15. Carbonyls, Carboxylic Acids and chirality

Transcription

1 15. rbonyls, rboxylic Acids nd chirlity homologous series functionl group prefix / suffix (* = usul use) exmple lkenes suffix -ene ethene lcohols suffix* prefix -ol hydroxy- Propn-1-ol hlogenolkne hlogen prefix chlorobromoiodo- l 1-chloropropne suffix -l prefix ldehydes formyl- ethnl suffix* prefix ketones -one oxo- Propnone crboxylic cids suffix -oic cid Ethnoic cid nitriles N suffix prefix -nitrile cyno- N Propnenitrile suffix* prefix mines -mine mino- N 2 N 2 Propylmine r propn-1-mine esters -yl ote Methyl ethnote Acyl chloride -oyl chloride 3 ethnoylchloride l l Amide -mide 3 ethnmide N 2 N 2 N Golby chemrevise.org 1

2 Aldehydes An ldehyde s nme ends in l It lwys hs the = bond on the first crbon of the chin so it does not need n extr number. It is by defult number one on the chin rboxylic cids These hve the ending -oic cid but no number is necessry for the cid group s it must lwys be t the end of the chin. The numbering lwys strts from the crboxylic cid end Ethnl propnoic cid If there re crboxylic cid groups on both ends of the chin then it is clled - dioic cid Ethnedioic cid Note the e in this nme Ketones Ketones end in -one When ketones hve 5 s or more in chin then it needs number to show the position of the double bond. E.g. pentn-2-one If two ketone groups then di is put before one nd n n e is dded to the stem The prefix oxo- should be used for compounds tht contin ketone group in ddition to crboxylic cid or ldehyde Propnone 3 Pentne-2,4-dione 2-oxopropnoic cid Nitriles These end in nitrile, but the of the N group counts s the first crbon of the chin. Note the stem of the nme is different : butnenitrile nd not butnnitrile. butnenitrile N 3 3 N 2-hydroxy-2-methylpropnenitrile rboxylic cid derivtives Esters Esters hve two prts to their nmes The bit ending in yl comes from the lcohol tht hs formed it nd is next to the single bonded oxygen. The bit ending in note comes from the crboxylic cid. (This is the chin including the = bond) Methyl propnote Acyl hlorides 3 dd oyl chloride to the stem nme 3 l ethnoyl chloride 3 l 2-methylpropnoyl chloride ( 2 ) 3 l l Pentnedioyl dichloride Amides Add mide to the stem nme N2 ethnmide 3 N 3 N,N-dimethylpropnmide Secondry nd tertiry mides re nmed differently to show the two (or three) crbon chins. The smller lkyl group is preceded by n N which plys the sme role s number in positioning side lkyl chin 3 2 N-methylpropnmide 3 N N 3 N,N,2-trimethylpropnmide N Golby chemrevise.org 2

3 15A hirlity pticl isomerism occurs in crbon compounds with 4 different groups of toms ttched to crbon (clled n symmetric crbon). These four groups re rrnged tetrhedrlly round the crbon. A crbon tom tht hs four different groups ttched is clled chirl (symmetric) crbon tom This cuses two different isomers tht re not superimposble to be formed. They re mirror imges A mixture contining 50/50 mixture of the two isomers (enntiomers) is described s being rcemte or rcemic mixture. Two compounds tht re opticl isomers of ech other re clled enntiomers. pticl isomers hve similr physicl nd chemicl properties, but they rotte plne polrised light in different directions. ne enntiomer rottes it in one direction nd the other enntiomer rottes it by the sme mount in the opposite direction. Mny nturlly occurring molecules contin chirl toms, but re usully found in nture s pure enntiomer Different systems of nomenclture re is existence for opticl isomers. D/L or +/- re commonly used, but both hve been superseded by the more useful nd informtive R/S system (this is not on the syllbus for informtion only). ne opticl isomer will rotte light clockwise (+)(clled dextrorottory). The other will rotte it nticlockwise(-)(clled levorottory). A rcemic mixture ( mixture of equl mounts of the two opticl isomers) will not rotte plne-polrised light. -ve enntiomer Anticlockwise rottion +ve enntiomer clockwise rottion Rcemte no rottion hemicl Rections nd pticl Isomers Formtion of rcemte A rcemte will be formed in rection mechnism when trigonl plnr rectnt or intermedite is pproched from both sides by n ttcking species N: 3 :N Nucleophilic ddition of N to ldehydes nd ketones (unsymmetricl) when the trigonl plnr crbonyl is pproched from both sides by the N ttcking species: results in the formtion of rcemte N 3 There is n equl chnce of either enntiomer forming so rcemte forms. No opticl ctivity is seen 3 N N Golby chemrevise.org 3

4 Formtion of rcemte with SN 1 mechnism Br : The Br first breks wy from the hlolkne to form plnr crboction intermedite The - ion cn then ttck from either side resulting in different enntiomers nd rcemte forms Becuse rcemte forms there will be no opticl ctivity in the products omprison with SN 2 mechnism In the SN 2 mechnism no intermedites re formed nd the rection occurs vi trnsition stte. Br : Br If the rectnt ws chirl then during the rection the opposite enntiomer would form. The product will rotte light in the opposite direction to the rectnt A rcemte cn lso be formed in the AS rection of the electrophilic ddition of Br to n unsymmetricl lkene δ + δ - Br If the lkene is unsymmetricl, ddition of hydrogen bromide cn led to isomeric products :Br :Br - The bromide cn ttck this plnr crboction from both sides leding to rcemte Br Br Br Mjor product s 90% Minor product 10% N Golby chemrevise.org 4

5 ompounds with = group 15B rbonyls: Aldehydes nd Ketones rbonyls re compounds with = bond. They cn be either ldehydes or ketones. 3 ethnl If the = is on the end of the chin with n ttched it is n ldehyde. The nme will end in l 3 3 propnone If the = is in the middle of the chin it is ketone The nme will end in -one Solubility in wter The smller crbonyls re soluble in wter becuse they cn form hydrogen bonds with wter. 3 3 Pure crbonyls cnnot hydrogen bond, but bond insted by permnent dipole bonding. Rections of crbonyls The = bond is polrised becuse is more electronegtive thn crbon. The positive crbon tom ttrcts nucleophiles. xidtion Rections 3 δ - δ + 3 nucleophile In comprison to the = bond in lkenes, the = is stronger nd does not undergo ddition rections esily. This is in contrst to the electrophiles tht re ttrcted to the =. Potssium dichromte K 2 r 2 7 is n oxidising gent tht cuses lcohols nd ldehydes to oxidise. xidtion of Aldehydes Primry lcohol ldehydes crboxylic cid Secondry lcohol Tertiry lcohols Rection: ldehyde crboxylic cid Regent: potssium dichromte (VI) solution nd dilute sulphuric cid. onditions: het under reflux Full Eqution for oxidtion r r 3+ bservtion: the ornge dichromte ion (r ) reduces to the green r 3+ ion ketones do not oxidise + [] R + [] R 2 Key point: Aldehydes cn be oxidised to crboxylic cids, but ketones cnnot be oxidised. Aldehydes cn lso be oxidised using Fehling s solution or Tollen s Regent. These re used s tests for the presence of ldehyde groups Tollen s Regent Regent: Tollen s Regent formed by mixing queous mmoni nd silver nitrte. The ctive substnce is the complex ion of [Ag(N 3 ) 2 ] +. onditions: het gently Rection: ldehydes only re oxidised by Tollen s regent into crboxylic cid nd the silver(i) ions re reduced to silver toms bservtion: with ldehydes, silver mirror forms coting the inside of the test tube. Ketones result in no chnge. Fehling s solution Regent: Fehling s Solution contining blue u 2+ ions. onditions: het gently Rection: ldehydes only re oxidised by Fehling s Solution into crboxylic cid nd the copper ions re reduced to copper(i) oxide.. bservtion: Aldehydes :Blue u 2+ ions in solution chnge to red precipitte of u 2. Ketones do not rect u u Ag Ag N Golby chemrevise.org 5

6 Reduction of crbonyls Regents: LiAl 4 In dry ether onditions: Room temperture nd pressure Type of rection: Reduction Role of regent: Reducing gent Aldehydes will be reduced to primry lcohols Reducing gents such s NB 4 (sodium tetrhydridoborte) or LiAl 4 (lithium tetrhydridoluminte) will reduce crbonyls to lcohols. Ketones will be reduced to secondry lcohols. propnl + 2[] Propn-1-ol propnone + 2[] Propn-2-ol Addition of hydrogen cynide to crbonyls to form hydroxynitriles Rection: crbonyl hydroxynitrile Regent: N in presence of KN onditions: Room temperture nd pressure Mechnism: nucleophilic ddition N 3 ()(N) hydroxy-2-methylpropnenitrile + N 3 ()N 2-hydroxypropnenitrile N 3 N 3 3 When nming hydroxy nitriles the N becomes prt of the min chin N The extr KN increses the concentrtion of the N - ion nucleophile needed for the first step of the mechnism R hydroxynitrile Nucleophilic Addition Mechnism δ - :- -N δ :N - N N Rection of crbonyls with iodine in presence of lkli Regents: Iodine nd sodium hydroxide onditions: wrm very gently The product I 3 is yellow crystlline precipitte with n ntiseptic smell nly crbonyls with methyl group next to the = bond will do this rection. Ethnl is the only ldehyde tht rects. More commonly is methyl ketones. 3 This rection is clled the Iodoform test I 2 + 4N I N + 3NI I 2 + 4N I N + 3NI +3 2 N Golby chemrevise.org 6

7 Rection with 2,4-dinitro phenylhydrzine 2,4-DNP rects with both ldehydes nd ketones. The product is n ornge precipitte, It cn be used s test for crbonyl group in compound. Use 2,4-DNP to identify if the compound is crbonyl. Then to differentite n ldehyde from ketone use Tollen s regent. The melting point of the crystl formed cn be used to help identify which crbonyl ws used. Tke the melting point of ornge crystls product from 2,4-DNP. ompre melting point with known vlues in dtbse N N 2 N N 2 You don t need to lern these equtions for the exm ddition 2,4-DNP 3 N N 2 N N 2 elimintion of wter 3 N N 2N N2 ornge precipitte 15 rboxylic Acids Acidity The crboxylic cid re only wek cids in wter nd only slightly dissocite, but they re strong enough to displce crbon dioxide from crbontes. 3 2 (q) 3 2- (q)+ + (q) Solubility in Wter The smller crboxylic (up to 4) cids dissolve in wter in ll proportions but fter this the solubility rpidly reduces. They dissolve 3 becuse they cn hydrogen bond to the wter molecules. ydrogen bonding in solid ethnoic cid 3 δ - δ + δ - δ - δ + δ - ydrogen bonding between dimer in solid ethnoic cid 3 Solid Ethnoic ppers to hve Mr of 120 Deloclistion The crboxylic cid slts re stbilised by deloclistion, which mkes the dissocition more likely. The deloclised ion hs equl - bond lengths. If deloclistion did not occur, the = bond would be shorter thn the - bond. 3 deloclised 3 The pi chrge cloud hs deloclised nd spred out. The deloclistion mkes the ion more stble nd therefore more likely to form. 3 N Golby chemrevise.org 7

8 Strength of crboxylic cids 3 2 deloclised 3 2 Alkyl groups electron relesing l deloclised l Incresing chin length pushes electron density on to the - ion, mking it more negtive nd less stble. This mke the cid less strong. Propnoic cid less cidic thn ethnoic cid Electronegtive chlorine toms withdrw electron density from the - ion, mking it less negtive nd more stble. This mke the cid more strong. hlorine electron withdrwing chloroethnoic cid more cidic thn ethnoic cid 2 - group electron withdrwing - In dibsic cid the second 2 - group withdrws electron density from the - ion, mking it less negtive nd more stble nd wekens the - bond. This mke the cid more strong. Methods of prepring crboxylic cids Full xidtion of Primry Alcohols Rection: primry lcohol crboxylic cid Regent: potssium dichromte(vi) solution nd dilute sulphuric cid onditions: use n excess of dichromte, nd het under reflux: (distill off product fter the rection hs finished) bservtion: the ornge dichromte ion (r ) reduces to the green r 3+ ion + 2 [] [] propn-1-ol Propnoic cid xidtion of Aldehydes Rection: ldehyde crboxylic cid Regent: potssium dichromte (VI) solution nd dilute sulphuric cid. onditions: het under reflux + [] Full Eqution for oxidtion r r 3+ R + [] R ydrolysis of Nitriles Rection: Nitrile crboxylic cid Regent: dilute hydrochloric/ sulphuric cid. onditions: het under reflux 3 2 N N 4 + N Golby chemrevise.org 8

9 The Rections of rboxylic Acids Reduction of crboxylic cids to lcohols Lithium tetrhydridoluminte (LiAl 4 ) is strong reducing gent Regents: LiAl 4 In dry ether onditions: Room temperture nd pressure Type of rection: Reduction Role of regent: Reducing gent rboxylic cids will be reduced to primry lcohols + 4[] Propnoic cid Propn-1-ol + 2 Slt formtion rections of crboxylic cids rboxylic cids cn form slts with metls, lklis nd crbontes. cid + metl (N) slt + hydrogen N N cid + lkli (N) slt + wter N 3 2- N The effervescence cused by production of 2 with crboxylic cids with solid N 2 3 or queous N 3 cn be used s functionl group test for crboxylic cids cid + crbonte (N 2 3 ) slt + wter N N xidtion of methnoic cid rboxylic cids cnnot be oxidised by using oxidising gents but methnoic cid is n exception s its structure hs effectively n ldehyde group + [] It forms crbonic cid ( 2 3 ) which cn decompose to give 2 Rection of crboxylic cid with phosphorous (V) chloride Rection: crboxylic cid cyl chloride Regent: Pl 5 phosphorous(v)chloride onditions: room temp This rection with Pl 5 (phosphorous(v)chloride) cn be used s test for crboxylic cids. You would observe misty fumes of l produced. 3 + Pl 5 3 l + Pl 3 + l 3 + Pl Pl 3 + l l N Golby chemrevise.org 9

10 Esterifiction rboxylic cids rect with lcohols, in the presence of strong cid ctlyst, to form esters nd wter. rboxylic Acid + Alcohol + Ester + wter The bit ending in note comes from the crboxylic cid nd includes the in the = bond. Esters hve two prts to their nmes, eg methyl propnote. The bit ending in yl comes from the lcohol tht hs formed it nd is next to the single bonded oxygen Ethnoic cid Ethnol Ethyl Ethnote + 2 The rection is reversible. The rection is quite slow nd needs heting under reflux, (often for severl hours or dys). Low yields (50% ish) re chieved. An cid ctlyst ( 2 S 4 ) is needed. Uses of Esters Esters re sweet smelling compounds tht cn be used in perfumes nd flvourings. Esters cn be used s solvents for polr orgnic substnces Ethyl ethnote is used s solvent in glues nd printing inks Esters cn hve plesnt smells For use in perfumes they need to be non toxic, soluble in solvent such s ethnol, voltile (turns into gs esily), nd not rect with wter. Although polr, they do not form hydrogen bonds (reson: there is no hydrogen bonded to highly electronegtive tom) thus, they hve much lower b.p. thn the hydrogen-bonded crboxylic cids they cme from. They re lso lmost insoluble in wter ydrolysis of esters Esters cn be hydrolysed nd split up by either heting with cid or with sodium hydroxide. i) with cid regents: dilute cid (l) conditions: het under reflux This rection is the reverse rection of ester formtion. When n ester is hydrolysed crboxylic cid nd n lcohol re formed ethyl propnote This rection is reversible nd does not give good yield of the products. ii) with sodium hydroxide regents: dilute sodium hydroxide conditions: het under reflux This rection goes to completion N N methyl propnote sodium propnote methnol The crboxylic cid slt product is the nion of the crboxylic cid. The nion is resistnt to ttck by wek nucleophiles such s lcohols, so the rection is not reversible. N Golby chemrevise.org 10

11 rboxylic cid derivtives: Acyl hlorides Acyl hlorides 3 l ethnoyl chloride Acyl chlorides re much more rective thn crboxylic cids The l group is clssed s good leving groups (to do with less effective deloclistion.) This mkes cyl chlorides nd cid nhydrides much more rective thn crboxylic cids nd esters Rection with wter hnge in functionl group: cyl chloride crboxylic cid Regent: wter onditions: room temp. Rl (l) + 2 R 2 + l (g) l (g) l bservtion: Stemy white fumes of l re given off Rection with lcohol 3 hnge in functionl group: cyl chloride ester Regent: lcohol onditions: room temp. Rl (l) R l (g) l l bservtion: Stemy white fumes of l re given off This rection for mking esters is much better thn using crboxylic cids s the rection is much quicker nd it is not reversible rection Rection with mmoni hnge in functionl group: cyl chloride primry mide Regent: mmoni onditions: room temp. Rection with primry mines hnge in functionl group: cyl chloride secondry mide Regent: primry mine onditions: room temp. Rl (l) +2N 3 RN 2 + N 4 l (s) 3 + 2N N 4 l (s) l N 2 bservtion: white smoke of N 4 l is given off 3 Rl +2 3 N 2 RN N 3+ l N 3+ l N 2 3 N 3 l N-methylethnmide N Golby chemrevise.org 11

12 Polyesters There re two types of polymeristion: ddition nd condenstion ondenstion Polymeristion The two most common types of condenstion polymers re polyesters nd polymides which involve the formtion of n ester linkge or n mide linkge. In condenstion polymeristion there re two different monomers tht dd together nd smll molecule is usully given off s side-product e.g. 2 or l. The monomers usully hve the sme functionl group on both ends of the molecule e.g. di-mine, di crboxylic cid, diol, dicyl chloride. Forming polyesters uses these rections we met erlier in the course rboxylic Acid + Alcohol Ester + wter Acyl chloride + Alcohol Ester + l If we hve the sme functionl group on ech end of molecule we cn mke polymers so we hve the nlogous equtions: dicrboxylic cid + diol poly(ester) + wter dicyl dichloride + diol poly(ester) + l Using the crboxylic cid to mke the ester or mide would need n cid ctlyst nd would only give n equilibrium mixture. The more rective cyl chloride goes to completion nd does not need ctlyst but does produce hzrdous l fumes. Terylene- common polyester n Benzene-1,4-dicrboxylic cid + n 2 2 Ethne-1,2-diol Terylene fbric is used in clothing, tire cords 2 2 n + 2n-1 2 The -1 here is becuse t ech end of the chin the nd re still present n ( 2 ) 3 l l Pentnedioyl dichloride + n Benzene-1,4-diol ( 2 ) 3 n + 2n-1 l N Golby chemrevise.org 12

13 It is lso possible for polymides nd polyesters to form from one monomer, if tht monomer contins both the functionl groups needed to rect 3 repeting units 3 2-hydroxypropnoic cid (lctic cid) repeting units poly(lctic cid) 4-hydroxypentnoic cid It is possible for some of these compounds to form vrious cyclic esters under different conditions from forming the polymer. You do not need to lern these but my be sked to deduce structures from informtion given 1 repeting unit hemicl rectivity of condenstion polymers polyesters cn be broken down by hydrolysis nd re, therefore, biodegrdble The rectivity cn be explined by the presence of polr bonds which cn ttrct ttcking species such s nucleophiles nd cids Polyesters cn be hydrolysed by cid nd lkli With l polyester will be hydrolysed nd split up in to the originl dicrboxylic cid nd diol With N n polyester will be hydrolysed nd split up into the diol nd dicrboxylic cid slt. N Golby chemrevise.org 13

14 15E. Spectroscopy nd chromtogrphy The effect of different types of rdition on molecules i infrred in nlysis infr red energy cuses bonds to vibrte. This cn be used to identify the types of bond in molecule ii microwves for heting- certin molecules bsorb the microwves cusing them to rotte iii rdio wves in nmr cn cuse the hydrogen nucleus to chnge its spin stte. This cn give us informtion bout the rrngements of hydrogens in molecule. iv ultrviolet in initition of rections UV energy cn brek bonds such s the l-l bond or -l bond NMR spectroscopy NMR spectroscopy involves interction of mterils with the lowenergy rdiowve region of the electromgnetic spectrum NMR spectroscopy is the sme technology s tht used in mgnetic resonnce imging (MRI) to obtin dignostic informtion bout internl structures in body scnners e.g. scnning for brin disorders The rdio wves used in proton nmr cuse the hydrogen nucleus to chnge its spin stte. Equivlent ydrogen toms. In n NMR spectrum, there is one signl for ech set of equivlent toms. In ddition the intensity (integrtion vlue) of ech signl is proportionl to the number of equivlent toms it represents. b b Ethnol hs 3 groups of different hydrogen toms c b c d d c d 4sets of equivlent s: rtio 6:1:2:3 1 signl 3 b 2 c 3 c 3 c 3 3 sets of equivlent s: rtio 3:2:9 b c sets of equivlent s: rtio 3:1:2 b c sets of equivlent s: rtio 3:2:3 Br b c d 4 sets of equivlent s: rtio 3:1:2:3 Solvents Smples re dissolved in solvents without ny 1 toms, e.g. l 4, Dl 3. This mens tht in the NMR the solvent will not give ny peks N Golby chemrevise.org 14

15 librtion nd shift A smll mount of TMS (tetrmethylsilne) is dded to the smple to clibrte the spectrum TMS is used becuse: its signl is wy from ll the others it only gives one signl it is non-toxic it is inert it hs low boiling point nd so cn be removed from smple esily 3 3 Si 3 3 tetrmethylsilne The spectr re recorded on scle known s the chemicl shift (δ), which is how much the field hs shifted wy from the field for TMS.. The δ is mesure in prts per million (ppm) is reltive scle of how fr the frequency of the proton signl hs shifted wy from tht for TMS δ chemicl shift (ppm) NMR shift The δ depends on wht other toms/groups re ner the more electronegtive groups gives greter shift δ ppm δ ppm N Golby chemrevise.org 15

16 Spin-Spin coupling in NMR In high resolution NMR ech signl in the spectrum cn be split into further lines due to inequivlent s on neighbouring toms. Splitting of pek = number of inequivlent s on neighbouring toms + 1 signl singlet doublet triplet qurtet quintet ppernce Split number of peks number of neighbouring inequivlent toms reltive size 1:1 1:2:1 1:3:3:1 1:4:6:4:1 Nuclei in identicl chemicl environments do not show coupling mongst themselves! b c The pek due to group will be triplet s it is next to b ( crbon with 2 s) The pek due to group b will be qurtet s it is next to ( crbon with 3 s) The pek due to group c will be singlet s it is next to crbon with no s) For 6 split peks use the term hextet or multiplet c b c The pek due to group c will be triplet s it is next to crbon with 2 s Shift Integrtion trce 3 b The pek due to group will be singlet s it is next to crbon with 0 s Shift Integrtion trce 3 The pek due to group b will be qurtet s it is next to crbon with 3 s Shift Integrtion trce 2 ppm N Golby chemrevise.org 16

17 Mss spectrometry Mesuring the M r of n orgnic molecule Spectr for 4 10 If molecule is put through mss spectrometer it will often brek up nd give series of peks cused by the frgments. The pek with the lrgest m/z, however, will be due to the complete molecule nd will be equl to the M r of the molecule. This pek is clled the prent ion or moleculr ion Mss spectrum for butne Moleculr ion Frgmenttion When orgnic molecules re pssed through mss spectrometer, it detects both the whole molecule nd frgments of the molecule. Moleculr ion formed: M [M] +. + e The molecule loses n electron nd becomes both n ion nd free rdicl Severl peks in the mss spectrum occur due to frgmenttion. The Moleculr ion frgments due to covlent bonds breking: [M] +. X + + Y. Reltively stble ions such s crboctions R + such s 3 2+ nd cylium ions [R-=] + re common. The more stble the ion, the greter the pek intensity. This process produces n ion nd free rdicl. The ion is responsible for the pek The pek with the highest mss/chrge rtio will be normlly due to the originl molecule tht hsn t frgmented (clled the moleculr ion). As the chrge of the ion is +1 the mss/ chrge rtio is equl to Mr. Mss spectrum for butne = 58 Eqution for formtion moleculr ion 4 10 [ 4 10 ] +. + e m/z 58 Equtions for formtion of frgment ions from moleculr ions [ 4 10 ] +. [ ] m/z 43 [ 4 10 ] +. [ 3 2 ] m/z 29 Mss spectrum for butnone The high pek t 43 due to stbility of cyl group 43 [ 3 ] + Eqution for formtion moleculr ion [ ] +. + e m/z 72 Equtions for formtion of frgment ions from moleculr ions [ ] +. [ 3 2 ] m/z [ 3 2 ] + [ 3 2 ] + 57 [ ] [ ] +. [ 3 ] m/z 43 [ ] +. [ 3 2 ] m/z 29 N Golby chemrevise.org 17

18 hromtogrphy hromtogrphy is n nlyticl technique tht seprtes components in mixture between mobile phse nd sttionry phse. Seprtion by column chromtogrphy depends on the blnce between solubility in the moving phse nd retention in the sttionry phse. A solid sttionry phse seprtes by dsorption, A liquid sttionry phse seprtes by reltive solubility The mobile phse my be liquid or gs. The sttionry phse my be solid (s in thinlyer chromtogrphy, TL) or either liquid or solid on solid support (s in gs chromtogrphy, G) If the sttionry phse ws polr nd the moving phse ws non- polr e.g. exne. Then nonpolr compounds would pss through the column more quickly thn polr compounds s they would hve greter solubility in the non-polr moving phse. (Think bout intermoleculr forces) PL stnds for high performnce liquid chromtogrphy. PL: sttionry phse is solid silic PL: mobile phse liquid In gs-liquid chromtogrphy G the mobile phse is inert gs such s nitrogen, helium, rgon. The Sttionry phse is liquid on n inert solid. Gs-Liquid hromtogrphy Gs-liquid chromtogrphy cn be used to seprte mixtures of voltile liquids. The time tken for prticulr compound to trvel from the injection of the smple to where it leves the column to the detector is known s its retention time. This cn be used to identify substnce. Flow control In gs-liquid chromtogrphy, the mobile phse is gs such s helium nd the sttionry phse is high boiling point liquid bsorbed onto solid. Smple in oven Some compounds hve similr retention times so will not be distinguished. disply Bsic gs-liquid chromtogrphy will tell us how mny components there re in the mixture by the number of peks. It will lso tell us the bundnce of ech substnce. The re under ech pek will be proportionl to the bundnce of tht component. rrier gs column detector Wste outlet It is lso possible for gs-liquid chromtogrphy mchine to be connected to mss spectrometer, IR or NMR mchine, enbling ll the components in mixture to be identified. G-MS is used in nlysis, in forensics, environmentl nlysis, irport security nd spce probes. Most commonly mss spectrometer is combined with G to generte mss spectr which cn be nlysed or compred with spectrl dtbse by computer for positive identifiction of ech component in the mixture. N Golby chemrevise.org 18

19 TL hromtogrphy (thin-lyer chromtogrphy) A mixture cn be seprted by chromtogrphy nd identified from the mount they hve moved. (n be used with mixtures of mino cids) Method: Thin-lyer chromtogrphy ) Wering gloves, drw pencil line 1 cm bove the bottom of TL plte nd mrk spots for ech smple, eqully spced long line. b) Use cpillry tube to dd tiny drop of ech solution to different spot nd llow the plte to ir dry. c) Add solvent to chmber or lrge beker with lid so tht is no more thn 1cm in depth d) Plce the TL plte into the chmber, mking sure tht the level of the solvent is below the pencil line. Replce the lid to get tight sel. e) When the level of the solvent reches bout 1 cm from the top of the plte, remove the plte nd mrk the solvent level with pencil. Allow the plte to dry in the fume cupbord. f) Plce the plte under UV lmp in order to see the spots. Drw round them lightly in pencil. g) lculte the Rf vlues of the observed spots. Wer plstic gloves to prevent contmintion from the hnds to the plte pencil line will not dissolve in the solvent tiny drop too big drop will cuse different spots to merge Depth of solvent if the solvent is too deep it will dissolve the smple spots from the plte lid to prevent evportion of toxic solvent Will get more ccurte results if the solvent is llowed to rise to ner the top of the plte but the Rf vlue cn be clculted if the solvent front does not rech the top of the plte dry in fume cupbord s the solvent is toxic UV lmp used if the spots re colourless nd not visible If using mino cids then ninhydrin spry cn be used insted of UV lmp to locte the spots R f vlue = distnce moved by mino cid distnce moved by the solvent Ech substnce hs its own R f vlue Mesure how fr ech spot trvels reltive to the solvent front nd clculte the Rf vlue. ompre Rf vlues to those for known substnces. Some substnces won't seprte becuse similr compounds hve similr Rf vlues. So some spots my contin more thn one compound N Golby chemrevise.org 19

20 Bringing it ll together 1. Work out empiricl formul Elementl nlysis 66.63% 11.18% 22.19% 2. Using moleculr ion pek m/z vlue from mss spectrum clculte Moleculr formul moleculr ion pek m/z vlue= / / /16 = =11.18 = =4 =8 =1 Mr empiricl formul 4 8 = 72 If Mr moleculr formul 144 then compound is Use IR spectr to identify min bonds/functionl group could be n ester, crboxylic cid or combintion of lcohol nd crbonyl. Look for IR spectr for = nd - bonds There is = but no - bsorptions, so must be n ester. - = 4. Use NMR spectr to give detils of crbon chin 4 peks only 4 different environments. singlet of re 9 3 At δ =0.9 Mens 3 3 groups Pek t δ 4 shows Are 2 suggests 2 Qurtet mens next to 3 2 Pek t δ 2.2 shows = Are 2 suggests 2 Singlet mens djcent to with no hydrogens 2 Pek t δ 1.2 shows R- 3 Are 3 mens 3 Triplet mens next to δ ppm Put ll together to give finl structure N Golby chemrevise.org 20