solutions to problems stereochemistry, building bridges to knowledge
DESCRIPTION
This paper includes solutions to problems cited on pages 43-55 in the paper titled "Stereochemistry, Building Bridges to Knowledge."TRANSCRIPT
1
SolutionstoProblemsStereochemistryBuildingBridgestoKnowledge
PhotooftheYangpuSuspensionBridgeinShanghai,China
1. Ameasuredmassofanopticallyactivecompoundisdissolvedin
anaproticsolventmakingatotalvolumeof50.0mL.Whenthissolutionisplacedina10.0cmpolarimetertube,theobservedrotationis+2.79o.Ifthespecificrotationis+93og-1dm-1mL,calculatethemassoftheopticallyactivesampleinthepolarimetertube.
+93o g−1 dm−1 mL = +2.79o
10.0 cm x 1 m100 cm
x10 dm1m
x x g50.0 mL
2
x=1.5g
2. Specifytheabsoluteconfigurationofthechiralcenters,ifany,in
thefollowingcompounds.Indicatewhetherthecompoundisopticallyactive.a.
S Opticallyactive Chiralcenter Themoleculeischiral
b.
Noplaneofsymmetry Themoleculeischiral Opticallyactive
+93o g−1 dm−1 mL x 1.0 dm x x g50.0 mL
= +2.79o
C
Br
CH2CH3H3C
H
CC CCH3
CH3H
H
3
c.
Planeofsymmetry Themoleculeisachiral Opticallyinactive
d.
R Opticallyactive Chiralcenter Themoleculeischiral
e.
Planeofsymmetry Themoleculeisachiral opticallyinactive
CC CCH3
CH3H
H
CH3
H
O
4
f.
opticallyactive Noplaneofsymmetry Twochiralcenters Themoleculeischiral
g.
Nitrogenmoleculesarenotchiralbecauseoftheumbrellaeffect;therefore,themoleculeisopticallyinactive.
Br
BrH
H
CH3 HCH2CH3
N
..
5
h.
Opticallyactive Noplaneofsymmetry Twochiralcenters Themoleculeischiral
i.
C
C
C
CH2OH
H
H
OH
OH
O
H
C
C
H
H
CH2CH3
CH2CH3
Br
Br
6
Themoleculeisopticallyinactive,becauseofinternalcompensation.
Themoleculepossessesaplaneofsymmetry. Themoleculehastwochiralcenters. Themoleculeisachiral.
J,
opticallyactive
C
H
CH2CH3
CH2CH2CH3CH3
7
3. Showhowdifferencesinthesolubilityofdiastereomericsaltsmaybeusedtoresolveopticallyactivealcohols,ROH.Hint:
C
C
O
O
O
+ ROH
C
C
O
OH
OR
O
phthalic anhydride an acid-ester
8
9
4. Inthefollowingreaction,determineifthechiralcenterinthereactantshasbeendisruptedinsynthesizingtheproducts:
(a)
Thereisnodisruptiontothechiralcenter.
(b)
Thereisnodisruptiontothechiralcenter
(c)
Thereisadisruptiontothechiralcenter
CCH3 COOH
H
OH
+ ROHH+
CH3 C
H
OH
COOR + H2O
C
CH3
COOH
H
+
CH3
C
H
+CNCH3CH2 H2O HCl2 + NH4ClCH3CH2
C
CH3
H
+
CH3
C
H
+CH3CH2 CH3CH2Br NaOH OH NaBr
10
(d)
Thereisdisruptiontothechiralcenter5. Thespecificrotationofanopticallyactivedextrorotatory
compoundis+56o.Calculatethepercentagecompositionofamixtureofenantiomersofthiscompoundwhoserotationis-22o.
Letx=thefractionofthedextrorotatorycompoundThen,1-x=thefractionoflevorotatorycompoundx(+56o)+(1-x)(-56o)=-22o56x-56+56x=-22112x=56–22112x=34x=34/112x=0.30thefractionofthemixturethatisdextrorotatory1-x=0.70thefractionofthemixturethatislevorotatory
6. Ascertainwhetherthefollowingstructuresaresuperimposable
ontheirenantiomers:
(a)
Thismoleculedoesnotsuperposeonitsmirrorimage.
+ C CH2CH3
CH3
H
ClAlCl3
C
H
CH2CH3
CH3HCl+
CH3
CH3
Br
Br
H
H
11
(b)
Thismoleculedoesnotsuperposeonitsmirrorimage.
(c)
Thismoleculesuperposesonitsmirrorimage.
(d)
Inthestaticmodel,themoleculedoesnotsuperposeonitsmirrorimage,buttheotherlonepaircanbeprotonated;therefore,themoleculeisopticallyinactive.
CH3
CH3
HH
C
C
CH3
CH3
OH
OH
H
H
OH3C
H
..+
12
(e)
Thismoleculedoesnotsuperposeonitsmirrorimage.
(f)
Thismoleculesuperposesonitsmirrorimage.
(g)
Thismoleculesuperposesonitsmirrorimage.
NCH3CH2
CH3
CH2CO2CH3
H
+ Cl-
Cl Cl
H H
Br
Br
H
H
13
7. Calculatethenumberofstereoisomerspossibleforthefollowingcompound:
2n=25=32isomers8. Usingchemicalequations,suggestapathwayforresolvingthe
followingenantiomers:
RS
SHO
HO
H
H
HH
H
OHCH3H3CCH2
C
CH3
CH3CH2
H
N
H
CH3
C
CH3
CH2CH3
H3C
H
H
N
14
9. Determinewhichcompoundsarenonsuperimposable
(dissymmetric)ontheirmirrorimages:
a.
Thismoleculeisnonsuperposableonitsmirrorimage.
C C CCl
Cl
H H
15
b.
Thismoleculeisnonsuperposableonitsmirrorimage.
c.
Thismoleculeissuperposableonitsmirrorimage.
d.
Thismoleculeissuperposableonitsmirrorimage.
CH3
H3C
C
C
COOH
COOH
OH
OH
H
H
C C CH
H
Cl
H
16
e.
Thismoleculeisnonsuperposableonitsmirrorimage.10. AcompoundwiththemolecularformulaofC7H16wasfoundtobe
opticallyactive.WhenC7H16istreatedwithBr2andlight,theresultingmonobrominatedmixtureisopticallyinactive,butresolvable.
(a) SuggeststructuresforC7H16andtheresulting
monobrominatedproduct.
(b) WriteamechanismfortheconversionoftheopticallyactiveC7H16totheopticallyinactivemonobrominatedmixture.
1.
17
2.
3.
Step3maybeenvisionedinthefollowingmanner:
18
11. Followingaretheidentifiedchiralcentersinanisatin,C15H20O8,andtheabsoluteconfiguration(R/Sdesignation)ateachchiralcenter.