Chapter 11 +12 +13 alkenes and alkanes and new organic chem Flashcards
Define organic chemistry
The chemistry of carbon containing compounds
Define hydrocarbon
Organic compounds that contain C&H atoms only
Define unsaturated hydrocarbons
The presence of multiple carbon carbon bonds like double carbon or triple carbon bonds
Define aliphatic hydrocarbons
A compound containing C and H joined together in straight chains, branched chains or non- aromatic rings with or without side chains
Define functional groups
A group of atoms responsible for the characteristics reactions of a compound
Define homologous series
A series of organic compounds with the same functional group but with each successive member differing by CH2
Define general formula
The simplest algebraic formula of a member of a homologous series
Define structural formula
The minimal detail that shows the arrangement of atoms in a molecule
Define displayed formula
The relative positioning of atoms and the bonds between them ie the structure drawn out including all the bonds
Define skeletal formula
The simplified organic formula, shown by removing H atoms from alkyl chains, leaving just a C skeleton and associated functional groups
Define aromatic
A compound containing benzene ring
How many bonds can C form?
4
How many bonds do H atoms form?
1
How many bonds do O atoms form?
2
How many bonds do N atoms form?
3
Define structural isomers
Compounds which have the same molecular formula but different structural formulae
Define homolytic fission
When a covalent bond breaks and each bonding atom receives 1 electron from the bonded pair, forming 2 radicals
Define radical
A species with an unpaired electrons
Where does homolytic fission occur?
In non polar molecules
Define heterolytic fission
When a covalent bond breaks and 1 bonded atom receives both electrons from the bonded pair
Explain heterolytic fission
A positive and negative ion are formed. When the bond breaks the bond will go to the atom which is most electronegative so it will receive both electrons from the 2 atoms
What are alkanes ?
Are saturated hydrogens that have c-c and c-h
The bonding between the C and H atoms is what type of bond
Sigma bond
Sigma bonds form when ….
2 orbitals overlap over a double bond
What affects the boiling point of alkanes?
Chain length
Branching
Explain how chain length affects boiling points
As the chain length increases, the molecule has more electrons, the strength of the London forces increases and therefor more energy is needed to overcome the forces of attraction and therefore boiling point increases
Explain how branching affects boiling points
If an alkane has 2 isomers one of which is branched, the branched chain will always have the lower boiling point.
A non branched isomer will have more points of contact the london forces are therefore stronger so the boiling point is higher
The reactivity of alkanes is ________ and they dont react with many chemicals like other organic substances do
Low
Why is the reactivity of alkanes low?
Because c-c and c-h bonds are strong and they need a lot of energy to create a reaction and also the c-c bonds are non-polar so so they dont attract positively or negatively charged chemicals
Incomplete combustion occurs when there is …..
The products are…..
Insufficient oxygen
Carbon monoxide and or carbon but water is always formed
What problems are associated with the carbon monoxide ?
CO is poisonous and odorless and colourless and so it is difficult to detect
It bonds with haemoglobin and prevents them from carrying oxygen around the body
CO forms in the internal combustion engine
It occurs in homes when oxygen supplies to appliances is blocked
Define substitution
When one atom or group is replaced by another atom or group
Define haloalkane
An alkane molecule in which one or more of the H atoms has been replaced by a halogen atom (F Cl Br I)
Define mechanism
A set of diagrams or series of equations that shows the path taken by electrons in a reaction
What are the reactants of the chlorination of methane?
Chlorine and methane
What conditions are needed for the chlorination of methane?
UV light
What is the name of the substitution that occurs when halogens such as Cl2 and Br2 is with alkanes
Radical substitution
What are the stages of radical substitution?
Initiation
Propagation
Termination
What is initiation and how does it work?
The energy from UV light causes the covalent bond in the Cl2 molecule to break by homolytic fission
Cl2 ——-> 2 Cl•
Explain the steps of propagation
The Cl• radical removes a H atom from methane , forming a methyl radical •CH3 and HCl
The •CH3 radical then reacts with a Cl2 molecule forming CH3Cl and Cl•
This is a chain reaction and occurs until there is no chlorine left
Explain termination
A molecule is reformed when 2 radicals combine
Eg
2Cl• ——-> Cl2
Why is it difficult to create pure products from the radical substitution of alkanes?
Because further substitution reactions occur as once a haloalkane has been produced during the propagation step it can undergo further substitution reactions to form products which contain more than 1 halogen atom
Substitution can happen at different places on the C chain. When the alkanes other than methane/ethane are used halogen atoms can substitute at more than 1 position on the chain
What are alkenes?
Unsaturated hydrocarbons that contain double c-c bond
What are Pi bonds?
Sideways overlap of adjacet p-orbitals above and below the bonding C atoms
A double bond consists of …….
A pi bond and a sigma bonded
The pi bond causes the molecule to have….
Restricted rotation
Around each c atoms there are 3 areas of …… or 3 ……. As the electrons in the bonded region repel each other as far apart as possible, the shape around each C atom is …… with bonded angles of approximately
Electron density
Bonded regions
Trigonal planar
120
Define stereoisomerism
Compounds with the same structural formula but with a different arrangement of atoms in space
Define E/Z isomerism
A type of isomerism in which different groups attached to each C of a Double c-c bond may be arranged differently in space because of the restricted rotation of the double c-c bond
Define cis-trans isomerism
A specific type of E/Z isomerism in which at least 2 of the substituent groups attached to each C atom in the double C-C bond are the same
What is a cis isomer?
Where the 2 identical substituent groups are both above or below the double c-c
What is trans isomerism?
Where one of the identical substituent groups is above and the other is below the double c-c bond
Summarise what the CIP priority rules are
Rules that involve allocating each atom/ group attached to each C in the C-C double bond either a high priority or low priority in order to determine whether the structure is E or Z
Priority is based on …
Atomic number
If there is more than 1 atom in the group when working out CIP priority rules
eg OH then….
You use the atomic number of the 1st atom
What happens if both atoms attached to the C of the C-C double bond are the same?
You look for the 1st point of difference and use the atomic number of these to determine the priority
Why is an alkene more reactive than an alkane?
Because of the presence of the C-C double bond
The pi bond is weaker than the sigma bond so it has a lower bond enthalpy
Define addition
When 2 atoms or groups are added across a double bond
Write an addition reaction equation
Ethene + X-Y ——> 1 X 2 Y ethane
What conditions are needed for catalytic hydrogenation?
150 degrees C
A nickel catalyst
What is catalytic hydrogenation?
It is addition of a hydrogen molecule and a catalyst is needed
Write a word equation for the reaction between ethene and hydrogen
Ethene and hydrogen ——> ethane
Write a symbol equation between ethene and hydrogen
CH2CH2 + H2 ——> CH3CH3
What is addition of a halogen?
What is this reaction called?
When a halogen is added to an alkene to make an organic compound
Halogenation
Write a word equation between propane and bromine
What is this equation called?
Propane and bromine goes to 1,2 1,2 bromopropane
Bromination
Write a symbol equation between propane and bromine
CH2CHCH3+ Br2 ——> CH2BRCHBRCH3
How do you test for an alkene?
Bromine water
It turns from orange to colourless if present
How are haloalkanes formed?
Alkenes react with hydrogen halides
Give 2 examples of a hydrogen halide
HCl - hydrogen chloride
HBr - hydrogen bromide
What happens when an alkene reacts with steam?
An addition reaction called hydration
What conditions do you need for hydration?
300 degrees C
60atm pressure
A catalyst of H3PO4
Define electrophile
An atom or group of atoms that is attracted to an electron rich centre or atom where is accepts a pair of electrons to form a new covalent bond
What does a curly arrow show?
The movement of a pair of electrons
Is bromine a polar or nonpolar molecule?
None polar
What happens to the electron density of the electrons in Br when in contact with an alkene?
The distribution is distorted because of the high electron density in the double C-C bond
Explain the process of electrophillic addition
The Br molecule is made into a temporary dipole with the delta positive attracted to the pi bond with a high electron density. Then an electron pair in the pi bond are attracted to the d+ and the pi bond breaks and a new bond between the c and br atom is formed. This means the Br-Br bond breaks and the shared pair of electrons go to the delta negative br. This is called heterolytic fission. This forms a carbocation and a bromide ion to form and the ion is attracted to the unstable cation. The lone pair from the bromide ion are used to form a bond with the carbocation and 1,2 dibromomethane is formed as the only product
Markownikoffs rule states that
When an unsymmetrical alkene reacts with a hydrogen halide the H of the hydrogen halide forms a bond with the C in the C-C double bond which has the greater number of H atoms and the fewest number of C atoms
When the C+ is attached to a maximum of 1 other C it is a
Primary carbocation
When the C+ is attached to 2C atoms is called a
Secondary carbocation
When the C+ is attached to 3c atoms it is called
A tertiary carbocation
Is a tertiary or primary carbocation more stable?
Tertiary
Explain how the stability of carbocations increases
The more alkyl groups attached to the C+ the greater the stability
Explain what a monomer is like in addition polymerisation
For addition polymerisation monomers have a c-c double bond and are unsaturated
Explain what polymers are like for addition polymerisation
The polymer has no c-c double bond and is therefore saturated
What forms from propene in a polymerisation reaction?
Poly(propene)
