CHE311
EXAM1KEY(Ch.1-4)
AnswersinBOLDRED
MultipleChoice(60%;2%each)
PleasemarktheletteroftheBESTanswertoeachquestionclearlyonyouranswersheet.Thankyou!
1.
WhatistheformalchargeonthecentralOofozone,basedupontheLewisstructureshown
intheimageontherightofthisproblem?
A.0
B.–1
C.–2
D.+1
2.
Thenitriteion(NO2–)isproducedbysomebacteriabythereductionofnitrates.WhichisNOTtrueofNO2–?
A.theoctetruleisbrokeninnitriteion
B.itsbestLewisstructurerequiresresonance
C.thesumofformalchargespresent=–1
D.thegeometryofnitriteionisbent
3.
Whichoftheseisastereoisomerofthesubstanceintheboxontheleft?AnswerA(transisomerofit)
B.
A.
O
O
O
C.
D.
4.
Whattypeofreactionisthis?CH3CH2CHBrCH3+NaOHàCH3CH2CH=CH2+NaBr+H2O
A.rearrangement
B.oxidation-reduction
C.elimination
D.addition
5.
HNO2hasaKa≈0.0007.In1.0MHNO2,whatisthestrongestacidpresentinsignificantamounts(>0.05M)?
A.H3O+
B.HNO2
C.HNO3
D.H2O
6.
InthelightofLewisacid-basetheory,whichoftheseisgoingtobealikelyLewisbase?
A.Ca2+
B.O2–
C.Na
D.CH4
7.
Alkanesarenonpolar,buttheelectrondensitywithinalkanesis
A.highestontheH
B.veryunpredictable
C.highestontheC
D.concentratedonCH3’s
8.
Inalkanes,the“n”innamesliken-butanestandsfortheterm
A.natural
B.nonreactive
C.native
D.normal
9.
Therootnameoftheparentchaininthemoleculeattherightis
A.nonane
B.di-octane
C.decane
D.octane
F
Cl
F
Cl
10.
Thecompound2,3,4-trimethyloctanecontains_______methyl,_______methylene,and________methinegroups.
A.2;6;2
B.5;3;3
C.6;4;2
D.4;4;3
11.
InMOtheory,themorelocalizedanorbitalisthe____________tendstobe.
A.higheritsenergy
B.loweritsenergy
C.lesspredictableit
12.
AstablehydrocarbonwiththeformulaC8H14wouldhavetohaveastructureincludinganyoftheseexcept:
A.twodoublebonds
B.atriplebondC.adoublebondandaringD.atriplebondandaring
13.
CombustionofwhichoftheseisomersofC8H18willproducetheLEASTenergy?
A.octane
B.2,4-dimethylhexane
C.2,5-dimethylhexaneD.2,3,4-trimethylpentane
14.
WhatisthesequentialoxidationnumberofthethreeCatoms(lefttoright)in
A.+2;–1;0B.+1;–2;–1C.–1;–1;+2D.+1;–2;+1
15.
Themaineffectoftorsionalstraininamoleculeitstoproduce
A.rotationaroundabondB.breakingofweakbondsC.eclipsingofadjacentatomsD.allofthese
16.
Thepointofmaximumpotentialenergyasreactantsproceedtoformproductsiscalledthe
A.tippingpoint
B.transitionstate
C.reactiveapex
D.heatofreaction
17.
In2,3-dimethylbutane,thelowestenergyconformationismostfullydescribedashaving
A.twoanti-H’swithadjacentgauchemethyls
B.twoanti-methylswithoneadjacentgauchemethyl
C.twopairsofanti-methyls+twogaucheH’s
D.twoanti-methylpairsandapairofeclipsedH’s
D.lessreactiveit
H
O
Br
Br
CHE311Exam1KEY
Page2
18.
Todeterminethelowestenergyconformationofamolecule,includingtheelectrostaticpotentialmap,weuse
A.valencebondtheory
B.molecularmechanics C.resonanceandVSEPR D.MOcalculations
19.
Whichoftheseisnotasignificantfactorintheunfavorable∆Hfofcyclopropanefromitselements?
A.anglestrain
B.diaxialstrain
C.torsionalstrain
D.stericstrain
20.
Thetwist-(orskew-)boatconformationofcyclohexaneismorestablethanthesimpleboatbecauseithas
A.noanglestrain
B.lesstorsionalstrain C.onlydiaxialstrain
D.onlyanti-ringcarbons
21.
Inthepreferredconformationof1,4-cis-dibromocyclohexane,thebrominesubstituentsare
A.bothequatorialB.bothaxialC.inanaxialandanequatoriallocationD.inboatflagpolepositions
22.
ThebicyclicspeciesontheleftofthisquestionhastheIUPACsystematicnameof
A.bicyclo[3.2.0]heptane
B.bicyclo[5.4]heptane
C.bicyclo[3.2.0]pentane
D.bicyclo[0.2.3]octane
23. WhichofthefollowingisomersofC6H13Clhasachiralitycenter?
A.1-chlorohexaneB.2-chloro-4-methylpentaneC.2-chloro-2-methylpentaneD.3-chloro-3-methylpentane
24.
Howmanyopticalisomers(enantiomersanddiastereomers)does3-bromo-2,4,5-trichlorohexanehave?
A.none
B.8
C.16
D.12
25.
Whichoftheseiscapableofbeingopticallyactivebutcanalsohavea(nonactive)mesoisomerform?
A.1,3-dichlorobutaneB.2,4-dichloropentaneC.1,2,3-trichlorobutaneD.2,3-dichloropentane
26.
Resolutionisachemicalprocessappliedtowhattypeofsubstancestoproduceisolatedchiralproducts?
A.meso-compounds
B.prochiralcompounds C.racemicmixtures
D.diastereomers
27.
Stableheteroatomchiralitycentershavebeenproducedforthefollowingexceptformostspecieshaving
A.trivalentN
B.tetravalentSi
C.trivalentS
D.trivalentP
28.
Fromthefollowingisomers,whicharechiralandwhichareapairofenantiomers?AnswerC
IIIIIIIV
H3C
CH3
A.II&III;II&III
B.I&IV;III&IV
CH3
C.II,III,&IV;II&III
CH3
D.I&IV;III&IV
29.
Inwhatwayarethetwomoleculesshownattherightrelatedto
eachother?BothhavetheformulaC6H10O2
A.botharechiral;theyareenantiomers
HO
B.onlyoneischiral;theyarediastereomers
C.neitherarechiral;theyaregeometricalisomers
D.botharechiral;theyareconstitutional(structural)isomers
30.
2-methylpentaneisasimpleachiralmolecule,butitcanbemadeintochiralproductswithproperreactions.
Howmanyofthecarbonatomsin2-methylpentanecanbeconsideredprochiral(prochiralitycenters)?
A.two
B.four
C.one
D.three
HO
OH
OH
Problemsonthenextpage.BesuretoclearlyDRAWOUTyouranswerstoproblemsaskingforstructuralinformation.
CHE311Exam1KEY
Page3
Problems(40%;20%each)
I.
DRAWOUTtheMOSTSTABLEoftheCHAIRconformersforeachofthefollowingtrimethylcyclohexanesand
thenRANKTHEMas“moststable”and“leaststable”(thethirdonewillbeintermediateinstability).Giveat
leastabriefstatementastowhyeachhastherelativestabilitythatyouspecify.
CH3
CH3
H3C
H3C
H3C
CH3
CH3
H3C
CH3 H
H
H
H3C
H
H
H
CH3
gauche
H
CH3
CH3
H
H
allmethylsequatorial,
buttwoaregaucheon
adjacentcarbons
H
H
H3C
H
H
H
H
H
H
CH3
H
H
H3C
H
H
onlytwomethylsare
equatorial;oneisaxial
thusthisistheLEASTSTABLE
H
CH3
H
H
H
H
CH3
H
allmethylsequatorial
andallareisolated,
thusMOSTSTABLE
II.
Menthol(1R,2S,5R)-2-Isopropyl-5-methylcyclohexan-1-ol)isthemajorflavorandcounterirritantinmint.
Fromthenamegivenabove,DRAWTHESTRUCTUREofmentholshowingtheproperabsoluteconfigurations
aroundeachchiralcarbon.Usethecyclohexanechairthathastheisopropylgroupinanequatorialposition.
(drawnforyou)BesuretodrawineveryHonthecyclohexylringinadditiontothe–OHand–CH3groups.
H3C
H3C
H
C
Anisomerofmentholthatexistsinnatureiscalledisomentholandis(1S,2R,5R)-2-Isopropyl-5-methyl-
cyclohexan-1-ol).Whatisthepropertermfortherelationshipbetweenmentholandisomentholintermsof
theiropticalisomerism?
Thiswouldbeadiastereomersinceonlytwoofthethreechiralitycentershavereversedchirality.