a level organic

state why Si(CH₃) is used in ¹NMR and explain how its properties make it suitable for use in ¹NMR:

Si(CH₃) aka. TMS:

• TMS as reference/calibration/standard/peak at 0

• inert (so unlikely to react w/ the sample)

• gives one signal (as has lots of equivalent Hs)

• signal in an area away from other typical H signals

• easy to remove/volatile/low bpt

state why CDCl₃ or CCl₄ is used in ¹NMR and explain how its properties make it useful for use in ¹NMR:

• CDCl₃ or CCl₄ solvent

• both have no Hs (so give no signals in spectrum)

• CCl₄ non polar (so good solvent for non polar organic molecules)

• CDCl₃ polar covalent molecules (so good solvent for polar organic compounds)

suggest why it is difficult to use Table B in the Data Booklet to predict the chemical shift for the peak given by the H atom labelled y (1)

H attached to both C-Cl and adjacent to C=O so doesn’t fit w/ data in table B

give the structure of TMS:

what does NMR stand for? what does it give info about?

• NMR = nuclear magnetic resonance

• gives info about the position of ¹³C or ¹H atoms in a molecule

what does it mean for ¹H atoms/¹³C atoms to be equivalent?

in the same chemical environment

what is chemical shift (δ)?

difference between TMS peak and peaks produced by substance under test

what does the vertical axis on an NMR spectrum represent?

intensity of absorption

what does the chemical shift depend on?

• depends on what other atoms/groups are near the ¹H/¹³C atom

• more electronegative groups give a greater chemical shift

give the components of a proton NMR spectrum and what information they provide:

• no. of peaks = no. of different ¹H environments

• chemical shifts = type of environment the ¹H atoms are in

• integration ratio = no. of no.s of H atoms on each environment

• splitting = no. of H atoms on adjacent C atom

give the components of a carbon-13 NMR spectrum and what information they provide:

• no. of peaks = no. of diff carbon-13 environments

• chemical shifts = type of environment ¹³C atoms are in

what is the integration ratio?

ratio of no. of hydrogen atoms in each environment

when does splitting not ocur?

• H atoms are equivalent

• H atoms on O atoms

can you fill in this table?

yes :)

what is the eqn used to determine splitting?

n + 1 (where n = no. of H atoms on adjacent C)

deduce the structure of Q (C₃H₇ClO) - explain your answer (5)

• integration ratio 2:2:3

• peak at 3.95:

  • has 2 Hs in environment, is a triplet so has 2Hs on adjacent C so must be CH₂-Cl next to CH₂

• peak at 3.65:

  • has 2 Hs in environment, is a triplet so has 2 Hs on adjacent C atom so must be O-CH₂ next to CH₂

• peak 3.35:

  • has 3 H atoms in its environment, is a singlet so has no H atoms on adjacent C atom so must be O-CH₃

give the eqn for the partial dissociation of carboxylic acids in water:

state where the PoE lies for the partial dissociation of carboxylic acids in water and explain why:

• PoE lies to the left as most molecules do not dissociate

• ∴ making carboxylic acids weak acids

give the general word eqn for the reaction between an acid and alkali:

acid + alkali → salt + water

give the general word eqn for the reaction between an acid and a carbonate:

acid + carbonate → carbon dioxide + salt + water

give the general word eqn for the reaction between an acid and a metal:

acid + metal → salt + hydrogen

give the eqn for the reaction between ethanoic acid and sodium hydroxide - name the product:

• CH₃COOH + NaOH → CH₃COO^-Na⁺ + H₂O

• CH₃COO^-Na⁺ = sodium ethanoate (this is a salt, not an ester!)

give the eqn for the reaction between ethanoic acid and ammonia - name the product:

• CH₃COOH + NH₃ → CH₃COO^-NH₄⁺

• ammonium ethanoate (this is a salt, not an ester!)

give the eqn for the reaction between ethanoic acid and sodium carbonate and name the product:

• 2CH₃COOH + Na₂CO₃ → CO₂ + H₂O + 2CH₃COO^-Na⁺

• 2CH₃COO^-Na⁺ = sodium ethanoate

give the eqn for the reaction between ethanoic acid and sodium and name the product:

• 2CH₃COOH + 2Na → H₂ + 2CH₃COO^-Na⁺

• 2CH₃COO^-Na⁺ = sodium ethanoate

give the eqn for the reaction between ethanoic acid and magnesium and name the product:

• 2CH₃COOH + Mg → H₂ + (CH₃COO^-)₂Mg²⁺

• (CH₃COO^-)₂Mg²⁺ = magnesium ethanoate

give the general eqn for the formation of esters and state the conditions - what is this process called?

• conc H₂SO₄ catalyst

• esterification (condensation reaction)

what is the ester functional group?

how do we name esters?

• first part - from alcohol used (on RHS)

• second part - from carboxylic acid used (on LHS)

give 4 uses of esters:

• solvents

• plasticisers

• perfumes

• food flavourings

give the general eqn for the acid hydrolysis of an ester - state the conditions and products:

• dilute acid (typically H₂SO₄) catalyst

• heated under reflux

• products = carboxylic acid and alcohol

give the general eqn for the base hydrolysis of an ester - state the conditions and products:

• heated under reflux

• products = salt (of the carboxylic acid) and alcohol

give and justify 4 safety measures necessary when heating under reflux in the formation of esters:

• use a fume cupboard - to avoid breathing in harmful/toxic/corrosive compounds

• add anti-bumping granules - to ensure smooth boiling/reduce size of bubbles

• use an electric heater/water bath - as compounds are flammable

• wear gloves - compounds may be corrosive

why might we shake the reaction mixture with aqueous sodium carbonate after making esters? what precaution should be taken when doing this and why?

• to neutralise/react with XS acid

• you should remove the stopper to prevent a buildup of pressure as CO₂ is produced

why may we add anhydrous magnesium sulfate when making esters?

drying agent

which alcohol are animal fats and vegetable oils made from in esterification?

propane-1,2,3-triol (glycerol)

give the general structure of a triglyceride (lipid):

give and explain one example where base hydrolysis may be used and give the word and symbol eqn:

making soap (saponification) - reacting a lipid w/ a strong base forms salts of the fatty acids and glycerol

what are biodiesels? how are they made?

• biodiesel (renewable fuel) = mixture of methyl esters of long-chain carboxylic acids

• produced by reacting vegetable oils w/ methanol in the presence of a catalyst

give the word and symbol eqn for making biodiesels:

during ester hydrolysis, 2 layers form in the separating funnel - suggest why ethyl ethanoate forms the upper layer (2)

• ethyl ethanoate is immiscible with/insoluble in water - if 1 mark - this point usually!

• ethyl ethanoate is less dense/has a lower density (than water)

why may anhydrous calcium chloride be added when heating under reflux to make an ester?

as a drying agent

what can chromatography be used for?

to separate and identify the components in a mixture

name the 3 types of chromatography:

• thin-layer chromatography (TLC)

• column chromatography (CC)

• gas chromatography (GC)

in chromatography, what does separation depend on?

the balance between solubility in the moving phase and retention by the stationary phase

what is thin-layer chromatography (TLC)?

chromatography in which a plate is coated w/ a solid and a solvent moves up the plate

what is column chromatography (CC)?

chromatography in which a column is packed w/ a solid and a solvent moves down the column

what is gas chromatography?

chromatography in which a column is packed w/ a solid/solid coated by a liquid and a gas is passed through the column under pressure at high temps

what is the moving/mobile phase?

• carries the soluble components of the mixture

• always a liquid or gas

what is the stationary phase?

• the solid the mobile phase moves over

• holds back components which are attracted to it

what affects the distance that each substance moves up the plate?

• components that are more soluble in the mobile phase will travel further up the plate i.e. move more quickly

• components that have a higher affinity for the stationary phase will travel less far up the plate i.e. move more slowly

describe the process of thin layer chromatography (TLC):

1. draw a line in pencil near the bottom of the TLC plate

2. add small drops of each mixture to be separated along the initial pencil line using a capillary tube

3. leave the spots to dry

4. place TLC plate in a beaker w/ a small amount of solvent - the level of the solvent must be below the baseline - and cover the top with a watch glass

5. the solvent (mobile phase) will move up the plate, separating the different substances in the mixture

6. leave until the solvent almost reaches the top of the plate and use a pencil to mark this as the solvent front

7. leave to dry

8. reveal using a UV lamp or using iodine/potassium permanganate

what is the purpose of the lid/watch glass in TLC?

• to prevent the solvent from evaporating

• so atmosphere in beaker is saturated w/ solvent vapour

give 2 methods of revealing TLC plates:

• put plate under UV lamp

• dip chromatogram into iodine to reveal the spots

state why components separate in chromatography:

difference in balance between solubility in the mobile phase and retention by the stationary phase

give the formula used to calculate R_f values - how can we use these values to identify the substance?

• R_f = distance moved by spot/distance moved by solvent

• compare R_f value to known value (same mobile/stationary phases must be used)

what is column chromatography typically used for?

purification of large quantities of organic compounds

describe the process of column chromatography (CC):

1. the sample to be purified is placed at the top of the column filled w/ the solid stationary phase

2. solvent is flushed through the column, carrying the mixture components at diff rates

3. components separate based on their solubility in the solvent and their adsorption to the stationary phase (retention)

4. the separated components exit the column and are collected for analysis

give 2 examples of stationary phases used in column chromatography:

• silica

• aluminium oxide

how may polarity affect retention in column chromatography?

more polar groups will be retained longer through the column i.e. they will come out later

describe the process of gas chromatography (GC):

1. liquid sample vaporised in heated chamber

2. inert gas - mobile phase - transports vaporised sample through chromatographic column containing the stationary phase - powder packed inside long capillary tube by an oil - which interacts differently with each component of the sample

3. components separated based on how they partition between the mobile gas phase and stationary phase

4. as they exit the column a detector records the separation producing a chromatogram with distinct peaks for each component

5. components leave the column at different times - this is the retention time

how can we use retention times to identify substances in GC?

• position of each peak determined by retention time of each substance

• area under the peaks = amount of each substance

• compare retention times to known values (same mobile/stationary phases must be used)

• (GC may be coupled w/ other spectrometers e.g. mass spec - substances separated out then mass spectrum for each is produced)

name a suitable developing agent for the separation of a polypeptide into its constituent AAs - state why the developing agent is needed:

• ninhydrin

• AAs are colourless/to make the AAs visible

how are condensation polymers hydrolysed?

conc HCl (any strong acid/alkali) - heat

(MS for polypeptide)

can you complete this table?

yes!

give the methods of polymer disposal:

• landfill

• incineration

• recycling

give the benefits and drawbacks of disposing of (addition) polymers in landfill:

benefits:

• useful for disposing of plastics which:

  • are too diff to recycle

  • are too diff to separate from other materials

  • there is not enough plastic to extract to make it economically viable

drawbacks:

• decomposition of waste in landfill produces methane - greenhouse gas

• risk of water contamination from waste leaching

• large amounts of land needed - unsustainable and expensive

give the benefits and drawbacks of incineration as a method of polymer disposal:

benefits:

• method of disposal if the plastics can’t be recycled

• E from burning can be used to generate electricity

drawbacks:

• can release toxic fumes so must be monitored e.g. PVC produces toxic HCl fumes

  • flue gas scrubbers used to neutralise toxic gases produced by firing a base at the flue gases

give the benefits and drawbacks of recycling as a form of polymer disposal:

benefits:

• cheaper

• less CO₂ produced than incineration

• reduces reliance on landfill

• preserves non-renewable raw materials e.g. crude oil

drawbacks:

• can be contaminated w/ other materials when being recycled

• diff to recycle due to wide variety of diff plastics

• diff to remake original plastic from recycled material

• sorting and process recycling of plastics more expensive than incineration

golf balls recovered from lakes and ponds can be used again even after being in water for several years - explain why these golf balls do not biodegrade (2)

(ignore the MS, say both!)

• C-C bonds are non polar/strong/not attacked by nucleophiles

• C-C bonds cannot be hydrolysed

what must each monomer have to make a condensation polymer?

at least 2 functional groups e.g. diols, dicarboxylic acids

give 3 examples of condensation polymers and the general word eqns for their formation:

• n(dicarboxylic acid + diamine) → polyamide

• n(dicarboxylic acid.+ diol) → polyester

• n(amino acid) → polypeptide

give the general eqn for the formation of a polyamide - name the linkage formed:

amide linkage

give 2 examples of polyamides and their uses:

• Kevlar - used to make bulletproof vests

• nylon-6,6 - used to make fibres e.g. in ropes/clothing

why are condensation polymers stronger than addition polymers?

• there are H bonds (as well as VDWs and DPDPs) between C=O, N-H and O-H groups and DPDPs between polarised groups in condensation polymers

• only VDWs between polyalkenes as the chains contain non-polar bonds

• H bonds/DPDPs are stronger than VDWs

give the eqn for making Kevlar and name the organic reactants - give 1 feature of Kevlar:

Kevlar has H bonds between polymer chains

give the eqn for making nylon-6,6 and name the organic reactants:

suggest an alternative way of making polyamides and give the small molecule produced:

• acyl chloride + amine

• small molecule = HCl

give the general eqn for the formation of a polyester and name the linkage:

give an example of a polyester, the eqn for making it and the names of the organic products:

Terylene - remember only 1 side of trailing bonds should have an O!

draw and name the mechanism that occurs between ethanal and acidified KCN:

nucleophilic addition

what is the product of nucleophilic addition w/ acidified KCN?

hydroxynitrile

which compounds can undergo nucleophilic addition?

aldehydes and ketones

why do asymmetrical ketones form racemates during nucleophilic addition, whereas symmetrical ketones do not?

for symmetrical ketones:

• attack from either side of carbonyl group is still =lly likely as carbonyl is planar

• but attack from either side would produce the same product as ketone is symmetrical

• so product is non-chiral and ∴ optically inactive

draw and name the mechanism that occurs between ethanal and acidified NaBH₄:

nucleophilic addition

for which reactions does nucleophilic addition w/ NaBH₄ occur?

• reduction of aldehyde to 1^o alcohol

• reduction of ketone to 2^o alcohol

give the functional group for an acid anhydride:

give the functional group for an acyl chloride:

give the functional group for an amide:

what is acylation? through which mechanism does it occur?

• addition of an acyl group

• occurs through a nucleophilic addition-elimination reaction

draw the nucleophilic addition-elimination reaction between ethanoyl chloride and water:

draw the nucleophilic addition-elimination reaction between ethanoyl chloride and ethanol:

draw the nucleophilic addition-elimination reaction between ethanoyl chloride and conc ammonia:

draw the nucleophilic addition-elimination reaction between ethanoyl chloride and methylamine (1^o amine):

what is an N-substituted amide?

amide where one of the H atoms bonded to the N has been substituted for an alkyl/aryl group

draw the nucleophilic addition-elimination reaction between ethanoic anhydride and ammonia:

fill out the products in this table:

fill out the products in this table:

what is optical isomerism? when does it occur?

• form of stereoisomerism

• occurs as a result of chirality in molecules

• limited to molecules w/ a single chiral centre

what is a chiral C?

C with 4 diff groups attached