Organic Chemistry

Menu Lessons 1-11: Lesson 1 – Homologous Series Lesson 2 – Isomers Lesson 3 – Meet the Families Lesson 4 – Alkanes Lesson 5 – Alkenes Lesson 6 – Alcohols Lesson 7 – Halogenoalkanes Lesson 8 – Reaction Pathways Lesson 9 – HL – Meet the Families (again) Lesson 10 – HL – SN1 and SN2 Revisited Lesson 11 – HL – More Nucleophiles

Menu Lessons 12-18: Lesson 12 – HL – Elimination Reactions Lesson 13 – HL – Condensation Reactions Lesson 14 – HL – Condensation Polymerisation Lesson 15 – HL – Geometric Isomerism Lesson 16 – HL – Optical Isomerism Lesson 17 – HL – More Reaction Pathways

Lesson 1 Homologous Series

Overview Copy this onto a double-page spread. You should add to it as a regular review throughout the unit.

Assessment This unit will be assessed by: A test at the end of the topic (75%)… An internal assessment (25%)

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Lesson 1: Homologous Series Objectives: Reflect on previous knowledge of organic chemistry Understand the term ‘homologous series’ Conduct the fractional distillation of crude oil Understand and use the variety of different types of formula used in organic chemistry

Organic Chemistry Organic chemistry is the chemistry of carbon containing compounds. From the very simple: methane To the very complex: Haem B

Homologous Series A homologous series is a family of compounds that differs only by the length of its hydrocarbon chain Members share: General formula Chemical properties Three such series are the: Alkanes Alkenes Alcohols

Homologous Series and Boiling Points What do you think will be the trend in melting/boiling points as you go down a homologous series? Why?

Formulas Draw the compound with the formula C4H8O

What did you get? Clearly a molecular formula is not enough!

Types of Formula Empirical Formula C4H8O C4H8O Molecular Formula C4H8O C4H8O Full Structural Formula Aka displayed formula Condensed Structural Formula Note the ‘=‘ used for the C=C double bond Skeletal formula Not required but v. useful Used in data booklet for complicated structures Do not use in exam answers! CH2=CHCH2CH2OH CH2=C(CH3)CH2OH

Thinking About Formulas Produce a table to summarise each of the formulas. Include columns for: What they show Pros Cons How you make them Draw full structural, condensed structural and skeletal formulas for at least 5 of the C4H8O compounds (not the cyclic ones)

Key Points Organic chemistry is the chemistry of carbon containing compounds A homologous series is a family of organic compounds differing only by the length of their carbon chains The melting and boiling point increases as you go down a homologous series Displayed formulas show the unambiguous arrangement of atoms in a compound

Lesson 2 Isomers

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Lesson 2: Isomers Objectives: Describe the term structural isomer Draw a name the non-cyclic alkanes Draw and name the straight-chain alkenes

Isomers Compounds with the same molecular formula but different structural formula The 20 different C4H8O compounds from last lesson are isomers of each other These are all structural isomers Same number of each atom, but bonded in a different order You would have even more if you included geometric and optical isomers

Structural Isomers of the Alkanes The (non-cyclic) alkanes have the general formula CnH2n+2 Draw full and condensed structural formulas for every isomer of every one of the alkanes up to n = 6 If you finish early, draw each as a skeletal formula

Did you get them all?

And skeletally

Naming Straight-chain alkanes Suffix: Tells us the functional group of the molecule For alkanes it is ‘-ane’ Prefix: Tells us the length of the longest carbon chain: 1 carbon: meth- 2 carbons: eth- 3 carbons: prop- 4 carbons: but- 5 carbons: pent- 6 carbons: hex- Example 1: ethane Example 2: butane: Task: write in the names of the 4 straight chain alkanes next to your diagrams from last slide

Naming branched-chain alkanes Start by naming the longest chain Add extras to say the size of a branch, its position and how many of that branch Branch Size: 1 carbon: methyl- 2 carbons: ethyl- 3 carbons: propyl- Position: Number the carbons in the longest chain Choose numbers to minimise the total numbers used Number of same branches One branch – nothing Two branches – di- Three branches – tri- Four branches – tetra- Example 1: 2-methylpropane Example 2: 2,3-dimethylbutane Task: name the remaining alkanes

The straight-chain alkenes Alkenes are the same as alkanes but have one C=C double bond. The suffix for the alkene homologous series is ‘-ene’ Task: draw full structural and skeletal formulas for each of the straight-chain alkenes up to C6 and name them. Do the branched ones as well if you have time Hint: you need to state the position of the double bond, but only if there is the possibility of multiple isomers: i.e. ‘but-2-ene’ or ‘hex-1-ene’ but only ‘ethene’ not ‘eth-1-ene’

Did you get them?

Key Points Structural isomers have the same number of each atom but they are connected differently When naming compounds The longest carbon chain forms the prefix The functional group tells you the suffix Sometimes numbers need to be used to tell you where this functional group is Side chains and other groups are named according to what they are, how many there are and their position

Lesson 3 Meet the Families

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Lesson 3: Meet the Families Objectives: Meet and learn to recognise the 7 functional groups required for the SL course Produce a mind-map summarising each of the homologous series

Functional Groups Table (landscape) You need to research and produce a mind- map summarising the following functional groups: Alkane Alkene Alcohol Aldehyde Ketone Carboxylic acid Halide/Halogenoalkane Your table should have four columns including: Name of functional group General structural formula (use ‘R’ to signify a carbon chain) Rules for naming them (including the position where relevant) A named example Relative volatility Relative solubility in water For alcohols and halides you should include a branch to explain the difference between 1o, 2o and 3o You should also have a branch called ‘Other Functional Groups’ that just allows you to recognise the groups: Amine Ester Benzene If HL you should leave space for four more functional groups

Building Organic Compounds Use molecular models to make any of the compounds mentioned in your mind-map: Draw it (structural and skeletal) Name it Give it to a friend and challenge them to do the same Only go up to 6 carbons Only include branched-chains for the alkanes

Key Points There are 7 functional groups we need to know in detail and 3 extra we need to be able to recognise We will look at each in detail over the rest of the unit

Lesson 4 Alkanes

Your notes and mind-map must be ready for me to inspect. Refresh Reviewing Your Notes You should spend 60 seconds reviewing your notes from last lesson before attempting this. Your notes and mind-map must be ready for me to inspect. The following is a computer-generated representation of the molecule, methyl 2- hydroxy benzoate, better known as oil of wintergreen. Deduce the empirical formula of methyl 2-hydroxy benzoate and draw the full structural formula, including any multiple bonds that may be present…The computer-generated representation shown does not distinguish between single and multiple bonds. Name all the functional groups present in the molecule. H C O

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Lesson 4: Alkanes Objectives: Explain the stability of the alkanes Observe the combustion of alkanes Describe the free-radical substitution reactions of alkanes and its mechanism Observe the free-radical substitution of hexane

Combustion of Alkanes The alkanes really don’t do much Combustion is of one of two notable reactions (this is why we use them for fuels) Complete combustion: alkane + oxygen  carbon dioxide + water Incomplete combustion: Alkane + oxygen  carbon + carbon monoxide + carbon dioxide + water The amounts of C, CO and CO2 will vary depending on conditions Task: Observe the combustion of the gas from the gas taps (propane/butane mix) and of a small amount hexane (in spirit burners). Hold the end of a clean boiling tube just over the flame for 15 seconds, this will collect soot from the flame. Record all observations clearly and try to account for them Include balanced equations to describe the (complete) combustion

Why so boring stable? There are at least two reasons why alkanes are so unreactive Task: Think back to your knowledge of molecular structure, and look at the tables of bond-enthalpies in the data booklet to see if you can work out why.

Halogenation Alkanes will undergo halogenation if reacted with a halide in the presence of u.v. light. For example: C2H6(g) + Cl2(g) CH3CH2Cl(g) + HCl(g) ethane chloroethane This reaction is an example of free radical substitution u.v.

Radicals Radicals are species with unpaired electrons They are crazy reactive Halogens form radicals when hit by uv light of the right frequency: Cl2 2 Cl• The dot after the Cl represents the unpaired electron and tells us we have a radical This process is called homolytic fission – the bond breaks equally with one electron going to each chlorine Task: draw Lewis structures for the Cl2 molecule and each of the Cl• radicals u.v.

Reaction Mechanism: Free Radical Substitution Cl2 2 Cl• Cl• + C2H6  C2H5• + HCl C2H5• + Cl2  C2H5Cl + Cl• Cl• + Cl•  Cl2 Cl• + C2H5•  C2H5Cl C2H5• + C2H5•  C4H10 Initiation Radicals formed by homolytic fission Propagation These steps feed each other the radicals needed to continue Termination Any two radicals can combine to terminate the reaction Concentration of radicals is low so this is a rare event u.v. A single radical can cause thousands of cycles of the propagation stage before it reaches termination This same mechanism applies to all of the halogens The alkane can be substituted multiple times, until every H has been replaced

Key Points Alkanes are unreactive They release a lot of energy on combustion, and are easy to handle which makes them good fuels Undergo free radical substitution to form halogenoalkanes and a hydrogen halide in the presence of UV light

Lesson 5 Alkenes

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Lesson 5: Alkenes Objectives: Describe the main addition reactions of the alkenes Extract an alkene from a citrus fruit

Reactivity of Alkenes Alkenes are considerably more reactive than alkanes and are a major industrial feedstock The reactivity is due to the double bond: The double bond contains 4 electrons This is a significant amount of charge which: Makes it attractive to electrophiles Enables it to polarise approaching molecules Most reactions of alkenes are addition reactions where two molecules come together to make one new one

Alkenes and hydrogen Alkene + hydrogen  alkane Reaction conditions: Hot Ni catalyst This is an addition reaction, in which the hydrogen adds across the double bond

Alkenes and hydrogen halides Alkene + hydrogen halide  halogenoalkane Reaction conditions: This reaction occurs very readily and needs no special conditions This is an addition reaction, in which the hydrogen halide adds across the double bond

Alkenes and halogens Alkene + halogen  dihalogenoalkane Reaction conditions: This reaction occurs very readily and needs no special conditions If the halogen used is an aqueous solution of bromine (bromine water), the orange-brown colour of bromine solution is decolourised. This is the standard test for alkenes.

Alkenes and water Alkene + water  alcohol Reaction conditions: Water must be steam Phosphoric or sulphuric acid catalyst This is the process used to make industrial ethanol Fermentation from sugar would be far too expensive!

Polymerisation Under the right conditions, alkene molecules will add to each other creating a polymer In this case, 1-bromo-2-fluoroethene polymerises to form poly-1- bromo-2-fluroethene Conditions: Vary from alkene to alkene but often include high pressure, temperature and a catalyst The carbons in the C=C double bonds form the carbon chain, everything else hangs off this chain

Drawing polymers Draw three-monomer lengths of the polymers formed by: Propene Styrene Pent-2-ene

Key Points Alkenes undergo addition reactions with: Hydrogen Hydrogen halides Halogens Water (steam) Alkenes undergo addition polymerisation Alkenes are very economically important due to the range of products they can make

Lesson 6 Alcohols

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Lesson 6: Alcohols Objectives: Explain the relative ease of combustion of the alcohols Describe the oxidation reactions of the alcohols Investigate the oxidation reactions of the alcohols

Alcohols as Fuels Alcohols combust more readily than equivalent alkanes but release less energy since they are already partially oxidised Alcohol + oxygen  carbon dioxide + water Alcohols are used as fuels: As a fuel for cars – either pure or blended with petrol Methanol as fuel for competitive motorsports including dragsters and monster trucks Much fuel ethanol is fermented from crops…crops that could otherwise be eaten, forcing up food prices. Is this ok?

Oxidation of alcohols The most important reactions of the alcohols are their oxidations A range of compounds will oxidise them so the oxidiser is often represented as [O] One oxidising agent you need to know is potassium dichromate, K2Cr2O7. When using this, orange Cr (VI) is reduced to green Cr (III) More on what this means in the oxidation and reduction unit See next slide for details

Oxidation reaction scheme

Key Points Alcohols are highly combustible Primary alcohols oxidise to form aldehydes, which oxidise to form carboxylic acids Secondary alcohols oxidise to form ketones Tertiary do not oxidise due to the 3 strong C-C bonds surrounding the –OH carbon

Lesson 7 Halogenoalkanes

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Lesson 7: Halogenoalkanes Objectives: Describe the substitution reactions of halogenoalkanes with a strong base Understand the SN1 and SN2 mechanisms for nucleophilic substitution Produce an animation showing the two different mechanisms

Nucleophilic Substitution One of the most important reactions undergone by halogenoalkanes is nucleophilic substitution A nucleophile is a ‘nucleus-loving’ species that is attracted to positive charges. Nucleophiles have either full negative charges or delta-negative charges Water and hydroxide are both nucleophiles In this case we can also call the reaction ‘hydrolysis’ The carbon in the carbon-halogen bond has a + charge due to the greater electronegativity of the halogen This makes it susceptible to attack by nucleophiles

Halogenoalkanes and strong bases A substitution reaction takes place, where the halogen atom is displaced by the hydroxide ion halogenoalkane + sodium hydroxide  alcohol + sodium chloride Conditions: Aqueous base Gently warmed (can at room temperature, but may be quite slow) This is a nuclephilic substitution. The C attached to the halogen is + due to the high electronegativity of the halogen The OH- ion (our nucleophile) is attracted to the + carbon A nucleophile is a species with a negative charge or a lone pair that is attracted to positive/delta-positive atoms

SN1 – Unimolecular nucleophilic substitution – animation here Unimolecular because only one molecule is involved in the rate determining step The rate determining step involves the spontaneous breaking of the carbon-halogen bond and is a heterolytic fission, forming a halide ion and a carbocation intermediate The stability of the carbocation intermediate is a key factor in SN1 The attack by the nucleophile (OH-) is very fast, but does need the carbocation to be formed first The rate is only dependent on the concentration of the halogenoalkane: Rate = k[halogenoalkane] Note: the curly arrows show the movement of pairs of electrons

SN2 – Bimolecular nucleophilic substitution – animation here Bimolecular because two molecules are involved in the rate determining step In the rate determining step, the nucleophile (OH-) attacks at the same time as the carbon-halogen bond breaks. The reaction passes through a negative transition state where the carbon has a ‘half-bond’ to both the –OH and the –Br with an overall negative charge The rate is dependent on both the concentration of the halogenoalkane and the nucleophile Rate = k[halogenoalkane][nucleophile]

SN1 or SN2? 1o halogenoalkanes predominantly undergo SN2 2o halogenoalkanes undergo a mix of SN1 and SN2 3o halogenoalkanes predominantly undergo SN1 You do not need to know why at SL, but will find out more at HL

Refresh Halogenoalkanes undergo substitution with strong bases to form alcohols The reaction has two possible mechanisms: SN1: the C-X bond breaks and then the nucleophile attacks SN2: the nucleophile attacks at the same time as the C-X bond breaks The mechanism depends on the halogenoalkane: 1o - SN2 2o - SN1 and SN2 3o - SN1