Unit 4 + 5 (2008- syllabus)

1. Unit 4 + 5 (2008- syllabus) 11 Aug 2011

2. Paper details • U4 Exam 1h 40m. 3 sections. (90 mks??). Section A,B & C • A = multiple choice (objective Q's) • B = Short answers & extended Q's inc. analysis and evaluation of practical work • C = Data questions and use of data

3. Paper details • U5 Exam 1h 40m. 90 marks. Section A,B & C • A = multiple choice (objective Q's) • B = Short answers & extended Q's inc. analysis and evaluation of practical work • C = Questions requiring extended answers. 'Senarios' may be given and students expected to answer Q's based on the chemistry presented. “Contemporary context questions”. • Sections B & C will be where a students can show their full ability. Knowledge from previous units required. • QWC considered. Data book can be used.

4. Unit 2.10(Organic I) Reaction summaryFollowed by Unit 4.8 Further organic chemistry (Organic II) Mike Allan Hamzah. INTEC 2010. My information here is free of all restrictions 

5. Unit 2.10 summary Recall of function groups… Functional groups. • Atoms or sequences of atoms causing deviations in electron density to that of its hydrocarbon equivalent. E.g ethanol & ethane (C=C, -X, -OH, -COOH <<< Unit 2.10) CMgBr, -COOH, COOR, CHO, CO, -NH2,-NHR, -NR2, -COX, CONR2, CN, Ether: R3C-O-CR3(R=H or carbon)

6. Pyrolysis(thermal cracking)not on syallabus Alkanes Alkanesof differenttypes andalkenes As fuels Functionalizationvia halogen radicals(need X2 and U.V.) CO2 + H2O Halogenoalkanes

7. ADDITION REACTIONS !!! cis- and trans- isomers possibledue to restricted C=C bond C-C X X C-C HO OH Alkenes C-C-C H X Hydrogenhalogenation Use MarkovnikovIf unsymmetrical Halogenation(X2) C=C HydrogenationH2(g) + Rayney nickel KMnO4(aq)& OH-(aq) polymerization Polymers poly(ethene) - PEpoly(propene) – PPpoly(vinylchloride) - PVCpoly(tetrafluoroethene) – PTFE Alkenes A diol

8. Nucleophilic substitution and Elimination reactions Halogenoalkanes C=C KOH(ethanolic)Reflux under heat(dehydrohalogenation)Elimination! C chainextended !!! KCNRefluxunder heat(ethanol solvent) C-X C-C≡N Excess c.NH3Reflux under heat KOH(aq)Reflux under heat Displaced X-This can thereforebe uses to testfor the (halogen)type of R-X After reflux add HNO3 (aq)THEN Ag(NO3)(aq) C-NH2 C-OH Polysubstitutionpossible. To 20 and 30 amine

9. Nucleophilic substitution, elimination, and oxidation reactions Alcohols C-O-Na+ sodium alkoxide O Aldehydes&ketones C=C Na(s) C c. H2SO4 170o(elimination) Al2O3(s) 300oC andP4O10can alsobe used R oxidation R’ C-OH If aldehyde oxidation COOH NaX and c.H2SO4Reflux under heat PCl5 / PCl3 / SOCl22P + 3Br22P + 3I2 Carbox. acids C-X K2Cr2O7 (aq) + H2SO4(aq)Distill for aldehydeReflux for carbox. acid. N.B. Initial alcoholmust be dry Halogenoalkane(alkyl halide)

10. 4.8 Further Organic 11 Aug 2011

11. 4.8 Further Organic enantiomers

12. 4.8 Further Organic 4.8.1 Chiralitya) recall the meaning of structural and E-Z isomerism (geometric/cis-trans isomerism) • Identify largest group by atomic number (or mass) on one side of db (e.g A & B) • Do the same on other side (D and G) • Atoms of greatest at# on same side of the db, then compound = Z isomer. Zis is cis E = trans

13. 4.8.1 Chiralityb) demonstrate an understanding of the existence of optical isomerism resulting from chiral centre(s) in a molecule with asymmetric carbon atom(s) and understand optical isomers as object and non-superimposable mirror images • Chiral = non superimposable on its mirror image. A pair of enantiomers is the result. • Asymetric = no element of mathematical symmetry(reflection, rotation, reflection & inversion) http://chemed.chem.purdue.edu/genchem/topicreview/bp/1organic/chirality.html http://astrobiology.berkeley.edu/Mars101/definitions.htm

14. A chiral centre is the atom around which the molecule is unsymmetrical – For A-level this is most likely to be a carbon atom. • A molecule and it’s non-superimposible mirror image, give a pair of enantiomers. i.e. each molecules is called an enantiomer of its mirror image

15. 4.8.1 Chiralityc) recall optical activity as the ability of a single optical isomer to rotate the plane of polarization of plane-polarized monochromatic light in molecules containing a single chiral centre and understand the nature of a racemic mixture • A substance is optically active if it rotates the plane of polarisation of monochromatic plane polarised light (ppl). [ pop of monoppl ] • One enantiomer will rotate light by some angle, say +x degrees, but the other enantiomer will rotate the plane of monochromatic ppl by the same magnitude but in the opposite direction, say –x degrees. Huh?...

17. Huh?... http://www.denhartog-scientific.nl/Producten/Polarimeter/Polarisg[1].jpg http://andromeda.rutgers.edu/~huskey/images/polarimeter.jpg

18. A mixture of an equal amount of a pair of enantiomers shows NO optical rotation – the rotations cancel. • Such a mixture is called a racemic mixture.

19. One source of chirality (the property of being chiral) is in aliphatics with 4 different gps on the same C atom (as at A-level) … but 4 diff gps isn’t the only way u can get chiral molecules. E.g. DNA helix, spirenes, etc… http://chemistry.umeche.maine.edu/CHY251/Chirality.gif

20. E,g, the molecule limonene • Different optical isomers can have radically different BIOLOGICAL properties. Phys props (other than optical rotation) usually the same. http://waynesword.palomar.edu/images/limonene.jpg

21. Drug Thalidomide – enantiomers showing severe detrimental different biological effects

22. Victims of Thalidomide

23. 4.8.1 Chiralityd) use data on optical activity of reactants and products as evidence for proposed mechanisms, as in SN2 and SN1 and addition to carbonyl compounds. • SN2(animation page)(OR video1vid2)rxns involveinversion of centre of chiraity(stereocentre). Product is optically active – will cause plane of polarisation of monochromatic ppl to rotate.Transition state.

24. SN2 “Stereochemistry at a glance By Jason Eames, Josephine Peach. Google books P42

25. 4.8.1 Chiralityd) use data on optical activity of reactants and products as evidence for proposed mechanisms, as in SN2 and SN1 and addition to carbonyl compounds. • SN1(animation page) rxns have the substrate give racemic mixtures (mixtures of both enantiomer products). Product mixture is optically inactive – no effect of plane of polarisation of monochromatic ppl.Carbocation intermediate (may rearrange).

26. SN1 “Mechanisms in organic reactions”  By Richard A. Jackson.Google books P104

27. 4.8.2 Carbonyl compounds a) give examples of molecules that contain the aldehyde or ketone functional group • Aldehydes RCHO R can be H or hydrocarbon. Methanal, ethanal, propoanal… benzaldehyde • Ketones RCOR’ R cannot be H, must be hydrocarbon (no methanone or ethanone) propanone(acetone), cyclohexanone Ald’s and ket’s with larger more complicated perfumes and flavourings. Volatility is important.

28. 4.8.2 Carbonyl compounds b) explain the physical properties of aldehydes and ketones relating this to the lack of hydrogen bonding between molecules and their solubility in water in terms of hydrogen bonding with the water Electron density maps Red = - Methanal(polar) gas Propanone (polar) Volatile liquid Can H bond with water.!! & both polar, so soluble in water up to a few C’s long.

29. Ethanal (not shown) is the first aldehyde to be liquid at RTP. Bpt > corresponding alkanes, but < than corresponding alcohols. http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ch17/figures/methanalepot.jpg http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ch17/figures/acetoneepot2.jpg

30. Aldehydes ‘n Ketones : : O O .. .. C C C C C H ketone aldehyde Aldehydes tend to be more reactive than ketones because, sterically, of the lack of extra alkyl chain as present in ketones. Also the alkyl chain, by inductive effect (+I), releases e- density to carbonyl and lowering charge on carbonyl, delocalizing the charge over the nearby area.

31. 4.8.2 Carbonyl compoundsc) describe and carry out, where appropriate, the reactions of carbonyl compounds. This will be limited to: • oxidation with Fehling’s or Benedict’s solution, Tollens’ reagent and acidified dichromate(VI) ions • reduction with lithium tetrahydridoaluminate (lithium aluminium hydride) in dry ether

32. Aldehydes ‘n Ketones OXIDATION Reduction Alcohols Carbonyls Carbox. acids 1O Alcohol aldehyde carboxylicacid 2O Alcohol ketone 3O Alcohol Aldehydes can undergo oxidn and Redn Ketones undergo Redn Acts as if a source of H- (a nucleophile) NaBH4(can be aq too!) LiAlH4in dry ether(esters can be reduced too!!!)

33. Aldehydes ‘n Ketones OXIDATION • Aldehydes can be oxidised by a number of compounds, some are employed as a TEST to discriminate aldehydes from ketones • Fehlings solution (Cu2+ complex) • Tollens reagent / test (ammoniacal silver nitrate – [Ag(NH3)2]+ complex • Acidified K2Cr2O7(aq) or acidified KMnO4(aq)

34. Aldehydes ‘n Ketones 1) Fehlings soln Fehlings A is a solution of CuSO4(aq) Fehlings B sodium tartrate solutionand NaOH Both solutions mixed together toform the chelated Cu2+ after initial Cu(OH)2 ppte seenby the bidentate tartrate ions surrounding the Cu2+- deprotonation of hexaaqua ligand does not occur – tartrate is a stronger ligand. Cu2+ only reacts in one way and that is to gain electrons! It causes the loss of e- from a different species  is an O.A. On heating (to inc. rate of rxn), a red Cu(I) oxide precipitate forms

35. Aldehydes ‘n Ketones 2) Tollens reagent AgNO3(aq) + few drops of NaOH(aq)  Ag(OH)(s) Add NH3(aq) until black ppte just dissolves.[Ag(NH3)2]+ forms {counter ion = - OH} Heat with aldehyde andAg(s) is depositedon walls of glass container.A silver mirror is formed. If solution or container is dirty grey / black Ag2O(s) ppte can form.

36. INTERVAL Picoplankton – an award winning micrograph image

37. Aldehydes ‘n Ketones - - - ↼ HCN H+ + -:CN ⇁ 4.8.2 Carbonyl compoundsc) describe and carry out, where appropriate, the reactions of carbonyl compounds. This will be limited to: iii. nucleophilic addition of HCN in the presence of KCN, using curly arrows, relevant lone pairs, dipoles and evidence of optical activity to show the mechanism • In rxn with of cyanide anions with halogenoalkanes,(nucleophilic substitution), X substitutes (leaves) with :C≡N, so simply use KCN in a mix of ethanol and water solvent and refluxing under heat. • However in the addition reactions with carbonyls, nucleophilic addition takes place. HCN(a gas) adds rapdily to carbonyls, • e.g ethanal + HCN(g)  2-hydroxypropanenitrile. CH3 CH(OH)-CN • HCN made by adding dil H2SO4 with KCN(in excess to allow sufficient –’ve CN ions

38. Aldehydes ‘n Ketones - - O C H3C H • Alkaline conditions don’t allow for the protonation of the carbonyl gp but do give high (:CN)- concentration. A compromise of about pH 5 gives the best results. Animation page H+ O: (or H-CN) C H3C CN :CN (Generates –(:CN) H OH * C H3C CN H A CYANOHYDRIN (an -hydroxy nitrile) is produced.These compounds are useful for (further) synthesis. Q: State a property of cyanohydrins…

39. Aldehydes ‘n Ketones Nitriles (CYANOHYDRINs)can undergo hydrolysis reactions OH OH Dilute acid(H2SO4) Heat underreflux O C C H3C C H3C CN OH H H An -hydroxyacid Dilute NaOH can also be used. Heat under reflux but like base hydrolysis of esters, the anion of the carboxylic acid will form!!!

40. Aldehydes ‘n Ketones TEST Specific for carbonyl…!!! The 2,4-dnp test This lone pair is the active one and attacks the carbonyl carbon Each hydrazine reacts with carbonyls to form a hydrazone. Hydrazine itself is very toxic and so is no longer used. The dinitrophenyl version is employed instead.

41. Aldehydes ‘n Ketones O C H3C H .. : : O C H - H3C TEST The 2,4-dnptest lp on N actsas a nucleophile N & O undergo protonexchange (3) (1) (2) (4) + .. (5) : O H (7) C ck H A hydrazone (6) H3C orange /Yellowppte ck

43. http://www.chem.ucalgary.ca/courses/351/Carey/Ch17/ch17-3-3-2.htmlhttp://www.chem.ucalgary.ca/courses/351/Carey/Ch17/ch17-3-3-2.html

44. Bp ofStartingCarbonylUnknown mp of2,4-DNPDerivative Bp ofStartingCarbonylUnknown mp of2,4-DNPDerivative 131 hexanal 104(107) 145 4-heptanone 75 145 5-methyl-2-hexanone 95 146 2-heptanone 89 147 3-heptanone 81 153 heptanal 108 156 cyclohexanone 162 169 3-methylcyclohexanone 155 173 2-octanone 58 179 benzaldehyde (PhCHO) 237 200 o-methylbenzaldehyde 194 204 p-methylbenzaldehyde 34 202 ethanoylbenzene 244 216 1-phenyl-2-propanone 156 217 (2-methylpropanoyl)benzene 163 218 propanoylbenzene 191 226 p-methylacetophenone 258 232 butanoylbenzene 191 235 4-phenyl-2-butanone 127 248 p-methoxybenzaldehyde 253 • 48 propanal 148 • 56 acetone 126 • 63 2-methylpropanal 187(183) • 75 butanal 123 • 80 2-butanone 117 • 91 3-methylbutanal 123 • 92 2-methylbutanal 120 • 100 2-pentanone 143 • 102 3-pentanone 156 • 103 pentanal 107(98) • 115 4-methyl-2-pentanone 95 • 128 5-hexen-2-one 108 • 4-methyl-3-penten-2-one 205 • 131 cyclopentanone 146 • 131 hexanal 104(107) • 145 4-heptanone 75 • 145 5-methyl-2-hexanone 95

45. Some aldehydes, some ketones and some alcohols… Specific reaction… Triiodomethane rxn(iodoform precipitation reaction) • DOES NOT: • Identify carbonyls from alcohols • Identify aldehydes from ketones !!!!!! !!!!!! !!!!!!

46. Triiodomethane rxn(iodoform precipitation reaction) • So what does it do? • Tests for methyl carbonyls • b) Tests for methyl alcoholswhich can be oxidised to methyl carbonyls. • Note: cannot be tertiary alcohols in that case!

47. Triiodomethane rxn(iodoform precipitation reaction) • Required reagents: • I2(aq) + NaOH(aq) • or • KI(aq) + NaClO(aq) • (ClO- is an O.A. and ‘dynamicallyconverts I- into I2 ) All these alpha H’sget replaced by I

48. Triiodomethane rxn(iodoform precipitation reaction) Forms rapidly (appropriate alcohol versions get oxidised to this acyl gp first) Triiodomethane (ioodoform), an unpolar SOLID, ends up breaking away. Carboxylate anion on other fragment dissolves in soln

49. Triiodomethane rxn(iodoform precipitation reaction) The triiodomethane smells like antiseptic or a dry cleaners (dry cleaners used to use trichloromethane – a compound (probably toxic: carconogenic, tetragenic and mutagenic – not that nice really and it’s said to destroy ozone.) Always better to ID iodoform from the ppte rather than the smell !!! Test may be problematical – my guess [I2] is too low in the ‘bench’ test solution.

50. Further Organic revision. Source: http://www.rod.beavon.clara.net/ Problem 1. Compound A, C3H80, gives steamy fumes when reacted with phosphorus pentachloride. On oxidation with acidified potassium dichromate solution A gives B, C3H60. This, with a source of H3C:- nucleophile, gives C upon addition of acid, C4H10O. C does not react with acidified potassium dichromate solution. Treatment of C with excess hot concentrated sulphuric acid gives D, C4H8, which on reaction with hydrogen bromide gives mainly 2-bromo-2-methylpropane. Find the structures of A to D, giving reasons and equations for the reactions which occur.