Organic Chemistry Flashcards
Define organic compounds
Compounds containing carbons (excluding oxides and carbonates)
Define functional group
A functional group is an atom or group of atoms in an organic molecule which is responsible for characteristic reactions of that molecule
Define homologous series
A homologous series is a family of compounds that all contain the same functional group and can be represented by the same general formula
What is the general formula of alkanes?
CₙH₂ₙ₊₂
What are the first five prefixes of organic molecules?
Meth-
Eth-
Prop-
But-
Pent-
Define molecular formula
The actual number of atoms of each element in a compound
Define empirical formula
The simplest ratio of atoms of each element in a compound
Define general formula
A general formula is a type of empirical formula that represents the composition of any member of an entire class of compounds
Define structural formula
This shows the unique arrangement of the atoms in a molecule without showing every bond
Define displayed (graphical) formula
This shows every atom and every bond in a molecule
Define skeletal formula
This shows the carbon chain skeleton of a compound with all the hydrogen atoms removed leaving just the functional groups attached to it
What is an alkyl group?
They are derived from alkanes but with a H missing
Often attached to organic molecules
What is the general formula of cycloalkanes?
CₙH₂ₙ
What is the general formula of haloalkanes?
CₙH₂ₙ₊₁X
(Where X = F, Cl, Br, I, At)
List the naming prefixes for haloalkanes
fluoro-
chloro-
bromo-
iodo-
Name the functional group and name suffix for the homologous series alcohols
Functional group = -OH
Suffix = -ol
Name the functional group and name suffix for the homologous series aldehydes
Functional group = -C=O (has to be on end)
Suffix = -al
Name the functional group and name suffix for the homologous series ketones
Functional group = -C=O
Suffix = -one
Name the functional group and name suffix for the homologous series carboxylic acids
Functional group = -COOH
Suffix = -oic acid
Name the functional group and name suffix for the homologous series nitriles
Functional group = -C≡N
Suffix = -nitrile
Name the functional group and name suffix for the homologous series amines
Functional group = -NH₂
Suffix = -amine
Define isomerism
Molecules with the same empirical formula but with their atoms arranged differently
Define structural isomerism and give the three subtypes
Compounds with the same molecular formula but different structures
- Chain
- Positional
- Functional group
Define stereo isomerism and give the two subtypes
Compounds with the same molecular and structural formula but the bonds are arranged differently in space
- Geometric
- Optical
Define chain isomerism
Compounds with the same molecular formula but the carbon chains are different
Define position isomerism
Compounds with the same molecular formula but the functional groups are in different positions on the carbon chain
Define functional group isomerism and give examples
Compounds with the same molecular formula but containing different functional groups
- Alkenes & cycloalkanes
- Alcohols & ethers
- Aldehydes & ketones
What happens to the melting and boiling point of hydrocarbons as chain length increases?
As chain length increases, so too does melting and boiling point:
- Mr ↑
- No of electrons ↑
- Van der Waals forces ↑
How does branching effect the melting and boiling point of hydrocarbons?
As branching increases, the melting and boiling point decrease:
- As branching ↑
- Molecules don’t pack together as closely
- So Van der Waals forces weaker
Define geometric isomerism
Compounds with the same molecular and structural formula but a different arrangement of the bonds
How can Z-isomers and E-isomers be differentiated?
E = Opposite
Z = Together
Why does stereoisomerism occur?
The carbon-carbon double bond prevent the carbon atoms and anything else attached from rotating
What is crude oil?
- A fossil fuel
- World’s major source of hydrocarbons
- Raw material
- Often located underneath the sea bed
What are the two main problems with crude oil?
- It is a mixture
- It produces too many long hydrocarbons and not enough short hydrocarbons compared to consumer demand
How are the hydrocarbons in crude oil separated?
Fractional distillation
Describe the distribution of hydrocarbons in a fractionating column
At the top:
- Small molecules
- Low b.p
- Very volatile
At the bottom:
- Large molecules
- High b.p
- Not very volatile
Describe what happens during fractional distillation
- Crude oil heated to about 400 degrees C
- Oil vapours enter the bottom of the fractionating column and start to rise up
- As the vapours rise, they cool down and condense back to liquid at different levels depending upon their boiling point
In order to obtain purer products, the fractions can be further processed by secondary distillations
Define cracking
Cracking is the process of taking larger, less useful hydrocarbon molecules and breaking them down to form smaller, more useful molecules
Give a word equation for cracking
Bigger alkanes → smaller alkanes + alkenes (+hydrogen)
Describe thermal cracking
- Needs a high temp (800C) and high pressure (700 kPa)
- Produces a high % of alkenes
- Involves a free radical mechanism
Describe catalytic cracking
- Uses a high temp (450C) and slight pressure
- Zeolite catalyst
- Produces mainly branched chain alkanes used as motor fuels
Why are alkanes almost non-polar?
- Electronegativities of C and H are very similar
- Resulting Van der Waals are very weak
Why are alkanes insoluble in water?
Water molecules held together by H-bonds, which are much stronger than the VdW between alkane molecules
Describe the reactivity of alkanes
Not very reactive. Do not react with acids, bases, oxidising or reducing agents.
Because:
- C-H & C-C bonds are much stronger than other single covalent bonds
- C-C bonds are non-polar and C-H bonds are virtually non-polar
Give the word equation for the complete combustion of alkanes
alkane + oxygen → carbon dioxide + water
Give the word equation for the incomplete combustion of alkanes
alkane + oxygen → carbon monoxide + carbon + water
(carbon monoxide and/or carbon)
Why is carbon monoxide dangerous?
It is a poisonous gas but is completely colourless and odourless
What are the dangers of particulates?
Particulates of C and CO can exacerbate asthma and cause cancer
What causes acid rain?
Sulphur dioxide formed when burning fossil fuels containing sulphur impurities
Explain how nitrogen oxides are formed in the internal combustion engine, despite there being no nitrogen present in alkanes
Nitrogen and oxygen in the air gain enough energy to combine due to the heat of a petrol engine when the sparks ignite the fuel
Give 2 environmental problems caused by oxides of nitrogen
Oxides of nitrogen may react with water vapour and oxygen in the air to form nitric acid. This causes:
- Acid rain
- Photochemical smog
Write 2 equations to show how nitrogen and oxygen react to become nitrogen dioxide
N₂(g) + O₂(g) → 2NO(g)
2NO (g) + O₂(g) → 2NO₂(g)
Write an equation to show how nitric acid can be formed when nitrogen dioxide reacts with oxygen and water vapour in the air
4NO₂ + O₂ + 2H₂O → 4HNO₃
Write an equation to show how sulphuric acid can be formed when sulphur dioxide reacts with oxygen and water vapour in the air
SO₂(g) + 1/2O₂(g) + H₂O(l) → H₂SO₄(l)
What is a flue gas?
Waste gases released during the burning of fossil fuels
What is flue gas desulphurisation?
The removal of sulphur dioxide from flue gases
Why is flue gas desulphurisation needed?
- Prevent SO₂ combining with O₂ and H₂O
- To form sulphuric acid
- Which can cause acid rain
Explain how flue gas desulphurisation using calcium oxide works
- Slurry of calcium oxide & water is sprayed into the flue gas
- This reacts with calcium oxide and water to form calcium sulfite
- Can be further oxidised to calcium sulphate (gypsum)
CaO(s) + 2H₂O(l) + SO₂(g) + 1/2O₂ → CaSO₄.2H₂O(s)
Name another compound (other than calcium oxide) that could be used for flue gas desulphurisation
Calcium carbonate
CaCO₃(s) + 1/2O₂(g) + SO₂(g) → CaSO₄(s) + CO₂(g)
One product of flue gas desulphurisation is gypsum. Why is this of economic benefit to powerstations?
Gypsum is saleable as it is used to make builders’ plaster and plasterboard
What is a catalytic converter?
Removes the pollutant gases from car exhausts by either oxidising or reducing them.
Converter contains a honeycomb of ceramic with metals such as platinum, palladium and rhodium spread on in a thin layer.
These metals catalyse reactions converting pollutants into relatively harmless products.
Name three pollutants and the harmless products they are converted into by a catalytic converter
Carbon monoxide → carbon dioxide
Nitrogen oxides → nitrogen
Unburnt hydrocarbons → water
Write an equation to show how carbon monoxide and nitrogen oxides can be converted to harmless products in a catalytic converter
2CO(g) + 2NO(g) → N₂(g) + 2CO₂(g)
Write a word equation to show how hydrocarbons and nitrogen monoxide can be converted to harmless products in a catalytic converter
Hydrocarbon + nitrogen oxide → nitrogen + carbon dioxide + water
Explain two adaptations of a catalytic converter
- Honeycomb shape for large SA
- Metal spread thinly to save on expense
What is the greenhouse effect?
The natural process by which the atmosphere traps some of the Sun’s energy, warming the Earth enough to support life. Global warming is the artificial increasing of the greenhouse effect due to a human-driven increase in greenhouse gases.
Name 3 greenhouse gases
- Carbon dioxide
- Water vapour
- Methane
Define ‘carbon neutral activity’
Activities that produce no carbon dioxide emissions overall
How are haloalkanes formed?
When an alkane and a halogen are mixed in sunlight they form a haloalkane
CₙH₂ₙ₊₂ + X₂ → CₙH₂ₙ₊₁X + HX
One HX molecule for every H lost
What are the 3 stages of a Free Radical Substitution Reaction?
Initiation - Free radicals formed
Propagation - Radicals used and reformed in a chain reaction
Termination - Radicals removed
Give an example of the initiation stage of a Free Radical Substitution Reaction
Cl₂ → 2Cl∙
Give an example of the propagation stage of a Free Radical Substitution Reaction
CH₄ + Cl∙ → ∙CH₃ + HCl
∙CH₃ + Cl₂ → CH₃Cl + Cl∙
Give two examples of the termination stage of a Free Radical Substitution Reaction
∙CH₃ + Cl∙ → CH₃Cl
∙CH₃ + ∙CH₃ → CH₃CH₃
What is ozone?
An allotrope of oxygen formed when UV allows an oxygen molecule to form a covalent bond with an oxygen atom
O₃
What was causing the depletion of ozone?
CFCs (compounds containing chlorine, fluorine and carbon)
Give 3 uses of CFC’s
- Refrigerator coolants
- Aerosol propellants
- Dry cleaning solvents
How do CFCs react with ozone?
- CFCs rise to stratosphere where UV light provides enough energy for C-Cl bond to break and form Cl∙
- Cl∙ then destroy ozone in chain reaction
O₃ + Cl∙ → O₂ + ∙ClO
O₃ + ∙ClO → 2O₂ + Cl∙
Overall: 2O₃ → 3O₂
What are the alternatives to CFC’s?
Hydrofluorocarbons (compounds containing on H, C and F)
What are haloalkanes?
Alkanes with H atoms substituted by halogen atoms
What makes something a primary haloalkane?
The halogen at the end of the carbon chain (attached to carbon which is only attached to one other carbon)
What makes something a secondary haloalkane?
The halogen in the middle of the carbon chain (attached to carbon which is attached to two other carbons)
What makes something a tertiary haloalkane?
The halogen at the junction of two carbon chains (attached to carbon which is attached to three other carbons)
Why are haloalkanes susceptible to attack by nucleophiles?
The C-X bond is polar. Bond enthalpy (strength) decreases down group 7.
Describe the method for testing for the presence of halide ions
- Set up 50 degrees Celsius water bath
- Place 2cm³ ethanol in a test tube
- Add 5 drops of suspected haloalkane
- Add 1cm³ AgNO₃, shake and allow to stand in the water bath
- If halide ions are present, a silver halide precipitate will form
Cl = AgCl = White ppt
Br = AgBr = Cream ppt
I = AgI = Yellow ppt
Describe and explain the reactivity trend of haloalkanes
Reactivity increase down group 7. This is because the bond enthalpy decreases down the so it requires less energy to break the C-X bond.
(Bond enthalpy is important here NOT polarity)
Define nucleophilic substitution
Where an electron pair donor replaces another atom or group of atoms during a reaction
Explain why haloalkanes commonly undergo nucleophillic substitution
Haloalkanes contain a polar C-X bond so the electron deficient C attracts nucleophiles
Define nucleophile
An electron pair donor
OH⁻ can react with haloalkanes as a nucleophile or as a base. What factors determine this?
- The reaction conditions
- Aqueous hydroxide ions & warm = substitution
- Ethanolic hydroxide ions & hot = elimination
- The structure of the haloalkane
- Primary = Substitution
- Secondary = Both
- Tertiary = Elimination
Define alkenes
Unsaturated hydrocarbons with the general formula CₙH₂ₙ
Describe and explain the trend in alkene boiling points
As carbon chain length increases, so does boiling point
- Mr ↑
- No. of electrons ↑
- Van der Waals forces ↑
- So boiling point ↑
Describe and explain the solubility of alkenes
Virtually insoluble in water. They are not polar so do not dissolve.
Describe how to assign E/Z isomers using Cahn-Ingold-Prelog notation (CIP)
Look at the atomic numbers of the atoms attached directly to the C=C (or subsequent atoms if they are the same)
Highest values opposite = E
Highest values together = Z
Describe the combustion reaction of alkenes and why they are not used as fuels
They burn in air to produce CO₂ and H₂O
e.g C₂H₄ + 3O₂ → 2CO₂ + 2H₂O
However, alkenes are not used as fuels as they are more valuable for other purposes i.e making plastics
Describe the addition of hydrogen to alkenes (no mechanism)
Alkenes react with hydrogen in the presence of a finely divide Ni catalyst at 150 degrees celsius
e.g C₂H₄ + H₂ → C₂H₆
One use of this reaction is making margarine
Describe the types of carbocation intermediates
Primary - The C+ at the end of the carbon chain (attached to carbon which is only attached to one other carbon)
Secondary - The C+ in the middle of the carbon chain (attached to carbon which is attached to two other carbons)
Tertiary - The C+ at the junction of two carbon chains (attached to carbon which is attached to three other carbons)
Describe and explain the trend of carbocation stability
Increase in stability from primary to tertiary:
- Alkyl groups ‘push’ electrons towards the C+ which gives it a positive induction effect
- More alkly groups on C+ = more stable C+
Unsymmetrical alkenes form the product that comes from the more stable carbocation
Define polymerisation
A process in which lots of small molecules called monomers join together to form a large molecules (polymer) which consists of repeating units
Define addition polymers
- Long chain molecules formed when lots of small molecules (called monomers) join together
- Nothing else formed.
- Monomers are based on ethene, which contains a c=c
- The monomers are normally reactive but the resulting polymer inert
What determines the properties of a polymer?
Its chemical structure and intermolecular forces.
For example:
Poly(ethene) - strong and flexible due to non-polar covalent bonds in the polymer chain and Van der Waals intermolecular forces
PVC (polyviolochlroide) - strong and hard due to polar C-Cl bonds and dipole-dipole intermolecular forces)
What are plasticisers and how do they work?
The properties of a polymer can be modified by adding substances called plasticisers. Placticiser molecules push chains apart which weakens the intermolecular forces and makes the substance more flexible.
What is the main problem with addition polymers?
They are unreactive so non-biodegradable and hard to dispose of
What are the two ways to produce alcohol (specifically ethanol)?
- Fermentation of sugars
- Hydration of ethene
Describe the production of ethanol by the fermentation of sugars
Carbohydrates from plants are broken down into sugars
Conditions = Yeast, 35 degrees Celsius, anaerobic
Rate of reaction = Slow
Purity of product = Aqueous solution of ethanol
Yield of product = Lower
Atom economy = 51%
Type of process = Batch
Describe the production of ethanol by the hydration of ethene
Crude oil is fractionated to obtain ethene. Ethene reacted with steam.
Conditions = H₃PO₄ catalyst, 300°c, 6.5x10³ kPa
Rate of reaction = Fast
Purity of product = Essentially pure
Yield of product = Higher
Atom economy = 100%
Type of process = Continuous
Define alcohols
A homologous series of compounds with general formula CₙH₂ₙ₊₁OH
Describe and explain the melting and boiling points of alcohols compared to alkanes
Alcohols have higher melting points than alkanes as the hydrogen bonding between alcohols is stronger than the Van der Waals forces between alkanes
Describe and explain the trend in alcohol solubility in water
As the length of the carbon chain increases, the solubility decreases
Short chain alcohols are soluble in water due to hydrogen bonding where as in longer chain alcohols the non-polar end dominates the properties and they become insoluble
Describe some uses of alcohols
- Solvents
- Fuels
- Ethanol is used in alcoholic drinks
What are the necessary conditions for the fermentation of sugars to form ethanol and why?
- Yeast
- 35°c = Temp cannot be higher, otherwise it would kill yeast
- Anaerobic = Aerobic conditions would oxidise alcohol to form carboxylic acid
- Aqueous
Why is the dehydration of alcohols useful?
Allows the production of alkenes from a renewable source so polymers can be made without needing finite crude oil
What is the test tube test for alkenes?
Shake with bromine water
Solution will turn from orange to colourless
What is the test tube test for halogenoalkanes?
- Add NaOH(aq)
- Warm
- Acidify with nitric acid
- Add aqueous silver nitrate
Solution will form precipitate of AgX
What is the test tube test for alcohols?
Add acidified K₂Cr₂O₇
Orange solution will turn green in the presence of primary or secondary alcohols
What is the test tube test for aldehydes?
Warm with Fehling’s solution
Blue solution turns to red precipitate
Warm with Tollens’ reagent
Silver mirror forms
What is the test tube test for carboxylic acids?
Add NaHCO₃(aq)
Carbon dioxide given off
What happens in an infrared spectrometer?
- A beam of infrared radiation containing a spread of frequencies is sent through a sample
- The radiation that emerges is missing the frequencies that correspond to the types of bonds found in the sample
- The instrument plots a graph of the intensity of the radiation emerging from the sample, called transmittance, against the frequency of radiation
- The frequency is expressed as a wave number, measured in cm⁻¹
Define racemic mixture
An equal mixture of optical isomers
Describe how to distinguish between two enantomers in a racemic mix
- Plane polarised light
- Will be rotated in opposite directions by each enantomer
Where is the footprint region of an infrared spec?
1500 to 400cm-1
Give the fermentation equation
C₆H₁₂O₆ → 2CH₃CH₂OH + 2CO₂
Why does CO2 absorb infrared radiation?
C=O bonds vibrate at the same frequency as IR
Describe how bioethanol is produced
Photosynthesis:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Fermentation:
C₆H₁₂O₆ → 2CH₃CH₂OH + 2CO₂
Combustion:
2C₂H₅OH + 6O₂ → 6H₂O + 4CO₂
Describe the environmental disadvantages of fermentation
- Deforestation/use of land
- Loss of biodiversity/habit
- 6CO2 in and 6CO2 out isn’t actually carbon neutral as fuel is used in production and distribution
