6:Organic Chemistry I Flashcards
What is a homologous series?
A group of compounds that have the same functional group and general formula
- each successive member is increased by CH2
What is the suffix for an alkane?
-ane
What is the prefix for a branched alkane?
Alkyl-
What is the suffix for an alkene?
-ene
What is the suffix for an alcohol?
-ol
What is the suffix for an aldehyde?
-al
What is the suffix for a ketone?
-one
What is the suffix for a carboxylic acid?
- oic acid
What is the prefix and suffix for a cycloalkane?
Cyclo- -ane
What are the steps of nomenclature?
1) Find the length of the stem
2) Functional group will give the suffix
3) Number the carbon chain so that the functional group sits on the lowest possible carbon
4) Make a note of the carbon number the functional group is attached to. Place this number before the suffix
5) Any side chains/less important chains are written as prefixes in alphabetical order
What is a chemical mechanism?
They are curly arrows that show the movement of electrons
- the curly arrow starts from an area of electrons to an electron deficient area
What are the types of mechanisms?
- Radical substitution
- Electrophilic addition
- Nucleophilic substitution
What is radical substitution used for?
Reacting halogens to alkanes to make halogenoalkanes
What is electrophilic addition used for?
Adding halogen and hydrogen halides to alkenes to make halogenoalkanes
What is Nucleophilic Substitution used for?
Primary halogenoalkanes and aqueous hydroxide to make alcohols.
Amines are made by reactions with ammonia
What are structural isomers?
Substances with the same molecular formula but different structural formula
What are the three different types of structural isomers?
- Chain
- Positional
- Functional group
What are chain isomers?
Isomers with the same molecular formula but different arrangement of the carbon skeleton
What are positional isomers?
Isomers with the same molecular formula but different position of the functional group on the carbon skeleton
What is a functional group isomer?
An isomer with the same molecular formula but different functional group
What are alkanes?
Saturated hydrocarbons
What are cycloalkanes functional group isomers with?
Alkenes
What is bond fission?
The breaking of a covalent bond
What are the two types of bond fission than can occur?
- Heterolytic fission
- Homolytic fission
What happens during heterolytic fission?
The bond break but the electrons are distributed unevenly to form two different ions
What happens during homolytic fission?
The bond breaks with the pair of electrons in the bond being shared equally to form two uncharged radicals.
What are the three stages of free radical chain reactions?
1) Initiation
2) Propagation
3) Termination
What happens during initiation in free radical chain reactions?
Radicals are produced normally using either visible light or UV (this process is called a photochemical reaction).
The bond breaks producing two radicals .
What happens during propagation in free radical chain reactions?
- The Cl radical reacts with a methane molecule to make a methyl radical
- The methyl radical reacts with a Cl2 molecule forming chloromethane and a Cl radical
This Cl radical can react with more methane thus making this a chain reaction
What is the equation that occurs during initiation in free radical chain reactions of making chloromethane?
Cl - Cl —> 2Cl°
UV used to produce this
What is the equation that occurs during propagation in free radical chain reaction of making chloromethane?
- Cl° + CH4 —> HCl + °CH3
- °CH3 + Cl2 —> CH3Cl + Cl°
What happens during termination in free radical chain reactions?
Two radicals react to make a stable non-radical molecule
What is the equation that occurs during termination in free radical chain reactions of making chloromethane?
°CH3 + °Cl —> CH3Cl
How can we reduce the likelihood of the production of di,tri and tetrachloromethane being formed when making chloromethane?
By adding excess methane
How does fractional distillation work?
- The vaporised oil enters the column and rises through the trays (the longest hydrocarbons don’t vaporise and run down to the bottom)
- The column has a temperature gradient (cooler at the top)
- As the vapour rises parts of the mixture condenses out at different temperatures.
What are the use of gas?
Used in LPG and stove gas
What are the uses of petrol?
Used in petrol cars
What are the uses of diesel oil?
Used as diesel fuel
What are the uses of kerosene?
Used as jet fuel and heating
What are the uses of fuel oil?
Used in ships and power stations
What are the uses of bitumen?
Used in roofing and tarmac
What are alkenes?
Unsaturated hydrocarbons with at least one double bond
What are sigma bonds?
2 ‘s’ orbitals, they align horizontally to give a single covalent bond
What are pi bonds?
The parallel overlap of 2 ‘p’ orbitals
-> ‘p’ orbitals are dumbbell shaped and when they merge they form two oblong shapes. One
on the top and one on the bottom
Why are pi bonds weaker than sigma bonds?
Sigma binds have direct overlapping of orbitals where as pi bonds have parallel overlapping which is less effective
Why are alkenes more reactive?
The double bond in alkenes have a high electron density
-> alkenes have both sigma and pi bonds between the bond
The pi bond sticks out so it’s open to attack from electrophiles. The pi bond also has low bond enthalpy.
Why are alkanes less reactive compared to alkenes?
- Alkanes only have a sigma bond
- They are non-polar
What are stereoisomers?
Isomers with the same structural formula but different arrangement of atoms in a space
What shape are atoms bonded to C=C bond?
Planar
Can atoms rotate around the C=C bond?
No, they are rigid
What is an Entgagen (E) isomer/trans-isomer?
Isomers that have the same group on the opposite side of the double bond (diagonal)
What is an Zusammen (Z) isomer/cis-isomer?
Isomers that have the same group on the same side of the double bond (horizontal)
How can we determine if an isomer is an E/Trans or Z/Cis isomer if there are four different groups around the double bond?
We use the Cahn-Ingold-Prelog rules
What are the Cahn-Ingold-Prelog rules for stereoisomers?
Rule 1: Label carbons on the double bond as ‘carbon1’ and ‘carbon2’
Rule 2: Calculate the atomic number of the first element directly bonded to the C=C. The atom with the highest atomic number is given higher priority
-> If atomic number is the same, check further down the chain to workout the priority
Why are alkenes attacked by electrophiles?
The double bond has high electron density. The electrophile adds to the molecule.
What are electrophiles?
Substances which are electro pair acceptors.
- they are deficient in electrons
What are examples of electrophiles?
- positively charged ions
- polar molecules (due to the δ+ part)
Where does the curly arrow start from electrophilic addition?
From the double bond
What conditions are required to form ethane from ethene (electrophilic addition)?
React with hydrogen gas.
150°C
Nickel catalyst
What is the chemical test for alkenes?
Decoloration of bromine water (addition reaction)
What is the colour change in the addition of bromine for the test for alkenes?
Brown-orange Bromine water turns colourless
What are the steps for the addition of bromine?
1) Br2 is polarised as electrons in the double bond (of alkene) repels electrons in Br2
2) An electron pair in the double bond is attracted to the δ+ Bromine and forms a bond (this breaks the Br-Br bond)
3) A carbocation intermediate (C+) is formed and the δ- Bromine is attracted to it
4) Colourless dibromoalkane is formed
What are the products of the hydration of alkene?
Alcohols
What conditions are used in the hydration of alkenes?
Steam and an acid catalyst (H+)
How can we make ethanol by the hydration of alkenes?
By reacting steam and ethene with a phosphoric acid catalyst.
A temperature of 300°C and pressure of 60atm is needed
- *this is a reversible reaction*
How are alcohols formed from alkenes?
- hydration
- acidified potassium manganate (VII)
How does adding acidified potassium manganate (VII) to alkenes turn them into alcohol?
Potassium manganate (VII) is an oxidising agent and oxidises the alkene to make a diol
What is the observation when acidified potassium manganate (VII) reacts with ethene?
Purple to colourless
What forms when alkenes react with hydrogen halides?
Halogenoalkanes
Describe the mechanism for the addition of hydrogen halide using HBr as an example.
1) HBr is polarised
2) An electron pair in the double bond is attracted to δ+ hydrogen and forms a bond. This breaks the H-Br bond
3) A carbocation intermediate is formed and Br- is attracted to C+
4) Bromoethane is formed
What is cracking?
The breaking of long hydrocarbon chain alkanes to shorter (more useful) hydrocarbons
What are the two types of cracking?
- thermal
- catalytic
What are the conditions required for thermal cracking?
1000°C and 70atm of pressure
What tends to be the main products of thermal cracking?
Alkenes , use to make polymers such as plastics
What are the conditions needed for catalytic cracking?
450°C with slight pressure and zeolite catalyst (to lower the temperature)
What tend to be the main products of catalytic cracking?
Aromatic hydrocarbons, useful in fuels for vehicles
What is an aromatic compound?
A compound that contains a benzene ring
What is a benzene ring?
Six carbons in a ring with a delocalised electron system
What is reforming?
Converting straight-chain alkanes into either branched-chain alkanes and/or cyclic hydrocarbons by heating them with a catalyst (platinum) to make them burn more efficiently
What compounds contribute to acid rain?
SO2 and oxides of nitrogen
Why is carbon monoxide bad?
It’s poisonous as it binds with haemoglobin better than oxygen
How can carbon monoxide be removed?
By using a catalytic converter
Why is soot bad?
It causes breathing problems
Makes buildings dirty
Clogs up engines
What happens when fossil fuels with sulphur based impurities burn?
Sulphur reacts with oxygen to form sulphur dioxide
-> sulphur dioxide is an acidic gas. It reacts with water to form sulphuric acid which causes acid rain (same can be said for oxides of nitrogen)
What metals do catalytic converters contain?
Platinum, rhodium and iridium metals
What are catalytic converters?
A device found in a vehicle to help reduce the amount of unburnt hydrocarbons and oxides of nitrogen from going into the atmosphere
What is biodiesel?
Diesel made from refining oils and fats
What is biogas?
Gas made from the breakdown of organic matter
What are the advantages of biofuels?
- they are renewable -> more sustainable than fossil fuels
- they are carbon neutral
What are the disadvantages of biofuels?
- expensive to convert to biofuel
- it may lead to a shortage of food growing land
What determines the amount of each product formed from reacting hydrogen halide with unsymmetrical alkenes?
There are two products.
It is determined by the stability of the carbocation intermediate
In the reaction between hydrogen halides and unsymmetrical alkenes, what makes the carbocation more stable?
The more alkyl groups bonded to the carbocation the more stable it will be
Why is a carbocation more stable when there are more alkyl groups attached to it?
The alkyl groups push electrons towards the positive carbocation, stabilising it.
Which carbocations are the most stable?
Tertiary (most stable) -> Secondary -> Primary (least stable)
What is Markownikoff’s Rule?
The major product when we add a hydrogen halide to an unsymmetrical alkene is where the hydrogen adds to the carbon with the most number of hydrogen attached to it already.
What are the monomers for addition polymers?
Alkenes
What are the two types of polymers?
- Natural (e.g. proteins and natural rubber)
- Synthetic (e.g poly(ethene) and poly(propane))
Why do most polymers need to be disposed carefully?
They are not biodegradable
What points are considered when making sustainable polymers?
- Reactants
- Solvents
- Raw materials
- Energy
- Waste
- Longevity
What are the advantages of biodegradable polymers?
- Crude oil doesn’t need to be used (which is non-renewable)
- Plant based polymers degrade and release CO2. This CO2 is absorbed by plants used to make the polymer
- Over the product’s lifetime plant based polymers use less energy to make than oil based ones
What are primary halogenoalkanes?
When the halogen is attached to the carbon which is attached to one alkyl group.
What are secondary halogenoalkanes?
When the halogen is attached to the carbon which is attached to two alkyl group.
What are tertiary halogenoalkanes?
When the halogen is attached to the carbon which is attached to three alkyl group.
What do halogenoalkanes form when they react with water?
They form alcohols via nucleophilic substition
Why is the reaction of halogenoalkanes slower with water than a hydroxide?
Hydroxides are stronger nucleophiles than water, so the reaction in quicker
What determines the reactivity of halogenoalkanes?
The bond strength
-> the halide ion gets larger down the group and this leads to a weaker bond
Which halogenoalkanes react the quickest?
Tertiary (quickest) —> Secondary —> Primary (Slowest)
In the halogen-carbon bond in a halogenoalkane, which atom is delta negative?
The halogen
(It’s more electronegative so it’ll pull the electrons towards itself)
What is a nucleophile?
A substance that is an electron donor
What are some example of nucleophile? (need to know for spec)
Ammonia - NH3
Hydroxide ion - OH-
Cyanide ion - CN-
What are the conditions required for the reaction of halogenoalkanes and hydroxide ions in nucleophilic substitution?
1) Warm aqueous sodium hydroxide (source of OH ions) -> water could be used but it’s a much slower reaction
2) Must be carried out in reflux
What happens when a halogenoalkane reacts with hydroxide ions via nucleophilic substitution?
The C-X bond breaks, both electrons move from the bond to the halogen. A new bond is formed between OH- and carbon
What is the product when halogenoalkane reacts with hydroxide ions via nucleophilic substitution?
Alcohol + halide ion
What are the conditions required for the reaction of halogenoalkanes and cyanide ions in nucleophilic substitution?
1) Warm ethanolic potassium cyanide (source of CN ions)
2) Carried out under reflux
What happens when a halogenoalkane reacts with cyanide ions via nucleophilic substitution?
The C-X bond breaks, both electrons move from the bond to the halogen. A new bond is formed between the CN- and carbon.
- as CN- has an extra carbon the carbon stem changes, therefore changing the name
What is the product when halogenoalkane reacts with cyanide ions via nucleophilic substitution?
Nitrile + halide ion
What are the conditions required for the reaction of halogenoalkanes and ammonia in nucleophilic substitution?
1) Heat with ethanolic ammonia
2) Must have excess ammonia
What happens when a halogenoalkane reacts with ammonia via nucleophilic substitution?
1) Ammonia will attach the δ+ carbon and will replace the halogen forming an intermediate
2) Another molecule of NH3 acts as a base by reacting with hydrogen (this is why we need the excess NH3)
What is the product when halogenoalkane reacts with ammonia via nucleophilic substitution?
Amine + ammonium ion (which reacts with the halide ion)
What are the conditions required for the reaction of halogenoalkanes and hydroxide ions in an elimination reaction?
1) Warm ethanolic sodium hydroxide (source of OH- ions)
2) Carried out under reflux
What happens when a halogenoalkane reacts with hydroxide ions via an elimination reaction?
1) The OH- ions will attach the hydrogen on a carbon adjacent to the carbon attached to the halogen. OH- acts as a base (proton acceptor) forming water.
2) The electrons in the bond move to form a double bond between two carbons
3) The C-X bond breaks, both electron move from the bond to the halogen
What is the product when halogenoalkane reacts with hydroxide ions via an elimination?
Alkene + water + halide ion
When reacting a halogenoalkane with sodium hydroxide, how do we know if the reaction will be elimination (forming alkene) or substitution (forming alcohol)?
The solvent decides whether the reaction is elimination or substitution
- When using ethanol as a solvent (OH acts as a base) - alkene is formed
- When using water as a solvent (OH acts as a nucleophile) - alcohol is formed
- When using a mixture of both solvents, both products are formed
How are chloroalkanes made?
By reacting alcohols with either PCl5 or HCl
- PCl5 used for Primary and Secondary
- HCl used of Tertiary
What are the products from the chlorination of alcohols with PCl5?
Chloroalkane + Hydrogen Chloride + Phosphorous Oxychloride
What are the conditions for the chlorination of alcohols with PCl5?
Room temperature (reaction is very vigorous so no heating is needed)
What are the products formed from the chlorination of alcohols with HCl?
Chloroalkane + Water
What conditions are needed for the chlorination of alcohols with HCl?
Room temperature
Which alcohols react the fastest in chlorination?
Tertiary alcohols
How are bromoalkanes made?
When an alcohol is reacted with a bromide ion source (KBr) and an acid catalyst (50% concentrated H2SO4) is used.
1) KBr reacts with H2SO4 to form HBr
2) Alcohol reacts with HBr
What are the products from the reaction of alcohol and bromide ions?
Bromoalkanes + Water
How are iodoalkanes made?
By reacting alcohols with PI3
What are the products when reacting alcohols with PI3?
Iodoalkane + phosphorous acid
What conditions are required for the forming of iodoalkanes?
Heated under reflux
What is dehydration?
A chemical change in which hydrogen and oxygen are eliminated in a ratio of 2:1 and a C=C bond is formed
What do alcohols form when they are dehydrated?
Alkene + Water
What is required for alcohols to be dehydrated?
A dehydrating agent (an acid catalyst). Either H2SO4 or H3PO4.
What happens during the dehydration of an alcohol?
An OH group and a hydrogen from an adjacent carbon is removed and a C=C bond is formed
What can the dehydration of non-primary alcohols lead to?
3 different alkenes forming (positional isomers and E/Z isomers)
What is the oxidising agent for the oxidation of alcohols?
Potassium dichromate
What happens to drichomate during the oxidation of alcohols?
It gets reduced.
Dichromate ions (orange) become chromium(III) ions (green)
What are primary alcohols oxidised to?
Aldehydes, them carboxylic acids
What must you do to stop the formation of carboxylic acid when oxidising a primary alcohol?
Once aldehyde is formed, distill the product. (Aldehyde has a lower boiling point than alcohols)
What are secondary alcohols oxidised to?
Ketones
What are tertiary alcohols oxidised to?
They can’t be oxidised using dichromate
Why do sigma bonds have high enthalpy?
There is a strong electrostatic attraction between the nuclei and shared pair of electrons due to the high electrons density between the nuclei.
Why is ethanol used in the hydrolysis of halogenoalkanes?
Halogenoalkanes are insoluble in water, ethanol ensures the halogenoalkane dissolves so it can react with the water molecules.
What is the equation between carbon monoxide and nitrogen oxide in a catalytic converter?
2CO + 2NO —Pt(s)—> 2CO2 + N2
What is the equation between oxygen and carbon monoxide in a catalytic converter?
2CO + O2 —> 2CO2
Why do branched or cycloalkanes have a lower boiling point than straight chained alkanes?
They have a lower surface area/ not so closely packed together. This means the intermolecular forces are weaker.
How many lone pairs does a hydroxide ion have?
Three
How many lone pairs does a cyanide ion have?
One
How many lone pairs does a ammonia molecule have?
One
How many lone pairs does a halide ion have?
Four
What is the test for chemical aldehydes?
Blue Fehling solution will turn brick red
What is the chemical test for carboxylic acid?
React with sodium carbonate to form bubbling
