Organic chemistry ( AS ) Flashcards
define empirical formula
simplest whole number ratio of atoms of an element in a compound
define molecular formula
gives us the actual number of atoms of an element in a compound
define displayed formula
shows every atom and every bond in a molecule
define structural formula
shows arrangement of atoms in a molecule without showing every bond
define skeletal formula
drawn as lines with each vertex being a carbon atom. carbon atoms not drawn, assumed all carbon atoms has all unspecified bonds as C-H
Give the suffixes for:
a) no double bond
b) at least one double bond
c) an alcohol
d) an aldehyde
e) a ketone
f) a carboxylic acid
a) -ane
b) -ene
c) -ol
d) -al
e) -one
f) -oic acid
Give the prefixes for:
A) CH3 group
B) C2H5 group
C) C3H7 group
D) C4H9 group
E) Cl group
F) Br group
G) I group
A) methyl
B) ethyl
C) propyl
D) butyl
E) chloro
F) bromo
G) iodo
Define structural isomerism
When molecules have the same molecular formula but differnt structural formula
What is positional isomerism
Functional group is attached to the main chain at a different place
What is functional group isomerism
Same atoms but a different functional group due to a different arrangement of atoms
What is chain isomerism
Hydrocarbon chain organised differently e.g. branched chains
Define stereoisomerism
When molecules have the same structural and molecular formula, but have a different arrangement of atoms in space
What is E-Z isomerism, and how are the E and Z isomers decided
-E-Z isomerism is caused by the limited rotation about C=C double bonds.
- if the two substitutes with the highest molecular mass are on the same side of the double bond, it’s the Z (zusammen) isomer.
- if they are on different sides, it’s the E (entgegen) isomer.
What is an Alkane
A saturated hydrocarbons contains C-H bonds only
What’s the general formula of an alkane?
CnH2n+2
Are their bonds polar? Why/why not?
Nonpolar - carbon and hydrogen have similar electronegativities
Which intermolecular forces do they have? Why?
Only van der waals forces of attraction - bonds are non polar
Are they soluble in water? Why?
Insoluble because hydrogen bonds in water are stronger than alkanes van der waals forces of attraction
How reactive are alkanes?
Very unreactive
Which reaction will alkanes undergo
Combustion and reaction with halogens
What is crude oil? How is it formed? Is it renewable? Why?
-Mixture of fractions(hydrocarbons with similar boiling points and properties)
-formed at high temperatures and pressures deep below earth’s surfa e over millions of years so they’re non-renewable
Name the fractions from high to low boiling point
1) Gases - fuel on site
2) Gasoline/petrol/naphtha-cars
3) kerosene/paraffin- jet fuel, lighting
4) Diesal oil- lorries/taxis
5) lubricating oil/ waxes - candles, engine oil
6) Fuel oil ships, power stations
7) Tar/ bitumen -roads/roofing
What is fractional distillation/how does it work?
1)Crude oil is heated until most of it vaporises
2) it’s then passed into a fractionating tower that’s cooler at the top than the bottom liquid fractions are piped off at the bottom
3) vapour rises up the column and via trays and bubble caps- condense when temperature is more than their boiling point
4) The shortest chain hydrocarbons condense at the top as they have the lowest boiling point
What is fracking, and how is it done?
Natural gas held within shale rock drill into shale, force pressurised water and sand into rock to fracture it, collect gas. HCl and methanol added to break up shale and prevent corrosion.
Pros/cons of fracking
Advantages
- gas supply for many years, reducing imported gas and electricity
Disadvantages
-lots of traffic to local area
- concern about the amount of water used
- chemical additives can pollute water supplies
-can cause small earthquakes
Why are alkanes cracked?
To turn a long chain alkanes, with is not very economically valuable, to a shorter chain alkane and alkene
What are the conditions for thermal cracking?
700-1200 K temperature
Up to 7000 kPa pressure
What are the main products of thermal cracking?
Alkenes
What are the conditions for catalytic cracking?
Lower temperature (720K)
Lower pressure( but above atmospheric)
Zeolite catalyst with honeycomb structure to give a large surface area to volume ratio
What are the main products of catalytic cracking?
Cycloalkanes, aromatic hydrocarbons, branches alkanes
Write an equation for the combustion of propane
C3H8 + 5O2 –> 3CO2 + 4H20
What is a fuel?
Something that releases heat energy when combusted
What is incomplete combustion, and what products are formed in the case of alkanes?
Combustion in a limited supply of oxygen
CO- carbon monoxide - poisonous
C- carbon- particulates- soot- global dimming
Which type of hydrocarbons are most likely to undergo incomplete combustion?
Longer chain hydrocarbons
Why is carbon monoxide bad?
It’s toxic/ poisonous
What is the environmental impacts of nitrogen oxides?
Form nitric acid –> acid rain, photochemical smog
What is the environmental impacts of sulfur impurities/ sulfur dioxide
Forms sulphuric acid which can cause acid rain
What is the environmental impacts of soot(carbon)?
Asthma, global dimming
What’s the environmental impact of unburnt hydrocarbons?
Photochemical smog
What is the environmental impacts of carbon dioxide?
Greenhouse gas, which causes global warming, increases global temperatures and speeds up climate change
What are flue gases?
Gases given out by the power stations
Write two equations for two different ways of desulfurising flue gases.
CaO(s)+2H2O(l)+SO2(g)+½O2(g)–> CaSO4.2H2O(s)
What are catalytic converters made up of?
Platinum, palladium,and rhodium
What do catalytic converters catalyse(equations)?
2CO(g)+2NO(g)–>N2(g)+2CO2(g)
Hydrocarbons+NO–>N2+CO2+H2O
What are greenhouse gases
Gases that trap infrared radiation, making the earth act like a greenhouse.
How are haloalkanes formed from alkanes?
Free radical substitution
What are the three stages of free radical substitution?
1)Initiation-breaking halogen bond to form free radicals
2)propagation-chain part of the reaction where products are formed but free radicals remains
3)termination-free radicals removed, stable product formed
What are the conditions needed for the formation of a free radical chlorine atom?
Presence of UV light
Write equations for the reaction of CH4 with Cl2 to form CH3Cl
Initiation:Cl2–>2Cl•(in presence of UV light)
Propagation:Cl•+CH4–>HCl+•CH3
•CH3+Cl2–>CH3Cl+Cl•
Termination: 2Cl•–>Cl2
•CH3+•CH3–>C2H6
•CH3+Cl•–>CH3Cl
What’s the job of the ozone layer?
Protects earth from harmful exposure to too much UV radiation
How do CFCs break the ozone layer down?
Free radical substitution
Write an equation for the overall decomposition of ozone into oxygen(O2)
2O3–>3O2
Write free radical substitution equation to show how Cl free radicals catalyse the breakdown of O3
Cl2–>2Cl•(presence of UV light)
Cl•+O3–>ClO•+O2
ClO•+O3–>2O2+Cl•
Are haloalkanes soluble in water?
Insoluble as C-H bonds are non-polar, not compensated for enough by C-X bond polarity
Do haloalkanes have a polar bond?why?
Yes polar, as halogen has a higher electronegativity than Carbon
Which intermolecular forces do they have? Why?
Permanent dipole-dipole and van der waals forces of attraction.
The C-X bond polarity created permanent dipoles
When would haloalkanes have a higher boiling point?
Increase in 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, because mass of halogen>mass of hydrogen
What is the most important factor in determining the reactivity?
Carbon-halogen bond enthalpy
What is the order of reactivity in haloalkanes?
The bond enthalpy of C-X decreases down the group, so reactivity increases down tye group
What is a nucleophile
Electron pair donor
Give three examples of nucleophiles
:OH
:CN
:NH3
What is nucleophilic substitution?
A reaction where a nuclephile donates a lone pair of electrons to a delta positive carbon atom, delta negative atom leaves the molecule
What are CFCs?
Chlorine-fluro-carbons- haloalkanes containing C,F and Cl only
Whats the problem with CFCs
They catalyse the breakdown of the ozone in the atmosphere via free radical substitution
What are CFCs being replaced with?
HCFCs(hydrogen,chlorine,fluorine,carbon)
HFCs(hydrogen,fluorine,carbon)
What are the conditions/reactants needed for the elimination reaction of haloalkanes?
Hot ethanolic sodium hydroxide or potassium hydroxide
What is formed in the elimination reaction of haloalkanes?
Alkane, water and halogen ion
What is an alkene?
Unsaturated hydrocarbons with a C=C double bond
What is the general formula of an alkene?
CnH2n
Why is there no rotation about the C=C double bond?
Due to the pi orbital- electron density above and below the single bond, it holds the carbon atoms in place
Are they more or less reactive than alkanes? Why?
More reactive, due to high electron density of double bond and the fact that the pi-bond is slightly easier to break
What intermolecular forces of attraction do they have?
Only van der waals due to non-polar bonds
Are alkenes soluble in water? Why?
No, non-polar bonds( van der waals<hydrogen bonding)
Name and describe the three kinds of isomers alkenes can have?
Chain isomers(branched chains)
Position isomers(C=C on different carbon atom)
Geometric E-Z isomers
Write an equation for the complete combustion of pent-2-ene
CH3CH=CHCH2CH3 + 7½O2 —> 5CO2 + 5H2O
What is a eletrophile?
Electron pair acceptor
What is the most stable type of carbocation intermediate? Why?
The most stable carbonation is the one that’s bonded to the most other carbon atom(tertiary carbocation)
What product will be formed from which kinds of carbocations?
Tertiary carbocations
What conditions are needed for the electrophilic addition of H2O to an alkene?
Acid Catalyst, usually phosphoric acid
What are the products of the reaction
An alcohol
What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?
Room temperature
What conditions are needed for the electrophilic addition of a halogen molecule to an alkene?
Room temperature
How does a molecule with a non-polar bond react as if it is an electrophil?
The C=C bond with a high electron density induces a temporary dipole in the halogen molecule
How would you turn the product(from sulfuric acid + ethene) into a alcohol and how does it show that sulfuric acid catalyses the addition of water to an alkene?
Add water
H2SO4 reforms
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 that combine to form a polymer usually have a C=C bond which breaks to leave a repeating pattern
What are plasticisrers
Small molecule that get between polymer chains to force them apart and allow them to slide over one another
Why do things that contain mainly C-C and C-H bonds not decompose easily?
Bonds are non polar so are not attacked by enzymes
Why is lack of biodegradabilty in compounds containing C-H and C-C bonds a problem?
Disposal is difficult
What is the functional group of an alcohol group?
Hydroxyl Group
-OH
General formula of an alcohol group
CnH2n+1OH
How does the boiling point of alcohol compare with other hydrocarbons?
Alcohols have a higher boiling point that other hydrocarbons because they have hydrogen bonding which are stronger intermolecular forces than Van der waals forces
What makes an alcohol primary,secondary and tertiary?
Primary Alcohols
- The Carbon bonded to OH is bonded to one other Carbon
Secondary Alcohol
- The Carbon bonded to OH is bonded to two other Carbons
Tertiary Alcohol
- The Carbon bonded to OH is bonded to three other Carbons
How can ethanol be made from crude oil?
Hydration of ethene with steam
( Phosphoric acid catalyst )
How can ethanol be made from glucose? and what are the conditions?
Fermentation of glucose in yeast
Conditions
- Enzymes
- Anaerobic conditions
- 35 C
What’s the equation for the fermentation of glucose in Yeast?
C6H12O6 —> 2C2H5OH + 2CO2
What does Carbon Neutral mean?
No Net emission of CO2 into the atmosphere
CO2 released during combustion = CO2 absorbed by plants during Photosynthesis
Why is it not entirely Carbon neutral to use ethanol?
Carbon emissions during transport
How do you test for alkenes and what is the positive result?
- Add Bromine water to a sample containing alkenes
Positive Result - if an alkene is present it will decolourise bromine water
How do you test for haloalkanes and what is the positive result?
- add warm NaOH acidified with HNO3
- add AgNO3
Positive Result
Precipitate of Ag-Halogen
Cl= White precipitate
Br= Cream precipitate
I= Yellow precipitate
How do you test for Alcohols and what is the positive result?
- add acidified potassium dichromate to a sample containing alcohol and heat it
Positive Result - for primary and secondary alcohol the solution goes from orange to green
Whats the test for aldehydes and what is the positive result?
1) Fehlings Soution
Positive result
-Brick red precipitate forms
2) Tollen’s Reagent
Positive result
-Silver mirror forms
How do you test for carboxylic acids and what is the positive result?
Add Sodium Carbonate or any carbonate
Positive result
- effervescence
What is high resolution mass spectrometry?
mass spec that gives MR to 3 or 4 dp
what does high res mass spec allow you to do?
Distinguish compounds that have the same MR to the nearest whole number, but are made up of different atoms and therefore have different values of MR
Why do atoms and chemical bonds absorb infrared radiation?
The bonds are constantly vibrating- they can absorb infrared radiation that is of the same frequency of their vibration
How does infrared spectroscopy work?
- Every bond has a unique vibration frequency in the infrared region of the EM spectrum
- Bonds absorb radiation that is of the same frequency of their vibration
- Infrared radiation that emerged from a sample is missing the frequencies that have been absorbed —> this info can be used to find the compounds functional group
what is the fingerprint region?
Area of the infrared spectrum below wavenumber of 1500cm-1
Many peaks, caused by complex vibrations of the whole molecule. unique to every compound
