3.3: Organic chemistry Flashcards
What is IUPAC?
The International Union of Pure and
Applied Chemistry
What are the prefixes based on the number of carbon atoms?
1: meth-
2: eth-
3: prop-
4: but-
5: pent-
6: hex-
7: hept-
8: oct-
9: non-
10: dec-
What is the homologous series?
a series of related chemical compounds with the same R (functional group) but differ in formula by a fixed no. or group of atoms
What is a functional group?
an atom/ group of atoms (e.g. carboxyl groups) that replaces H in an organic compound and defines structure of family of compounds, determining the family proteins
What are the general functional groups of each homologous series?
- alkanes (-ane): R-CH3 or R-CH2-R1
- alkenes (-ene): R-HC=CH-R
- alcohol (-ol): R-OH
- aldehydes (-al): H-R=O
- kentones (-one): R-C(=O)-R
- carboxylic acid (-oic acid)
- halokane (chloro-,bromo-,iodo-,methyl-): R-I
What are the IUPAC rules of alkane nomenclature?
- find and name the longest continuous carbon chain (with R group) a.k.a. parent chain
- identify and name groups attatched to the chain
- number the chains conscutively, starting at the end nearest a substituent group (lowest possible numbers!!)
- designate the location of each substituent group by an appropriate no. and name
- assemble the name, listing groups alphabetically, excluding no. stems
What are the different formulas? e.g. butane
general, molecular, structural, displayed and skeletal
general- a chemical formula applicable to a series of compounds (e.g. CnH2n+2)
molecular- actual no. of atoms in a molecule (e.g. C4H10)
structural- the minimal detail that shows the arrangement of atoms in a molecule (e.g. CH3CH2CH2CH3)
displayed- the relative positioning of atoms and the bonds between them (e.g. H-C-C-C-C-H)
skeletal- the simplified organic formula, shown by removing hydrogen atoms from alkyl chains, leaving just a carbon skelenton and associated functional groups ( e.g. ^/
What is an alkane?
- Alkanes are saturated hydrocarbons.
- alkanes consist of single carbon-carbon bonds
- The general formula for an alkane is CnH2n+2
- Except for alkanes in a ring structure, where it is CnH2n
- methane (CH4), is the most simple alkane
What are properties of alkanes?
- Alkanes do not dissolve in water, as they are non polar (the electronegativity of carbon and hydrogen is similar).
- Because the water molecules are held together by H-bonds, and alkanes by VdW forces, they do not interact with each other.
What is crude oil?
- Crude oil is often called a fossil fuel because it is made from the breakdown of organic matter, such as plants and animals.
- made up of dead plankton
- Crude oil is a non-renewable fuel as, although crude oil is being formed – it takes millions of years.
- Burning fossil fuels releases carbon dioxide – a greenhouse gas. Further more, impurities in the fossil fuels such as sulfur react with oxygen on combustion releasing sulfur dioxide.
How does fractional distillation occur?
- Crude oil heated
- The mixture passes into a tower that is cooler at the top than the bottom
- The vapours pass up the tower via trays containing bubble caps until they arrive at a point that is cool enough to condense
- The mixture of liquids (fractions) are piped off at approximately similar chain lengths
- The shorter chain HCs condense nearer the top where it is cooler as they have lower forces of attraction and therefore lower boiling points
- The residue left at the bottom (bitumen) consists of very long chain HCs that are used as tar on roads
Why does alkane cracking take place?
- Crude oil often contains a very high proportion of long chain hydrocarbons, these are less useful than then short chain hydrocarbons that we often associate with fuels.
- Cracking breaks longer hydrocarbons into a shorter alkane and an alkene.
-
Benefits of industrial cracking: Converts useless long chain alkanes to useful short chain alkanes, resulting in less waste, Creates ethene, an extremely useful precursor to making polyethene. This
can be sold for profit.
What is a free radical?
Free radicals are highly reactive species
with and unpaired electron.
What are the conditions and what occurs in thermal cracking?
- Conditions: Temp: 700-1200K, Pressure: 7000kPa
- Products: The carbon chain can break in any number of places, and hydrogen may be produced. This means that there is a high proportion of alkenes created.
- The covalent bond between 2 carbons splits equally, each carbon receiving and electron. These then go on to form a shorter alkane and an alkene. The conditions are intense so only maintained momentarily, usually around a second.
What are the conditions and what occurs in catalytic cracking?
- Conditions: Temp: <720 Pressure: >1atm Zeolite catalyst
- Products: The products are also a mixture of alkanes and alkene, mainly of short chains (less than C=5), used in motor fuels. These are branched alkanes, cycloalkanes and aromatic compounds.
- Zeolite catalysts are honeycombed structure to give enormous surface area, they consist of silicon dioxide an aluminium oxide.
How do you test for the presence of alkenes?
Bromine water
orange–> colourless if positive
Differences between thermal and catalytic cracking?
Products:
It is a slight over-simplification but the zeolites used in catalytic cracking are chosen to give high percentages of hydrocarbons with between 5 and 10 carbon atoms - particularly useful for petrol (gasoline). It also produces high proportions of branched alkanes and aromatic hydrocarbons like benzene.
Thermal cracking gives mixtures of products containing high proportions of hydrocarbons with double bonds - alkenes
Write an equation for the complete combustion of
methane
CH4(g) + 2O2(g) -> CO2(g) + H2O(l)
ΔH = -890 kJmol-1
- Alkanes are generally very unreactive, they wont react with acids,
bases, oxidising agents or reducing agents. However they are very
flammable and will react with halogens in the right conditions. - this reaction gives out a lot of energy. Hydrocarbons are used as fuels because they release a lot of heat on combustion. The more carbons present the more energy is released.
What are impacts of burning fossil fuels?
- Burning fossil fuels pollutes the environment.
- Carbon dioxide is always given off when fossil fuels are burnt, it is an essential part of the earths atmosphere, however rising levels are causing an increase in the earths atmosphere and hence climate change.
- When hydrocarbons are burnt in a limited supply of oxygen, incomplete combustion occurs (generally longer chains).
- CH4(g) + 1.5O2(g) -> CO(g) + 2H2O(l)
- If even less oxygen is available, solid carbon may form.
- Carbon monoxide is a toxic gas and carbon particulates in the atmosphere can exacerbate asthma and are carcinogens.
What are pollutants of alkane combustion?
Carbon monoxide (CO)- Produced during incomplete combustion of hydrocarbons, Toxic gas for humans.
Nitrous oxides (NOx)- The reaction between oxygen and nitrogen in the air, at the high temperatures of combustion, May react with water vapour and oxygen in the air to form nitric acid, a component of acid rain.
sulfur dioxide (SO2).- Formed when sulfur impurities in fossil fuels react with oxygen, May react with water vapour and oxygen in the air to form sulfuric acid, a component of acid rain.
Carbon particulates.- Incomplete combustion of hydrocarbons, Trigger asthma attacks in asthmatics and may cause cancer.
Unburnt hydrocarbons.- Evaporation from fuel, or non-combustion, Significant greenhouse gases and contributors to photochemical smog, which causes health problems.
Carbon dioxide (CO2)- Produced when fossil fuels are burnt, An important greenhouse gas, but in higher concentrations is a cause of
climate change.
Water vapour (H2O(l))- Naturally occurring, but increases with increasing temperature, A greenhouse gas.
How to reduce pollutants (sulfur dioxide)?
- In many power stations, sulfur impurities is coal can react with oxygen to for sulfur dioxide.
- Calcium carbonate (or calcium oxide) can be sprayed on the flue gas to remove the sulfurous oxides.
- Reacting with lime wash is shown here, reacting lime (CaO) produces gypsum, a useful building material.
CaCO3(s) + 1.5O2(g) + SO2(g)-> CaSO4(s) + 2CO2(g)
How to reduce pollutants (nitrous oxides)?
- Apart from sulfur, the internal combustion engine produces most of the pollutants that you have come across.
- IT is compulsory that all vehicles are fitted with catalytic converters to reduce nitrous oxide and carbon monoxide emissions.
2CO(g) + 2NO(g) N2(g) + 2CO2(g)
What is the greenhouse effect?
- Like the glass in a greenhouse, gases in our atmosphere trap energy from the sun from leaving. This is important as it keeps our planet warm enough for life to survive.
- However, the earth is getting warmer, and the majority of scientists agree that is as a result of human production of carbon dioxide.
- Furthermore, as temperature increases, more water changes from the liquid state to a vapour, this exacerbates the effect of global warming. There is therefore a drive for us to reduce our emissions.
- Activities that do not release carbon dioxide overall, are called carbon neutral.
What are halogenoalkanes?
- Halogenoalkanes are alkanes with one or more halogen groups.
- Halogenoalkanes can be formed by putting a mixture of an alkane and a halogen into bright light
- the UV light cause a reaction mechanism to occur resulting in a mixture of different halogenoalkanes forming.
CH4(g) + Cl2 (g)–>C6H13Br(g) + HBr(g)
What is free radical substitution?
These are reactions in which one hydrogen atom in a molecule is replaced by a halogen or group of atoms to produce a halogenoalkane.
- initiation: creates a free radical
- propogation: 2 steps that progress a reaction and end with a free radical
- termination: removes the free radical
formation of halogenoalkanes
1.Initiation
FRS
- The chlorine molecule absorbs a quantum of ultra violet light that is of enough energy to break the Cl-Cl single bond.
- The atoms are identical, so split evenly, each chlorine atom taking one electron from the bond. This is homolytic fission.
- This creates two chlorine free radicals. Often shown as Cl..
formation of halogenoalkanes
2.Propogation
FRS
This occurs is two stages:
- The chlorine free radical takes a hydrogen from methane, becoming stable hydrogen chlorine, creating a methyl free radical.
- Single headed curly arrows show the movement of a single electron.
- The methyl free radical is too, very reactive, so reacts with a chlorine molecule, generating another chlorine free radical.
- These steps occur thousands of times before the radicals are destroyed.
formation of halogenoalkanes
3.Termination
- Termination is any reaction that removes free radicals:
- This may occur if two chlorine free radicals react with each other.
- Chain reactions are not actually a very useful method of producing halogenoalkanes. This is because a mixture of lots of different halogenoalkanes is formed.
- Longer chain alkanes may also produce many isomers of products as the chlorines can replaces any hydrogen on then chain.
What are halogenoalkanes?
Halogenoalkanes are much more reactive than alkanes. They have many uses, including as refrigerants, as solvents and in pharmaceuticals. The use of some halogenoalkanes has been restricted due to the effect of chlorofluorocarbons (CFCs) on the atmosphere.
What is bonding like in halogenoalkanes?
The electron pair in the carbon-halogen bond will be dragged towards the
halogen end, leaving the halogen slightly negative (δ-) and the carbon
slightly positive (δ+) - except in the carbon-iodine case.
Although the carbon-iodine bond doesn’t have a permanent dipole, the bond is very easily polarised by anything approaching it.
What is a nucleophile?
A nucleophile is a species (an ion or a molecule) which is strongly attracted to a region of positive charge in something else.
Nucleophiles are either fully negative ions, or else have a strongly - charge somewhere on a molecule. Common nucleophiles are hydroxide ions, cyanide ions, water and ammonia.
- has at least one lone pair or negative charge
WHAT HAPPENS IN THE NUCLEOPHILIC SUBSTITUTION REACTIONS BETWEEN HALOGENOALKANES AND HYDROXIDE IONS (HYDROLYSIS)?
- The halogenoalkane is heated under reflux (heating with a condenser placed vertically in the flask to prevent loss of volatile substances from the mixture) with a solution of sodium or potassium hydroxide, the halogen is replaced by -OH and an alcohol is produced. Halogenoalkanes do not mix with water, so ethanol is used as a solvent. Water is present
- The reaction mechanism shows dipoles, curly arrows, charges and lone pairs
- nuclephile attacts carbon atom
- C-Halogen bond gos to Halogen
WHAT HAPPENS IN ELIMINATION REACTIONS BETWEEN HALOGENOALKANES AND HYDROXIDE IONS (ELIMINATION)?
- This is when a halogenoalkane is heated under reflux with a concentrated solution of sodium or potassium hydroxide in ethanol.
- In elimination reactions, the hydroxide ions have a very strong tendency to combine with hydrogen ions to make water in other words it acts as a
base - removing a hydrogen as a hydrogen ion from the carbon atom next door to the one holding the bromine. There is no water present. - The OH- ion takes one of the hydrogens from the CH3 group, but it only needs the hydrogen nucleus (a hydrogen ion). That means that the two electrons which originally joined the hydrogen to the carbon aren’t being used any more.
- Those two electrons (represented by a curly arrow) move to form a double bond between the two carbon atoms.
- The approach of those electrons repels the electrons in the carbon-bromine bond right out onto the bromine, throwing the bromine off as a negative ion.
- The attack could equally well have been on any of the other hydrogens on the left-hand carbon, or on any on the right-hand one - it simply depends on what the OH- ion hit.
What are CFCs and their uses?
CFCs stand for chlorofluorocarbons
Their uses included:
- Refrigerant coolants
- Blowing agents
- Solvents
- Aerosol propellants
Why do we use CFCs?
- CFCs were a non toxic replacement for ammonia in refrigerant fluids
- They were deemed safe as they were inert, not flammable, odourless and could be safely compressed
- Moreover, they are very cheap
- Also used as blowing agents, solvents and aerosol propellants
What is the issue with CFCs?
- CFCs remain unchanged in troposphere for decades, CFCs break down in the stratosphere
- UV rays cause CFCs to break down releasing chlorine radicals
- These radicals then collide with ozone and break down the ozone layer
- Chlorine radicals about 1000 x more likely than anything else to react with ozone
- One chlorine radical can deplete about 100,000 ozone molecules 1 million tonnes of CFCs put into atmosphere
What’s happening to the ozone layer as a result of CFCs?
- A ‘hole’ in the ozone layer over the Antarctic was detected in the 1980s
- A technique that measures how strongly the atmosphere absorbs UV was used
- Less UV absorbed at the poles, indicating a thinning in the ozone layer
