper (II) sulfate in water
what happens if a small amount of butyl amine is added to copper sulfate solution
- if we add a small amount of butyl amine to copper sulfate solution → pale blue precipitate is formed
- [Cu(OH)2(H2O)4]
- precipitate forms when complex is neutral
as the amine removes 2 H+ → acting as a base to form the compound above (originally there were two OH2 ligands attached)
what happens if a large amount of butylamine is added to copper sulphate solution- draw the complex formed
- if we add more butyl amine → 4 ligands will be exchanged with the amine
- form this complex which is a deep blue solution
- charged complex
- copper → partial ligand substitution
- if the amine is larger we may get a different shape complex
how do amines react with acyl chlorides
- reaction with primary amines produces N-substituted amides and HCL
- this is a vigorous reaction
- produces a solid white product
chlorine swapped with amide to form N-substituted amide
what is an N-substituted amide
traditional amides have 2 hydrogens but one of the hydrogens have been substituted for an alkyl group which is why its called N-substituted
what is the reaction of ethanoyl chloride and butylamine
HCl can react further to form butylammonium chloride
what is the overall reaction for ethanoyl chloride + butylamine
how do amines react with acids
- amines also react with acids and form alkaline solutions
- amines are bases so react with acids to form salts however they dont form water
write equation for butyl amine + HCL
how can amines be used to produce basic solutions
- smaller amines are soluble in water
- can dissolve to form alkaline solutions
- unlike some bases where there is an OH group amines react with water to produce the OH- ion → makes the solution basic
butyl amine + water - write equation
what are amides
- amides are derivatives of carboxylic acids
- have the functional group -CONH2
- (AMINES DONT HAVE CARBONYL GROUP)
draw an example of an amide (N-propanamide)
like a carboxylic acid but have an NH2 group instead of an OH group
have a CO group
what is an N substituted amide
has a carbonyl group
- one of the hydrogens is replaced with an alkyl group
- alkyl group represented by R in the image
how can amides be produced
- acyl chlorides react with ammonia and primary amines
- reaction of acyl chloride with ammonia produced amides
ethanoyl chloride + ammonia - draw in displayed formula
- vigorous reaction
- white misty fumes of HCL gas produced
ethanoyl chloride + primary amine- draw in displayed formula
reaction of acyl chlorides reacts with primary amines to produce N-substituted amides
what are the 3 main types of condensation polymers
- polypeptide
- polyamides
- polyesters
what is condensation polymerisation
- condensation polymerisation is where 2 different monomers with at least 2 functional groups react together
- when they react a link is made and water eliminated
- link determines the type of polymer produced
how are polyamides formed
formed by reacting dicarboxylic acids and diamines together
functional group on either side → allows chains to be formed
amide links are formed
draw the reaction of a dicarboxylic acid and diamine in displayed formula
what is a repeat unit
repeat unit - one unit in square brackets with bonds extended out of the bracket (with a small n next to it)
how are polyesters formed
formed by reacting dicarboxylic acid and diols together
draw the reaction of a dicarboxylic acid and diol in displayed formula
how can you work out the monomer from the polymer chain
- the monomer can be determined by finding the repeat unit
- either look for an amide or ester link
- the monomer can be found by breaking the bonds in these links and add H or OH to either end of both molecules
- these are the units used to make the polymer in the first place
what does an amide link look like
amide link ⇒ HN-CO
what does an ester link look like
ester link → CO-O
how can monomers be produced from condensation polymers
- condensation polymers can be hydrolysed to produce monomers
- split with water
what is the structure of amino acids
have an amino group (-NH2) and carboxyl group (-COOH)
also have an organic side chain → represented by R
why are amino acids able to rotate plane polarised
- amino acids are chiral molecules → they have 4 different groups around a central carbon atom
- they rotate plane polarised light
how are amino acids named
1) find the longest carbon chain → since amino acids contain a carboxylic acid the ending of the amino acid name would be -anoic acid
2) number the carbons
3) note the number where the NH2 group sits → name it amino
4)name any other groups
what is a zwitterion
- amino acids sometimes exist as zwitterions
- a zwitterion is a molecule with both positive and negative ions
this is when both the carboxyl and amino groups are ionised→ when they both have a charge
recall the properties of amino acids
amino acids are amphoteric → have acidic and basic properties
have a chiral centre
when do zwitterions exist for amino acids ?
zwitterions only exists at the amino acids isoelectric point
what is the isoelectric point and what is it dependent on
- the isoelectric point is the pH at which the average overall charge in zero
- this is dependent on the R group
draw an example of a zwitterion
what happens if pH is lower than he isoelectric point
if the pH is lower than the isoelectric point then COO- is likely to accept a H+
what happens if pH is higher than the isoelectric point
if the pH is higher than the isoelectric point then NH3+ is likely to lose a H+
what is TLC and what does it do
Thin Layer Chromatography allows us to separate and identify amino acids as they have different solubilities
what is the stationary and mobile phase of TLC
- uses a stationary phase of silica or alumina mounted on a glass/metal plate
- mobile phase → liquid solvent
draw and label the set up for TLC
a pencil base line is drawn and drops of amino acid mixtures are added
how do you carry out TLC
1) place plate in a solvent → base line must be above the solvent level
2) leave until the solvent has moved up to near the top of the plate
remove and mark the solvent front and allow to dry
3) left with a chromatogram
why is the baseline drawn above solvent level
if it isnt the amino acids will dissolve in the solvent
how does TLC work
it works by the amino acid mixture spots dissolving in the solvent
what happens if some parts of the amino acid mixture doesnt dissolve
some chemicals in the mixture may not dissolve much and stick to the stationary phase quickly
how can amino acids be identified using TLC
amino acids can be identified by calculating the Rf value from the chromatogram and comparing them to known Rf values
the number of spots on the plate tells you how many amino acids make up the mixture
why may Rf value change
- Rf values are fixed for each amino acids
- however Rf values changes if temp, solvent or makeup of TLC plate changes
what are gringard reagents
- Grignard reagents are used to help carbon-carbon bond formation
- without a Grignard reagent this would be very difficult
what type of regents are grignard reagents
Grignard reagents are organomagnesium compounds
how are grignard reagents made- give the general equation
are made by reacting a halogenoalkane with magnesium in dry ether
how can you make a carboxylic acid using a grignard reagent
carboxylic acids can be made by reacting a Grignard reagent with carbon dioxide
1)in dry ether, we bubble carbon dioxide in Grignard reagent
2) we add a dilute acid e.g dilute HCL to the solution
draw the equation for the production of a carboxylic acid using a grignard reagent
explain the production of a carboxylic acid using a grignard reagent by explaining what the reagents do
- a new C-C bond is formed when the R breaks off the Grignard reagent and bonds with the C in CO2
- this breaks the C double O bond in CO2 to form R-COO-
- the HCL protonates the R-COO- to form the carboxylic acid
how can alcohols be made using gignard reagents
alcohols can be made by reacting a Grignard reagent with aldehydes and ketones
1) in dry ether, we bubble aldehyde/ketone (carbonyl compound) in Grignard reagent
2) add dilute acid to the solution
draw the equation for the production of an alcohol using a grignard reagent
explain the production of a alcohol using a grignard reagent by explaining what the reagents do
- new C-C bond is formed when the R breaks off the Grignard reagent and bonds with the C in the carbonyl group
- this breaks the C double O bond
- the HCL protonates to form the alcohol
what is molecular formula
the actual number of atoms in a molecule or element→ molecular formula
what is empirical formula
the simplest whole number ratio of atoms in a compound→ empirical formula
how to calculate empirical formula
1) write out elements involved
2) write the percentages as masses
3) divide these by RAM to get number of molecules
4) divide all the numbers by the smallest number of moles which gives the ratio
5) write the formula
how do you work out molecular formula from empirical formula
- work out Mr of empirical formula
- divide by Mr of molecular formula
- use the number you worked out from the previous step to multiply all of the atoms in the empirical formula
compare and contract the bromination of phenol with the bromination of benzene
both electrophilic substitution
no need for halogen carrier for phenol
oxygens lone pair of electrons interacts with the benzene ring of delocalised e- so electrophilic attack more lilkely
bromination of phenol requires bromine in aq solution whereas for benzene requires liquid bromine
tri-substitution of phenol whereas mono for benzene
bromination of phenol requires room temp whereas benzene require heating under reflux
why is the apparatus for distillation instead of reflux not an efficient way to produce a carboxylic acid from an alcohol
ethanol would be oxidised to ethanal
because ethanal has a low bpt
what is the purpose of anti bumping granules
they provide a surface for bubbles to form
recall facts about benzene
carcinogen
aromatic
liquid state
from crude oil
recall facts about benzene
carcinogen
aromatic
liquid state
from crude oil
unreactive
properties change when in a compound
what is the enthalpy change of formation kekules model of benzene and the actual enthalpy change of formation and what does this suggest
kekule = +252 kj mol -1
actual = +49 kj mol-1
actual structure is more stable
not much energy is needed to put it together
what conditions are needed for benzene to undergo addition reactions
because of the ring of delocalised e- in benzene need a temp of 150C and a Ni-Raney catalyst
benzene + 3H2 and conditions
cyclohexane (doesnt have delocalised e- ring)
Ni-Raney catalyst
150C
why are the reactions different when benzene reacts with halogens in the dark and light
light provides energy which disrupts benzene ring
what is the reaction of benzene + halogen in the dark
reaction will not occur
so we use a halogen carrier
e.g AlCl3, iron (iii) bromide (FeBr3), or iron filings
they accept a lone pair of electrons from one of the halogen atoms which induces a positive charge
mono (one) substitution
can control the substitutions
what is the reaction of benzene + halogen in the light
readily undergoes addition in the light
multiple substitutions, uncontrollable
halogen could add onto all of the carbons in benzene
forms 1,2,3,4,5,6-hexabromocyclohexane
what is the full equation for the creation of the strong electrophile in the nitration of benzene
HNO3 + 2H2SO4 -> NO2+ + 2HSO4- + H3O+
conc conc
draw the mechanism for the nitration of benzene
what is needed to produce the strong electrophile to nitrate a phenol and why
dilute nitric acid and dilute sulfuric acid
this is because oxygen has a lone pair of electrons which is drawn into the delocalised electron ring and increases the electron density
so phenol is more susceptible to attack from electrophiles
what is the advantage of heterogenous catalysts
easier to remove as its in a different state
why do amino acids have high melting temperatures
they can form zwitterions with positive and negative charges
so they can for electrostatic forces of attraction between molecules which require a lot of energy to overcome
how would you use chromatography to find out the amino acids which make up a mixture using known samples of amino acids
spot the solution of unknown and known solutions onto the chromatogram
put the chromatogram in the solvent and allow the solvent to rise
amino acids are colourless so spray ninhydrin onto the chromatogram to show the amino acids as oloured
calculate Rf values
compare calculated Rf values to known values
