Basic Concepts and Hydrocarbons Flashcards
What is a functional group?
A group of atoms responsible for the characteristic reactions of a molecule
What does nomenclature mean?
Naming organic compounds
How many bonds to carbon form?
4
What is the functional groups of alcohols?
-OH
What is the functional group of carboxylic acids?
-COOH
What is the functional group of alkenes?
-C=C-
How many bonds do oxygen form?
2
What is the general formula?
An algebraic formula that can describe any member of a family of compounds
What is the general formula of alcohols?
CnH2n+1OH
What is a homologous series?
A family of compounds that have the same functional group and general formula
What do consecutive members of a homologous series differ by?
-CH2-
What is the general formula for alkanes?
CnH2n+2
What is the molecular formula?
Gives the actual number of atoms of each element in a molecule
What is the empirical formula?
Gives the simplest whole number ratio between atoms of each element in a compound
How do you find the empirical formula if given the molecular formula?
Divide the molecular formula by the smallest number of atoms for a given element in a molecule
What is the functional group of an ester?
-COO
What is the structural formula?
Shows the atoms carbon by carbon, with the attached hydrogen and functional groups
E.G. Ethane = CH3CH3
What is a displayed formula?
It shows how all the atoms are arranged, and all the bonds between them
What does the skeletal formula show?
Just the carbons, joined in a zig-zag to show where each bond ends
What is an aromatic compound?
An organic compound that contains a benzene ring
What are the 2 ways of drawing a benzene ring?
⏣ or ⌬
What is an aliphatic compound?
Compounds that contain carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings
What is an alicyclic compound?
An organic compound that contains carbon and hydrogen joined together in a non-aromatic ring (doesn’t contain a benzene ring)
What is an alkyl group?
A hydrocarbon fragment with general formula CnH2n+1
What is a saturated compound?
A compound that only contains single carbon-carbon bonds (C-C)
What is an unsaturated compound?
A compound that can contain carbon-carbon double bonds, triple bonds or aromatic groups
In structural isomers, the …. is the same, but the …. is different?
In structural isomers the molecular formula is the same, but the structural formula is different
What are the 3 types of structural isomers?
Chain isomers
Positional isomers
Functional group isomers
What is a chain isomer?
Where the carbon skeleton is arranged differently- as a straight chain or branched in different ways
What is the difference in chemical properties for chain isomers?
The chemical properties are the same
What is the difference in physical properties for chain isomers?
Physical properties (e.g. boiling point) are different because the shape of the molecule has changed
What are positional isomers?
A molecule with the same molecular formula as another molecule, but with the functional group in a different position
Describe the chemical and physical property differences for positional isomers
They have different chemical and physical properties
What are functional group isomers?
A molecule with the same molecular formula as another molecule, but with atoms arranged in different functional groups
Describe the chemical and physical property differences for functional group isomers
The physical and chemical properties are very different
What is the general formula for alkanes?
CnH2n+2
What is a hydrocarbon?
A molecule that contains only Hydrogen and Carbon
Are alkanes saturated or unsaturated?
Saturated, as they contain only carbon-carbon single bonds
What is a cycloalkane?
A type of alkane with one or more non-aromatic carbon rings
What is the agreed system for naming organic compounds?
IUPAC
What does IUPAC stand for?
International Union of Pure and Applied Chemistry
When was the IUPAC set up?
1919
Why was the IUPAC set up?
The aim was to create internationally accepted standards in Chemistry so that research could be shared more easily around the world
How many carbons does Meth- have?
1
How many carbons does Eth- have?
2
How many carbons does Prop- have?
3
How many carbons does But- have?
4
How many carbons does Pent- have?
5
How many carbons does Hex- have?
6
How many carbons does Hept- have?
7
How many carbons does Oct- have?
8
How many carbons does Non- have?
9
How many carbons does Dec- have?
10
When naming organic compounds, what has the suffix -‘ol’?
Alcohols e.g. Methanol
When naming organic compounds, what has the prefix ‘Chloro-‘
Chloroalkanes e.g. Chloromethane
What are the 2 parts to the name of a straight-chain alkane?
- The stem has the name given for however many carbons there are e.g. 5 carbons = Pent-
- All have the ending ‘-ane’
What is the side chain prefix for 1 carbon atom?
Methyl
What is the side chain prefix for 2 carbon atoms?
Ethyl
What is the side chain prefix for 3 carbon atoms?
Propyl
What is the side chain prefix for 4 carbon atoms?
Butyl
What is the side chain prefix for 5 carbon atoms?
Pentyl
What is the side chain prefix for 6 carbon atoms?
Hexyl
How do you name branched alkanes?
Count the longest chain of carbon atoms and then work out what side chains there are
In an alkane, what is the shape and bond angle around each carbon atom?
Tetrahedral, 109.5°
Why is the shape around a carbon atom tetrahedral?
Because there are 4 pairs of bonding electrons, so they all repel each other equally
What is a sigma (σ) bond
A bond formed when 2 orbitals overlap directly between the bonded atoms
How do covalent bonds form?
They can form between 2 atoms if they’re arranged so that the outer atomic orbitals overlap
What determines the strength of a sigma bond?
How well the orbitals overlap
Why do σ bonds have a high bond enthalpy?
Because The high electron density between the nuclei means there is a high electrostatic force of attraction between the nuclei and the shared pair of electrons
What is the strongest type of covalent bond?
σ-bonds
Are alkanes reactive or unreactive?
Unreactive
What are the 2 reasons why alkanes are unreactive?
- The C-C and C-H σ-bonds have a large bond enthalpy, so take a lot of energy to break
- The bonds are non-polar, so they won’t attract any positively or negatively charged particles to react with them
Describe the trend in boiling points with increasing sizes alkanes
The boiling point increases
Why does the boiling point of alkanes increase as they become longer?
Between the molecules are London forces. When the carbon chain gets longer the London forces increase so it takes more energy to overcome them
Why does the strength of the London forces increase with a longer carbon chain?
Because the alkane has a larger molecular surface area so there is more surface contact between the molecules and there are more electrons to interact with
Describe why the boiling point increases for the first 6 alkanes
As the alkane gets longer, the number of electrons in the molecules and the surface contact between molecules increases. So the London forces are stronger, taking more energy to overcome
Which has a higher boiling point, a branched-chain alkane or straight-chain alkane?
Straight-chain alkane
Why do branched-chain alkanes have a lower boiling point than straight-chain alkanes?
Branched-chain alkanes can’t pack so closely together and so have a smaller surface contact - meaning London forces are reduced
Do alkanes undergo complete or incomplete combustion when burned with enough oxygen?
Complete combustion to form CO2 and H2O
Why do smaller alkanes burn more easily?
They’re more volatile (turn into gas easier)
Why do alkanes make good fuels?
Some energy is needed to break the covalent bonds, but a lot more energy is released by forming new product bonds
Larger alkanes release more… than smaller alkanes, because more CO2 and H2O are formed?
Larger alkanes release more energy per mole than smaller alkanes, because more CO2 and H2O are formed?
Name 2 uses of propane?
Central heating and as cooking fuel
What is the molar volume of all gases at standard temperature and pressure?
24 dm^3
What type of combustion occurs if there isn’t much oxygen around when burning an alkane?
Incomplete combustion
What are the products of incomplete combustion?
Carbon Monoxide and Water
Why is carbon monoxide dangerous?
Carbon Monoxide is better at bonding to the haemoglobin in your bloodstream than oxygen is. This means that if you breathe some in, it’ll bond to the haemoglobin, meaning less oxygen reaches your cells
What makes carbon monoxide hard to detect?
It’s a colourless, odourless gas
What is bond fission?
Breaking a covalent bond
What is a single covalent bond?
A shared pair of electrons between 2 atoms
What are the 2 types of bond fission?
Heterolytic fission
Homolytic fission
What is heterolytic fission?
Where the bond breaks unevenly with one of the bonded atoms receiving both electrons from the bonded pair
What are the 2 products of heterolytic fission?
A positively charged cation and a negatively charged anion
What is the general equation for heterolytic fission?
XY —> X+ + Y-
What is homolytic fission?
Where the bonds break evenly and each bonding atom receives one electron from the bonding pair
What are the products of homolytic fission?
2 electrically uncharged radicals
What is a radical?
A particle with an unpaired electron
What is the general equation for homolytic fission?
XY —> X• + Y•
What is a reaction mechanism?
A diagram using curly arrows to show the movement of electrons in a reaction
How are haloalkanes formed?
By reacting a halogen with an alkane
What is a photochemical reaction?
A reaction that’s started by light
How does a haloalkane form from the reaction between a halogen and an alkane?
During the formation of the haloalkane, the Hydrogen atom is replaced by a halogen atom in a radical substitution reaction
Describe the reaction of the synthesis of chloromethane
A mixture of methane and chlorine exposed to UV light reacts (with a small explosion) to form chloromethane
What is the equation for the synthesis of chloromethane?
CH4 + Cl2 —> CH3Cl + HCl
What are the 3 stages of the reaction mechanism for the synthesis of chloromethane?
Initiation
Propagation
Termination
What occurs in the initiation step of a reaction mechanism?
Radicals are produced
What is photodissociation?
When the sunlight provides enough energy to break some of the covalent bonds
What is the equation for the initiation step in the reaction mechanism of the synthesis of chloromethane?
Cl2 —> 2Cl• (homolytic fission)
What occurs in the propagation step of a reaction mechanism?
Radicals are used up and created in a chain reaction
What are the 2 equations for the propagation step for the synthesis of chloromethane?
Cl• + CH4 —> CH3• + HCl (chlorine radical attacks methane)
CH3• + Cl2 —> CH3Cl + Cl• (the new methyl radical then attacks a chlorine molecule)
What occurs in the termination step of a reaction mechanism?
Radicals are used up
What has to happen to terminate a reaction mechanism in the termination stage?
2 radicals have to form together to create a stable molecule (thus terminating the chain reaction)
What are the 3 possible equations for the termination stage in the synthesis of chloromethane?
CH3• + Cl• —> CH3Cl
CH3• + CH3• —> C2H6
Cl• + Cl• —> Cl2
What is the biggest problem with radical substitution if you’re trying to make a specific product?
You don’t only get the product after the termination stage, you get a mixture of products
What other products, apart from chloromethane, are made in the radical substitution of chlorine and methane?
Dichloromethane
Trichloromethane
Tetrachloromethane
What is the best way to reduce the chance of by-products forming in radical substitutions?
Add the alkane in excess
Why does adding the alkane in excess reduce the chance of by-products forming for radical substitution?
Because it means there’s more of a chance for the halogen radical to collide only with the alkane molecules, rather than the haloalkane molecules
What is the general formula of an alkene?
CnH2n
Are alkenes saturated or unsaturated?
Unsaturated, because they contain the double C=C bond
What is the suffix if an alkene has 2 double bonds?
..diene
What is a double bond made up of?
Sigma bond (σ-) and a Pi bond (π-)
How does a σ-bond form?
2 orbitals overlap directly between the bonded atoms
How is a π-bond formed?
When 2 p-orbitals overlap sideways
Which is strongest, σ-bonds or π-bonds?
σ-bonds
Why are π-bonds weaker than σ-bonds?
The electron density is spread out above and below the nuclei, meaning the electrostatic attraction between the nuclei and the shared pair of electrons is weaker
Why is a double bond not twice as strong as a single bond?
Because a double bond contains σ-bonds and π-bonds (which are weaker than σ-bonds) whereas a single bond just contains σ-bonds
Describe what a double bond looks like?
A bit like a hot dog (The π-bond is the bun and the σ-bond is sandwiched in the middle)
Does a double carbon-carbon bond have a high or low electron density?
High, because there are 2 pairs of electrons
Are alkenes reactive or unreactive?
Reactive, because they have a high electron density
What is an electrophile?
An electron-pair acceptor
What does having π-bonds make alkenes reactive?
Because π-bonds stick out above and below the rest of the molecule, so are likely to be attacked by particles that have a low electron density and can accept the pair of electrons
Which is more reactive, alkenes or alkanes?
Alkenes, because they contain a double bond
What is the shape and bond angle around a C=C double bond in an alkene?
Trigonal Planar, 120°
Why is the shape around the carbon in a C=C double bond trigonal planar?
Because the 3 bonds repel each other as much as possible
Why can’t atoms in C=C double bonds not rotate around the bond?
Because the p-orbitals have to be in a fixed position in order to overlap and form a π-bond
What are stereoisomers?
A molecule that has the same structural formula, but its atoms are in a different arrangement in space
Why do some alkenes have stereoisomers?
Because the atoms can’t rotate around the C=C bond
What are the 2 types of stereoisomers?
E-isomers
Z-isomers
Which stereoisomer is it if the 2 priority groups are on the same side of the double bond?
Z-isomer
Which stereoisomer is it if the 2 priority groups are on the opposite sides of the double bond?
E-isomer
Why don’t alkanes form stereoisomers?
Because the atoms can rotate around C-C single bonds
What is the essential requirement for stereoisomers?
Because you must have 2 different groups at each end of the C=C bond
What is the Cahn-Ingold-Prelog (CIP) rules for finding which stereoisomer a molecule is?
The highest priority group at each end of the carbon is the one with the highest atomic number directly bonded to the carbon atom
What is cis-trans isomerism?
A special type of E/Z isomerism where the 2 carbon atoms each side of the double bond have at least one group in common
Which is the cis-isomer?
The molecule with 2 identical groups on the same side of the C=C bond
Which is the trans-isomer?
The molecule with 2 identical groups on opposite sides of the C=C bond
What is electrophilic addition?
A reaction mechanism where a double bond in an alkene opens up and atoms are added to the carbon atoms
Why do electrophilic addition reactions occur?
Because electrophiles haven’t got many electrons, so they attack places which have a high electron density (such as the C=C bond in an alkene)
What is a nucleophile?
An electron-pair donor
What is a carbocation?
Organic ion containing a positively charged carbon atom
How can you make an alkane from an alkene?
Reacting the alkene with H2, so that electrophilic addition reaction occurs
What are the conditions needed to convert an alkene into an alkane by reacting H2 with the alkene?
150°C and a nickel catalyst
What is the product of the reaction between an alkene and a halogen?
A dihaloalkane
What would you observe if you added bromine water to a solution containing C=C bonds?
The solution would change colour from orange to colourless
Why does the solution turn colourless when bromine water is added to a solution containing C=C bonds?
Because the C=C bond opens up and the 2 Br atoms are added to the carbon atoms forming a dibromoalkane
How do you produce an alcohol from an alkene?
Hydrate the alkene by steam
What conditions are needed to hydrate an alkene to form an alcohol?
300°C
60-70 atm
Solid phosphoric acid catalyst
What can be said about the yield of producing ethanol by hydrating ethene?
The yield is low, but the unreacted ethene gas can be recycled
What reaction forms a haloalkane from an alkene?
The electrophilic addition of an alkene reacting with hydrogen halide
What is Markownikoff’s Law?
If the hydrogen halides are added to a symmetrical alkene, such as ethene, only one product can form. If it’s added to an unsymmetrical alkene then there are 2 possible products
What determines how much of each product if formed in electrophilic addition reactions?
How stable the cation formed in the middle of the reaction is
What is a primary cation?
A cation bonded to one alkyl group
What is a secondary cation?
A cation bonded to 2 alkyl groups
What is a tertiary cation?
A cation bonded to 3 alkyl groups
Which carbocation is the most stable?
Carbocations with more alkyl groups, as they’re more stable because the alkyl groups move the electrons towards the positive charge (to stabilise it)
Why are more stable carbocations more likely to form than less stable ones?
The first step of the electrophilic addition is more likely to lead to the formation of the most stable carbocation
What is the product of which there is most of from electrophilic addition called?
Major product
What is a polymer?
A long molecule formed from lots of monomers joining together
What is a monomer?
The individual small alkenes (with a chain length of 2 carbons)
What is an addition polymer?
A long-chain molecule made by lots of small alkene molecules adding together
For addition polymerisation reactions, what letter do you need to right next to both products and reactants?
N, to show that there is repeating units N amount of times
How do you find the monomer of a long-chain polymer?
Find the repeating unit (carbon chain of 2) and add a double bond
Why are polymers not biodegradable?
Because they’re unreactive
Why is polymers not being biodegradable a problem?
Because it means they’re very hard to dispose of
What are 2 advantages of using landfill sites?
They’re cheap
Don’t release toxins such as HCl
What are 2 advantages of burning polymer waste?
Saves on landfill sites
Produces energy
What is a disadvantage of burning polymer waste?
Pollution, as PVS turns into toxic HCl
Give 2 sustainable ways of disposing of polymers?
Burn it to produce energy
Crack it to smaller molecules, more useful molecules
What is PVC?
Polyvinylchloride
Where is PVC used?
In window frames
What is PTFE?
Poly(tetrafluoroethene)
Where is PTFE used?
Lubricants and non-stick frying pans because it’s frictionless
What is poly(propene) used for?
Rope because it’s strong
What are the 3 reasons why we use landfill to dispose of plastic?
If the plastic is difficult to separate from other waste
If plastic is not in sufficient quantities to make separation financially worthwhile
If plastic is too technically difficult to recycle
What are most plastics made from?
Non-renewable oil fractions
Why does recycling plastic make sense?
You’re conserving the non-renewable oil fractions
What are the 2 methods of recycling plastics?
Melting and then remoulding
Cracking into monomers
What happens to the waste toxic gas produced from when you burn plastics?
It’s passed through scrubbers which can neutralise toxic gas such as HCl
What are biodegradable polymers made from?
Can be made from materials such as starch or from hydrocarbon isoprene
What are 2 advantages of using renewable raw materials?
They’re infinite resources, so won’t run out like oil will
Over their lifetime, some plant-based polymers save energy compared to oil-based plastics
What are 2 disadvantages of using biodegradable polymers?
They need the right conditions to decompose
More expensive than oil-based equivalents
Give 2 examples of where biodegradable polymers are used?
Plastic sheeting used to protect plants from frost
Some packaging
