Topic 6 Organic Chemistry 1 Flashcards
What is a hydrocarbon?
Molecule only contains hydrogen and carbons
Define homologous series
- same general formula
- SIMILAR CHEMICAL properties
- TREND in PHYSICAL properties
- same functional groups
Define functional group
The group of the molecule that determines which group the molecule is a member of and its physical and chemical properties
Give the suffixes for:
a) No double bonds
b) At least one double bond
c) An alcohol
d) An aldehyde
e) A ketone
f) A carboxylic acid
a) No double bonds -ane
b) At least one double bond -ene
c) An alcohol -ol
d) An aldehyde -al
e) A ketone -one
f) A carboxylic acid -oic acid
What does saturated mean?
Organic compounds which only contain single bonds
What are unsaturated compounds?
Organic compounds that contain at least one carbon carbon double covalent bond
Define structural isomerism
When molecules have the same molecular formula but different structural formula
What are the 3 ways in which structural isomers can be formed?
- Alkyl groups can be in different places
- Functional groups can be bonded to different parts
- There can be different functional groups
What are stereoisomers?
Organic compounds with the same molecular formula but have different arrangement of atoms in space
What is E-Z isomerism and how are E and Z isomers differentiated?
E-Z isomerism is caused by the limited rotation about C=C
double bonds. If the two substituents with the highest molecular mass are on the same side of the double bond, it is the Z (zusammen) isomer [zame zide].
If they are on different sides, it is the E (entgegen) isomer
What is Cis-trans isomerism?
Special type of E/Z isomerism where the two substituents on each carbon atom are the same
What is homolytic fission?
It happens when each bonding atom receives one electron from the bonded pair forming two radicals
What is heterolytic fission?
When one bonding atom receives both electrons from the bonded pair
What are radicals?
Highly reactive, neutral species
How is a covalent bond formed from two radicals?
The radicals collide and the electrons are involved the bond formation
Describe the process of fractional distillation of crude oil
- The oil is pre-heated then passed into a column.
- The fractions condense at different heights and the temperature of column decreases upwards
- The separation of the fuels depends on boiling point which depends on size of molecules. The larger the molecule the larger the London forces
- Similar molecules (size, bp, mass) condense together and so are collected at the same fraction
- Small molecules condense at the top at lower temperatures and big molecules condense at the bottom at higher temperatures.
What is the reforming of crude oil?
It is processing of straight-chain hydrocarbons into branched-chain alkanes and cyclic hydrocarbons for efficient combustion.
Describe the 𝜎 (sigma) bond in alkane
The sigma bond is a covalent bond which has a direct overlap of the s orbitals of the bonding atoms.
What reactions will alkanes undergo?
Combustion and reaction with halogens
What type of reaction is combustion?
Oxidation reaction
What is the colour of the bunsen burner flame during complete combustion?
Blue flame
Which type of hydrocarbon are most likely to undergo incomplete combustion?
Longer chains
What are the pollutants formed in the combustion of alkanes?
Carbon monoxide, oxides of nitrogen and sulfur, carbon particulates and unburned hydrocarbons
What is the environmental impact of carbon monoxide?
It is toxic/poisonous, binds to haemoglobin
What is the environmental impact of soot (carbon)?
Asthma, cancer, global dimming
What are the environmental impacts of nitrogen oxides?
NO is toxic and can form smog
NO 2 is toxic and acidic and forms acid rain
What are the environmental impacts of unbranched hydrocarbons?
They contribute towards formation of smog
What is the importance of catalytic converter?
These remove CO, oxides of nitrogen and
unburned hydrocarbons (e.g. octane,
C8H18) from the exhaust gases, turning
them into less toxic products CO 2 , N 2
and H 2 O.
What are biofuels?
They are fuels developed from renewable resources. Alcohols and biodiesel are two examples of renewable plant- based fuels
What are the advantages of biofuels?
- Reduces of use of non-renewable fossil fuels
- Use of biodiesel is more carbon-neutral
- Fossil fuels can be used feedstock for organic compounds
- Less large scale pollution
What are the disadvantages of biofuels?
- Less food crops may be grown because crops for biofuel would be grown instead
- Reduction of rain forests have to be cut down to provide land
- Shortage of fertile soils
How are halogenoalkanes formed from alkanes?
Radical substitution
In the presence of what does alkane react with halogens?
UV light
What are the three stages of free radical substitution?
Initiation - breaking halogen bond to form free radicals
Propagation - chain part of the reaction where products are formed but free radical remains
Termination - free radicals removed, stable products formed
What are the limitations of free radical substitution?
If there is excess halogen further substitution will take place therefore the desired product will be harder to separate from the others.
What is a 𝜋 bond?
Overlap of p orbitals sideways above and below the 𝜎 bond.
What are alkenes?
Unsaturated hydrocarbons that contain at least one C=C bond made up of a 𝜋 bond and a 𝜎 bond
What bond restricts the rotation of carbon atoms?
𝜋 bond
What is the angle and shape of a double bond?
Trigonal planar
120°
What is the qualitative test for alkanes?
This tests for C=C double bond using bromine water. If the alkane is present bromine water decolourises.
Are they more or less reactive than alkanes? Why?
More reactive due to high electron density of double bond and the fact the pi-bond is slightly easier to break
What are the types of isomers that can be formed using alkenes?
E/Z isomers - due to the restricted rotation
Cis-trans isomers - if two of the same substituents are attached to each carbon
What is an electrophile?
Species that are electron pair acceptors
What is the most stable type of carbocation intermediate? Why?
Alkyl groups have a positive inductive effect, so the most stable carbocation is the one bonded to the most other carbon atoms i.e. A tertiary carbocation
Major products will be formed from which kinds of carbocations?
Tertiary (or the most stable available)
What conditions are needed for the electrophilic addition of H 2
O to an alkene? What is this type of reaction called?
Steam in the presence of an acid catalyst, usually phosphoric acid
Reaction is called hydration
What are the product(s) of the hydration reaction?
An alcohol
What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?
Hydrogen halide gases must be at room temperature
What is the reaction called when a halogen is added to alkene?
Halogenation
How does a molecule with a non-polar bond react as if it is an electrophile?
C=C double bond with a high electron density induces a temporary dipole in the halogen molecule → δ+ atom attracted to double bond
How can an alkene be converted into alkane? What is the reaction called and what are the required conditions?
Alkene + hydrogen = Alkane
Hydrogenation
Conditions → 150°C, nickel catalyst
What is an addition polymer?
Many monomers bonded together via rearrangement of bonds without the loss of any atom or molecule
What are monomers? What form do they usually take?
Molecules which combine to form a polymer
Usually have a C=C bond which breaks to leave a repeating pattern
What are the ways in which plastics can be disposed? (6)
● Landfill
● Combustion
● Electricity generation
● Reuse
● Recycle
● Organic feedstock
What are the disadvantages of recycling?
● Plastics must be sorted into different types
● Expensive
● Labour intensive
● Requires high technology
How can chemists limit the problems caused by polymer disposal?
- Developing biodegradable polymers
- Removing toxic waste gases caused by incineration of plastics
Explain what happens in organic feedstock
Plastics are separated and broken down into small organic molecules through a series of reaction. The molecules can then be used produce plastics and in other industries
What are haloalkanes?
Saturated organic compounds that contain carbon atoms and at least one halogen atoms
Are halogenoalkanes soluble in water?
Insoluble as C-H bonds are non-polar, not compensated for enough by C-X bond polarity
Do halogenoalkanes have a polar bond? Why?
Yes polar, as halogen has a higher electronegativity than C (halogen is δ-, carbon is δ+)
What type intermolecular forces do halogenoalkane have? Why?
Permanent dipole-dipole and London forces of attraction
C-X bond polarity creates permanent dipoles
When would halogenoalkanes have higher boiling points?
Increase Carbon chain length
Halogen further down group 7
How would the mass of a haloalkane compare with the mass of an alkane of the same chain length?
Greater as mass of halogen > mass of H
What is the most important factor in determining halogen reactivity?
The strength of carbon halogen bond
What would bond polarity suggest the order of reactivity would be?
C-F would be most reactive as most polar bond
What would bond enthalpies suggest the order of reactivity would
be?
C-I would be most reactive as lowest bond enthalpy
What is the trend in reactivity of primary, secondary and tertiary haloalkanes?
● The tertiary halide produces a precipitate almost instantly.
● The secondary halide gives a slight precipitate after a few seconds.
● The primary halide takes considerably longer to produce a
precipitate.
Define nucleophile
Electron pair donor
Give 3 examples of nucleophiles
:OH -
:CN -
:NH 3 -
What is nucleophilic substitution?
A reaction where a nucleophile donates a lone pair of electrons to δ+ C atom, δ− atom leaves molecule (replaced by nucleophiles)
What is hydrolysis?
A reaction where water is a reactant
What reactant often produces hydroxide ions for hydrolysis?
Water
What fission does water undergo to produce OH- ?
Heterolytic fission
What are the conditions/reactants needed for the elimination reaction of haloalkanes?
NaOH or KOH dissolved in ethanol (no water present)
Heated
What is formed in the elimination reaction of haloalkanes?
An alkene, water and halogen ion
How can you convert a haloalkane into an amine?
Reagent: NH 3 dissolved in ethanol
Conditions: Heating under pressure in a sealed tube
Mechanism: Nucleophilic Substitution
Type of reagent: Nucleophile - ammonia
How do you convert halogenoalkane into alkene?
Use ethanolic potassium hydroxide to produce alkenes (where the hydroxide ion acts as a base)
How do you produce nitriles from haloalkane?
Use potassium cyanide to produce nitriles (where the cyanide ion acts as a nucleophile)
How can you compare the rate of hydrolysis of haloalkanes?
Aqueous silver nitrate is added to a halogenoalkane and a silver halide precipitation is formed. The quicker the precipitate is formed the faster the rate of
hydrolysis.
AgI (s) - yellow precipitate [fastest]
AgBr(s) – cream precipitate
AgCl(s) – white precipitate
What is the functional group of an alcohol?
Hydroxyl group -OH
What kind of intermolecular forces do alcohols have? Why?
Hydrogen bonding, due to the
electronegativity difference in the OH bond
How do alcohols’ melting point and boiling point compare to other hydrocarbons’ of similar C chain lengths? Why?
Higher, because they have hydrogen bonding (strongest type of intermolecular force) → stronger than London forces
Are alcohols soluble in water? Why does solubility depend on chain length?
Soluble when short chain - OH hydrogen bonds to hydrogen bond in water
Insoluble when long chain - non-polarity of C-H bond takes precedence
What forms if you partially oxidise a primary alcohol?
An aldehyde
What conditions are needed to partially oxidise a primary alcohol?
Dilute sulphuric acid, potassium dichromate (VI), distill product as it’s produced, gentle heating
What forms if you fully oxidise a primary alcohol?
A carboxylic acid
What conditions are needed to fully oxidise a primary alcohol?
Concentrated sulphuric acid, potassium dichromate (VI), reflux, strong heating
What forms if you oxidise a secondary alcohol?
A ketone
What conditions are needed for the oxidation of a secondary alcohol?
Concentrated sulphuric acid, potassium dichromate (VI), strong heating
Is it possible to oxidise tertiary alcohol?
No
What is a dehydration reaction?
A reaction where water is lost to form an organic compound
What are the products of dehydration reaction of alcohol?
Alkene and water
Concentrated sulfuric acid or
concentrated phosphoric acid and 170°C
How can you produce bromoalkanes from alcohols?
Use 50% concentrated sulfuric acid and potassium bromide
How do you prepare and purify of a liquid organic compound?
- Heat under reflux
- Extract with a solvent in a separating funnel
- Distill
- Dry with an anhydrous salt
- Determine boiling temperature
