Paper 2 Misconceptions Flashcards
Why is TMS used as a reference standard for chemical shifts?
Generates one sharp peak always found on far right of spectrum.
Highly volatile and unreactive
What does number of peaks tell you on C13 NMR and H1 NMR?
Number of environments
What does the location of the peaks tell you in C13 NMR and H1 NMR?
Type of proton environment
What does the integration value/area under each peak tell you for H1 NMR?
Number of H+ in the environment
What does the splitting tell you in H1 NMR?
Number of H+ in adjacent environments
Singlet
No H next to it
What solvent do we use when testing NMR of hydrogen based substances?
D2O
CCl4
Problems with nucleophilic subs with excess NH3 to produce primary amine
Further substitution to produce a secondary tertiary or quaternary amine
Problems with nucleophilic subs with KCN and reduction to produce primary amine
KCN is toxic, lower percentage yield and is 2 steps
Uses of quaternary ammonium salts
Hair conditioner
Longer the carboxylic acid chain is the..
less soluble it is- hydrocarbon chain is longer and insoluble
Uses of esters
Plasticisers
Perfumes
Flavourings
Ester formation reaction conditions and reagent
H2SO4 catalyst
Water byproduct
Warm and reflux
Acid catalysed hydrolysis of ester
Carboxylic acid and alcohol
Base catalysed hydrolysis of ester
Salt of carboxylic acid and alcohol
Use of carboxylic acid salt formed from base hydrolysis of triester
Soap
Use of biodiesel
Conserve crude oil supplies
Reduce amount of CO2 released
Why are acid anhydrides used more commonly than acyl chlorides
Less corrosive
Side product is COOH not HCl
Outline essential features of fractional distillation of crude oil that enables crude oil to be separated
Compounds have diff BPS
BP depends on length of compound
Hotter at bottom of column
Heavier molecules condense and collect at bottom
Reaction mixture still reacting in continuous monitoring method. How do we solve this?
To stop reaction, QUENCH.
Add large volume of cold, distilled water to both cool and dilute the reaction, reducing the rate.
The volume of gas produced from a reaction could be measured at regular intervals. What is the problem with this?
Records amount of product produced when this order of reaction is about reactants, so the volume would need recording into reactant conc.
Continuous monitoring graph labels and how to measure progress of reaction
Conc v time
- Take samples at regular intervals
- Use visible indicator such as gas volume
Initial rates graph labels and key points
Rate v conc
Volume ∝ Conc
When total volume is constant, the volume of reactant is proportional to its conc
Properties of ordinary PVC vs plasticiser PVC
PVC is made of long, closely packed together polymer chains- hard and brittle. Used in drain pipes.
Plasticiser PVC is more flexible- used for electrical cable insulation and clothing
Mechanical recycling
Plastics sorted into different types and washed
Ground into pellets
Pellets melted down and remoulded into new objects
Feedstock recycling
Plastics sorted into different types
Heated to temp which breaks their polymer bonds
Repolymerised to form new plastics
Addition polymer
An Addition Polymer is a long chain formed from many monomers and no other product is formed.
Condensation polymer
In a condensation reaction, two molecules join to form a larger one, with a small molecule such as H2O or HCl being released
Two types of condensation polymer
Polyamide
Polyester
Uses of terylene
Carpets
Clothing
Uses of nylon and properties
Used as fibres in clothing
Elastic, strong abrasion resistant
Uses of kevlar and properties
Used in manufacture of body armour and crash helmets
Strong, light, heat resistant
Why are addition polymers not biodegradable?
Have non polar C-C bonds that cannot be hydrolysed
Why are condensation polymers biodegradable?
They can be hydrolysed under acidic or basic conditions
Delta positive C of polar C-O bond can be attacked by nucleophiles
Acid hydrolysis of polyamide
NH3+ and COOH
Base hydrolysis of polyamide
COONa and NH2
Acid hydrolysis of polyester
OH and COOH
Base hydrolysis of polyester
COONa and OH
Acidic conditions for amino acids
Protonated so become NH3+ including R group
Alkaline conditions for amino acids
Deprotonated so COO- including R group
What are enzymes described as?
Stereospecific
How can the amount of further substitution be reduced?
Excess of alkane used
Properties of CFCs
non-toxic
inert gases
volatile
Primary alcohol to Aldehyde
1 [O]
Distillation
Primary alcohol to carboxylic acid
2 [O]
Reflux
Aldehyde to carboxylic acid
1 [O]
Reflux
Secondary alcohol to ketone
1 [O]
Reflux
Advantage of hydration of ethene
Large scale continuous production method
Disadvantage of hydration of ethene
High temp and pressure needed- increases cost
Advantage of fermentation
Uses renewable resources
Disadvantage of fermentation
Slow rate of reaction
Advantage of biofuels
Come from raw renewable materials to conserve crude oil supplies
Disadvantage of biofuels
Many other carbon costs in their production so they aren’t carbon neutral (CO2 released during transportation and distillation)
Use of condenser
Water passes around outside tube w distillate to cool it
Use of antibumping granules
Prevents large bubbles from forming
Why is reflux used to oxidise alcohol into carboxylic acid
Reflux doesnt allow any reactant vapour to escape
OH in alcohols
Finger like/Test tube shape
OH in acids
Mitten shape
Where is the fingerprint region?
Fingerprint region is the area of the spectrum below 1500cm-1
Dynamic equillibrium
Forward and backward reaction occur at equal rate
Conc of reactants and products is constant
EMP
Most likely energy of particles in a sample
Emean
Mean energy of particles
Why does kinetic energy graph start from origin?
No particles have no energy
Higher temp graph KE
Curve shifts right
Peak lower
Area under curve beyond activation energy increases
Lower conc graph KE
Peak lower
Area under curve smaller
Formation of primary amine in 2 steps
Nucleo subs Haloalkane to nitrile
Reduction using H2 and Ni catalyst
Formation of phenylamine
Electrophilic substitution to form nitrobenzene
Reduction using Sn and conc HCl
Is secondary or primary carbocation more stable?
Secondary
Explain why a nucleophile would attack a haloalkane with Br in a nucleophilic substitution reaction
Bromine more electronegative than carbon
C is electron deficient
Lone pair on nucleophile donated to electron-deficient carbon
Explain the bonding in and the shape of a benzene molecule
Stage 1 Bonding
1a) Each C has three (covalent) bonds
1b) Spare electrons (in a p orbital) overlap (to form a pi cloud)
1c) delocalisation
Stage 2 Shape
2a) Planar
2b) Hexagon/6 carbon ring/120o bond angle
2c) C–C bonds equal in length / C–C bond lengths between single and double bond
Stage 3 Stability
3a) Expected Ho hydrogn of cyclohexatriene = –360 kJ mol–1
3b) Ho hydrogn benzene (is less exothermic) by 152 kJ mol–1
3c) Benzene lower in energy than cyclohexatriene / Benzene is more stable
Two ways of maximimising yield of propanal by distillation of reaction mixture
Cool distillate
Keep temp of reaction mixture below bp of the thing added e.g. propan-1-ol
