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Organic Chemistry. Main Menu Menu Lessons 1-11:  Lesson 1 – Homologous Series Lesson 1 – Homologous Series  Lesson 2 – Isomers Lesson 2 – Isomers 

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Presentation on theme: "Organic Chemistry. Main Menu Menu Lessons 1-11:  Lesson 1 – Homologous Series Lesson 1 – Homologous Series  Lesson 2 – Isomers Lesson 2 – Isomers "— Presentation transcript:

1 Organic Chemistry

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

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

4 Main Menu Lesson 1 Homologous Series

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

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

7 Main Menu We Are Here

8 Main Menu 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

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

10 Main Menu 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

11 Main Menu 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?

12 Main Menu Formulas  Draw the compound with the formula C 4 H 8 O

13 Main Menu What did you get?  Clearly a molecular formula is not enough!

14 Main Menu Types of Formula  Empirical Formula C 4 H 8 O C 4 H 8 O  Molecular Formula C 4 H 8 O C 4 H 8 O  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! CH 2 =CHCH 2 CH 2 OH CH 2 =C(CH 3 )CH 2 OH

15 Main Menu 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 C 4 H 8 O compounds (not the cyclic ones)

16 Main Menu 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

17 Main Menu Lesson 2 Isomers

18 Main Menu We Are Here

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

20 Main Menu Isomers  Compounds with the same molecular formula but different structural formula  The 20 different C 4 H 8 O 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

21 Main Menu Structural Isomers of the Alkanes  The (non-cyclic) alkanes have the general formula C n H 2n+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

22 Main Menu Did you get them all?

23 Main Menu And skeletally

24 Main Menu 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

25 Main Menu 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

26 Main Menu 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’

27 Main Menu Did you get them?

28 Main Menu 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

29 Main Menu Lesson 3 Meet the Families

30 Main Menu We Are Here

31 Main Menu 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

32 Main Menu 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 1 o, 2 o and 3 o  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

33 Main Menu 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

34 Main Menu 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

35 Main Menu Lesson 4 Alkanes

36 Main Menu Refresh  The following is a computer-generated representation of the molecule, methyl 2- hydroxy benzoate, better known as oil of wintergreen. a) 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. b) Name all the functional groups present in the molecule. H H H H H H H H C C C C C C C C O O O 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.

37 Main Menu We Are Here

38 Main Menu 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

39 Main Menu 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 CO 2 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

40 Main Menu 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.

41 Main Menu Halogenation  Alkanes will undergo halogenation if reacted with a halide in the presence of u.v. light.  For example:  C 2 H 6 (g) + Cl 2 (g) CH 3 CH 2 Cl(g) + HCl(g) ethane chloroethane  This reaction is an example of free radical substitution u.v.

42 Main Menu Radicals  Radicals are species with unpaired electrons  They are crazy reactive  Halogens form radicals when hit by uv light of the right frequency:  Cl 2 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 Cl 2 molecule and each of the Cl radicals u.v.

43 Main Menu Reaction Mechanism: Free Radical Substitution  Cl 2 2 Cl  Cl + C 2 H 6  C 2 H 5 + HCl  C 2 H 5 + Cl 2  C 2 H 5 Cl + Cl  Cl + Cl  Cl 2  Cl + C 2 H 5  C 2 H 5 Cl  C 2 H 5 + C 2 H 5  C 4 H 10  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  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 u.v.

44 Main Menu 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

45 Main Menu Lesson 5 Alkenes

46 Main Menu We Are Here

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

48 Main Menu 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

49 Main Menu 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

50 Main Menu 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

51 Main Menu 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.

52 Main Menu 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!

53 Main Menu 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

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

55 Main Menu 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

56 Main Menu Lesson 6 Alcohols

57 Main Menu We Are Here

58 Main Menu 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

59 Main Menu 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?

60 Main Menu 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, K 2 Cr 2 O 7.  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

61 Main Menu Oxidation reaction scheme

62 Main Menu 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

63 Main Menu Lesson 7 Halogenoalkanes

64 Main Menu We Are Here

65 Main Menu Lesson 7: Halogenoalkanes  Objectives:  Describe the substitution reactions of halogenoalkanes with a strong base  Understand the S N 1 and S N 2 mechanisms for nucleophilic substitution  Produce an animation showing the two different mechanisms

66 Main Menu 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

67 Main Menu 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

68 Main Menu S N 1 – Unimolecular nucleophilic substitution – animation hereanimation 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 S N 1  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

69 Main Menu S N 2 – Bimolecular nucleophilic substitution – animation hereanimation 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]

70 Main Menu S N 1 or S N 2?  1 o halogenoalkanes predominantly undergo S N 2  2 o halogenoalkanes undergo a mix of S N 1 and S N 2  3 o halogenoalkanes predominantly undergo S N 1  You do not need to know why at SL, but will find out more at HL

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


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