structural elucidation soln

7/27/2019 Structural Elucidation Soln

1/21

StructuralElucidationinOrganicChemistry

224

Topic10.3:StructuralElucidationinOrganicChemistry

1. HCI/2009/P3/Q3e

2. DHS/2009/P3/Q2b

ThecarbontohydrogenratioofPis1:2.Pdoesnotcontainbenzenering,butcouldcontain alkenegroup.P undergoes electrophilic addition with hydrogen chloride gas to form QandRinunequalproportion.Pisanunsymmetricalalkene.QandRarehalogenoalkanes.Q and R undergo nucleophilic substitution with sodium hydroxide to form S and Trespectively.SandTarealcohols.Sisnotoxidizedbyacidifiedpotassiummanganate(VII).

Sisatertiaryalcohol.Tisoxidizedbyacidifiedpotassiummanganate(VII)toform U.T is a primary or secondary alcohol. U could be carboxylic acid orketone.


2/21


225

U undergoes neutralisation / acid base reaction with sodium carbonatetoliberatecarbondioxidegas.Uisacarboxylicacid,henceTisaprimaryalcohol.P undergoes (strong) oxidation with acidified potassium manganate (VII) to

formV,C5H10O,whichhasonlyoneoxygenatom,andcarbondioxide.Phasaterminalalkenegroup.Visaketone.V undergoes condensation with 2,4-dinitrophenylhydrazine to form anorangeprecipitate.Visaketone/carbonylcompound.V undergoes reduction with lithium aluminium hydride to form W, whichdoesnotexhibitopticalactivity.Wisasecondaryalcoholandisasymmetricalmolecule.

PQR

STUVW

C C

H

H

CH2CH3

CH2CH3

C CH

H CH2CH3

CH2CH3H

ClC CCl

H CH2CH3

CH2CH3H

H

C CH

H CH2CH3

CH2CH3H

OH C COH

H CH2CH3

CH2CH3H

H C COH

O CH2CH3

CH2CH3

H

O C

CH2CH3

CH2CH3

OH C

CH2CH3

CH2CH3

H


3/21


226

3. IJC/2009/P3/Q1f

4. ACJC/2009/P2/Q4b

5. JJC/2009/P2/Q6c


4/21


227

(ii)ExcessNH3,heatunderrefluxinethanol

6. MJC/2009/P3/Q4c

7. NJC/2009/P3/Q2e


5/21


228

8. NYJC/2009/P3/Q5c

STRUCTURES

[1] Mis

C

CH3

CH CH

OH

CH CH CH3

[1] Nis

C

CH3

O

[1] Ris

C

O-

O

Na+

[1] Pis

COH

O

CC

OH

O

O

[1] Qis

C CH3

OH

O EXPLANATIONOFTHEREACTIONSDESCRIBED[1] Mdecolourisesaqueousbromineduetoelectrophilicadditionacrossthealkene(C=C)functionalgroup.[1] Mproduceswhitefumes(ofHCl)withPCl5duetoasubstitutionreactionofthe(secondary)alcoholfunctionalgroup.


6/21


229

[1] Mproduced3compounds,N,PandQwithhotacidifiedpotassiummanganate(VII)duetooxidativecleavageofthe(2)alkenefunctionalgroupspresent.[1] NdoesnotundergomildoxidationwithFehlingsreagentasitisnotanaldehyde.

[1] Ngivesayellowppt(ofCHI3)andsaltRwithaqalkalineiodineduetothe(mild)oxidation(andcleavage)oftheCH3CORgroup.[1] Pgivesaneffervescence(ofCO2)withNa2CO3(s)duetoaneutralizationreactionwiththecarboxylicacidfunctionalgroup.[1] Pgivesanorangeprecipitatewith2,4-DNPHduetocondensationwiththeketonefunctionalgroup.[1] Qgivesaneffervescence(ofCO2)withNa2CO3(s)duetoaneutralizationreaction

withthecarboxylicacidfunctionalgroup.[1] Qdoesnotgiveanorangeprecipitatewith2,4-DNPHduetotheabsenceofacarbonylfunctionalgroupforcondensation.

9. RJC/2009/P2/Q4(a),(b)

(a) Structural/positionalisomerism(b) Geometricisomerism

C CH H

CH3

HO

OCH3

C C

H

CH3H

HO

CH3O

cis trans

10. SAJC/2009/P3/Q4c

Information Deduction

StereoisomerA - contains either an alkene with non-

identicalgroupsonthesamecarbonor

chiralcarbon

A reacts with hot acidified potassium

manganate(VII)solution

-Aundergoesoxidation

-AcontainsC=C


7/21


230

B forms a yellow precipitate with hot

alkalineiodinesolution.

-BcontainsCH3CO-

(donotacceptCH3CHOH-)

Cold alkaline hydrogen cyanide was

added to B and the mixture was

reducedtoformcompoundC

-Bisaketonewhichundergoes

nucleophilicadditionwithHCN

-Ccontainsanaminefunctionalgroup

CompoundDformedwhiteprecipitate

withethanolicsilvernitratesolution.

-Dcontainschloroalkanewhichforms

AgCl

CompoundDwasreactedwith

phosphorouspentachloridetoform

compoundE.

-Disanalcoholorcarboxylicacid

(donotacceptDcontainsOHgroup)

whichundergoesnucleophilic

substitution/displacementreactionto

formEwhichisaanacidchloride.

CompoundsCandEwerethenreacted

toformtwocompoundsFandG,with

identical molecular formulaC7H14O2NCl.

-condensationreactiontookplace

CompoundFisneutral. -FisanamideorFdoesnotcontain

phenol/carboxylicacid/amine.

Compound Structure Compound Structure

A CH2ClC

H

CCH2CH3

CH3

D CH2Cl

C O

HO

B

C

CH2CH3

CH3

O

E


8/21


231

C

C

CH2CH3

CH3

HO CH2NH2

F

C

CH2CH3

CH3

HO CH2NHCOCH2Cl

G

C

CH2CH3

CH3

CH2ClCOO CH2NH2

11. SAJC/2009/P3/Q5c

Information Deduction

Both A and B do not react with

Na2CO3

-AandBdonothaveCOOH

AandBdonotgivepositivetest A and B do not contain any methyl

ketoneCH3CO-orCH3CHOH-group

0.370 g of A reacts with sodium to

form a flammable gas that takes up

125.8cm3ofspaceat32.5

oCand101

kPa.

FlammablegasH2

NoofmolesofA=0.370/74=0.005

mol

101000 x 125.8 x 10-6 =n x 8.31 x

(273+32.5)

NoofmolesofH2=0.005mol

-moleratioofA:H2=1:1

-Acontains2alcoholgroups

BdoesnotreactwithNa -BdoesnotcontainOHgroup.

*Alternatively,studentscangiveequationstoillustratethereactionsundergoneby AandB

Structure Structure

A B


9/21


232

or any structure with two OH

groups (not CH3CHOH-) and

C=C.

*

*[notstable]

or

12. SRJC/2009/P3/Q3e


10/21


233

2+

2+

&+ &+&+

(

)CH2Br

13. TJC/2009/P3/Q1b

HighC:HratioinfersthatPisanaromaticcompound.

P

WithanhydrousaluminiumchloridePundergoeselectrophilicsubstitutionreaction

toformQ.AstheOHisanactivatinggroup,thesubstituentwillbedirected

totheorthoorparaposition.

Q

OR

Pundergoeselectrophilicsubstituitionasitdecolourisesaqueousbromine toform

whitepptR.Ris2,4,6-tribromophenolas-OHisahighlyactivatinggroup.

Q reactwithaqueousbrominetoformwhiteppt S, withthesamenoofbromine

atomspermoleculeofR. AsQhasa C-Cdoublebond,electrophilicaddition

takes place as well. This implies that 1 Br will be attached to one of the

carbonsoftheC-Cdoublebonds.Thus,only2Brwillbeattacheddirectlyto

thebenzene.

S

2+

CH2CH=CH2


11/21


234

Sisopticallyactivebecauseofitschiralcarbon.ThemirrorimageofSisnon-superimposable.

14. TPJC/2009/P3/Q1d

(i)

O O

OHOH Br Br

Br

BrA B C D E AundergoeselectrophilicadditionwithHBrtoform DandE.Aundergoesvigorousoxidation/oxidativecleavagewithhotacidifiedKMnO 4toformC.

Ccanundergoneutralizationoracid-basereactionwithaqueousNa 2CO3toliberateCO2gas.Bundergoesvigorousoxidation/oxidativecleavagewithhotacidifiedKMnO 4toformCO2BundergoeselectrophilicadditionwithHBrfollowedbynucleophilicsubstitutionwithaqueousNaOHtoformhexan-2,3,5-triol. (ii)Acannotformcis-transisomersasitisacyclicalkeneandthetransisomerwillresultinbondanglestrain.Bcanformapairofcis-transisomers asithasanC=Cbondwitheachcarbonbondedtotwodifferentgroupsofatoms.

H

H HH

trans cis hexan-2,3,5-triolhas3chiralcarbons, henceno.ofopticalisomers=2 3=8

YJC/2009/P3/Q5c15.


12/21


235

ACJC/2009/P3/Q4b16. A has amine group being basic. No reaction with aq Br2 shows absence of

phenylamine.Aisaketone..Ahasabenzenering,andis2,4directing.Aundergoes

nucleophilic substitution with aq OH- forming C. C has a primary alcohol forming

COOHconfirmingbyreactionwithcarbonate.Aundergoeselimination. A

CH2NH2

COCH2Cl

BCH

2NH

2

CO N N

H

NO2

CH2Cl

NO2


13/21


236

C

CH2NH2

CO

CH2OH

DCH2NH2

CO

CH2OH

E

CH2

NH

C

O

IJC/2009/P3/Q3a17. (i)

(ii)

IJC/2009/P3/Q5d18.


14/21


237

SRJC/2009/P3/Q3e19.

CH3 C C

Cl Cl

CH2Cl

CH3H A

CH3 C C

OH OH

CH2OH

CH3H B

CHI3 C

C COH

CH2OH

CH3

O

Na+-O D

HOOC C

OH

COOH

CH3 E

NYJC/2009/P3/Q5c20.

STRUCTURES

[1] Mis

C

CH3

CH CH

OH

CH CH CH3


15/21


238

[1] Nis

C

CH3

O

[1] Ris

C

O-

O

Na+

[1] Pis

COH

O

CC

OH

O

O

[1] Qis

C CH3

OH

O

EXPLANATIONOFTHEREACTIONSDESCRIBED[1] Mdecolourisesaqueousbromineduetoelectrophilicadditionacrossthealkene(C=C)functionalgroup.

[1] Mproduceswhitefumes(ofHCl)withPCl5duetoasubstitutionreactionofthe(secondary)alcoholfunctionalgroup.[1] Mproduced3compounds,N,PandQwithhotacidifiedpotassiummanganate(VII)duetooxidativecleavageofthe(2)alkenefunctionalgroupspresent.[1] NdoesnotundergomildoxidationwithFehlingsreagentasitisnotanaldehyde.[1] Ngivesayellowppt(ofCHI3)andsaltRwithaqalkalineiodineduetothe(mild)oxidation(andcleavage)oftheCH 3CORgroup.

[1] Pgivesaneffervescence(ofCO2)withNa2CO3(s)duetoaneutralizationreactionwiththecarboxylicacidfunctionalgroup.[1] Pgivesanorangeprecipitatewith2,4-DNPHduetocondensationwiththeketonefunctionalgroup.[1] Qgivesaneffervescence(ofCO2)withNa2CO3(s)duetoaneutralizationreactionwiththecarboxylicacidfunctionalgroup.


16/21


239

[1]Qdoesnotgiveanorangeprecipitatewith2,4-DNPHduetotheabsenceofacarbonyl functionalgroupforcondensation.

RI/2009/P3/Q1c-e

21.

(c) CompoundDis

DdoesnotcontainOHnorCOOHsinceitdoesnotreactwithsodium.

ItisadiesterformedwhenOHandCOOHgroupsofonelacticacidmoleculereactswiththeCOOHandOHgroupsrespectivelyofanotherlacticacidmolecule.

(d)(i) Ehasachiralcentreasitrotatesplanepolarisedlight. E isan aldehyde sinceit reactswithFehlings solution to give areddish brown

precipitate.

AmountofhydrogenevolvedwithsodiumpermolofE=0.24

0.0124

=1mol

HencetwodisplaceableHarepresenttherearetwoOHgroup.

Eis (ii) Eisanalcohol. The stability ofits anion is lowerthan thestabilityof the anionof

lacticacidastheanionisdestabilisedbytheelectrondonatingCH2CH(OH)CHOgroup.

Lacticacidis amuchstronger acidasits anionforms twoequivalent resonancestructureswiththenegativechargeonOdelocalisedovertwoelectronegativeOatoms.

(e)(i) maleicacidfumaricacid

(ii) Intramolecular hydrogenbonding occurs in maleic acid and thus it has lower

meltingpointastherearelesssitesforintermolecularhydrogenbonding.

& &

& &

222

2

+ +

+


17/21


240

RI/2009/P3/Q5b22.

(b) Information Deductionofstructure

FormulaofG=C8H11O3N Indexofunsaturation

=(2x8+211+1)=4

(orhighCtoHratio)

Gislikelytocontainabenzenering/aromatic.

Grotatesplanepolarisedlight. Gislikelytocontainatleastonechiralcarbon.

Ggivesavioletcolourationwith

neutralFeCl3solution

G is a phenol with violet colourtion formed by

complexformation.

Greactswith2molofaqNaOH Thereare2phenolicOHgroupinG,reactingwith

OHviaacid-basereaction.

G is insoluble in water but

dissolvesindilH2SO4.

G is likely to contain an amine group, withNH2

beingprotonatedbyH+.

G is oxidised by K2Cr2O7 to

form a product which reacts

with 2,4DNPH to give an

orangeppt.

G is a secondary alcohol and is oxidised to a

ketonebyK2Cr2O7.

H is formed by reaction of G

withAl2O3

H is formed from G by dehydration, it is likely an

alkene.

H reacts with aq Br2 to form

C8H7O3NBr4.

The product is likely to be a bromohydrin formed

by electrophilic addition and electrophilic

substitutionintoactivatedbenzenering.

G reacts with ClCOCOCl to The phenol, secondary alcohol and amine reacts

intramolecularhydrogenbond

+


18/21


241

form J which has 3 hexagonal

rings.

withClCOCOClvianucleophilicsubstitution.

3 hexagonal ring cyclic esters and amides

formed with the phenolicOHs andalcoholicOH

andamineonadjacentcarbonatoms.

SRJC/2009/P3/Q5a

TPJC/2009/P3/Q4b24.

23. (a) GundergoesoxidationwithacidifiedKMnO4.

HundergoesnucleophilicsubstitutionwithPCl5.

o Hisanalcoholorcarboxylicacid

o Jisahalogenoalkaneoracylchloride

Jundergoesreductionwithtininconcentratedhydrochloricacid.

o Jcontainsnitrobenzeneo Kcontainsphenylamine

K reacts with (C2H5)2NCH2CH2OH through esterification/nucleophilic

substitution/acylation

o Jmustcontainacylchloride

o Hisacarboxylicacid

Kis

COClH2N

or

COOHH2N

Jis

COClNO2

His

COOHNO2

GisNO2 CH3

or

NO2 C OH

H

H orCNO2

O

H

(7outof8marks)


19/21


242

TPJC/2009/P3/Q5c25.


20/21


243

F

CH3

CH2C

HO H

O

GCH

3

CH2C

HO H

OBr

HCOOH

COOH

HO


21/21


CH3

CH2

CHO

HO Cu2+ - -

CH3

CH2COO-

-OCu

2O H

2O

+ 2 + 5 OH

+ + 3

CH3

CH2CHO

HO

COOH

COOH

HO CO2 H2O

+ 7O

+ + 2

structural elucidation soln

Documents