RDC 9729_02 H2 Chemistry Practice 1 MS

Q1)(a)(i)1. Diproticreferstoanacidthatdonatesamaximumoftwoofitsprotonstootheratoms[0.5]2. Organicacidreferstoanacidthatislargelymadeof carbon, hydrogenandoxygenatoms[0.5] (ii) 1. Bondangleis90degrees[1]2. Duetoringstrainwhichforcesthebondstobe90degreesratherthan120degrees[1] (b)(i)1. Singlebondsanddoublebondshavedifferent lengths-singlebondsarelongerwhiledoublebondsareshorter[0.5]2. Increasedelectrondensityinabondmeansstronger EFOAwithnucleus,hencebondlengthdecreases[0.5] (ii) Any3arrowscorrect-[0.5]Any6arrowscorrect-[1] (iii)1. Electronscanbedelocalisedintopielectroncloudsystemacrosstheentiremolecule[0.5]2. HencealltheC-Cbondsarepartialdoublebondsandhaveapartialdoublebondlength[0.5]

(c)1. SquaricacidhasahigherpH2. Reason1:Squaricacidisdiproticwhileethanoicacidismonoprotic-twiceasmanyH+ionscanbedonatedpermoleculeofsquaricacidthanethanoicacid3. Reason2:SquaricacidhasmorehighlyENoxygenatomsthatdispersethenegativechargeontheconjugatebase,increasingitsstabilityandhenceincreasingitsacidstrength.Ethanoicacidhowever,involveselectrondonatingalkylgroupsthatintensifiesthenegativechargeontheconjugatebaseanddestabilisesit.4. Reason3:Negativechargecanbedispersedtoagreaterextentinconjugatebaseofsquaricacidbecausethepielectroncloudsystemisspreadacrossthewholemolecule,whilethatofethanoicacidisonlyspreadacrossCOO- Point1+1correctreason-1mPoint1+2correctreasons-2m (d)(i)Dicarbonate: Ethylenetetracarboxylate: Benzenehexolate: 1correctstructure-0.5m

2correctstructures-1m3correctstructures-2mPenalise0.5monce,maximumtwice,ifcandidategavetheprotonatedforminsteadofthedeprotonatedform (ii) 1. Oxidisation[0.5]2. asspeciesloseselectronsinordertoneutralisethenegativecharge[0.5]3. Moreunstableasoxygenatoms[0.5]4. Donothaveafullyfilledvalenceshell[0.5] (iii)Letzbeave.oxidationno.+k+xz-2y=-mz=(2y-m-k)/x[1][0.5]ifworkingiscorrectbutalgebraicmanipulationiswrong Q2)(i) 1. Species(ketoandenol)2. withthesamemolecularformula3. ofC3 H6 O,4. butdifferentstructuralformula-5. asketohasC=O6. butenolhasHO-C=C 4-5points:0.5m6points:1m (ii)

[1]RejectifstereoisomersdrawnwithchiralcarbonbeingtheoneattachedtoOHgroup

(iii) Compound1:C=SchangesCompound2:C=Nchanges● BODifthereis2consecutivedoublebonds,i.e.S=C=C-NHorHS-C=C=NHCompound3:C=OchangesCompound4:C=OchangesbutformsdifferentdoublebondtodifferentcarbonAcceptvariations,suchasC=SandC=Ochangesinthesamecompound. [1]percompound (iv)1. AlkenesinvolveC=C[ideaoftwosameatoms]2. Haveequalelectronegativity3. willnotbedeprotonatedeasily[0.5]perpoint (v)1. Lactam-lactim[0.5]2. Amide-imidicacid[1]3. Enol-ketone[0.5] Penalise0.5mforeveryadditionalwrongtautomerpair (v)

[0.5]forany2structurescorrect[1]forall4structurescorrect 1. AtlowpH,NH2groupisprotonatedduetohigh[H+]conc2. AspHincreases,carboxylicacidisdeprotonatedfirstasconjugatebasehighlystabilisedby2highlyENOatoms3. NH3+isthendeprotonatedtoremovethechargeaspHexceeds7vianeutralisationforstability4. OHgroupisdeprotonatedthelastbecauseithasaveryhighpKavalueasthealkoxideisdestabilisedbytheelectrondona