4.1 - Basic Concepts and Hydrocarbons Flashcards
Define the term homologous series
A series of organic compounds having the same functional group ad with each successive member differing by CH2.
Define the term functional group
A group of atoms responsible for the characteristics of a compound
What is meant by an aliphatic compound?
A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings e.g. butane
What is meant by an alicyclic compound?
An aliphatic compound arranged in non-aromatic rings or without side chains E.g. cyclohexene
What is meant by an aromatic compound?
A compound containing at least one benzene ring e.g. Benzene
Define the term saturated
A molecule that only has single carbon to carbon bonds
Define the term unsaturated
A molecule that contains at least one carbon doubled bonded to another carbon atom
Define the term structural isomer
Compounds with the same molecular formula but different structural formulae e.g. butane and 2-methylpropane
What forms can structural isomers occur in?
Chain isomers (different chain length) Positional isomers (functional groups in different positions Functional group isomers (Completely different functional groups)
Do structure isomers have the same PHYSICAL properties?
No they don’t!/ They possess different physical properties such as BP, MP, and differences in density
Do structure isomers have the same CHEMICAL properties?
Most isomers show SIMILAR chemical properties if the same functional group is present. However, it is best to have a look at each structure and apply any knowledge of the chemical which is given to us in the question
Define heterolytic fission
The unequal breaking of a covalent bond, in which one bonding atom receives BOTH electrons from the bonding pair, forming OPPOSITELY CHARGED IONS.
Define homolytic fission
The equal breaking of a covalent bond, in which each atom receives ONE electrons from the bonding pair, forming 2 radicals.
Define the term radical
A high reactive species with an unpaired electron.
Give an overview of alkanes
- Saturated - Each carbon atom has 4 bonds - Usually aliphatic - General formula of CnH2n+2
Explain the tetrahedral shape and bond angle around each carbon atom in terms of electron pair repulsion
Each carbon atom has 4 bond pairs. So they will repel each other equally. This means that the molecule forms a tetrahedral shape around each carbon.
What bond angle do alkanes have?
109.5
Explain why longer chained alkanes have a higher boiling point than shorter chained alkanes
Between the molecules in an alkene, there are induced dipole-dipole interactions. The longer the carbon chain, the larger the surface area. As the surface area increases, it means that there are more induced dipole-dipole forces and these forces. Therefore, as molecules get longer, it takes MORE ENERGY to overcome the induced dipole-dipole interactions, resulting in a higher BP.
Explain how branching effects the boiling point of alkanes?
Branched chains are less compact than straight chains. This means that they can’t pack closely together and they have a smaller surface contact. This means that they have less induced dipole-dipole interactions, so a lower BP.
Explain the low reactivity of alkanes in terms of bond enthalpy
Alkanes have sigma bonds. These sigma bonds have a high bond enthalpy so are difficult to break
Explain the low reactivity of alkanes in terms of polarity
The bonds in alkenes are non-polar so they don’t attract nucleophiles or electrophiles. This means that alkanes don’t react easily.
What products are produced in complete combustion
CO2 + H2O
What products are produced in incomplete combustion
CO + H2O or C +H2O
What is the name of the reaction that turns an alkane into a haloalkane
Free radical substitution.
What regents are needed for free radical substitution
Halogen Alkane
What conditions are needed for free radical substitution?
UV light
What are the names of the 3 steps of free radical substitution
Initiation - Free radicals produced via homolytic fission. Propagation - Free radicals are used and regenerated Termination - Free radicals react together to get a mixture of products.
List problems of Free Radical Sub
Mixture of products Potential of structural isomerism
How can we avoid further substitution? (Free Radical Sub)
Have EXCESS alkane
Give an overview of alkanes
- Unsaturated (C=C bond) - General formula = CnH2n - Bond angle of 120
How are sigma bonds formed?
Overlap of orbitals directly between the bonding atoms
Define the term sigma bond
A covalent bond resulting from the formation of a molecular orbital by end-to-end overlap of atomic orbitals
How are pi-bonds formed?
SIDEWAYS overlap of adjacent p-orbitals above and below the bonding atoms.
Define the term pi bond
A covalent bond resulting from the formation of p-orbitals overlapping side-to-side in a straight line connecting to the nuclei of the atom
List features of a sigma bond
- High bond enthalpy - 3 methods to make it - Electrostatic attraction is localised in one position - End-to-end overlap - Sigma bond is between bonding atoms and nuclei
List features of a pi bond
- Low bond enthalpy - 1 way to make it - Electrostatic attraction is spread out - Sideways overlap - Pi bond is above and below the bonding atoms and the nuclei
What is the bond angle of alkenes and why?
Bond angle = 120 Carbon atoms in a C=C bond and all the atoms bonded to these carbons all lie in the SAME PLANE. Because of the way they’re arranged, they’re actually said to be trigonal planar- the atom attached to each double bonded carbon are at the corners of an imaginary triangle (double check this explanation)
Define the term stereoisomers
Compounds with the same molecular formula and structural formula but with a different arrangement in space
What is needed for stereoisomerism to occur?
- Restriction of the C=C cond - The double bonded carbons each have TWO DIFFERENT ATOMS attached to it
What are the different types of stereoisomers?
E/Z Cis/Trans
Define E/Z isomerism
A special type of stereoisomerism where we name compounds based on their ‘priority’
What does an E isomer mean?
The priority groups are on OPPOSITE sides
What does a Z isomer mean?
The priority groups are on the SAME side
When do we use cis/trans naming systems?
When there are two identical groups attached to each carbon atom CIS = Attached on the same side TRANS = Attached on different sides
Explain the reactivity of alkenes in terms of the relatively low bond enthalpy of the pi bond
The low bond enthalpy of the pi-bond means that the pi-bond is weak and doesn’t require much energy to break.
Explain why alkenes are likely to get attacked by electophiles
Thre is a spread of electron density. Electrophiles are attracted to areas of high electron density.
Describe the addition of hydrogen to alkenes to form alkanes
Name - Hydrogenation Reagents - Hydrogen and an alkene Conditions - Finely divided nickel cataylst Product - Alkanes
Describe the addition of a halogen to an alkene
Name - Electrophilic addition Regents - Halogen Conditions - Room Temp
Describe how we can test for saturation
We use bromine water and we add it to an alkene. Observation - Decolourisation (Orange to colourless)
Describe the additon of water to an alkene
Name - Direct Hydration Regents - Steam (330 degress celsisus) Conditions - Phosphoric acid catalyst and hgh pressure (6MPa) Porduct = Alcohol
Define the term electrophile
Electron pair ACCEPTOR
Define the term nucleophile
Electron pair DONOR
What is Markownioff’s rule?
Major product formed via the MOST STABLE carbocation. OR When a compound (HX) is added to an unymmetrical alkene, the hydrogen (From the HX) becomes attached to the carbon with the most hydrogens already attached to it. This forms the MAJOR PRODUCT.
Define polymerisation
The process in which monomers are turned into to polymers
How can polymers be sustainable?
- Burning them for energy production - Using them as organic feedstock for the production of plastics
List the 3 ways polymers can be disposed
- Reuse - Landfill - Incineration
Describe the disposal of polymers via reusing them
Polymers can be reused if we remould them (melting it down and remoulding into something new - Can be cracked into smaller monomer units (cracking forms an alkene and alkane)
What is the problem with reusing polymers?
We need to separate plastics out and not all plastics can be recycled and then resued. Therefore, there is a COST aspect to this. Furthermore, energy is needed to remould the plastic, so it is not fully sustainable (not full environmentally friendly)
Describe the disposal of polymers via landfill
Plastics are put in landfill as they are too difficult to recycle. They are too difficult to recycle because they are unreactive
Describe the disposal of polymers via incineration
Polymers can be incinerated to produce energy. However, the burning of certain polymers such as PVC, can release HCl which is highly acidic and may cause harm to humans. HCl is a TOXIC gas
How can we deal with the problem caused in the combustion of polymers?
Release the fumes by using SCRUBBERS (bases such as CaCO3. These scrubbers reduce the impact to the environment.
Describe the benefits to the environment of biodegradable polymers
- Can be reused - Degrades faster than non-biodegradable polymers - Can be made from renewable resources such as plants, wheat and maize
What is a photo-degradable polymer?
Polymers that decompose when exposed to light
