6 - Organic Chemistry I Flashcards
What is a hydrocarbon?
It is a compound consisting of hydrogen and carbon only.
What does saturated mean?
A hydrocarbon containing single carbon-carbon bonds only.
What does unsaturated mean?
A hydrocarbon containing a C=C double bond.
What is molecular formula?
The formula which shows the actual number of each type of atom in the molecule.
What is empirical formula?
Shows the simplest whole number ratio of atoms of each element in a compound.
What is general formula?
It is the algebraic formula for a homologous series.
What angle is the HCH bond in C2H6? and shape of the molecule?
Tetrahedral. 109.5°
What is a homologous series?
Families of organic compounds with the same functional group and same general formula.
What is a functional group?
An atom or a group of atoms which when present in different molecules, causes them to have similar chemical properties.
Functional group of aldehydes?
COH
functional group of carboxylic acids?
COOH
functional group of ketones?
CO (with carbons on either side of the carbon with the oxygen bonded to it).
functional group of esters?
COO
What is the prefix for alcohol groups?
hydroxy-
What is a structural isomer?
They are molecules with the same molecular formula but with different structures.
What are the different types of structural isomers?
- chain isomerism
- position isomerism
- functional group isomerism.
What are chain isomers?
Compounds with the same molecular formula but different structures of the carbon skeleton.
What are position isomers?
Compounds with the same molecular formula but different structures due to different positions of the same functional group on the same carbon skeleton.
What are functional group isomers?
Compounds with the same molecular formula but with atoms arranged differently to give different functional groups.
What is an example of a functional group isomer?
alkene and cycloalkane with the same number of carbons and hydrogens.
- general formula for alkenes and cycloalkanes are the same.
- cycloalkanes are a functional group isomer of alkenes.
what are stereoisomers?
They are compounds with the same structural formula but have a different spatial arrangement of atoms.
What kind of isomerism can only be exhibited by alkenes?
E-Z steroisomerism
Why does E-Z stereoisomerism occur?
- There is restricted rotation around the C=C double bond.
- There are two different groups/atoms attached to each carbon in the double bond.
Naming E and Z steroisomers?
- if the priority group/atom is on the same side of the double bond, Z (together)
- if the priority group/atom is on opposite sides of the double bond, E (opposite).
If the two priority groups are the same, what are the isomers called instead of E/Z?
- instead of E, trans.
- instead of Z, cis
General formula for alkanes?
CnH2n+2
- they are saturated hydrocarbons.
How are alkane fuels obtained?
They are obtained from the fractional distillation, cracking and reforming of crude oil.
What does crude oil consist of?
A mixture of hydrocarbons with different chain lengths and different boiling points.
What are the stages of fractional distillation?
- crude oil is vaporised
- it is then passed into a fractionating column
- the vapour is cooled as it rises
- hydrocarbons condense at different heights based on boiling points
- mixtures of similar fuels called fractions are collected
What is cracking
The conversion of long chain hydrocarbons to smaller hydrocarbon molecules by the breaking of C-C bonds.
- High Mr alkanes -> smaller Mr alkanes + alkenes.
Economic reasons for catalytic cracking?
- shorter chain hydrocarbons are higher in demand (e.g petrol and naptha) than larger fractions.
- to make use of excess larger hydrocarbons and supply the demand for short chain hydrocarbons.
- products of cracking are more useful and valuable than the starting materials.
What is reforming?
The processing of straight-chain hydrocarbons into branched-chain alkanes and cyclic-hydrocarbons for efficient combustion.
What is complete combustion and what are the products?
- alkanes burn with complete combustion in excess oxygen.
- CO2, H2O.
What is complete combustiinon and what are the products?
- alkanes burn with incomplete combustion in limited amounts of oxygen
- CO/C, H2O
Environmental consequences of CO?
- highly toxic
Environmental consequences of C?
- (soot)
- causes global dimming
- can cause respiratory problems
combustion of sulfur in alkanes?
sulfur-containing alkane fuels produce SO2 when burned.
Environmental consequences of SO2?
- dissolve in atmospheric water and produce acid rain.
- acidic
Combustion of N2? and NO?
- forms NO
- forms NO2
Environmental impact of NO?
- toxic and can form smog.
Environmental impact of NO2?
- toxic, acidic, and forms acid rain.
Environmental consequences of CO2?
contributes to global warming
Environmental consequences of unburnt hydrocarbons
- contributes to formation of smog.
Catalysts present in catalytic converters?
- platinum
- palladium
- rhodium
- coated on a ceramic honeycomb (large surface area).
How do catalytic converters work?
- CO is oxidised to form CO2.
- unburned hydrocarbons are oxidised to form CO2 an H2O.
- NO and CO react to form N2 and CO2.
2NO + 2CO -> N2 + 2CO2 - pollutants are removed by converting them into harmless gases.
Why are fossil fuels oil non-renewable?
Fossil fuels reserves will eventually reserved. They are being used up faster than they can be replenished.
What are alternative fuels?
They are fuels that have been derived from renewable resources.
Examples of alternative fuels and their sources?
- alcohols and biodiesel
- both derived from plants which is a renewable resource.
How is are alcohols such as ethanol produced?
produced from the fermentation of sugars from plants.
How is biodiesel produced?
Biodiesel is present in vegetable oils. Processing is not needed to be learned.
advantages of biofuels?
- reduction of use of fossil fuels (finite).
- renewable.
- more carbon-neutral
disadvantages of biofuels?
- less food crops may be grown.
- more land may be used to not grow food crops.
- deforestation to provide land.
- shortage of fertile soils.
What is a free radical?
a reactive species with an unpaired electron
What is homolytic fission?
When a bond is broken and one electron goes to each atom to form two radicals.
What is heterolytic fission?
When a bond is broken and both electrons goes to one atom to form ions.
General formula for alkenes?
CnH2n
unsaturated hydrocarbons? which ones?
- alkenes?
- cycloalkenes
What is in a c=c double bond?
- alkenes have a c=c double bond.
- this double bond consists of 1 sigma and 1 pi bond.
- why are pi bonds vulnerable to attack by electrophiles?
pi bonds are exposed and have high electron density above and below the two nuclei.
Why are pi bonds weaker than sigma bonds?
- Electron density is above and below the two nuclei.
- electron density is further away from the nuclei.
enthalpy of double bond
enthalpy for a c=c double bond is lower than the sum of the enthalpy for a sigma and pi bond.
What is an electrophile?
an electron pair acceptor.
Alkene to alkane?
- hydrogenation
- hydrogen H2(g)
- nickel catalyst, heat
- addition.
alkenes to dihalogenoalkanes?
- halogenation
- halogen X2
- room temperature
- electrophilic addition
- heterolytic fission
alkene to halogenoalkene?
- halogenation
- Hydrogen halides HX (X=Cl, Br, I)
- bubble gas through alkene at room temperature
- electrophilic addition
- heterolytic fission.
If the alkene is unsymmetrical, addition of hydrogen bromide can lead to two isomeric products.
major product is formed via the more stable carbocation intermediate.
tertiary > secondary > primary
Why are tertiary carbocation intermediates more stable than primary and secondary?
- greater number of methyl groups surrounding the positive carbon.
- the methyl groups are electron releasing and reduce the charge on the carbocation, stabilising it.
alkene to diol?
- oxidation
- Potassium manganate (VII). KMnO4
- in H2SO4 solution with water.
- when reacted, MnO4- ions will turn purple to colourless
- can be used for a test for alkene functional group.
reaction of alkenes and bromine water?
- BrOH
- room temperature
- addition
- colour change from orange to colourless.
- test for alkene functional group.
Alkene to alcohol
- hydration
- steam H2O(g)
- high temperature 300 to 600 degrees C
- concentrated H3PO4.
what are addition polymers formed from?
alkenes.
Incineration (disposal of waste polymers)
- rubbish is burnt and energy produced is used to generate electricity.
- some toxins can be released
- volume of rubbish will greatly reduce.
- incinerator converts polymer waste into energy.
recycling (disposal of waste polymers)
- saves raw materials (polymers formed from compounds produced from crude oil). Recycling saves crude oil reserves.
- polymers need collecting /sorting. Expensive in energy and manpower.
- thermoplastic polymers can be melted and reshaped.
- recycling involves converting polymer waste into other materials.
Feedstock for cracking (disposal of waste polymers)
waste polymers can be cracked into gases. This produces a feedstock that can be used in other chemical reactions, often to make new polymers.
How are waste products (caused by incineration of plastics) removed?
- e.g HCl is reacted with a base/carbonate. The acidic HCl gas is neutralised to form a salt and water.
development of biodegradable polymers.
- biodegradable polymers can be broken down by microbes in the environment
What is a primary halogenoalkane?
one alkyl group attached to the C atom bonded to the halogen atom.
What is a secondary halogenoalkane?
two alkyl groups attached to the C atom bonded to the halogen atom.
What is a tertiary halogenoalkane?
three alkyl groups attached the C atom bonded to the halogen atom.
Which molecules match with which mechanism?
- alkanes: free radical substitution
- alkenes: electrophilic addition
- halogenoalkanes: nucleophilic substitution
what is a nucleophile?
an electron pair donor
Halogenoalkane to alcohol?
- nucleophilic substitution
- warm H2O
- alcohol and hydrogen halide formed
Halogenoalkane to alcohol 2?
- nucleophilic substitution
- aqueous KOH (aq)
- OH- acts as nucleophile
- heat under reflux
- alcohol and potassium halide formed.
Halogenoalkane to alkene?
- elimination reaction
- ethanolic KOH
- OH- acts as a base
- alkene, potassium halide, water formed.
Why is ethanolic KOH used for halogenoalkane to alkene?
to minimise water to prevent alcohol forming.
Halogenoalkane to primary amine?
- nucleophilic substitution
- ammonia (NH3) in a sealed tube
- ammonia acts as a nucleophile
- primary amine, ammonium halide formed.
Halogenoalkane to nitrile?
- nucleophilic substitution
- ethanolic potassium cyanide, heated under reflux
- cyanide ion acts as a nucleophile
- nitrile, potassium halide formed.
in comparing rates of hydrolysis of halogenoalkanes, what solution is used?
silver nitrate solution.
in comparing rates of hydrolysis of halogenoalkanes, why is ethanol used?
Ethanol acts as a co solvent for the halogenoalkane and the silver nitrate solution and ensures that the hydroxide ions can react with the halogenoalkanes.
observations in in comparing rates of hydrolysis of halogenoalkanes? What precipitate is formed with the silver nitrate solution?
silver halide precipitate
- chloroalkane: no precipitate (very slow)
- bromoalkane: silver bromide, cream precipitate.
- iodoalkane: silver iodide, yellow precipitate
in comparing rates of hydrolysis of halogenoalkanes, which one has the fastest rate of hydrolysis and why?
- iodoalkane
- C-I bond is weakest with lowest bond enthalpy, so breaks most easily.
- iodine is the most electronegative so the d+ on the carbon is the greatest. Therefore more prone to attack by nucleophile.
in comparing rates of hydrolysis of halogenoalkanes, which one reacts the fastest? Primary, secondary, tertiary?
- tertiary halogenoalkanes react the fastest.
What are primary alcohols?
alcohols where 1 alkyl group is attached to the C bonded to the hydroxyl (OH) group.
What are secondary alcohols?
alcohols where 2 alkyl groups are attached to the C bonded to the hydroxyl (OH) group.
What are tertiary alcohols?
alcohols where 3 alkyl groups are attached to the C bonded to the hydroxyl (OH) group.
Products of combustion of alcohols?
CO2 and H2O
- they burn with a clean flame.
Alcohols + PCl5
chloroalkanes
- chloroalkane, POCl3, HCl
Alcohols + KBr + 50% conc H2SO4
bromoalkanes
- the KBr and acid produces HBr
- HBr reacts with alcohol to produce bromoalkane, water.
Alcohols + red phosphorus + iodine
iodoalkanes
- red phosphorus and iodine react to produce PI3.
- PI3 reacts with alcohol to produce iodoalkane and phosphorus acid (H3PO3).
What oxidising agent is used in the oxidation of primary and secondary alcohols?
potassium dichromate (VI) in dilute sulfuric acid solution
What do primary alcohols oxidise to when heated under reflux?
- aldehydes then carboxylic acids
What do secondary alcohols oxidise to when heated under reflux?
ketones.
Why can’t tertiary alcohols be oxidised?
- due to a lack of hydrogen atoms bonded to the carbon with the OH group.
How do you test for an aldehyde?
- By using Fehling’s solution (containing blue Cu2+ ions)
- heat gently
- aldehydes oxidised into carboxylic acid and Cu2+ ions reduced to copper(I) oxide.
- blue ions in solutions turns into red precipitate of Cu2O
- ketones do not react.
- can be used to distinguish between aldehydes and ketones.
Alcohol + concentrated phosphoric acid?
- heated with concentrated phosphoric acid
- dehydration reaction
- alkene, water molecule is formed
- elimination reaction
- heated
How is a water molecule formed in the dehydration of alcohols?
- OH is removed from the carbon and joined with an H from the adjacent carbon.
Why can multiple products be formed in the dehydration of a secondary or tertiary alcohol?
The H removed from the adjacent carbon to the carbon with the OH group can be on either side of the carbon with the OH group. So, the C=C double bond can be formed on two sides.
