TOPIC 6: ORGANIC CHEMISTRY Flashcards
Name the Nomenclature stems?
Carbon number:
1: meth-
2: eth-
3: prop-
4: but-
5: pent-
6: hex-
7: hept-
8: oct-
9: non-
10: dec-
Define Homologous series?
A homologous series is a group of organic compounds that have the same functional group and general formula.
Consecutive groups of a homologous series differ by -CH2
Prefix or suffix of an alkane?
-ane eg propane
Prefix or suffix of a branched alkane?
alkyl (-yl) eg methyl
Prefix or suffix of an alkene?
-ene eg propene
Prefix or suffix of a halogenoalkane?
chloro/bromo/iodo eg chloroethane
Prefix or suffix of alcohols?
-ol eg ethanol
Prefix or suffix of aldehydes?
-al eg ethanal
Prefix or suffix of ketones?
-one eg propanone
Prefix or suffix of cycloalkanes?
cyclo-…-ane eg cyclohexane
Prefix or suffix of carboxylic acids?
-oic acid eg ethanoic acid
What is addition?
joining two or more molecules together to form a larger molecule
What is elimination?
when a small group of atoms breaks away from a larger molecule
What is substitution?
when one species is replaced by another
What is Hydrolysis?
splitting a molecule into two new molecules by adding H+ and OH- derived from water
What is Oxidation?
any reaction in which a species loses electrons
What is Reduction?
any reaction in which a species gains electrons
Example of radical substitution?
radical subsititution of halogens in alkanes to make halogenoalkanes
Example of electrophillic addition?
electrophillic addition of halogens and hydrogen halides to alkenes, to make halogenoalkanes
Example of nucleophilic substitution?
nucleophilic substitution of primary halogenoalkanes with aqueous potassium hydroxide to make alcohols and with ammonia to make amines
What is a nucleophile?
Nucleophiles are electron pair donors they are often negatively charged ions that contain a lone pair of electrons and are electron rich. Nucleophiles are attracted to electron poor areas so they attack positive ions eg the C+ atom in a polar carbon-halogen bond. (nucleophilic substitution)
What is an electrophile?
Electrophiles are electron pair acceptors they are often postitively charged ions.They ar eelctron poor so they are attracted to places that are electron rich. They like to react with negative ions, atoms with lone pairs and the electron rich area around the C=C bond
What is radical?
Radicals have an unpaired electron and are very reactive. They will react with anything positive, negative or neutral.
What are isomers?
Two molecules are isomers if they have the same molecular formula but different structural formula
Name the three types of structural isomers?
- Chain isomers
- Positional isomers
- Functional group isomers
What are chain isomers?
Chain isomers are when the carbon skeleton can be arranged differently for example a straight chain or branched. These isomers have similar chemical properties but their physical properties like boiling point will be different because of the change in the shape of the molecule
What are positional isomers?
The skeleton and the functional group could be the same only with the functional group attached to another carbon atom. These also have different physical properties and the chemical properties might be different too
What are Functional Group isomers?
The same atoms can be arranged into different functional groups. These have very different physical and chemical properties eg C4H8O2 into butanoic acid and methyl propanoate
When can atoms rotate as much as they want?
Around single C-C bonds
What is the general formula for am alkane?
CnH2n+2
What is an Alkane?
An alkane is a hydrocarbon it only contains carbon and hydrogen atoms. Alkanes are saturated-all the carbon-carbon double bonds are single bonds
What is the bond fission?
The breaking of a covalent bond
What is a single covalent bond?
A shared pair of electrons between two atoms
Define Heterolytic fission
Heterolytic fission is when the bond breaks unevenly with one of the bonded atoms receiving both electrons from the bonded pair. Two different substances can be formed -a positively charged cation and a negatively charged anion.
Define Homolytic fission
Homolytic fission is when the bond breaks evenly and each bonding atom receives one electron from the bonded pair. This produces two electrically uncharged radicals that have an unpaired electron
How are Halogenoalkanes formed?
Halogens react with alkanes in photo-chemical reactions. Photo-chemical reactions are started by ultraviolet light. A hydrogen atom is substituted by chlorine or bromine. This is radical substitution
Describe the reaction mechanism initiation stage to produce radicals in radical substitution
- Initiation: Radicals are produced sunlight provides enough energy to break the CL-CL bond- this is photodissociation. The bond splits equally and each atom gets to keep one electron- this is homolytic fission. The atom becomes a highly reactive radical cl. because of its unpaired electron.
Describe the reaction mechanism propagation stage to produce radicals in radical substitution
- Propagation: During propagation reactions, radicals are used up and created in a chain reaction.
eg
1) Cl. attacks a methane molecule
2) The new methyl radical CH3 can attack another Cl2 molecule and produces a Cl. radical again
3) The new Cl. can attack another CH4 molecule, and so on,until all the Cl2 or CH4 molecules are wiped out
Describe the reaction mechanism termination stage to produce radicals in radical substitution
- Termination: In termination reactions, radicals react together to form stable molecules
1) If two free radicals join together, they make a stable molecule
2) There are heaps of possible termination reactions
What is the issue with Radical Substitution?
- if you are trying to make a particular product then the issue is that you don’t only get the product your after but a mixture of products.
- Another problem with radical substitution is that it can take place at any point along the carbon chain you get a mixture of structural isomers
Describe the process of Fractional distillation
- The crude oil (petroleum) is vaporised at about 350 degrees.
- The vaporised crude oil goes into a fractionating column and rises up through the trays. The largest hydrocarbons dont vaporise and run to the bottom and form a gooey mixture.
- As the crude oil vapour goes up the fractionating column it gets cooler.
- The alkane molecules have different chain lengths and therefore different boiling points so each fraction condenses at a different temperature.
- The hydrocarbons with the lowest boiling points don’t condense they are drawn off at the top of the column.
Why is cracking used?
Heavy large hydrocarbon chains are often not in demand so cracking can be used to break the C-C binds to make them into lighter and smaller hydrocarbons like petrol as they are more in demand
What are the two types of cracking
- Thermal Cracking
2. Catalytic Cracking
What is Thermal Cracking?
- Thermal Cracking takes place at a high temperature of about 1000 degrees ad high pressure of around 70 atm.
- It produces a lot of alkenes.
- These alkenes are used to make valuable products such as polymers.
What is Catalytic Cracking?
- Catalytic Cracking uses a zeolite catalyst at a slight pressure and high temperature of about 450 degrees.
- It mostly produces aromatic hydrocarbons and motor fuels
- Using a catalyst cuts costs as the catalyst speeds up the reaction and a lower pressure and temperature can be used
What is knocking and how to prevent it
- Knocking is where alkanes explode on their own accord when the fuel/air mixture in the engine is compressed
- Straight chain alkanes are the most likely hydrocarbons to cause knocking adding branched chains and cyclic hydrocarbons to the petrol mixture makes knocking less likely to happen
What is reforming?
- Reforming uses a Catalyst (platinum stuck on aluminum oxide) to convert straight-chain alkanes into branched chain alkanes and cyclic hydrocarbons
Equation for alkane+oxygen
in a combustion reaction like this you will get carbon dioxide and water
Incomplete combustion products?
Carbon monoxide,carbon and water (there could also be some carbon dioxide)
When do combustion reactions happen?
Between gases so liquid alkanes have to be vaporised first
Why is carbon monoxide so toxic?
Carbon monoxide binds to the hemoglobin better than oxygen so less oxygen can be carried around the body leading to oxygen deprivation
Acid rain?
Burning fossil fuels that contain sulfur produces Sulfor dioxide gas which when it enters the atmosphere dissolves in moisture and is converted to sulfuric acid
How is nitrogen oxide produced?
When oxygen and nitrogen in the air react together due to the high pressures and temperture in the car engine. When oxides of nitrogen escape into the atmosphere they dissolve in moisture and are converted into nitric acid which can fall as acid rain
What do catalytic converters do and list an equation example?
Catalytic converters stop pollutants such as carbon monoxide from leaving the car. They get rid of these pollutants by using a platinum catalyst
For example: nitrogen monoxide and carbon monoxide can be converted into nitrogen and carbon dioxide eg 2NO+CO–>N2+C02
Name the fossil fuels
Coal, oil and natural gas
Define Biofuels
Biofuels are fuels made from living matter over a short period of time
Name some examples of Biofuels
- Bioethanol: Ethanol can be made by the fermentation of sugar from crops such as maize
- Biodiesel: Made by refining renewable fats and oils such as vegetable oil
- Biogas: Produced by the breakdown of organic waste matter
Problems surrounding Biofuels?
- Petrol car engines and other transport would need their engines to be modified to use fuels with high ethanol concentrations this is also costly so third world countries will not benefit
- The land used to grow crops for fuels cant be used to grow food this means that some countires may not have enough space to grow food for eating
General formula for an alkene?
CnH2n
What is a sigma bond and how is it formed?
- A sigma bond is found in a single covalent bond and is formed when two orbitals overlap in a straight line in the space between the two atoms.
- This gives the highest possible electron density. The high electron density between the nuclei means there is a strong electrostatic attraction between the nuclei and shared pair of electrons.
- This means that sigma bonds have a high bond Enthalpy
What is a pi bond and how is it formed?
- A PI bond is formed when two lobes of two orbitals overlap sideways .Its got two parts to it one below and one above.
- In a PI bond the electron density is spread out above and below the nuclei. This causes the electrostatic attraction between the nuclei and shared pair of electrons to be weaker than in sigma bonds
- PI bonds have a relatively low bond enthalpy
What bonds are found in a single covalent bond?
Sigma Bonds
What bonds are found in a double covalent bond?
A double bond is made up of a sigma bond and a PI bond
Define Covalent bond?
A covalent bond is the strong electrostatic attraction between the two positive nuclei and the shared electrons in the bond
What is an E Isomer?
The same groups are positioned across on opposite sides diagonally
What is a Z isomer?
The same groups are either both below or above the double bond
Feature of double bonds?
- Cant rotate the atoms cannot rotate about the double bond this is what causes alkenes to form stereoisomers
What are stereoisomers
Stereoisomers have the same structural formula but a different arrangement in space.They occur when the two double bonded carbon atoms each have two different atoms or groups attached to them
What rule do you use and describe the rule for isomers when the groups are different
Use the CIP rules
- Atoms with a larger atomic number are given a higher priority assign priority numbers
- Then apply E/Z rule
What is a cis isomer?
A cis isomer is when the same groups are on the same side of the double bond
What is a trans isomer?
A trans isomer is when the same groups are on opposite sides of the double bond
What happens in an electrophilic addition reaction?
in an electrophillic addition reaction the alkene double bond opens up and atoms are added to the carbon atms this is because it is attacked by electrophiles
How can you produce an alkane?
- Adding Hydrogen to C=C bonds (alkenes) produces Alkanes
- It needs a nickel catalyst and a temperature of 150 degrees
- Margarine is made by adding hydrogen to the unsaturated vegetable oils by removing the double bonds you raise the melting point so it is solid at room temperature
How can you produce Alcohols?
- Alkenes can be hydrated by steam at 300 degrees and a pressure of 60-70 atm
- The reaction needs a solid phosphoric acid catalyst
How can you produce Dihalogenoalkanes give an example
- Halogens will react with alkenes to form dihalogenoalkanes
- This is an electrophillic addition
EXAMPLE OF BROMINE:
- The double bond will repel the electrons in Br2 polarising Br-Br
- Heterolytic fission of Br2 occurs, the Br+ will bond with the C atom
- You get a positively charged carbocation intermediate, the Br- now moves over and bonds to the other C atom forming 1,2 dibromoethane
What is the test for carbon-carbon double bonds
Shake an alkene with brown bromine water and the solution quickly decolourises . This is because bromine is added across the double bond to form colorless dibromoalkane
How do you make a diol?
- Shake an alkene with acidified potassium manganate and the purple solution will be decolorised
- The alkene is oxidised and you made a diol
What is Markownikoff’s rule?
The major product from addition of a hydrogen halide to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrogens already attached
What is another way to form a halogenoalkane?
Alkenes can undergo addition reactions with hydrogen halides-to form halogenoalkanes
What is the most stable carbocation?
The tertiary carbocation that has three alkyl groups
What is a polymer?
Many monomers joined together by bonds. The polymer does not include any double bonds
What does a monomer have?
The monomer shows the C=C bond
What can happen to waste plastics?
- Reused
- Buried
- Burned
How can waste plastics be re-used?
- The plastic is sorted into different types
- Some plastics can be recycled by melting and remoulding them
- Some plastics can be cracked into monomers and these can be used to make more plastics
Describe the process in Burning Waste Plastics?
- Waste plastics can be burned this process must be controlled to reduce toxic gases
- Eg polymers that contain chlorine can produce HCL when they are burned- this has to be removed
- Waste gases from combustion are passed through scrubbers which can neutralise gases by allowing them to react with a base
How do chemist ensure that when making polymers it is sustainable?
- Use reactant molecules that are safe and environmentally friendly.
- Renewable raw materials should be used wherever possible.
- Limit waste products
- Energy use should be kept to a minimum
Define Halogenoalkane?
A Halogenoalkane is an alkane with at least one halogen atom in place of a hydrogen atom
What is a primary Halogenoalkane?
A primary Halogenoalkane has two hydrogen atoms and one alkyl group
What is a secondary Halogenoalkane?
A secondary Halogenoalkane has just one hydrogen atom and two alkyl groups
What is a tertiary Halogenoalkane?
A tertiary Halogenoalkane has no hydrogen atoms and three alkyl groups
How can you form Alcohols from Halogenoalkanes?
Halogenoalkanes can be hydrolysed to form alcohols (The carbon halogen bond is broken) just add water this is a nucleophilic substitution reaction
General Equation:
R-X + H20–> R-OH +H+ + X-
Describe the relationship between the halogens, hydrolysis and bond enthalpy
- The larger the halogen the longer the C-X bond and the lower the bond enthalpy.
- Iodoalakenes which is the largest of the halogens has the lowest bond enthalpy so is hydrlyses the quickest
What is nucleophilic substitution?
When a nucleophile bonds with the delta + carbon of a halogenoalkane and be substituted for the halogen
Describe the process of Halogenoalkanes reacting with Aqueous KOH to form Alcohols
Halogenoalkanes react with hydroxide ions by nucleophilic substitution to form alcohols. You can use warm aqueous potassium hydroxide and do the reaction under reflux.
General Equation:
R-X + KOH–> ROH+ KX ( R represents an alkyl group)
What is an alkyl group?
These are alkanes with one H removed eg -CH3 or -C2H5
How do you form a Nitrile?
Reflux a halogenoalkane with potassium cyanide in ethanol, then the cyanide ions will react with the halogenoalkane by nucleophilic substitution to form a nitrile
How do you form an Amine?
- Halogenoalkanes react with ammonia to form amines.
- If you warm a halogenoalkane with excess ethanolic ammonia the ammonia swaps places with the halogen to form a primary amine (nucleophilic substitution)
What is an Amine?
Amines are organic compounds they’re based on ammonia but one or more of the hydrogen atoms are replaced by alkyl groups
How do you get an alkene from a halogenoalkane?
- React a halogenoalkane with a warm alkali dissolved in ethanol, you get an alkene
- The mixture must be heated under reflux
How do you produce a chloroalkane?
- If you react an alcohol with PCL5 (phosphorus pentachloride) a choloroalkane is produced
General Equation: ROH+PCL5–>RCL+HCL+POCL3
2.You can also make chloroalkanes if you react an alcohol with hydrochloric acid
General Equation: ROH+HCL–>RCL+H20
How is a bromoalkane produced?
Alcohols will react with compounds containing bromide ions in a substitution reaction.
- The hydroxyl group -OH is replaced by the bromide so the alcohol is transformed into a bromoalkane
- The reaction also requires an acid catalyst such as 50% concentrated sulfuric acid
How do you make Iodoalkanes?
- You can make an Iodoalkane from an alcohol by reacting with phosphorus triiodide PI3.
- PI3 is usually ade within the rection mixture by refluxing the alcohol with ‘red phosphorus’ and iodine.
General Equation: 3ROH + PI3–>3RI +H3PO3
How do you make Alkenes from alcohols?
- Eliminating water from alcohols in an eleimination reaction can form alkenes.
- The alcohol is mixed with an acid catalyst such as concentrated phosphoric acid. The mixture is then heated
- When an alcohol dehydrates it eliminates water
Key thing to remember from turning alcohols into alkenes?
There are two possible alkene products from one elimination reaction depending on which side of the hydroxyl group the hydrogen is eliminated from
What agent can be used to mildly oxidise alchohols and what is the agent reduced to?
You can use the oxidsing agent acidified dichromate Cr2O7 2-/H+
What do primary alcohols oxidise to?
They oxidise to aldehydes and then to carboxylic acids
What do secondary alcohols oxidise to?
They oxidise to ketones only
What do tertiary alcohols oxidise to?
They wont be oxidised
How do you test whether the compound is an aldehyde or ketone?
Use Benedicts Solution. This is a blue solution of copper II ions dissolved in sodium carbonate.
If ALDEHYDE:
1. The blue copper II ions are reduced to a brick-red precipitate of Copper I oxide
If KETONE:
1. Nothing happens as ketones cant be easily oxidised
What other compound can you use to see whether the compound is an aldehyde or ketone?
You can also use Fehlings solution which contains copper II ions dissolved in sodium hydroxide. The colour change from blue to red in the presence of an aldehyde is the same. Again, nothing happens with a ketone
How do you get an aldehyde from an alcohol?
Gently heating ethanol for example with potassium dichromate solution and sulfuric acid in a test tube should produce ethanal (an aldehyde).
To get just the aldehyde, you need to get it out of the oxidising solution as soon as its formed. You can do this by gently heating excess alcohol with a controlled amount of oxidising agent in distillation apparatus, so the aldehyde is distilled off immediately
How do you get a carboxylic acid from an alcohol?
The alcohol has to be vigorously oxidised. The alcohol is mixed with excess oxidising agent and heated under reflux
