Topic 4 - Core Organic Chemistry Flashcards
What do all organic compounds contain?
Carbon
How many known carbon compounds are there?
10 million
How many new carbon compounds are discovered each year?
300,000
What does organic mean?
living
What do hydrocarbons contain?
carbon and hydrogen atoms only
What is the bonding like in hydrocarbons? What does this mean?
covalent so bonding between molecules is weak
Alkane general formula
CnH2n+2
Are Alkanes saturated or not?
Saturated
What does saturated mean?
no C=C carbon double bonds
Alkene general formula
CnH2n
What does unsaturated mean?
contains one or more C=C carbon double bonds
Are Alkenes saturated or unsaturated?
unsaturated
Number of carbons and formula of methane
1 C1H4
Number of carbons and formula of ethane
2 C2H6
Number of carbons and formula of propane
3 C3H8
Number of carbons and formula of butane
4 C4H10
Number of carbons and formula of pentane
5 C5H12
Number of carbons and formula of hexane
6 C6H14
Number of carbons and formula of heptane
7 C7H16
Number of carbons and formula of octane
8 C8H18
Number of carbons and formula of nonane
9 C9H20
Number of carbons and formula of decane
10 C10H22
Define homologous series
A homologous series is a series of organic compounds having the same functional group but with each successive member differing by CH2-
Define functional group
A functional group is a group of atoms responsible for the characteristic reactions of a compound
What is the carboxyl group and where is it found?
COOH is the carboxyl group, found in carboxylic acids
What do functional groups determine?
the pattern of reactivity
What does the carbon chain length determine?
physical properties such as melting/boiling points
What are aliphatic alkanes like?
Carbon atoms arranged in chains (branched and unbranched)
What are alicyclic alkanes like?
Carbon atoms arranged in ring structures
What are aromatic alkanes like?
carbon atoms using benzene structure
What is the alcohol group?
OH
How else can C2H5 be written?
CH3CH2
How else can C3H7 be written?
CH3CH2CH2
What is R?
The alkyl group (the alkane subtract a H)
Haloalkane functional group
- Cl
- Br
- I
Aldehyde functional group
-CHO
Ketone functional group
-C(CO)C-
Carboxylic acid functional group
-COOH
Ester functional group
-COO
What is the stem?
This is the number of carbon atoms in the longest chain bearing the functional group
What is the prefix?
This shows the position and identity of any side chain substituents
What is the suffix?
This shows the functional group is present
How to get stem name?
Take ‘ane’ off the alkane name
Alkene suffix
-ene
Alkyne suffix
-yne
Carboxylic acid suffix
-oic acid
Alcholol suffix
-ol
Aldehyde suffix
-al
Ketone suffix
-one
Acyl chloride suffix
-oyl chloride
amide suffix
-amide
CH3 - prefix
methyl
Cl- prefix
Chloro
Br- prefix
Bromo
I- prefix
Iodo
OH- prefix
Hydroxy
C2H5- prefix
ethyl
C3H7- prefix
propyl
C4H9- prefix
butyl
RULES FOR NAMING (6)
- number the longest carbon chain from one end to give the lowest numbers to the side chains
- Sidechain names appear in alphabetical order
- Each side chain is given its own number
- If identical side-chains appear more than once, prefix with di, tri, tetra, penta, hexa etc
- Numbers are seperated from names by hyphen (2-methylheptane)
- Numbers are seperated from numbers by a comma (2,3-dimethylbutane)
Define molecular formula
tells us the actual number and type of atom in a compound
Define empirical formula
this is the simplest whole number ratio of atoms in compound
Give the general, structural, molecular and empirical formula of butane (allowed to use paper to work out)
General formula CnH2n+2
CH3 CH2 CH2 CH3 is the structural formula
Molecular formula is C4H10
Empirical formula is C2H5
What do skeletal formulas show?
These show carbon chains and major functional groups only, H’s are not shown
In skeletal formulas where are the carbons?
At the end of lines
Define structural isomer
Structural isomers are compounds with the same molecular formula but different structural formulae.
Give an example of a structural isomer
C3H10 can be shown in two ways:
.CH3CH2CH2CH3
.CH3CH(CH3)CH3
How can isomers with functional groups form?
In compounds containing a functional group, the functional group can be at different positions along the carbon chain.
Can different functional groups have the same molecule formula? example.
Sometimes two molecules containing different functional groups have the same molecular formula. Aldehydes and Ketones with the same number of carbon atoms have the same molecular formulae. The molecular formula C3H6O could represent propanal or propanone.
Can isomers change smell?
yes
Give an example of isomers that change smell?
Linalool and geraniol are isomers and have similar chemical properties that are used in perfumes.
Linalool smells of lavender and geraniol of roses.
What two ways can covalent bonds be broken?
homolytic fission or heterolytic fission.
What is homolytic fission?
When covalent bonds break by homolytic fission, each of the bonded atoms take one of the shared pairs of electrons from the bond.
.Each atoms now has a single unpaired electron
What is a radical?
.An atom or groups of atoms with an unpaired electron
What is herolytic fission?
When a covalent bond breaks by heterolytic fission, one of the bonded atoms takes both of the electrons from the bond
.The atom that takes both electrons becomes a negative ion
.The atom that does not take the electron becomes a positive ion
What is the reaction mechanisn?
information about how the reaction takes place
In a reaction mechanism, what do curly arrows show?
the movement of electron pairs when bonds are being broken or made.
In a reaction mechanism, what do hald-headed curly arrows show?
show the movement of a single unpaired electron in mechanisms involving mechanisms.
What are the 3 types of reactions?
Addition, subsituton and elminiation
What happens in an addition reaction?
In an addition reaction, two reactants join together to form one product.
What happens in a substitution reaction?
In a substitution reaction, an atom or group of atoms is replaced by a different atom or groups of atoms.
What happens in an elimination reaction?
An elimination reaction involves the removal of a small molecule from a larger one. In an elimination reaction, one reactant molecule forms two products. Usually through a catalyst.
Define structural isomers
Molecules with the same molecular formula but a different structural formula
What do double bonds not do?
Rotate
Define stereoisomers
These are molecules with the same molecular formula, the same structural formula but a different spatial arrangement of atoms
For geometric isomerism what must a molecule have?
. A c=c double bond (non rotating)
. Each c must have 2 different groups attached
In geometric isomerism if it’s opposite it’s an _ isomer
E
In geometric isomerism if it’s together it’s a _ isomer
Z
In terms of isomers what does trans mean? How to remember?
Trans, across the isomer, the E isomer, think trans-Atlantic
In terms of isomers what does cis mean? How to remember?
Cis, adjacent isomer, the Z isomer, think stays the same
What is the cahn-ingold-prelog nomenclature?
.A more up to date system gives priority to groups based on their atomic number (high number = high priority) when thinking where elements go on isomers
Why is a cation called such?
it is positive and so goes to the cathode
Why is an anion called such?
it is negative and so goes to the anode
What is an electrophile?
A positive species which is able to accept a pair of electrons (means electron loving)
What is a nucleophile?
A negative species which is able to donate a pair of electrons (means nucleus loving)
Alkanes are saturated, what does this mean?
single bonds between carbons only
Alkane general formula
CnH2n+2
What allowed crude oil to remain for millions of years?
The are among the most stable organic compounds – lack of reactivity
What are alkanes components of?
oil and gas
What are alkanes mainly used as?
fuels to release energy
What leads to the formation of sigma bonds?
The overlap of orbitals directly between the bonding atoms leads to the formation of sigma bonds (σ-bonds).
What happens around sigma bonds?
Free rotation
Describe the relationship between boiling points straight alkanes
As the carbon chain increases the boiling point increases
Explain the relationship between boiling points straight alkanes
As the carbon chain length increases the surface are of interaction between molecules increases and thus the size of the London forces also increases (due to the greater number of electrons and thus size of temporary and induced dipoles), hence more energy needs to be provided to disrupt these stronger London forces, leading to a higher boiling point.
Describe the relationship between boiling points and branched alkanes
As the amount of branching increases, the boiling point goes down
Explain the relationship between boiling points and branched alkanes
As the amount of branching increases the surface area of interaction between molecules decreases and thus size of the London forces also decreases, hence less energy needs to be provided to disrupt these weaker London forces, leading to a lower boiling point.
Why are alkanes quite unreactive?
.C-C and C-H bonds are strong (have high bond enthalpy)
.C-C bonds are non-polar
.C-H are virtually non-polar
What happens with the complete combustion with alkanes?
In a plentiful supply of oxygen, combustion of alkanes will always lead to the production of CO2 and water.
What happens with the incomplete combustion with alkanes?
In a limited supply of oxygen, combustion of alkanes will lead to the production of CO (carbon monoxide) and water.
What does a covalent bond in a diatomic halogen molecule need to be broken?
UV light
What are the mechanistic steps in homolytic fission?
The initiation step, the propagation step and the termination step
What is the termination phase in homolytic fission?
addition of two three radicals
General mechanism of homolytic fission
X2 UV light X● + X●
CaHb + X● CaHb-1 + HX
CaHb-1● + X2 CaHb-1X + X●
CaHb-1● + X● CaHb-1X
Evaluate the substitution of alkanes
.Further substitution can occur with more H’s being replaced by additional bromines
.Additionally substitution can occur at different points in a carbon chain
Alkene general formula
CnH2n
Does an alkene exist with 1 carbon?
no
Are alkenes saturated or unsaturated?
Unsaturated
What is the test for alkenes?
bromine water is decolourised (orange to colourless)
What is a pi bond?
these are formed by the sideways overlap of the two adjacent p orbitals
Chemical formula of limonene
C10H16
What is limonene responsible for?
The smell and flavour of lemons and oranges
What happens in an alkene addition reaction?
The double bond opens up and allows two atoms to join to it
What happens in a hydrogenation of an alkene?
Addition reaction with hydrogen
Conditions for hydrogenation of alkene
nickel catalyst and 150’C
Why does the Z isomer have a lower boiling point?
It cant pack as closely together
What happens with hydration of alkenes?
.Alkenes will react with steam, H2O, in the presence of phosphoric acid, H3PO4, to produce alcohols
What does bromine water test for?
Unsaturation
Why is HBr polar?
Br is more electronegative
Explain how electrophilic addition works using HBr as an example
HBr is polar due to electronegative Br
The pi electrons attracted towards the Hs+, i.e. pi bond breaks
Hs+ acts as an electrophile (accepts a pair of electrons)
H-Br bond breaks via heterolytic fission
What is an electrophile?
‘electron loving’, able to accept a pair of electrons
What is a nucleophile?
‘nucleus loving’, able to donate a pair of electrons
Why is Br2 non-polar?
Both Br atoms have the same electronegativity
How does Br2 react with an alkene?
Bromine is none polar due to each atom having the same electronegativity
But as bromine approaches the pi bond on the alkene, it repels the electrons in the bond and pushes them away, giving the bromine atoms slight charges
The pi electrons induce a dipole in the non-polar Br2 molecule as it approaches the bond
This means electrophilic addition can ensue
In electrophilic addition, in the stage between the adition of the electrophile and the addition of the other atom, what is the alkene called? Why?
A carbocation (or carbonium ion) as it has a positive charge
What forms of carbocations are there?
Primary, secondary and tertiary
How do +I affects increase stability?
Carbon centres have a positive inductive effect (+I). This pushes electron density towards the C+ and helps to stabilise it.
The more +I effects,
the more stable the carbonium ion
The more stable ions are,
more favourable
Which product of electrophillic thing is more favourable?
Major product
What is markownikoffs rule?
The major product is produced when the negative part of the molecule joins to the carbon with the least number of attached H (hydrogen) atoms within the double bond.
What is the order of carbonium ion stability? Why?
Primary carbonium ions are less stable than secondary, which are less stable than tertiary, because:
- Primary = 1 x +I
- Secondary = 2 x +I
- Tertiary = 3 x +I
Draw the electrophillic mechanism for HCl and CH3CH=CH2
Check notes from 29.1.20
When drawing polymer reactions, what does the ‘n’ mean?
lots
When drawing polymer reactions, where do the brackets go?
Around the monomer in the polymer, over the bonds on the edge
When is an addition polymer formed?
when lots of small alkene monomers join together to form a long chain molecule called a polymer (and no other product).
What is polyethene used in?
carier bags
What is polystyrene used in?
used in cups, packaging and cutlery
What is polytetrafluorine (PTFE) used for?
Non-stick coatings
Scientific name for polystyrene
polyphenylethene
Example of PTFE
teflon
Describe structure and resultant properties of high density poly(ethane) (HDPE)
straight polymer chains, chains packed tightly together, strong forces between chains, strong and tough material, high melting point
Describe structure and resultant properties of low density poly(ethane) (LDPE)
branched polymer chains, chains cant pack close together, weak forces between chains, weak but flexible material, low melting point
What does the type of polymer depend on?
the temperature and catalyst used during production
Pros of polymers we use
- Readily available
- Cheap to use
- More convenient than alternatives (glass, metal, paper and cardboard)
- Lack of reactivity makes them suitable for storing food
Cons of polymer we use
- Non-biodegradable
- Growing amount of waste has environmental effects, for example killing marine life
How does recycling polymers reduce their environmental impact?
by conserving finite fossil fuels as well as decreasing the amount of waste going into landfill.
How are polymers recycled?
First the polymers have to be sorted, as if they are mixed then the product is rendered useless, and then they are chopped into flakes, washed, dried and melted. The recycled polymer is cut into pellets and used by manufacturers to make new products.
Why is PVC recycling hazardous?
The disposal and recycling of PVC is hazardous due to the high chlorine content and the range of additives present in the polymer. Dumping PVC in landfill is not sustainable and, when burnt, releases hydrogen and chlorine (a poisonous gas), and other pollutant like toxic dioxins.
How is PVC recycled?
Solvents dissolve the polymer, high-grade PVC is then recovered by precipitation from the solvent, and the solvent is used again.
Why are some polymers difficult to recycle?
as they are from petroleum or natural gas, they have a high stored energy value
What happens to some waste polymers that are difficult to recycle?
Waste polymers can be incinerated to produce heat, which generates steam to turn a turbine to produce electricity
What is feedstock recycling?
.Feedstock recycling describes the chemical and thermal processes that can reclaim monomers, gases, or oil from waste polymers
What do the products of feedstock recycling resemble?
those produced from crude oil in refineries
What can products of feedstock recycling be used as?
raw materials for the production of new polymers
Name an advantage of feedstock recycling
that it can handle unsorted and unwashed polymers
What are bioplastics produced from?
Bioplastics produced from plant starch, cellulose, plant oils, and proteins
Are bioplastics renewable and sustainable?
Yes
Why are bioplastics good?
not only protects our environment but also conserves natural resources
How are biodegradebale polymers broken down?
.Biodegradable polymers are broken down by microorganisms into water, carbon dioxide and, biological compounds
What do biodegradaeble polymers usually contain?
These polymers are usually made of starch or cellulose, or contain additives that alter the structure of traditional polymers so that microorganisms can break them down
When compostable polymers degrade, they leave no what?
No visible or toxic residues
Why are bin liners made from plant starch good?
can be used as bin liners for food waste, so the food and bin liner can be composted together
What is replacing polystyrene?
Compostable plates, cups and food trays made from sugar cane fibre
What are photodegradable polymers based on and when are they used?
Where plant based polymers aren’t available, photodegradable oil-based ones are being developed
How are photodegrable polymers broken down?
These polymers contain bonds that are weakened by absorbing light to start the degradation. Alternatively, light absorbing additives are used
Alcohol general formula
CnH2n+1OH
Name first 6 alcohols
methanol, ethanol, propanol, butanol, pentanol, hexanol
Name the isomers of butanol
Butan-1-ol
Butan-2-ol
2-methylpropan-1-ol
2-methylpropan-2-ol
Describe the process of fermentation
- Extract sugar (glucose) from crops
- Add yeast to glucose (enzymes in yeast act as a catalyst)
- Fermentation occurs
What type of process if fermentation?
Batch process
What is the optimum temperature for fermentation?
30-40’C
Fermentation equation
C6H12O6 –> 2CH3CH2OH + 2CO2
Advantages of fermentation
.Sugars are a renewable resource
.Batch process, so the equipment is cheap
.More carbon neutral (bio fuel)
Disadvantages of fermentation
.Very slow
.Very impure - needs further processing, fractional distillation, which takes time and money
.Batch process, so high labour costs
Describe the hydration of ethene to form ethanol
.Extract crude oil from the ground
.Oil refinery - fractional distillation then cracking to get ethene
.Hydration (addition of steam)
Is the hydration of ethene a continuous process?
yes
Needed environment for hydration of ethene
.Phosphoric acid catalyst
.High temperature and pressure
Equation for hydration of ethene
C2H4 + H2O –> CH3CH2OH
Advantages of hydration of ethene
.Fast reaction
.Pure product
.95% yield (initially 5% but can recycle unreacted ethene)
.Continuous (cheaper man power)
Disadvantages of hydration of ethene
.High technology equipment needed, expensive initial cost
.High energy costs for high pressure
.Ethene is non-renewable
How do alcohols compare, when looking at physical properties, to the corresponding alkanes?
alcohols are less volatile, have higher melting points and greater water solubility than the corresponding alkanes.
Why do alchohols have a higher boiling point than alkanes?
.Hydrogen bonding in alcohols gives higher boiling point
Why does the gap bewteen boiling points start to narrow as the chain length incerases for alchohl and alkanes?
the significance of hydrogen bonding decreases, and London forces increase, therefore gap between boiling points starts to narrow
Describe and explain solubility in alcohols
.Alcohols such as methanol and ethanol are soluble in water as hydrogen bonds form between the –OH group of the alcohol and the water molecules
.As the chain length increases, the influence of the –OH group decreases, and the solubility of the alcohol decreases
.Carbon chains are hydrophobic
How can alcohols be classified?
primary, secondary and tertiary
What does alcohol classification depend on?
depends on the number of hydrogen atoms and alkyl groups attached to the carbon atom that contains the alcohol function group
Describe the structure of primary alcohols
.Primary has at least 2 hydrogens attached to the carbon with the alcohol group, plus either a carbon centre or another H
Describe the structure of secondary alcohols
.Secondary has 1 hydrogens attached to the carbon with the alcohol group, plus 2 more carbon centres
Describe the structure of tertiary alcohols
.Tertiary has 0 hydrogens attached to the carbon with the alcohol group, plus 3 more carbon centres
What is an oxidising agent?
helps something to gain oxygen/lose electrons
What can primary alcohols be oxidised into?
Aldehydes
What is the formula for Sodium/potassium dichromate(VI)?
Na2Cr2O7
K2Cr2O7
What colour is Cr2O7^2-?
Orange
What colour is Cr^3+?
Green
Cr2O7^2- + 14H^+ + 6e^- –>
2Cr^3+ + 7H2O
When oxidising agents oxidise what happens to themselves?
They are reduced
What does the oxidation of aldehydes lead to?
Carboxylic acid
aldehyde + [o] –>
Carboxylic acid
CH3CHO + [o] –>
CH3COOH
Ethanol to ethanal is …
mild oxidation
Ethanol to ethanoic acid is …
further oxidation
What is required for further oxidation?
Reflux then distillation
What is reflux?
continuous evaporation then condensation, where the reactants cannot escape the flask
Alcohol + 2[o] –>
Carboxylic acid
CH3CH2OH + 2[o] –>
CH3COOH + H2O
What is [o]?
An oxidizing agent
Structure of an aldehyde?
A carboxylic acid group but just H instead of OH
Oxidation of secondary alcohol formula
Secondary alcohol + oxidising agent ketone + water
Can ketones be further oxidised?
No
Why can’t tertiary alcohols be oxidised?
Due to lack of hydrogen on OH carbon
Name 2 dehydrating agents, what does this mean?
Concentrated sulphuric acid (h2so4) or concentrated phosphoric acid (h3po4) are dehydrating agents i.e. they can remove water from molecules
Cyclohexanol + H3PO4 –>
Cyclohexene
What happens in dehyrdation reactions?
A hydrogen from the carbon with the OH group and a neigbouring arbon are removed
Which haloalkanes have the strongest bond?
C-F, then C-Cl, then C-Br, then C-I
Draw the mechanism of 2-bromobutane + :OH-
Check your notes
What is a haloalkane?
C-X
X = F, Cl, Br, I
Why are haloalkanes so reactive?
Halogens are very electronegative, so dipoles are formed, which makes them reactive
What is a nucleophile?
donates a pair of electrons
Example of nucleophile
hydroxide
Equation for hydrolysis of haloalkane
Haloalkane + hydroxide alcohol + halogen
Factors affecting covalent bonds strength:
- Shielding
- Nuclear charge
- Atomic radius
For haloalkanes, why does hydrolysis increase in rate of reaction as you go down the group?
the strength of the bond between the halogen and the carbon becomes weaker as you go down the group.
What is the practical for determining the rate of reaction for haloalkane?
Haloalkane + ethanol + silver nitrate, time for precipitate
Draw HFC
Check notes
What is the ozone layer doing now HFC’s have been introduced?
repairing, 3O2 –> 2O3
Equations to show Nitrous oxide effect on ozone
NO- + O3 –> O2 + NO2-
NO2- + O3 –> NO- + 2O2
Draw CFC
Check notes
equations to show chlorine free radical effect on ozone
O3 + Cl- –> OCl- + O2
OCl- + O3 –> Cl- + 2O2
Condensed version of chlorine free radical ozone equaions
2O3 –> 3O2
What is the ozone layer
Ozone is a layer in the stratosphere which stops UV rays
What is ozone
O3
What are CFC’s
chlorofluorocarbons
How is a Cl free radical formed from CFC’s
Weakest bond broken by UV rays from sun (C-Cl)
What do we now use instead of CFC’s? Why?
We now instead use HFC’s (hydrofluorocarbons), which doesn’t make any free radicals, so the hole is now closing
What do CFC’s do to ozone?
Turn it into` oxygen
Halogenoalkane general formula
Cn¬H2n+1X
Where X is a halogen
What are halogenoalkanes?
Halogenoalkanes are similar to alkanes but with one or more of the hydrogen atoms replaced by a halogen
halogen prefixes
Fluorine Fluoro –
Chlorine Chloro –
Bromine Bromo –
Iodine Iodo –
Number of groups prefixes
One - Two Di – Three Tri – Four Tetra – Five Penta –
For halogenoalkanes, what is an r group?
A chain of carbon atoms can be represented by R when drawing the structure, this is referred to as an R group
What is a primary haloalkane?
- Primary (1’) halogenoalkanes
Have one R group attached to the carbon linked to the halogen
What is a secondary haloalkane?
- Secondary (2’) halogenoalkanes
Have two R groups attached to the carbon linked to the halogen
What is a tertiary haloalkane?
- Tertiary (3’) halogenoalkanes
Have three R groups attached to the carbon linked to the halogen
Halogenoalkanes contain a polar carbon-halogen bond, the polarity arises from …
… the different electronegativity of the carbon and halogen atoms
Halogen atoms are more electronegative than carbon atoms, the bonded electron pair is attracted more towards …
… halogen atom than towards the carbon atom
Down the halogens, how does electronegativity change?
It decreases
Describe how nucleophilic substitution can happen with haloalkanes
- Nucleophiles (Nu-) attack the carbon of a carbon–halogen (C–X) bond, because the electron pair on the nucleophile is attracted towards the small positive charge on the carbon
- The electrons in the C–X bond are repelled as the Nu- approaches the carbon atom
- The Nu- bonds to the carbon and the C–X bond breaks. The two electrons move to the halogen, forming a halide ion
- The halide is substituted, so this is a nucleophilic substitution reaction
Give examples of nucleophiles
H2O, -OH, NH3
When halogenoalkanes react with an aqueous solution of hot hydroxide ions, a nucleophilic substitution reaction occurs to produce …
… alcohol
Hydrolysis is …
… a reaction with water or aqueous hydroxide ions that breaks a chemical compound into two compounds
How can the rates of hydrolysis reactions of haloalkanes be measured?
.Alkaline hydrolysis with NaOH(aq)/H2O, reflux:
R-X + OH- R-OH + X-
.Acidification with dilute nitric acid, this removes excess NaOH which would otherwise form a precipitate with the silver nitrate in the next stage, preventing detection of any silver halides
.Addition of AdNO3(aq) ¬shows the presence of aqueous halide ions
Ag+(aq) + X-(aq) AgX(S)
For haloalkane hydrolysis, the intensity of the precipitate indicates …
… the extent and rate of the hydrolysis
Method of rates of hydrolysis investigatio n
- Set up water bath to a temperature of 50’C at the start of the lesson
- Set up five test tubes and allow them to reach 50 ‘C
- Place a separate test tube containing silver nitrate into the water bath and allow this to reach the same temperature
- One tube at a time, add 1cm3 of the silver nitrate solution, mix the contents and start the timer
- Note the time it takes for a precipitate to form
- Repeat this with the other tubes and note the results
Why is ethanol used for hydrolysis practical of halogenoalkanes?
- Halogenoalkanes are insoluble in water, but soluble in ethanol
What is the ozone layer and what does it do?
.A high concentration of O3 molecules about 15-30Km above the Earth’s surface
.Ozone absorbs a high proportion of the Sun’s ultraviolet radiation
.If there was a lower concentration of ozone in the stratosphere, then …
… ultraviolet radiation would manage to get to Earth, and cause harm to us through burns and skin cancer
.The Ozone layer goes through a cycle of reaction that are altered by …
… the addition of halogenoalkanes in the atmosphere
Link between ozone depletion and global warming?
OZONE DEPLETION IS NOTHING TO DO WITH GLOBAL WARMING
What are chlorofluorocarbons? Examples
.Chlorofluorocarbons are a family of organic compounds that contain chlorine atoms and fluorine atoms, examples include dichlorodifluoromethane and 1, 1, 1-trichloro-2, 2, 2-trifluoroethane
.In the 1930’s, CFC’s were developed for use as …
… refrigerants, to cool the air inside refrigerators
.They were also found to be useful in other products like aerosol sprays and form fire extinguishers
.They are inert, and used to be widely used as …
… they do not react with other substances
.At ground level, CFC’s are very stable, but once they …
… reach the atmosphere they absorb UV radiation from the Sun which breaks their covalent bonds to form highly reactive free radicals
What do free radicals from CFC’s do?
These react very quickly with ozone molecules in a free radical chain reaction
just one chlorine radical can destroy around _______ ozone molecules
100,000
CFC reaction with Ozone in steps
Initiation –
.The UV breaks the weaker C-Cl bond within the CFC molecule
.CF2Cl2 -> CF2Cl + Cl ●
Propagation –
.The chlorine radical Cl’ is very reactive and reacts with ozone molecules
.Cl ● + O3 -> ClO ● + O2 step 1
.ClO ● + O3 -> Cl ● + 2O2 step 2
.Propagation step 2 regenerates a Cl’ free radical, so the 2 steps repeat in a cycle over and over again
CFC reaction with ozone overall equation
O3 + O –> 2O2
What led to the Motreal Protocol, what was the Montral Protocol and what was its effect?
.The effect of CFC’s on the Ozone layer was established in the 1970’s
.In 1987, an international agreement called the Montreal Protocol was put in place – it froze the production of CFC’s and agreed to phase out their use from 1990
.Since CFC’s are so stable, it will be many years till they disappear from the atmosphere
.Some Ozone depletion has therefore continued since the phasing out of CFC’s
What is distillation?
a separating technique that is used to collect a product from an organic synthesis reaction
What is reflux?
a technique used in organic synthesis to ensure that a reaction mixture does not boil away
To heat under reflux you need:
.Pear-shaped flask
.Heating mantle
.Condenser
Method for using a seperating funnel:
- Mount an iron ring on a clamp stand and put the separating funnel in it.
- Remove the stopper and make sure that the tap at the bottom is closed.
- Carefully pour the mixture into the funnel so that the funnel is no more than half full. Wash out the reaction vessel with water and add this to the mixture in the funnel – there should still be some air in the funnel. Put the stopper back.
- Take the funnel out of the ring and invert it. Open the tap to equalise the pressure. Turn the tap back to closed. Gently shake the mixture in the funnel and equalise the pressure as required. Repeat until you no longer hear a ‘whistle’.
- Replace the funnel in the iron ring and give the mixture time to separate into layers.
- Remove the stopper, put a beaker under the spout and open the tap. Collect the lower (water) layer in a beaker. Turn the tap off. As the organic product is in the upper layer, this aqueous layer can be discarded.
- Using a clean, dry beaker open the tap and collect the desired organic product.
- Shake the liquid with a small amount of drying agent and pour the final dry product into a clean, dry container.
What are drying agents, with examples, and how do you use them?
Inorganic salts such as magnesium sulphate (MgSO4) and calcium chloride (CaCl2) absorb water slowly to become hydrated. The anhydrous salts can be used to dry other chemicals:
.Add a few spatulas of the drying agent to the organic product
.If the drying agent clumps together, add some more
.When the drying agent remains free-moving the organic product is dry
.Use gravity filtration and collect the filtrate, which is the dry organic product
What is redistillation?
the purification of a liquid by performing multiple distillations
Example of when redistillation is used?
For instance, when ethanol is made by fermentation, distillation is used to remove the ethanol from the mixture of water, yeast and any remaining sugar, then the distillate is usually distilled again to purify the ethanol further
List and draw the needed functional groups for year 12
Check notes
For the functional group of unsaturated hydrocarbon, list the reagents and observation
.Add a few drops of bromine water to the sample and shake
.Bromine water decolourises
What happens when you mix a carbonyl and acidified potassium dichromate (VI)
Ketones - no change
Aldehydes - orange turns green
What happens when you mix carbonyl and fehling solution?
Ketones - no change
Aldehydes - dark red precipitate
What happens when you mix carbonyl and tollens’ reagent?
Ketons - no silver mirror
Aldehydes - silver mirror
What happens when you mix carboxylic acid with a reactive metal?
effervescence (hydrogen)
What happens when you mix carboxylic acid with a metal carbonate?
effervescence (carbon dioxide)
What happens when you mix alcohol (warm) with an equal volume of carboxylic acid and a few drops of H2SO4?
Sweet smell of an ester after a short time
Give an example of a compound with multiple functional groups
Paracetamol, aspirin, niacin
What happens to the reactivity of functional groups when there are multiple in a compound?
The chemical reactivity of each functional group is usually the same as it would be on its own
What is aspirin?
Aspirin is an analgesic (painkiller) and was original obtained from willow bark. It has a number of functional groups including a carboxylic acid and an aromatic ring
What is Niacin?
Vitamins help our bodies to work more efficiently. Many vitamins are complex organic molecules with several functional groups. Vitamin B3, also known as niacin, has the IUPAC name pyridine-3-carboxylic acid. It is needed for healthy hair, eyes, skin and liver. This organic molecule contains nitrogen in a stable structure known as a pyridine ring and a carboxylic acid functional group.
Draw the synthetic routes
check notes
Uses of Mass spectroscopy
- Identify molecular mass of unknown compounds
- Determine the abundance of each isotope in an element
- Gain information about the structure and chemical properties of molecules
Modern uses of mass spectroscopy
- Monitor breath of patients during surgery
- Detecting banned substances in athletes
- Analysing molecules in space
- Detecting toxic chemicals in marine life
How is mass spectroscopy used in space? example
.Mass spectrometers have been included on-board several space probes
.In 2005, the Huygens probe landed on the surface of Titan, the largest moon of Saturn
What did the Huygens probe find out about the atmosphere of Titan?
.During the descent towards the surface of Titan, the mass spectrometer analysed the atmospheric composition at various heights, it was found that the atmosphere consists of mainly nitrogen and methane but the presence of argon-40 was also detected
What does a mass spectroscopy do?
.Determines the mass of a molecule or isotope by measuring mass to charge ratio of ions
How, basically, does a mass spectroscopy work?
.Sample introduced via a sample inlet
.Ionisation of sample by electron impact, chemical ionisation, electrospray or laser
.Ions accelerated into mass analyser
.Ions separated due to mass-to-charge ratio by deflection from magnetic field or time of flight
.Ions detected and spectrum generated by computer
Steps of mass spectroscopy
Vaporisation, ionisation, acceleration, deflection, detection
In depth how does mass spectroscopy work
.Vaporization – the sample material is introduced into the spectrometer as a gas, solid samples first need to be heated and vaporized
.Ionisation – As the sample vapour passes across the electron beam, high-energy electrons in the beam knock out electrons in the sample atoms, ionizing them into positive ions
.Acceleration – an electric field is created using a series of negatively charged plates, the positive ions are attracted towards these plates and accelerated towards an electromagnet
.Deflection – the electromagnet creates an electromagnetic field (EMF) that deflects the ions, the amount by which they are deflected depends on their mass to charge ration (m/z) (high m/z deflects a small amount, low m/z deflects a large amount, specific m/z deflected to the collection plate), ions with a specific m/s for a given strength of the EMF are deflected through a slit in a negatively-charged collector plate onto a detector screen
.By varying the strength of the EMF, ions with different m/z values can be deflected through a narrow slit and on to the collector plate
.Detection – Once ions strike the collector they induce a current, which is amplified and converted into a mass spectrum, the more ions of a particular m/z, the greater the current and the larger the peak
What happens when molecules become ionised in mass spectroscopy? Example equation
Molecules become ionised and lose an e-, giving a molecule ion M+
C2H5OH + e- C2H5OH+ + e-
In mass spectroscopy, is the mass loss of e- noticeable?
.The mass loss of e- is negligible
In mass spectroscopy, molecular ion mass =
.Molecular ion mass = molecular mass of compound
In mass spectroscopy, what is detected and analysed?
.Molecular ion detected and analysed
How is fragmentation caused in mass spectroscopy? Example
.Excess energy from ionisation can be transferred to molecular ion making it vibrate
.This can cause bonds to weaken and can split molecular ions into fragments (fragmentation)
C2H5OH+ CH3 + CH2OH+
Are molecular ion fragments detected in mass spectroscopy?
Yes
How can unknown compounds be identified with mass spectroscopy?
.Although the molecular ion peak for 2 isomers will be the same m/z value, fragmentation patterns will be different
.Each organic compound has a unique mass spectroscopy, which can be used as a ‘fingerprint’ for identification
How can you get molecular mass from mass spectroscopy?
The peak with the highest m/z is formed by the molecular ion, and the value of m/z is equal to the relative molecular mass of the compound
.The peak at the highest m/z on the mass spectrum is formed by the heaviest ion that passes through the spectrometer
.Unless all molecules of the original substance break up, this corresponds to the molecular ion of the sample substance
.Although MS can be analysed by viewing it is now often linked to a …
… database and a match found which gives identification of an unknown compound
What is the M+1 peak?
.You will also see a very small peak one unit after the M+ peak, this is referred to as the M+1 peak
Why is the M+1 peak there?
.The M+1 peak exists as 1.1% of carbon is present as the carbon-13 isotope, this will mean a small number of molecules have a carbon-13 atom, and hence a mass one unit greater than the Mr (M peak)
Number of carbon atoms =
((height of M+1 peak)/(height of M peak)) x 100
What can high resolution mass spectrometery not do?
High resolution mass spectrometry cannot differentiate between structural isomers using the M+ peak alone
Covalent bonds can absorb what?
Infrared energy
.Different bonds absorb different __________ of infrared energy
wavelengths
Bonds can also vibrate in different ways – these are called what?
Molecular vibrations
Methanal can undergo symmetrical stretching of the carbon-hydrogen bonds, what does this mean?
this means that both carbon-hydrogen bonds stretch in time with each other
Methanal can undergo asymmetrical stretching of the carbon-hydrogen bonds, what does this mean?
this means that the carbon-hydrogen bonds stretch out of time with each other
Methanals carbon-oxygen bond can also stretch as a result of what?
absorbing infrared energy
.Carbon hydrogen bonds can also absorb infrared energy causing them to …
… bend
.Different types of stretches and bends are caused by different _________ of infrared energy
wavelengths
.Energy from infrared radiation is only transferred to a bond if …
… the bond has a dipole that changes as it vibrates
Does the symmetical stretch in carbon dioxide occur? Why?
.The symmetrical stretch in carbon dioxide does not result in an overall change in dipole of the molecules so no IR energy is transferred to the bonds
Does the asymmetical stretch in carbon dioxide occur? Why?
.The asymmetrical stretch in carbon dioxide does result in an overall change in dipole of the molecule, so IR energy is transferred to the bonds
Does the bending in carbon dioxide occur? Why?
.The bending vibration in carbon dioxide does result in an overall change in dipole of the molecule, so IR energy is transferred to the bonds
.One asymmetrical stretch and one bend will both result in a change in the overall dipole, and so are said to be what?
IR Active
.The IR spectrum of carbon dioxide shows what? why?
two absorption due to these vibrations (asymmetrical and bending)
.On absorbing infrared radiation bonds will vibrate, either _____ or _____
bending or stretching
.Every bond vibrates with a unique frequency, this is picked up by the …
… spectrometer
Vibration depends on what?
- Bond strength
- Bond length
- Mass of the bonded atoms
What does an infrared spectrometer do?
.An infrared spectrometer records the frequencies of infrared energy absorbed by a sample
How does an infrared spectrometer work?
.The sample of solid or liquid is prepared by being pressed between two salt plates, which are transparent to infrared radiation
.The sample is placed in the infrared spectrometer and the cover is closed
.Infrared radiation is fired at the sample, some frequencies are absorbed, while the remaining frequencies pass through and are registered by the detector on the far side of the sample
.The radiation that doesn’t pass through has been absorbed by bonds in the material, causing them to stretch and/or bend, the pattern of frequencies absorbed is unique to the substance being tested
.The results of the spectroscopy are plotted on a screen as a graph of percentage transmission of radiation against wavenumber
Draw a diagram of an infrared spectrometer
check notes
For infrared spectrometery, what is a peak?
A peak (downwards is still a peak) is characteristic of a vibration of a particular group
How do breathalyzers work at the station?
.At the police station, the motorist blows into a more accurate breathalyzer, containing an IR spectrometer
.The breathalyzer calculates the percentage of alcohol in the breath by looking at the size of the absorption due to the C–H bond stretch in the alcohol
How can infrared spectrometery b used in forensic science?
to analyse paint fragments from vehicles in hit-and-run offences
What are some uses of infrared spectrometery?
- Monitoring the degree of unsaturation in polymers
- Quality control in perfume manufacture
- Drug analysis
Bond: C-O
Location:
Wavenumber (cm-1):
Location: Alcohols, esters, carboxylic acids
Wavenumber (cm-1): 1000-1300
Bond: C=O
Location:
Wavenumber (cm-1):
Location: Aldehydes, ketones, carboxylic acids, esters, amides
Wavenumber (cm-1): 1640-1750
Bond: C-H
Location:
Wavenumber (cm-1):
Location: Organic compounds with a C-H bond
Wavenumber (cm-1): 2850-3100
Bond: O-H
Location:
Wavenumber (cm-1):
Location: Carboxylic acids
Wavenumber (cm-1): 2500-3300 (very broad)
Bond: N-H
Location:
Wavenumber (cm-1):
Location: Amines, amides
Wavenumber (cm-1): 3200-3500
Bond: O-H
Location:
Wavenumber (cm-1):
Location: Alcohols, phenols
Wavenumber (cm-1): 3200-3550 (broad)
What are important functional groups to know for IR spectrometry AS?
- O-H (hydroxyl) group for alcohols
- C=O (carbonyl) group for aldehydes and ketones
- COOH (carboxyl) group in carboxylic acids
What is an infrared spectrum?
.An infrared spectrum is a plot of transmission of infrared radiation against wavenumber
What is wavenumber?
1/wavelength
What are dips in IR spectrums caused by?
.Any wavelength that is absorbed by the sample will transmit less than the others, forming a dip or ‘peak’ in he graph
What do peaks at different points on IR spectrums represent?
.Peaks at different wavenumbers identify different functional groups
What is the fingerprint region on an IR spectrum and where is it?
.The region below 1500cm-1, usually called the fingerprint region, has many peaks that are difficult to assign
.The pattern of these peaks is unique to a particular compound
What is the units of wavenumber?
Cm-1
How can a substance be identified from its fingerprint region?
.A substance may be identified by comparing the IR spectrum to a database of reference spectra
.An exact match in the fingerprint region identifies a compound
