module 6 Flashcards
aliphatic definition
straight or branched chain organic substances
aromatic or arene definition
includes one or more ring of six carbon atoms with delocalised bonding
benzene structure
- molecular formula = C6H6
- six C atoms in a hexagonal ring, with one H atom bonded to each C atom
- each C atom is bonded to two C atoms and one H atom by single covalent sigma bonds
- this leaves one unused electron on each C atom in a p orbital
- the six p electrons are delocalised in a ring structure above and below the plane of carbon atoms
- planar molecule
- all C-C bonds are the same length
- H-C-C bond angle = 120 degrees
evidence for why benzene has a delocalised structure
- bond length intermediate between short C=C and long C-C
- △H hydrogenation less exothermic than expected when compared to △H hydrogenation for kekule structure
- only reacts with Br2 at a high temp or in the presence of a halogen carrier
what type of reactions does benzene undergo
electrophilic substitution
comparison of benzene with alkenes: reactions with bromine
- alkenes react with bromine easily at room temp. benzene requires a halogen carrier
- in benzene, electrons in pi bonds are delocalised. in alkenes, pi electrons are localised between two carbon atoms
- benzene therefore has a lower electron density than C=C. benzene therefore polarises bromine less ad induces a weaker dipole in bromine than an alkene would
toxicity of benzene
carcinogen and therefore banned for use in schools
nitration of benzene
- forms?
- reagents
- mechanism
- electrophile
- formation of electrophile equation
- temperature and why
- nitrobenzene
- concentrated nitric acid in the presence of conc sulfuric acid (catalyst)
- electrophilic substitution
- NO2+
HNO3 + 2H2SO4 = NO2+ + 2HSO4- +H3O+
- 60 degrees. using higher temps means a second nitro group could be substituted onto different positions on the ring
importance of the nitration of benzene
- important step in synthesising useful compounds
- eg explosive manufacture like TNT and formation of amines from which dyestuffs are manufactured
halogenation of benzene
- forms?
- reagents
- conditions
- mechanism
- formation of electrophiles equations
- bromobenzene/ chlorobenzene
- bromine or chlorine
- FeBr3/ AlCl3/ FeCl3
- electrophilic substitution
AlCl3+Cl2 = AlCl4- + Cl+
FeBr3 + Br2 = FeBr4- + Br+
Friedel crafts alkylation
- forms?
- reagents
- conditions
- mechanism
- formation of the electrophile
- alkylbenzene
- chloroalkane and anhydrous aluminium chloride catalyst
- heat under reflux
- electrophilic substitution
AlCl3 + CH3CH2Cl = CH3CH2+ + AlCl4-
Friedel crafts acylation
- forms?
- reagents
- conditions
- mechanism
- formation of the electrophile
- phenyl ketone
- acyl chloride and anhydrous aluminium chloride catalyst
- heat under reflux (50 degrees)
- electrophilic substitution
AlCl3 + CH3COCl = CH3CO+ + AlCl4-
are phenols weakly or strongly acidic?
what will they react with compared to carboxylic acids?
weakly - weaker than CA
both will react with sodium metal and NaOH
only CA’s will react with sodium carbonate as a phenol is not a strong enough acid to react
reaction of phenol with bromine
- reagents
- conditions
- produces?
- explain reactivity
Br2
room temp
white solid
in phenol, the lone pair of electrons on the oxygen (p-orbital) are partially delocalised into the ring. the electron density increases and the Br2 is more polarised
what are phenols used in
the production of plastics, antiseptics, disinfectants and resins for paints
reaction of phenol with nitric acid
- reagents
- conditions
4M HNO3
room temp
effect of side groups on substitution
electron donating groups eg OH and NH2 will force substitution to occur on the 2 and 4 positions on the ring
electron withdrawing groups eg NO2 will force substitution to occur on the 3 position on the ring
solubility of carbonyls in water
smaller carbonyls are soluble as they can form H bonds with water
explain the reactivity of carbonyls
the C=O bond is polarised because O is more electronegative than carbon. The positive carbon atoms attracts nucleophiles
tollens reagent
- reagent
- conditions
- reaction
- observation
- equation
- formed by mixing aqueous ammonia and silver nitrate - active substance is the complex ion of [Ag(NH3)2]+
- heat gently
- aldehydes are oxidised into a CA. the silver(I) ions are reduced to silver atoms
- silver mirror forms
- CH3CHO + 2Ag+ + H2O = CH3COOH + 2Ag + 2H+
reduction of carbonyls
- reagents
- conditions
- forms
- mechanism
- NaBH4 in aq ethanol or LiAlH4
- room temp and pressure
- aldehydes will be reduced to primary alcohols
- ketones will be reduced to secondary alcohols
- nucleophilic addition
catalytic hydrogenation reduction of carbonyls
- reagent
- conditions
hydrogen and Ni catalyst
high pressure
addition of hydrogen cyanide to carbonyls
- forms
- reagents
- conditions
- mechanism
- why not use HCN
hydroxynitrile
NaCN and dilute H2SO4
room temp and pressure
nucleophilic addition
toxic gas that is difficult to contain
2,4 DNP
- reacts with?
- forms?
- how to identify product
carbonyls
orange precipitate
take the melting point of orange crystals and compare with known values in a database
acidity of carboxylic acids
- weak acids in water and slightly dissociate
- strong enough to displace carbon dioxide from carbonates
solubility of carboxylic acids in water
- smaller CA (up to c4) dissolve in water but after this solubility rapidly reduced
- dissolve because they can hydrogen bond to water molecules
CA’s and delocalisation
- CA are stabilised by delocalisation, which makes the dissociation more likely
- the pi charge cloud has delocalised and spread out, the delocalisation makes the ion more stables and therefore more likely to form
strength of carboxylic acids
- effect of chain length
- effect of electronegative atoms
- increasing chain length pushes electron density on to the COO- ion , making it more negative and less stable. this makes the acid less strong
- this is because alkyl groups are electron releasing
- electronegative chlorine atoms withdraw electron density from the COO- ion, making it less negative and more stable. this makes the acid stronger
functional group test for carboxylic acids
- react CA with solid Na2CO3 or aqueous NAHCO3
- effervescence caused by the production of CO2
can CA’s be oxidised
-no
- except for methanoic acid
- forms carbonic acid (H2CO3) which decomposes to give CO2
esterification of carboxylic acids
- reacts with?
- reagents
- forms
- reversible?
- alcohol + CA = ester
- strong sulfuric acid catalyst, reflux
- ester and water
- yes
- yield is low, and the reaction is slow
esterification using acid anhydrides
- forms?
- reagent
- conditions
- are acid anhydrides more reactive than CA
- ester
- alcohol
- room temp
- yes, reaction is not reversible and a higher yield is achieved
2 reactions to hydrolyse esters
- with acid
- reagents: dilute HCl
- conditions: heat under reflux
- forms a CA and an alcohol
- reversible and does not give a good yield of products - with NaOH
- reagents: dilute NaOH
- conditions: heat under reflux
- forms a salt and an alcohol
- not reversible
- reaction goes to completion
formation of acyl chlorides from a carboxylic acid
- reagent
- conditions
reagent: SOCl2
conditions: room temp
- forms acyl chloride, SO2 and HCl
acyl chloride + water
- forms
- reagent
- conditions
- observation
- carboxylic acid
- water
- room temp
- steamy white fumes of HCl and given off
acyl chloride + alcohol
- forms
- reagent
- conditions
- observation
- ester
- alcohol
- room temp
- steamy white fumes of HCl are given off
acyl chloride + ammonia
- forms
- reagent
- conditions
- observation
- primary amide
- ammonia
- room temp
- white smoke of NH4Cl given off
acyl chloride + primary amine
- forms
- reagent
- conditions
- secondary amide
- primary amine
- room temp
acyl chloride + phenol
- forms
- reagent
- conditions
- observation
- ester and HCl
- phenol
- room temp
- steamy white fumes of HCl are given off
primary aliphatic amines base properties
- are they stronger bases than ammonia
- act as bases as the lone pair of electrons on the nitrogen is readily available for forming a dative covalent bond with a H+ and so accepting a proton
- yes, as the alkyl groups are electron releasing and push electrons towards the N atom
base strength of aromatic amines
- do not form basic solutions
- as the lone pair of electrons on the N delocalise with the ring of electrons in the benzene ring
- the N is therefore less able to accept protons
amines reaction with acids
- forms
- how to convert back to amine
- is the product soluble?
ammonium salts
- these salts will be solid crystals if the water is evaporated due to strong ionic interactions
- addition of NaOH
- yes due to ionic salt
how are primary amines formed
- mechanism?
- between what?
- reagent
- how to form 2 and 3 amines
- nucleophilic substitution
- haloalkanes and ammonia
- excess ammonia dissolved in ethanol
- using an excess of ammonia can limit further substitution and maximise the amount of primary amine formed
- react a primary/ secondary amine with haloalkane
reducing nitroarenes to aromatic amines
- reagent
- conditions
- mechanism
- Sn and conc HCl
- heating
- reduction
draw the general structure of an alpha amino acid
are amino acids amphoteric
yes, they have a basic and acidic group so can act as a base and an acid
zwitterion definition
- are amino acids zwitterions
- explain the high mp of amino acids
a molecule that has both a positive and a negative charge at the same time but is overall electrically neutral
- yes
- ionic interaction between the zwitterions explains the high mp of amino acids
isoelectric point of amino acid
the pH at which the amino acid has no overall charge
- this is where it exists as a zwitterion
how can the isoelectric point of an amino acid be different
- if the side R group of an amino acid contains an acidic or basic group
- an amine group on the R group may make the isoelectric point be greater than ph 10
- a CA group on the R group may make the isoelectric point be ph less than 3
acidity and basicity of amino acids
- amine group is basic
- CA is acidic
- act as weak buffers and will only gradually change pH if small amounts of acid or alkali are added
hydrolysis of di-peptides/ proteins
- if proteins are heated with concentrated acid or alkali, they can be hydrolysed and split back into their constituent amino acids
chiral carbon atom definition
a carbon atom that has 4 different groups attached
when does optical isomerism occur
- what are the properties of optical isomers
- in carbon compounds with 4 different groups attached to a carbon
- these 4 groups are arranged tetrahedrally around the carbon
- they have similar physical and chemical properties, but rotate plane polarised light in different directions
- one enantiomer rotates in one direction and the other rotates by the same amount in an opposite direction
are amino acids chiral
yes
two compounds that are optical isomers of each other are called…
enantiomers
two types of polymerisation
addition and condensation
why are poly(alkenes) chemically inert
- due to the strong C-C and C-H bonds
- non-polar nature of the bonds and therefore are non-biodegradable
chemical reactivity of condensation polymers
- can be broken down by hydrolysis with an acid or alkali
- therefore, are biodegradable
- reactivity explained by the presence of polar bonds which can attract attacking species such as nucleophiles and acids
are condensation polymers photodegradable
yes as the C=O bond absorbs radiation
haloalkanes to nitrile reaction
- reagent
- conditions
- mechanism
- type of reagent
- KCN dissolved in ethanol/water mixture
- heat under reflux
- nucleophilic substitution
- nucleophile, :CN-
carbonyl to hydroxynitrile reaction
- reagent
- conditions
- mechanis,
- sodium cyanide and dilute sulfuric acid
- room temp and pressure
- nucleophilic addition
- NaCN supplies the nucleophilic CN- ions. H2SO4 supplies the H+ ions
nitriles to amine
- type of reaction
- reagents
- reduction
- LiAlH4 in ether, or H2 with a nickel catalyst
nitriles to CA
- type of reaction
- reagent
- hydrolysis
- strong acid
testing for functional groups
1. alkene
2. carbonyl
3. aldehyde
4. CA
5. primary or secondary alcohol and aldehyde
6. halokalkane
7. phenol
- bromine water
- orange colour decolourises - 2,4 DNP
- orange precipitate formed - tollens reagent
- silver mirror forms - carbonate ions eg sodium carbonate
- effervescence of Co2 evolved - sodium dichromate and sulphuric acid
- orange to green colour change - warm with aq silver nitrate in ethanol
- slow formation of white precipitate - will react with Na and NaOH, bot with carbonate ions
- fizzing with Na and no reaction with sodium carbonate
a liquid stationary phase is separated by…
a solid stationary phase is separated by…
relative solubility
adsorption
rf value =
distance moved by the amino acid/ distance moved by the solvent
- then compare rf value to those for known substances to identify
TLC method
- wearing gloves, draw a pencil line 1cm above the bottom of a TLC plate and mark spots for each sample, equally spaced along line
- use a capillary tube to add a tiny drop of each solution to a different spot and allow the plate to air dry
- add solvent to chamber or large beaker with a lid so that is no ore than 1cm in depth
- place the TLC plate into the chamber, making sure that the level of solvent is below the pencil line. Replace the lid to get a tight seal
- when the level of the solvent reaches about 1cm from the top of the plate, remove the plate and mark the solvent line with a pencil, allow the plate to dry in the fume cupboard
- place the plate under a UV lamp in order to see the spots. draw around them lightly in pencil
- calculate the rf values for the observed spots
during TLC why do we
- use a pencil line
- use a tiny drop of solution
- specify the depth of solvent
- use a lid
- dry in a fume cupboard
- use a UV lamp
- as it wont dissolve in the solvent
- too big a drop will cause different spots to merge
- if the solvent is too deep it will dissolve the sample spots from the plate
- to prevent evaporation of toxic solvent
- as the solvent is toxic
- if the spots are colourless and not visible
what is gas liquid chromatography used for
- what are the mobile and stationary phases
- to separate mixtures of volatile liquids
- mobile phase: gas
- stationary phase: high bp liquid absorbed onto a solid
retention time definition
time taken for a particular compound to travel from the injection of the sample to where it leaves the column to the detector
- can be used to identify a substance
what is Gas Chromatography-Mass Spectrometry used for
- in analysis, forensics, environmental analysis. airport security and space probes
what is added to a spectroscopy sample to calibrate the spectrum
tetramethylsilane (TMS)
Si(CH3)4
what solvents are used to dissolve samples for spectroscopy
CCl4 - non-polar so used for non-polar organic molecules
CDCl3 - polar covalent molecule good for polar organic molecules
why is TMS used
- its signal is away from all the others
- it only gives one signal
- gives strong signal so only a small amount needed
- it is non-toxic
- it is inert
- it has a low boiling point so can be removed from sample easily
a suitable carrier gas for use in gas liquid chromotography is
needs to be an unreactive gas eg nitrogen
in chromatography which can be the mobile phase
liquid or gas
which phase do compounds with a high rf value have a greater affinity for
the mobile phase
