Module 4 -Core Organic Chemsitry Flashcards
Outline carbon
In group four, with four electrons in its outer shell. Each atom can form four covalent bonds. They can bond to other carbon atoms to form long chains.
What is a hydrocarbon
A compound containing only carbon and hydrogen atoms.
What is a saturated hydrocarbon
A hydrocarbon with only single bonds
What is an unsaturated hydrocarbon
Contains carbon-carbons multiple bonds
What is a homologous series
A family of compounds with similar chemical properties whose successive members differ by the addition of a -CH2 group
What is the simplest homologous series
Alkanes
What is a functional group
Part of an organic molecule that is responsible for the molecules chemical properties
What does nomenclature mean
The system that has rules of nomenclature for organic compounds.
What is an aliphatic hydrocarbons
Carbons joined to each other in unbranched or branched chains
What is an alicyclic hydrocarbon
Carbon atoms are joined to each other in a ring (cyclic) structure
What is an aromatic hydrocarbon
Some or all of the carbon atoms are found in a benzene ring (C6H6)
What are the three homologous series of aliphatic hydrocarbons and what are they
Alkanes - containing single C-C bonds
Alkenes - containing at least one double C-C bond
Alkynes - containing at least one triple C-C bond
What does the stem of the name of an organic compound indicate
The number of carbons atoms in the longest continuous chains in the molecule (e.g. prop-)
What does the prefix of the name of an organic compound indicate
A prefix can be added before the stem, often to indicate the presence of side chains or a functional group
What does the suffix of a name of an organic compounds indicate
A functional group
Outline the steps of naming an aliphatic alkane
- All alkanes have the suffix -ane
- Identify the longest continuous carbon chain
- Identify side chains (alkyl groups) which is added as a prefix to the name of the parent chain
- Add numbers before any alkyl groups to show the position of the alkyl groups on the parent chain
How do you identify the longest chain in an organic compound if there are two or more possible chains of the same length
The chain with the most branches is considered the longest chain
How do you name alicyclic alkanes
The prefix cyclo- in front of the stem is used to show that the C atoms are arranged in a ring structure
How do you name alkenes
Suffix is -ene and the position of the double C-C bond in the chain must be stated for alkenes that have four or more C atoms in the longest chain
What is the suffix/prefix for an alkene
suffix -ene
What is the suffix/prefix for an alcohol
suffix -ol
prefix hydroxy-
What is the suffix/prefix for a haloalkane
prefix chloro-, bromo-, iodo-
What is the suffix/prefix for an aldehyde
suffix -al
What is the suffix/prefix for a ketone
suffix -one
What is the suffix/prefix for a carboxylic acid
suffix -oic acid
What is the suffix/prefix for an ester
suffix -oate
What is the suffix/prefix for an acyl chloride
suffix -oyl chloride
What is the suffix/prefix for an amine
prefix amino-
suffix -amine
What is the suffix/prefix for a nitrile
suffix -nitrile
How are multiple side chains ordered in organic compound names
In alphabetic order
What is the molecular formula
The number and type of atoms of each element present in. molecule. Different molecules can have the same molecular formula.
What is the empirical formula
The simplest whole-number ratio of the atoms of each element present in a compound.
What is the general formula
The simplest algebraic formula for any member of a homologous series. You can use the general formula to generate the molecular formula for any member of that homologous series.
What is the displayed formula
The relative positioning of all of the atoms in a molecule and the bonds between them.
What is the structural formula
Uses the smallest amount of detail to show the arrangement of the atoms in a molecule, It shows clearly which groups are bonded together. (e.g. CH3CH2CH3)
What is the skeletal formula
A simplified organic formula you remove :
-All if the C and H labels
-Any bonds to H atoms
This leaves a C skeleton and any functional groups
-A line presents a bind
-An intersection of two lines represents a C atom
-The end of a line represents a -CH3 group
What is a structural isomer
Compounds with the same molecular formula, but different structural formulae
Outline isomers with the same functional group
The functional group can be at different points along the Carbon chain.
Outline isomers with different functional groups
-Sometimes two molecules containing different functional groups have the same molecular formula.
-Aldehydes and ketones with the same number of carbon atoms have the same molecular formula.
What is homolytic fission
When a covalent brand breaks and each of the bonded atoms takes one of the shared pair of electrons from the bond.
-Each atom has a single unpaired electron
-An atom or groups of atoms with an unpaired electron is called a radical
What is heterolytic fission
-When a covalent bond breaks and one of the bonded atoms takes both of the electrons from the bond
-Both a negative and position ion is formed
What are curly arrows
Show the movement of electron pairs when bonds are being broken or made.
What is an addition reaction
Two reactants join to form one product
What is a substitution reaction
Atom or group of atoms is replaced by a different atom/group of atoms
What is an elimination reaction
-Removal of a small molecule from a larger molecule
Outline alkanes
Saturated hydrocarbons that are main components of natural gas and crude oil. They are amongst the most stable organic compounds. They are mainly used as fuels.
What is the general formula of an alkane
CnH2n+2
What is a sigma bond
The result of overlapping of 2 orbitals, one from each bonding atom, positioned on line directly between bonding atoms.
Outline the bonding in an alkane
Each carbon atom is joined to four other atoms by sigma bonds.
-Each overlapping orbital contains one electron so the sigma bond has two electrons that are shared between the bonding atoms
What is the shape of an alkane
-Each C atom is surrounded by 4 electron pairs in four sigma bonds. Repulsion between these results in a 3D tetrahedral arrangement around each C atom. Each bond angle is approximately 109.5°.
-The sigma bonds act as axes around which the atoms can rotate freely, so these shapes are not rigid.
Outline the boiling point trend in alkanes
-Boiling point increases as the carbon chain increases
-Molecules have a larger surface area so there is greater contact between molecules so London forces between molecule are therefore greater.
How does branching affect the boiling point of alkanes
They reduce London Forces as less surface area contact between layers, therefore boiling point is lower in branched chain alkanes compared to straight chain isomers
Outline the solubility of alkanes
-Non-polar so soluble in non-polar solvents
-They interact and form new London Forces, overcoming the old ones.
-Non-polar therefore insoluble in polar solvents
-A lot of energy required to overcome the hydrogen bonding in water; any interaction of an alkane and water will result in new London Forces and this is not energetically equivalent to overcoming old London Forces and Hydrogen bonding
Why are alkanes not very reactive
-The C-C and C-H sigma bonds are strong
-C-C bonds are non-polar
-the electronegativity of Carbon and Hydrogen is so similar that the C-H bond can be considered to be non-polar
Outline combustion of alkanes
All alkanes react with a plentiful supply of oxygen due to their lack of reactivity to produce carbon dioxide and water
Outline complete combustion of alkanes
-In a plentiful supply of oxygen, alkanes burn completely produce carbon dioxide and water.
Outline the incomplete combustion of alkanes
-In a limited supply of oxygen there is not enough oxygen for complete combustion. When oxygen is limited during combustion the hydrogen atoms in the alkane are always oxidised to water, but the combustion of the carbon may be incomplete the so CO or C are formed
Outline carbon monoxide
-Colourless, odourless and highly toxic
-Combines irreversibly with haemoglobin RBCs to form carboxyhaemoglobin preventing oxygen passing around the bidy
Why are alkanes used as fuels
Readily available, easy to transport, burn in a plentiful supply of oxygen to release no toxic products.
How do alkanes react with halogens
-In the presence of sunlight, alkanes react with halogens. The high-energy UV radiation present in sunlight provides the initial energy for a reaction to tia place.
-This is a substitution reaction, as a hydrogen atom in the alkane has been substituted by a halogen atom.
How does the mechanism for halogenation of alkanes work
Radical substitution takes place in three stages:
-Initiation
-Propagation
-Termination
Outline the initiation of bromination of alkanes
The covalent bond in a bromine molecule is broken by homolytic fission. Each bromine atom takes one electron from the pair forming two highly reactive bromine radicals. The energy for this bond fission is provided by UV radiation
Outline the propagation of bromination of alkanes
The reaction propagates through two propagation steps, a chain reaction.
(e.g.) methane) 1. A bromine radical reacts with a C-H bond in the methane, forming a methyl radical and a molecule of hydrogen bromide
2. Each methyl radical reacts with another bromine molecule, forming the organic product bromomethane, CH3Br together with a new bromine radical
Outline the termination of bromination of an alkane
-In the termination stage, two radicals collide, forming a molecule with all electrons paired. There are a number of possible termination steps with different radicals in the reaction mixture
1. Br° + Br° > Br2
2. CH3° + CH3° > C2H6
3. CH3° + Br° > CH3Br
-When two radicals collide and react, both radicals are removed from the reaction mixture stopping the reaction
What are limitations of radical substitution in organic synthesis
Although radical substitution gives us a way of making haloalkanes this reaction has problems that limit its importance for synthesis of just one organic compound
Outline the structure of alkenes
-Unsaturated hydrocarbons; alkene molecules contain at least one carbon to carbon double bond in their structure. Aliphatic alkenes that contain one double bond have the general formula CnH2n
-Alkenes can be branched, contain more than one double bond, or be cyclic. Whilst branched alkenes have same general formula, cyclic alkenes and alkenes with more than one double bond do not.
Outline double bond in alkenes
-For each carbon atom of the double bond, three of the four electrons are used in three sigma bonds, one to the other carbon atom of the double bond and the other two electrons to two other atoms
-This leaves one electron on each carbon atom of the double bond not involved in sigma bonds. This electron is in a p-orbital.
-A pi bond is formed by the sideways overlap of two p-orbitals, one from each carbon atom of the double bond. Each carbon atom contributes one electron to the electron pair in the pi bond. The pi electron density is concentrated above and below the line joining the two nuclei of the bonding atoms.
Outline how the double bond allows movement in alkenes
-The pi-bond locks the two carbon atoms in position and prevents them from rotating around the double bond. This makes the geometry of alkenes different from that of the alkanes, where rotation is possible around every atom.
What is the shape around carbon atoms in a double bond
-Trigonal planar as there are three regions of electron density around each of the carbon atoms
-The three regions repel each other as far apart as possible,so the bond angle around each carbon atom is 120°
-All of the atoms are in the same plane
What is a stereoisomer
Compounds with the same structural formula but different arrangement of atoms in space
Why do stereoisomers arise around a double bond
Rotation about the double bond is restricted and the groups attached to each carbon atom are fixed
What do molecules require to have E/Z isomerism
-A C=C double bond
-Different groups attached to each carbon atom of the double bond
What is required for cis-trans isomers to be present
-One of the attached group on each carbon atom of the double bond must be a hydrogen
What is a cis isomer
Has the hydrogen on each carbon in the double bond on the same side of the molecule
What is a trans isomer
The hydrogen atoms are diagonally opposite each other
What are the Cahn-Ingold-Prelog rules
The atoms attached to each carbon atom in a double bond are given priority upon their atom number.
-If the groups of higher priority are on the same side of the double bond, the compound is the Z isomer
-If the groups of higher priority are diagonally placed across the double bond, the compound is the E isomer
Are alkanes or alkenes more reactive and why
Alkenes are much more reactive due to the pi-bond is on the outside of the double bond, the pi-bond readily breaks and alkenes undergo addition reactions easily
-The bond enthalpy of the pi bond is lower than that of a single carbon done
Outline addition reactions of alkenes
Addition of a small molecule across the double bond, causing the pi bond to beak and new bonds to form. For example with:
-Hydrogen in the presence of a nickel catalyst
-Halogens
-Hydrogen halides
-Steam in the presence of an acid catalyst
Outline hydrogenation of alkenes
When an alkene is mixed with hydrogen and passed over a nickel catalyst at 423K, an addition reaction takes place to form an alkane
What are the conditions needed for hydrogenation of alkene
A nickel catalyst and 423K
Outline halogenation of alkenes
Rapid reaction at room temperature.
How can bromination of alkenes be used to identify if a C=C bond is present (unsaturated)
-When bromine water (an orange solution) is added drop wise to an alkene sample bromine adds across the double bond.
-The orange colour disappears i indicating the presence of a C=C bond.
-Any compound containing a C=C bond will decolorise bromine water
Outline addition reactions of alkenes with hydrogen halides
Alkenes react with gaseous hydrogen halides at RTP to form haloalkanes.
-If the alkene is a gas, then the reaction takes place when the two gases are mixed.
-If the alkene is a liquid the hydrogen halide is bubbled through it.
-Alkenes also react with concentrated hydrochloric or concentrated hydrobromic acid, which are solutions of the hydrogen halides in water
Outline the hydration of alkenes
Alcohols are formed when alkenes react with steam, in the presence of a phosphoric acid catalyst H3PO4. Steam adds across the double bond.
What are the conditions for hydration of alkenes
-Steam
-Phosphoric acid catalyst H3PO4
Outline electrophilic addition reactions
-The double bond in an alkene is a region of high electron density as the presence of the pi electrons
-This attracts electrophiles
What is an electrophile?
An atom or group of atoms that is attracted to an electron rich centre and accepts an electron pair. An electrophile is usually a positive ion or a molecule containing an atom with a partial positive charge
Outline the reaction between but-2-ene and hydrogen bromide
-Forms a single addition product:
1. Bromine is more electronegative than hydrogen so HBr is polar
2. The electron pair in the pi bond is attracted to the partially positive hydrogen atom, causing the double bond to break
3. A bond forms between the hydrogen atom of the H-Br molecule and a carbon atom that was part of the double bond.
4. The H-Br bond breaks by heterolytic fission, with the electron pair going to the bromine atom
5. A bromide ion and carbocation are formed. A carbocation contains a positively charged carbon atom
6. In the final step the Br- ion reacts with the carbocation to form the addition product
How do alkene react with non-polar molecules by electrophilic addition (eg Br2 and propene)
Bromine adds to propene to form a single addition product
Outline the reaction for the reaction between propene and bromine
- This interaction causes polarisation of the Br-Br bond, with one end of the molecule becoming Br+ and the other Br- (induced dipole)
- The electron pair in the pi-bond attracted to the Br+ end of the molecule, causing the double bond to break
- A bond has now been formed between one of carbon atoms from the double bond and bromine atom
- The Br-Br bond breaks by heterolytic fission, with the electron pair going to the Br- end of the molecule
- A bromide ion and a carbocation are formed
- In the final stage of the reaction mechanism the Br- ion reacts with the carbocation to form the addition product of the reaction
What is Markownikoff’s rule
-When a hydrogen halide reacts with an unsymmetrical alkene the hydrogen of the hydrogen halide attaches itself to the carbon atom of the alkene with the greater number of hydrogen atoms and smaller number of carbon atoms
How are carbocations classified
The number of alkyl groups attached to the positively charged carbon atom. An alkyl group is normally represented by the symbol -R.
What kind of carbocation is most stable and
-Tertiary carbocations are the most stable
-Each alkyl group donates and pushes electrons towards the positive charge of the carbocation. The positive charge is spread over the alkyl groups. The more alkyl groups attached to the positively charged carbon atom, the more charge is spread out, making the ion more stable.
What are polymers
Large molecules formed of many repeating units of smaller molecules known as monomers
What is addition polymerisation
Unsaturated alkene molecules undergo addition polymerisation to produce long saturated chains containing no double bonds. Many different polymers can be formed, each with its own specific properties depending on the monomer used.
How is industrial polymerisation carried out
-High temperatures
-High pressure
-Catalysts
Outline addition polymers
-Very high molecular masses
-Usually named after the monomer that reacts to form their giant molecules prefixed by ‘poly’
How to write addition polymerisation equation
-A general equation can be balanced using the symbol ‘n’
-A repeat unit is the specific arrangement of atoms in the polymer molecule that repeats over and over again
-The repeat unit is always written in square brackets
-After the bracket you place a letter n to show that there is a large number of repeats
Outline Poly(ethene)
-Made by heating a large number of ethene monomers at high pressure
-One of the most commonly used polymers - you will come across it in supermarket bags, shampoo bottles, and children’s toys
Outline poly(chloroethene)
PVC can be prepared to make a polymer that is flexible or rigid.
-Can be pipes, films and sheeting, bottles, flooring, insulation and cable sheathing, ducts and profiles etc.
Outline poly(propene)
-Used to make children’s toys, packing crates, guttering, uPVC windows, and fibre for ropes
Outline poly(styrene)
-Used for packaging material and also in food trays and cups due to its thermal insulating properties
Outline poly(tetrafluoroethene)
Used as coating for non-stick pans, permeable membrane for clothing and shoes, and cable insulation
Why is disposing of polymers a problem (reactivity and availability)
-Readily available, cheap to purchase, and more convenient than alternatives
-Lack reactivity that makes polymers suitable for storing food and chemicals safely also presents chemists with a challenge in their disposal
-Many alkene-based polymers are non-biodegradable
What is the affect or growing amount of polymer waste
Has serious environmental effects such as killing marine life
Outline recycling as a disposal method of waste polymers
-Reduces environmental impact by conserving finite fossil fuels as well as decreasing the amount of waste going to landfill.
-Discarded polymers have to be sorted by type
-The recycling process is undermined if polymers are mixed as this renders the product unusable
-Sorted polymers are chopped into flakes, washed, dried and melted. The recycled polymer is cut into pellet and used by manufacturers to make new products
Outline PVC recycling as a disposal method of waste polymers
-The disposal and recycling of PVC is hazardous due to the high chlorine content and the range of additives present in the polymer
-Dumping PVC in landfill is not sustainable and when burnt realises HCl (toxic) and pollutants
-Used to be ground and reused, but now solvents are used to dissolve the polymer. High grade PVC is then recovered by precipitation from the solvent and it is used again
Outline using waste polymers as fuel as a disposal method of waste polymers
-Some polymers are difficult to recycle. As they are derived from petroleum or natural gas, they have a high stored energy value. Waste polymers can incinerated to produce heat, generating steam to drive a turbine producing electricity.
Outline feedstock recycling as a disposal method of waste polymers
-Describes the chemical and thermal processes that can reclaim monomers, gases or oil from waste polymers. The products from feedstock recycling resemble those produced from crude oil in refineries. These materials can be used as raw materials for the production of new polymers. A major advantage of feedstock recycling is that it is able to handle unsourced and unwashed polymers.
Outline bio plastics
Produced from plant starch, cellulose, plant oil and proteins offer a renewable and sustainable alternative to oil based products. The use of bio plastics not only protects our environment but also conserves valuable oil reserves.
Outline biodegradable polymers
-Broken down by microorganisms into water, CO2 and biological compounds. These polymers are usually made from starch or cellulose or contain additives that alter the structure of traditional polymers so that microorganisms can break them down.
Outline compostable polymers
Degrade and leave no visible or toxic residues. Compostable polymers based on poly(lactic acid) are becoming more common as an alternative to alkene based polymers
Outline how biodegrade polymers are currently being put in use
-Supermarket bags made from plant starch can be used as bin liners for food waste so that the waste and bag dan be composted together.
-Compostable plates, cups and food trays made from sugar can fibre are replacing expanded polystyrene.
-As technology advances they are more likely to be used in packaging, electrons and fuel-efficient and recyclable vehicles
Outline photodegradable polymers
Oil based polymers being developed which contain bonds that are weakened by absorbing light to start the degradation. Alternatively, light absorbing additives are used.
What is the functional group of alcohols
-OH
Outline methanol formula and uses
CH3OH
-High performance fuel because of its efficient combustion and an important chemical feedstock
-Can be converted into polymers, paints, solvents, insulation, adhesives and other useful products
Outline ethanol uses
Alcoholic drinks, fuel, a solvent and sometimes a feedstock
Compare alcohol solubility in water to corresponding alkane
-Alcohols are more soluble as they can form hydrogen bonds either water, whereas alkanes which are non-polar cannot form hydrogen bonds with water
-Methanol and ethanol are completely soluble in water
-As the hydrocarbon chain increases in size the influence of the -OH group becomes smaller and long-chains are less soluble
Compare volatility and boiling points of alcohols and the corresponding alkanes
Alcohols have intermolecular forces H-bonds in liquid state to hold the alcohol molecules together. These bonds must be broken in order to change the liquid alcohol into a gas which requires more energy compared to alkanes which only require energy to break London Forces
Outline primary alcohols
The -OH group is attached to a carbon atom that is attached to two hydrogen atoms and one alkyl group
Outline secondary alcohols
The -OH group is attached to a carbon atom that is attached to one hydrogen atom and two groups.
Outline tertiary alcohols
The -OH group is attached to a carbon atom that is attached to no hydrogen atoms and three alkyl groups
Outline the combustion of alcohols
-Alcohols burn completely in a plentiful supply of oxygen to produce carbon dioxide and water. The equation shows the complete combustion of ethanol
-It is exothermic and releases a large quantity of energy in the form of heat
Outline the oxidation of alcohols
Primary and secondary alcohols can be oxidised by an oxidising agent usually potassium dichromate, acidified with H2SO4. If the alcohol is oxidised the orange solution containing dichromate ions is reduced to a green solution contains chromium ions.
Oxidation of primary alcohols to form an aldehyde
Gently heated using distillation and using an oxidising agent not in excess. The dichromate ions change colour from orange to green
Oxidation of primary alcohols to form an aldehyde
Gently heated using distillation and using an oxidising agent not in excess. The dichromate ions change colour from orange to green
Oxidation of primary alcohol to form a carboxylic acid
Heated strongly under reflux with an excess of acidified potassium dichromate (oxidising agent). Using excess ensures the alcohol is full oxidised
Heating under reflux ensures any aldehyde formed intiitwlly in the reaction also undergoes oxidation to the carboxylic acid
