Organic Chemistry Flashcards
Suggest a reason why some reactions occur by a mechanism involving a carbocation where others do not
Reactions involving carbocations tend to be tertiary carbocations since they are more stable than primary carbocations
Conditions of producing ethanol from ethene
- CONCENTRATED phosphoric acid catalyst
- high temperature
- high pressure
Suggest and explain a reason why an alcohol might not be easily oxidised
Tertiary alcohol so has no hydrogens on carbon attached to -OH for oxygen to remove
Give reasons why a major product for a reaction is formed
Formed from a tertiary/secondary carbocation which is more stable because :
- more alkyl groups bonded to carbon
- donate electron density (inductive effect) for greater stability
Suggest what physical properties of a homologous series change as chain length increases
Boiling / Melting Point
Density
Viscosity
Reason for E/Z isomerism
Restricted rotation around C=C bond
Suggest why alkenes do not react with warm aqueous sodium hydroxide
OH- acts as a nucleophile so high electron density of double bond repels it
Suggest reasons why ethene is not made from elimination reactions of haloalkanes in industry
- halogenoalkanes are expensive/ not readily available
- low yield
- slow reaction
What is meant by propagation step
Radicals formed and used
Suggest why haloalkanes are susceptible to attacks by nucleophiles
Bond between halogen and carbon is polar
Carbon atom is electron deficient/ partially positive
Features of a homologous series
- gradual change in physical properties as relative molecular mass increases
- same chemical properties
- same functional group
- same general formula
Suggest an economic reason for cracking fractions of crude oil
Meet high demand of more useful/ high value products which are in low supply using less useful products
Nucleophile + Electrophile
- nucleophile = electron pair donor
- electrophile = electron pair acceptor
Production of ethanol by hydration
- electrophilic addition reaction
- continuous process
- low percentage yield since reversible
- high atom economy (no waste products/ ethanol only product)
- unsustainable since ethene is finite (comes from crude oil)
- requires energy to produce steam
Production of ethanol by fermentation
- anaerobic respiration of yeast
- high percentage yield
- low atom economy since carbon dioxide water product
- sustainable since crops are renewable
- energy required for distillation
Suggest why distillation produces aldehydes
- volatile components can escape / distill off
- partial oxidation
Suggest why reflux produces carboxylic acids
- volatile components cannot escape so are refluxed
- complete oxidation
Suggest what the other product of oxidation of alcohols is
Water (always one mole - even when carboxylic acid is produced)
Conditions for production of ethanol by fermentation
- enzymes (yeast)
- anaerobic
- 25 - 42 degrees C
Suggest how you can tell when fermentation of glucose is complete
No more bubbles suggesting carbon dioxide is not produced
Suggest role of H+ in hydration of alkenes
Catalyst since it is not used up
Suggest properties of CFCs
Volatile
Non toxic
Non flammable
Inert
Structural isomers
Same molecular formula but different structure / arrangement of atoms
Uses of CFCs
- aerosol propellant
- dry cleaning solvent
- refrigerant
Suggest why a alkene might not have E/Z isomerism
One carbon atom is C=C bond is joined to two of the same groups
Empirical formula
Simplest whole number ratio of the number of atoms of each element in a compound
Molecular formula
Shows actual number of atoms of each element in a compound
Displayed formula
Shows every atom and bond is a compound
Structural formula
Shows unique arrangement of atoms in a compound without showing all bonds
Free radical
Highly reactive species with an unpaired electron formed when a covalent bond breaks evenly (each atom has one electron)
Suggest another reason for cracking
Alkene with can produce polymers
Conditions for thermal cracking
- high temperature
- high pressure
Mechanism for thermal cracking
Free radical substitution
Conditions for catalytic cracking
- warm temperature
- slight pressure
- zeolite catalyst
(silicon dioxide and aluminium oxide)
Evidence of catalytic cracking
- branched alkanes
- cycloalkanes
- aromatic compounds
Plasticisers
Small molecules that get between polymer chains forming them apart allowing them to slide over each other
Suggest why plastics are not biodegradable
- long saturated alkane backbone
- C-C and C-H bonds are non polar
- unreactive so enzymes cannot attack
Suggest what is meant by reflux and an advantage of it
- condensing and re collecting solvent vapour
- allows mixture to be boiled indefinitely without significant loss in volume
Suggest why gases are passed through sodium hydroxide in dehydration of ethanol using sulphuric acid
Remove carbon dioxide and sulphur dioxide from side reactions
Suggest a drawback of using sulphuric acid in dehydration of ethanol
- sulphuric acid is a strong oxidising agent
- oxidises alcohol into carbon dioxide and is reduced to sulphur dioxide
Compare sigma and pi bond and hence suggest why alkene should are more reactive than alkanes
Sigma bond is stronger than pi bond since there is stronger orbital overlap. Alkene have a pi bond which is weak making them highly reactive.
Conditions for electrophilic addition with ammonia
Excess ammonia
Reflux
High temperature/pressure
Suggest why there needs to be an excess of ammonia in reaction between electrophilic addition
Otherwise amine group would react with haloalkane
State which conditions favour elimination and substitution
Elimination - dissolved in ethanol - high temperature - tertiary haloalkane Substitution - aqueous - room temperature - primary haloalkane
What are the mechanisms for hydration and dehydration reactions
Hydration = Addition Dehydration = Elimination
Alternatives of CFCs
- HFCs
- alkanes
Stereoisomers
Same structural formula but different arrangement of atoms in space
Functional Isomers Examples
Ether - Alcohol
Aldehyde - Ketone
Carboxylic acid - Ester
Alkene - Cyclic alkane
Evidence of thermal cracking
MAINLY alkene produced
Addition Polymerisation conditions
- low temperature (exothermic)
- high pressure
