4.1 Basic Concepts & Hydrocarbons Flashcards
What is a homologous series?
A series of organic compounds having the same functional group, with each successive member differing by CH2
What is a functional group?
A group of atoms responsible for the characteristic reactions of a compound
What is the formula for an alkyl group?
CnH2n+1
What is an aliphatic hydrocarbon?
A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings
What is an alicyclic hydrocarbon?
An aliphatic compound arranged in non-aromatic rings with or without side chains
What is an aromatic hydrocarbon?
A compound containing a benzene ring
What is a saturated hydrocarbon?
A hydrocarbon containing only carbon and hydrogen atoms joined by single covalent bonds
What is an unsaturated hydrocarbon?
A hydrocarbon containing carbon and hydrogen atoms only, joined by double or triple bonds including aromatic rings
What is the formula for alkanes?
CnH2n+2
What are the three rules for naming branched alkanes?
Stem - longest carbon chain
Suffix - end of the name, most important functional group
Prefix - the front
What are the different types of functional groups?
Alcohol - OH (ol)
Aldehyde - CHO (al)
Carboxylic Acid - COOH (oic acid)
Haloalkane - F, Cl, Br, I (fluro, chloro, bromo, iodo)
Ketone - C-CO-C (one)
What is a general formula?
Simplest algebraic formula for all organic compounds in a homologous series
What is a structural formula?
Gives the minimum detail for the arrangement of atoms in a molecule
What is a displayed formula?
Shows the relative positions of atoms and the bonds between them
What is empirical formula?
Simplest whole number ratio of atoms of the elements in a compound
What is molecular formula?
Shows the numbers and types of atoms in a compound
What is skeletal formula?
Simplified structural formula drawn by removing hydrogen atoms from alkyl chains, leaving just the carbon skeleton and any functional groups
What are structural isomers?
Compounds with the same molecular formula but different structural formula
What are the three ways that structural isomerism can happen?
The alkyl groups could be in different places
Functional group could be bonded to different parts of parent chain
Functional group could be different
What is stereoisomerism?
Compounds with the same molecular formula and structural formula but having different arrangements of atoms in space
What is E/Z isomerism?
A type of stereoisomerism caused by the restricted rotation around the double bond
What are the Cahn-Ingold-Prelog rules?
To name E/Z stereoisomers
- locate C=C double bond and its substituents
- assign high priority of each substituents on each carbon based on its RAM
- if highest priority groups on same side - Z/if highest priority groups on opposite side - E
What is cis-trans isomerism?
A special type of E/Z isomerism where there is a hydrogen and non-hydrogen group on each carbon atom
If the hydrogens are on the same side - cis
If the hydrogens are on opposite sides- trans
What is homolytic fission?
When each bonded atom receives one electron from the bonded pair, forming two radicals
X-Y –> X’ + Y’
Half headed curly arrow represents movement of one electron
What is heterolytic fission?
When one bonding atom receives both electrons from the bonded pair resulting in a positive ion (cation) and negative ion (anion) being formed
X-Y –> X+ + Y-
What is a radical?
A species with an unpaired electron
What is a curly arrow?
Model the flow of electrons during reaction mechanisms
What is the bonding in alkanes?
Saturated hydrocarbons containing single C-C and C-H bonds
Sigma bonds - overlap of orbitals between bonded atoms and can rotate
C and H have similar electronegativities so C-H sigma bonds have low polarity
Electrons are moving so there may be a lack of balance in charge distribution = instantaneous dipole, induces dipoles in neighbouring molecules = London forces
Tetrahedral shape with bond angle of 109.5 degrees
What is the effect of chain length on boiling point of alkanes?
The longer the chain, the higher the relative molecular mass
Larger molecules have more surface areas of contact so more London forces
More energy is required to overcome this intermolecular attraction
What is the effect of branching on boiling point of alkanes?
The more branched a compound is, the fewer surface area interactions there are between molecules as they cannot fit together neatly
Fewer London forces so less energy required to overcome these intermolecular attraction
Why do alkanes have a low reactivity with many reagents?
All the covalent bonds in the alkanes molecules have high bond enthalpies so a large amount of energy is required to break the bonds
The C-H sigma bonds have very low polarity because of the similarities in electronegativity
What happens when an alkane undergoes complete combustion?
Alkane and oxygen react to produce carbon dioxide and water
Used in fuels - alkanes transfer their stored chemical energy into thermal energy
What happens when an alkane is combusted with a limited supply of oxygen?
Incomplete combustion
Alkane and oxygen react to produce toxic gas carbon monoxide and water
Product combinations:
- CO + H2O
- CO2 + CO + H2O
- CO2 + CO + C + H2O
What is the reaction between an alkane and chlorine or bromine called?
Radical substitution
Under UV light
What is the mechanism for radical substitution?
Initiation - formation of the radicals
Cl2 –> Cl’ + Cl’
Propagation - two repeated steps that build up desired product in side reaction
CH4 + Cl’ –> ‘CH3 + HCl
‘CH3 + Cl2 –> CH3Cl + Cl’
Termination - two radicals collide and make a stable product
Cl’ + Cl’ –> Cl2
‘CH3 + ‘CH3 –> C2H6
‘CH3 + ‘Cl –> CH3Cl
Only one product is desirable (CH3Cl) so reaction has low atom economy
What is the bonding in alkenes?
Unsaturated hydrocarbon containing a C=C double bond
Pi bond - sideways overlap of adjacent p-orbitals above and below the bonding C atoms;
this type of bond can only be formed after sigma bonds;
hold atoms in position by restricting rotation around the double bond;
reactive part of molecule due to high electron density around it
Sigma bond - (C-H covalent bonds)overlap of orbitals directly between bonding atoms
What is the shape of alkene molecules?
Trigonal planar with 120 degrees bond angle
Each electron density (covalent bonds between C, C-H sigma bonds, C=C sigma and pi bond) repeal each other by the same amount
Why are alkenes more reactive than alkanes?
The pi bond has a lower bond enthalpy than a sigma bond so it breaks first in chemical reactions
What are electrophiles?
Species that are electron pair acceptors
What happens in electrophiles addition reactions?
Two or more molecules become bonded to make one product
In alkenes, the pi bond breaks and a small molecule is added across the two carbon atoms to make a saturated organic product
What are the types of addition reactions?
Hydrogenation
Halogen action
Hydration
Hydrogen halides
What is hydrogenation?
The addition reaction in which hydrogen is being added across a C=C double bond
Conditions - 150 degrees and a nickel catalyst
C2H4 + H2 –> C2H6
What is halogenation?
The addition reaction where a halogen is added across a C=C double bond
The alkene becomes saturated and a dihaloalkane is formed
Can be used to tests for saturation - when bromine solution or iodine solution is mixed with a saturated compound there is no reaction but there is a colour change with a unsaturated compound as an addition reaction occurs
C2H4 + Br2 –> C2H4Br
(Electrophilic addition mechanism)
What is hydration?
The addition reaction between a gaseous alkene and steam
Conditions - 300 degrees, 65 atm, H3PO4
C2H4 + H2O –> C2H5OH
What is hydrogen halide addition?
The addition reaction in which a hydrogen halide is added across a C=C bond producing a haloalkane
Hydrogen halide bubbled through alkene
C2H4 + HBr –> C2H5Br
Major/minor product:
when a hydrogen halide is added to an unsymmetrical alkene, two products are possible - the hydrogen becomes attached to the C with most hydrogen atoms to start with
Primary, Secondary, Tertiary (carbocations with alkyl groups attached are more stable than those with just hydrogen atoms)
What happens during a polymerisation reaction?
Alkenes have their pi bonds broken and the electrons from the pi bond make a sigma bond with a neighbouring molecule
How are plastics (polymer waste) disposed of?
Landfill
Combustion
Reusing, Recycling
Organic Feedstock
What are the drawbacks of landfill sites?
After rubbish is buried, the conditions turn from normal atmospheric to anaerobic and there is a limited supply of water
This reduces rate of decomposition of biodegradable materials
As many plastics are non-biodegradable, the waste does not break down and becomes a danger to wildlife
What are the drawbacks of combustion of waste polymers?
Plastics contain large amounts of carbon and they have a Hugh calorific value so their energy could be used to generate electricity or drive turbines
However, their combustion releases carbon dioxide
Carbon dioxide is a greenhouse gas and is linked to climate change
Other toxic or polluting gases could be made like HCl
What are the drawbacks of recycling?
The plastics must be sorted into different types
Expensive as it is labour intensive and requires high technology to automate
Plastics are cleaned, melted down or reshaped into new products - limited market for recycled plastic as there are concerned about quality and contamination
What is organic feedstock?
After plastics have been sorted into different types, a series of chemical reactions can be used to break down the plastic polymers into small organic molecules
Allows recovered chemicals to be used in other industrial processes
What are biodegradable polymers?
Materials are affected by the action of microorganism so and environmental conditions, leading to its decomposition
What are photodegradable polymers?
A material made from a renewable source that is biodegradable
Addition polymers that are weakened by absorption of light which breaks it down and it is not possible to stop the process
