1. Name the homologous series
C4H10
C4H8
In groups discuss everything you know about these 2 homologous series.
What type of hydrocarbons do they belong to?
What about C6H12? What structures are possible with this molecular formula?
What type of hydrocarbons do these belong to?
What about C6H6?

2. a formula of C6H6 STRUCTURE OF BENZENE a molecular mass of 78 and
Primary analysis revealed benzene had...
an empirical formula of CH and
a molecular mass of 78 and
a formula of C6H6

3. a formula of C6H6 HAD ALTERNATING DOUBLE AND SINGLE BONDS
STRUCTURE OF BENZENE
Primary analysis revealed benzene had...
an empirical formula of CH and
a molecular mass of 78
a formula of C6H6
Kekulé suggested that benzene was...
PLANAR
CYCLIC and
HAD ALTERNATING DOUBLE AND SINGLE BONDS

4. STRUCTURE OF BENZENE
HOWEVER...
• it did not readily undergo electrophilic addition - no true C=C bond
• only one 1,2 disubstituted product existed
• all six C—C bond lengths were similar; C=C bonds are shorter than C-C
• the ring was thermodynamically more stable than expected

5. To explain the above, it was suggested that the structure oscillated
STRUCTURE OF BENZENE
HOWEVER...
• it did not readily undergo electrophilic addition - no true C=C bond
• only one 1,2 disubstituted product existed
• all six C—C bond lengths were similar; C=C bonds are shorter than C-C
• the ring was thermodynamically more stable than expected
To explain the above, it was suggested that the structure oscillated
between the two Kekulé forms but was represented by neither of
them. It was a RESONANCE HYBRID.

6. Benzene
To be able to describe and explain the structure of benzene
To know specific reactions associated with benzene and other common substituted aromatic compounds
C6H6
= benzene
= an aromatic hydrocarbon
= an arene

7. X-ray diffraction and evidence for benzene’s structure
Two structures are used to represent benzene:
The KEKULÉ structure;
The modern DELOCALISED structure – 1930s
Cyclohexa-1,3,5-triene Bond lengths would be 0.154nm and 0.134nm alternating
X-ray diffraction data has shown that the carbon atoms in benzene are at the corners of a REGULAR HEXAGON. These data have also shown all C-C bonds to be 0.139nm; therefore an intermediate between a single and double bond

8. Thermochemical data and stability of benzene
When unsaturated hydrocarbons are reduced to the corresponding saturated compound, energy is released. The amount of heat liberated per mole (enthalpy of hydrogenation) can be measured.
When cyclohexene (one C=C bond) is reduced to cyclohexane, 120kJ of energy is released per mole.
C6H10(l) + H2(g) C6H12(l)
If benzene contained three separate C=C bonds how much energy would it release per mole when reduced to cyclohexane
Theoretically, if benzene contained three separate C=C bonds it would release 360kJ per mole when reduced to cyclohexane
C6H6(l) + 3H2(g) C6H12(l)
Benzene releases only 208kJ per mole when reduced, putting it lower down the energy scale
Theoretical
- 360 kJ mol-1
(3 x -120) 2 3
Experimental
- 208 kJ mol-1
- 120 kJ mol-1

9. Thermochemical data and stability of benzene MORE STABLE THAN EXPECTED
Benzene is 152kJ per mole more stable than expected.
This value is known as the RESONANCE ENERGY.
MORE STABLE THAN EXPECTED
by 152 kJ mol-1
Theoretical
- 360 kJ mol-1
(3 x -120) 2 3
Experimental
- 208 kJ mol-1
- 120 kJ mol-1

10. Consider the electron configuration of carbon1 1s 2 2s 2p
The electronic configuration of a carbon atom is 1s22s22p2
If you provide a bit of energy you can promote (lift) one of the s electrons into a p orbital. The configuration is now 1s22s12p3 1 1s 2 2s 2p
Why would this be favourable?

11. Hybridisation of orbitals
The four orbitals (1 x s and 3 x p) combine (HYBRIDISE) to give 4 new orbitals. All four orbitals are energetically equivalent.
2s22p2
2s12p3
4 x sp3
HYBRIDISE
sp3 HYBRIDISATION

12. Hybridisation of orbitals
Alternatively, only 3 orbitals (1 x s and 2 x p) combine (HYBRIDISE) to give 3 new orbitals. All 3 orbitals are energetically equivalent. The remaining 2p orbital is unchanged.
2s22p2
2s12p3
3 x sp2 2p
HYBRIDISE
sp2 HYBRIDISATION

13. Hybridisation of orbitals
2s22p2
2s12p3
3 x sp2 2p
HYBRIDISE
sp2 HYBRIDISATION
2s22p2
2s12p3
4 x sp3
HYBRIDISE
sp3 HYBRIDISATION

14. Alkanes vs Alkenes
In ALKANES, the 4 sp3 orbitals repel each other into a tetrahedral arrangement.
In ALKENES, the 3 sp2 orbitals repel each other into a planar arrangement and the 2p orbital lies at right angles to them

15. Alkenes Covalent bonds are formed by overlap of orbitals.
An sp2 orbital from each carbon overlaps to form a single C-C bond.
The resulting bond is called a SIGMA (δ) bond.

16. Alkenes
The two 2p orbitals also overlap. This forms a second bond; it is known as a PI (π) bond.
For maximum overlap and hence the strongest bond, the 2p orbitals are in line.
This gives rise to the planar arrangement around C=C bonds and a shorter bond than in the corresponding alkane (0.134nm).

17. Ethene
2 sp2 orbitals overlap to form a sigma bond between the 2 carbon atoms
2 2p orbitals overlap to form a pi bond between the 2 carbon atoms
s orbitals in hydrogen overlap with the sp2 orbitals in carbon to form C-H bonds
the resulting shape is planar with bond angles of 120º

18. Structure of benzene – a delocalised structure
Theory: Instead of three localised (in one position) double bonds,
the six p (p) electrons making up those bonds are delocalised around the ring by overlapping the p orbitals. There would be no double bonds and all bond lengths would be equal. It would also give a planar structure.
6 single bonds
one way to overlap
adjacent p orbitals
another
possibility
delocalised pi
orbital system
This final structure fits with the reactivity of benzene:
Very stable
Resistant to electrophilic addition, typically seen in alkenes.
Undergoes electrophilic substitution, which does not affect the delocalised pi orbital system.

19. Benzene X-ray studies show that,
A Benzene molecule is a flat (planar) molecule. All carbon and hydrogen atoms lie in the same plane.
It has a regular hexagon structure with all six carbon atoms lying at the corners. Each carbon atom is bonded to three other atoms.
All carbon-carbon bond lengths are equal at 139 pm.
All CC angles (or CH angles) are equal at 120°.
IR spectra show that benzene does not have the typical strong absorptions of CH bonds in CH2 and CH3 groups in the wavenumber range cm-1 , nor the C=C absorption of an alkene, like oct-1-ene, just below 1700 cm-1. Instead, and unlike alkanes and alkenes, benzene has strong absorptions at about 3050 cm-1and 750 cm-1. All this provides further evidence that benzene does not have normal C-C or C=C bonds in its structure.

20. How do you name benzene derivatives with more than one substituent?
Naming arenes
Be careful, this can be confusing!
Names use either phenyl (C6H5- notation) or the benzene notation.
General rule is that when a hydroxy (OH) or amine (NH2) group is substituted into the ring, they use the PHENYL notation – Phenol and phenylamine respectively.
In majority of other cases, compounds named as substituted products (derivatives) of benzene, e.g. nitrobenzene (C6H5-NO2) or methylbenzene (C6H5-CH3)
How do you name benzene derivatives with more than one substituent?

21. 1,3,5-trichlorobenzene

22. 1-bromo-4-chlorobenzene

23. phenylamine

24. Benzene – Key reactions
Benzene reacts mainly via electrophilic substitution.
The electron density of the benzene ring attracts electrophiles.
Reactions are NOT addition. Instead, electrophiles substitute into the ring, maintaining the delocalised structure and stability of the ring.
N.B. Benzene can be drawn as either:
BUT remember, benzene IS NOT made up of alternating single and double bonds!

25. Reactions of benzene (derivatives)
The reactions of arenes
The simplest and most important arene is benzene. Unfortunately, benzene is toxic and mildly carcinogenic, so it cannot be used except in research and certain industrial processes. Fortunately, the reactions of benzene are also given by many of its derivatives and in the experiments below you will be using methoxybenzene
Besides studying the reactions of arenes you will also be comparing arenes with alkanes and alkenes by repeating the methoxybenzene tests with cyclohexane and cyclohexene.
Wear goggles for the whole of this class practical and remember to keep bottles of methoxybenzene, cyclohexane and cyclohexene well away from any flames.
A Combustion
Working in a fume cupboard, put 3 drops of methoxybenzene on a small pea-sized ball of mineral wool in a crucible. Set fire to the methoxybenzene using a lighted splint.
Repeat the test with cyclohexane and then with cyclohexene.
Describe and compare the flames from each compound.
Write an equation for the combustion of methoxybenzene bearing in mind what you have observed.

26. B Bromination
Carefully, add 5 drops of methoxybenzene to 1 cm3 of 2% bromine in an inert solvent. Dip a glass rod in concentrated ammonia and bring this near the mouth of the test tube to see if fumes of hydrogen bromide have been produced.
Repeat the test with cyclohexane and then with cyclohexene.
Describe what happens with each compound.
Which of the compounds
a) reacted with the bromine
b) reacted to produce hydrogen bromide?
Which of the compounds have taken part in
a) substitution reactions
b) addition reactions?
(Hint: Would HBr be produced in an addition reaction?)
Write possible equations for the reactions which have occurred. (Remember that the reactions of methoxybenzene will involve the benzene ring.)

27. C Nitration
Carefully add 1 cm3 of concentrated nitric acid to 1 cm3 of water. Then, add 5 drops of methoxybenzene and warm the mixture in a water bath.
Describe what you observe.
When methoxybenzene reacts with nitric acid, one of the products is methoxynitrobenzene, CH3O-C6H4-NO2. Write a possible equation for the reaction.
In this class practical, like many others with organic chemicals, you have used toxic, corrosive and highly flammable materials. What steps have been taken in this practical to use them safely and successfully?

28. Key reactions of benzene
Nitration:
Reagents conc. nitric acid and conc. sulphuric acid (catalyst)
Conditions heat under reflux at 55°C
Equation C6H HNO3 C6H5NO H2O
nitrobenzene
Halogenation:
Reagents chlorine and a halogen carrier (catalyst)
Conditions reflux in the presence of a halogen carrier (Fe, FeCl3, AlCl3).
Chlorine is non polar so is not a good electrophile.
The halogen carrier is required to polarise the halogen
Equation C6H Cl2 C6H5Cl HCl

29. Key reactions of benzene
Sulfonation
Reagents ‘fuming’ sulfuric acid (mixture of conc H2SO4 and dissolved SO3 – conc H2SO4 at r.t. does not react in this way)
Conditions room temperature
Equation C6H SO3 C6H5SO3H (benzene sulfonic acid)
[H+]
Hydrogenation
Reagents H2 in presence of Ni catalyst
Conditions Heat at 200ºC
Equation C6H H2 C6H12

30. Key reactions of benzene
Friedel-Crafts: Alkylation
Overview Alkylation involves substituting an alkyl (methyl, ethyl) group – hard to limit substitutions (alkyl groups activate ring)
Reagents Halogenoalkane (RX) and anhydrous aluminium chloride AlCl3
Conditions reflux
Electrophile a carbocation R+ (e.g. CH3+)
Equation C6H C2H5Cl C6H5C2H HCl

31. Industrial Alkylation
Industrial Alkenes are used instead of haloalkanes but an acid must be present
Phenylethane, C6H5C2H5 is made by this method
Reagents ethene, anhydrous AlCl3 , conc. HCl
Electrophile C2H5+ (an ethyl carbonium ion)
Equation C6H C2H4 C6H5C2H5 (ethyl benzene)
Mechanism the HCl reacts with the alkene to generate a carbonium ion
electrophilic substitution then takes place as the C2H5+ attacks the ring
Use ethyl benzene is dehydrogenated to produce phenylethene (styrene);
this is used to make poly(phenylethene) - also known as polystyrene

32. Key reactions of benzene
Friedel-Crafts: Acylation
Overview Acylation involves substituting an acyl (methanoyl, ethanoyl) group Electron withdrawing carbonyl ensures monosubstitution
Reagents Acyl chloride (RCOX) and anhydrous aluminium chloride AlCl3
Conditions Reflux 50°C
Electrophile RC+= O ( e.g. CH3C+O )
Equation C6H CH3COCl C6H5COCH HCl

33. Mechanisms of substitution
Describe the mechanism of the electrophilic substitution reactions of benzene in:
Nitration
Friedel-Crafts reactions
Halogenation
including the formation of the electrophile

34. Electrophilic substitution - steps
Formation of the electrophile e.g. NO2+
Electrons from ring form intermediate
H+ removed from intermediate reforming ring of delocalised electrons
Reform catalyst
Delocalisation remains over 5 carbons

35. Formation of the electrophile
Nitration
HNO3 + H2SO4  H2NO3+ + HSO4-  H2O + NO2+ + HSO4-
Alkylation
CH3CH2Cl + AlCl3  CH3CH2+ + AlCl4-
Acylation
CH3COCl + AlCl3  CH3CO+ + AlCl4-
Halogenation
Br2 + FeBr3  Br+ + FeBr4-

36. Phenol Increased acidity: delocalisation of charge
melting point (°C)
boiling point (°C)
C6H5OH
182
C6H5CH3
-95.0
111
Increased acidity: delocalisation of charge
Decrease acidity: high electronegativity of oxygen
 Very weak acid

37. Reactions of phenol

38. Reactivity of phenol Increased electron density
Easier to donate electrons

39. Amines Methylamine: CH3NH2 Dimethylamine: (CH3)2NH
Trimethylamine: (CH3)3N

40. Reactions of amines
i characteristic smell Fishy! ii miscibility with water Short chain alkylamines – soluble Long chain or arylamines – insoluble Increasing solubility: hydrogen bonding and reaction with water Decreasing solubility: Non-polar organic chains and rings Aryl amines less alkaline than alkyl amines – why? iii formation of salts with acid Form ionic salts that are more soluble than the original amine R-NH2 + HCl  RNH3+ + Cl-

41. Hexaaquacopper (II) ion
Hydrated metal ions 2+ O H O H O H Cu
Covalent bond O H O H
Dative bond O H
Hexaaquacopper (II) ion

42. Hydrated metal ions Cu H O H O O-H Covalent bond H O O-H Dative bond O

43. Tetraamminediaquacopper (II) ion
An ammine complex ion 2+ O H
NH3
H3N Cu
NH3
H3N O H
Tetraamminediaquacopper (II) ion

44. Reactions of amines
iv complex ion formation with copper(II) ions Lone pair of electrons on nitrogen forms dative bonds to metal cation v treatment with ethanoyl chloride and halogenoalkanes Amines act as nucleophiles

45. Reactions of amines
Cause of formation of secondary, tertiary and quaternary amines

46. Preparation of phenylamine
Nitration of benzene
Reduction of nitrobenzene
N.B. LiAlH4 is not a suitable reagent

47. Preparation of phenylamine

48. Formation of diazonium ions
NaNO2/HCl (forms HNO2 in situ)
RNH R-N+≡N Cl-
Alkyl diazonium ions decompose on formation to form R+ + N2 (g)
R+ joins with nearest nucleophile to form e.g. ROH or RCl
Benzenediazonium ions are stable below 10oC
Why is this reaction done at 5oC?

49. Reactions of benzenediazonium ion
If allowed to warm above 10oC:
forms benzene cation and nitrogen gas
cation reacts to form e.g. phenol or chlorobenzene
Reaction with phenol or phenylamine class compounds – azo dyes
N.B. In fact the phenol has formed phenoxide in the solution of sodium hydroxide

50. Azo dyes
Predict the structure of the azo dye formed between benzenediazonium and napthalene-2-ol

52. Homework Synthetic techniques
Tuesday: organic preparation practical assessment
Produce a hand illustrated description of each of these techniques:
refluxing
purification by washing, eg with water and sodium carbonate solution
solvent extraction
recrystallization
drying
distillation
steam distillation
melting temperature determination
boiling temperature determination
Review questions 1-3 p 206

53. Amines and amides
Why is the amine basic when the amide isn’t?

54. What would happen if…
1,6-diaminohexane came into contact with hexan-1,6-dioyl chloride?
Draw the products
What class of reaction is this?

55. Polymers Addition Alkenes Double bonds open
Initiator starts reaction e.g. peroxide
Polystyrene

56. Addition polymers POLYTHENE

57. Addition polymers POLYTETRAFLUOROETHENE (PTFE – Teflon)

58. Addition polymers POLYPROPENE

59. Addition polymers POLYCHLOROETHENE (PVC)

60. Polymers Condensation
Diol and dioyl chloride/dioic acid or diamine and dioyl chloride/dioic acid
Small molecule eliminated

61. Condensation polymerisation Formation of nylon

62. Simplified condensation polymerisation
H2N--NH2 HOOC--COOH H2N--NH2 HOOC--COOH 
-HN--NHOC--COHN--NHOC--CO-
H-O-H H-O-H H-O-H

63. chloroethene
tetrafluoroethene
propene
Poly(propene)
Poly(tetrafluoroethene)
Poly(chloroethene)

64. Properties of polymers
Nylon (polyamide)
Soften above their melting temperatures, Tm, thermoplastics
The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity.
The planar amide (-CO-NH-) groups are very polar, so nylon forms multiple hydrogen bonds among adjacent strands. Because the nylon backbone is so regular and symmetrical nylons often have high crystallinity and make excellent fibres.
Parallel strands can participate in extended, unbroken, multi-chain β-pleated sheets, a strong and tough supermolecular structure similar to that found in natural silk.
When dry, polyamide is a good electrical insulator. However, polyamide is hygroscopic. Nylon is less absorbent than wool or cotton.

65. Properties of polymers
Poly(ethenol) (PVA, Polyvinyl alcohol )
Water soluble polymer
It is odourless and nontoxic.
It has high tensile strength and flexibility, as well as high oxygen and aroma barrier properties.
However these properties are dependent on humidity. The water, which acts as a plasticiser, will then reduce its tensile strength.
It is fully degradable and dissolves quickly
Used as a water-soluble film useful for packaging. An example is the envelope containing laundry detergent in "liqui-tabs".

66. Amino acids
i acidity and basicity and the formation of zwitterions ii separation and identification by chromatography iii effect of aqueous solutions on plane polarised monochromatic light iv formation of peptide groups in proteins by condensation polymerization v reaction with ninhydrin.

67. Proteins
Structure
Where R can be a variety of groups e.g. -H glycine -CH3 alanine -CH2CH2COOH glutamic acid -CH2OH serine -CH2SH cysteine -CH2CH2CH2CH2NH2 lysine
Proteins are pH sensitive – predict the structure of an amino acid at pH1, 7 and 12
In neutral solutions the acid group (-COOH) loses its hydrogen ion becoming negative and the amine group gains a hydrogen ion to become positive:
H3N+CH2COO-
Zwitter ion

68. Isoelectric point
The charges cancel so it would not be attracted towards either a positive or negative electrode (iso = same)
In acidic conditions (pH < 7 e.g. fruit or vinegar) hydrogen ions are added to the –COO-
H3N+CH2COOH
This would be attracted towards the cathode (negative electrode)
In alkaline conditions (pH > 7 e.g. baking soda) hydrogen ions are taken from the positive amine group
H2NCH2COO-
This would be attracted towards the anode (positive electrode)
The acidic (e.g. glutamic acid and aspartic acid) and basic (e.g. ornithine, arginine, lysine and histidine) side chains are also affected
Different proteins have their isoelectric points at different pHs depending on the combination of acidic and basic side groups
pH effects proteins because removing charges from side chains removes the electrostatic attractions between different sections and the tertiary structure unravels (denatures) e.g. souring milk – pH 4.6 the protein separates as curd

69. The two enantiomers of alanine, D-Alanine and L-Alanine
Of the standard α-amino acids, all but glycine can exist in either of two enantiomers, called L or D amino acids, which are mirror images of each other.
While L-amino acids represent all of the amino acids found in proteins during translation in the ribosome, D-amino acids are found in some proteins produced by enzyme posttranslational modifications

70. Polymerisation - condensation

72. Using chromatography
Chromatography involves the separation and identification of compounds using a stationary phase (solid) and a mobile phase (liquid or gas).

73. Identifying amino acids - ninhydrin and Rf values