Post on 25-Jul-2016
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SolutionstoProblemsAlkanes
BuildingBridgestoKnowledge
PhotoofawaterwaycanalinShanghai,China
1. NamethefollowingcompoundsusingtheIUPACsystemofnomenclature:
(a)
2,5-dimethylheptane
(b)
CH3 C
CH2CH3
CH2CH2 CH
H CH3
CH3
CH3 C CH2CH2 CHCH2
H CH3
CH3
CH
CH3 CH3
2
2,3,6-trimethyloctane
(c)
3-methylpentane(d)
3-methylhexane
(e)
4-ethyl-2-methylheptane
CH2CH3CH
CH3
CH2
CH3
CH3
CH3CH2CH
CH2CH2CH3
CH2CH3
CH3
CH3
CH2CH2CH3
CHCH2CH
3
(f)
2,4,4-trimethylhexane
(g)
3,4-dimethylhexane
(h)
3-ethyl-2-methylnonaneor3-isopropylnonane
(i)
5-ethyl-3,5-dimethylundecane
CH2CH3
CH3
CH3
CH3CHCH2CCH3
CH2CH3
CH3
CH3
CHCH
CH3CH2
CH3
CH3
CHCH
CH3(CH2)4CH2
CH3CH2
CH2CH3
CH3 CH3
CH3(CH2)4CH2
CH3CH2
C CH2CH
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2. Writeabalancedchemicalequationforthefollowingreactions:(a)
(b)
majorproductminorproduct
(c)
(d)
n (2n + 2) 2C H + O →
n (2n + 2) 2 2 23n + 1C H + O n CO + (n + 1) H O
2⎛ ⎞ →⎜ ⎟⎝ ⎠
h3 2 3 2CH CH CH + Br ν⎯⎯→
CH3CH2C
Br
CH3
H + Mg(1) dry ether
H2O(2)
CH3C C CH2CH3 + H22Pt
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(e)
(f)
(g)
(h)
CH3CH2C
Br
CH3 +
H
Na
CH3CH2CH3 + CH2N2hν
hνCH3
CH3
CH3
CH3C + C C OH
H
CH3CH2CH2Br + [(CH3)2CH]2CuLi
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3. Suggestmechanismsforthefollowingconversions(Amechanismisaseriesofelementarystepsthatrationalizetheformationofproducts.Whenaddedtogether,thesumofthestepsfortheproposedmechanismshouldresultintheequationthatrepresentsthereactantsandtheproducts.)(a)
Theadditionofsteps2and3accountsforthereactantsandproducts.
(b)3CH3CH2Br+4Li+CuBr→CH3CH2CH2CH3+CH3CH2Cu+4LiBr
3. CH3CH2・+Li→CH3CH2Li3.CH3CH2・+Li→CH3CH2Li4.CH3CH2Li+CuBr→CH3CH2Cu+LiBr5.CH3CH2Cu+CH3CH2Li→(CH3CH2)2CuLi6.(CH3CH2)2CuLi+CH3CH2Br→CH3CH2CH2CH3+CH3CH2Cu+LiBr
Theadditionofsteps1-6resultsin
3CH3CH2Br+4Li+CuBr→CH3CH2CH2CH3+CH3CH2Cu+4LiBr(c)
h4 2 3CH + Cl CH Cl + HClν⎯⎯→
1. Cl2 hn⎯ →⎯ 2 Cli
2. Cl ⋅ + CH4 → CH3 ⋅
3. CH3 ⋅ + Cl2 → CH3Cl + Cl ⋅
1. CH3CH2Br + Li → [CH3CH2 Br]− . + Li+
1. CH3CH2Br + Li → [CH3CH2 Br]− . + Li+
2. [CH3CH2 Br]− . + Li+ → CH3CH2 ⋅ + LiBr2. [CH3CH2 Br]− . + Li+ → CH3CH2 ⋅ + LiBr
3 2 3 2 2 32 CH CH Br + 2 Na CH CH CH CH + 2NaBr→
1. CH3CH2Br + Na → [CH3CH2 Br]− . Na+
2. [CH3CH2 Br]− . Na+ → CH3CH2 ⋅ + NaBr
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Theadditionofsteps1-5resultsin
4. Calculate∆Hfor
IfthebonddissociationenergiesinkJ/molare
bond bonddissociationenergy,kJ/molC-H 410Br-Br 192C-Br 280H-Br 364
3. CH3CH2Br + Na → [CH3CH2 Br]− - Na+
4. [CH3CH2 Br]− - Na+ → CH3CH2 ⋅ + NaBr
5. CH3CH2 ⋅ + CH3CH2 ⋅ → CH3CH2CH2CH3
3 2 3 2 2 32 CH CH Br + 2 Na CH CH CH CH + 2NaBr→
3 3 2 3 2CH CH + Br CH CH Br + HBr→
ΔHr = +410 kJ/mol + 192 kJ/mol -280 kJ/mol -364 kJ/molΔHr = -42 kJ/mol
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5. Sketchapotentialenergyversusreactioncoordinatesdiagramforthefollowingreaction:
Mechanism:
Onthegraph,indicatethe:
(a) IntermediatesForthissystem,themorestableintermediateis
(b) enthalpyofreaction(c) energyofactivation,Eact(d) transitionstate
Thefirstactivatedcomplexatthefirsttransitionstateis
whereX=BrThesecondactivatedcomplexatthesecondtransitionstateis
CH3CH2CH3 + Br2hν
(CH3)2CHBr + HBr
1. Br2 hν⎯ →⎯ 2 Br ⋅2. CH3CH2CH3 + Br ⋅ → (CH3)CH ⋅ + HBr3. (CH3)3CH ⋅ + Br2 → (CH3)2 CHBr + Br ⋅
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whereX=BrUsethefollowingdatatoapproximatethepotentialenergydiagram.
Bond bonddissociationenergy,kJ/mol
C-H 413Br-Br 192C-Br 280H-Br 364
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5. Benzo[a]pyreneisacarcinogeniccompoundwhichhasbeendetectedingrilledsteaks.Combustionanalysisof3.22mgofbenzo[a]pyreneproduced11.25mgofCO2and1.38mgofH2O.(a)Calculatetheempiricalformulaofbenzo[a]pyrene.
(b)Inanexperiment,2.523gofbenzo[a]pyrenelowersthemeltingpointof50.0gramsofcamphorto170.6oC.Calculatethemolecularmassofthecarcinogen.
11.25mg x 12 g/mol44 g/mol
= 3.07 mg of C
1.38 mg x 2.0 g/mol18 g/mol
= 0.153 mg of H
3.07 mg12 mg/mmol
: 0.153 mg1.0 mg/mmol
= 1.67:1
C1.67H
C5H3
ΔTf = 40.0 K kgmol
m
451.6 K - 443.8 K = 40.0 K kgmol
x
2.523 gMW
0.050 kg7.8K
40.0 K kgmol
x 0.050 kg= 2.523 gMW
9.75 x 103 mol = 2.523 gMW
MW = 2.523 g9.75 x 103 mol
= 259 g/mol
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(c) Calculatethemolecularformulaforbenzo[a]pyrene.
6. DrawtheNewmanprojectionformulasforCH3CHBrCH2CH3andsketchthe
potentialenergyversusrotationdiagramfora360orotationof2-bromobutanealongC2andC3carbonatoms.
(C5H3)x = 259 g/mol63 x = 259 g/molx = 4(C5H3)4 =C20H12
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8. Suggestsynthesesforthefollowingcompoundsfromorganiccompoundscontainingnomorethanfourorfewercarbonatomsandanyothernecessaryinorganicreagents.
(a)(CH3)2CHCH3
(b)CH3CH2CH2CH2CH2CH2CH2CH3
(c)CH3CHDCH3whereDisdeuterium,anisotopeofH
(d) CH3CH2CH2CH2TwhereTistritium,anisotopeofH
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9.Calculatethepercentageofmonochlorinatedproductsanticipatedinthemonochlorinationof2,4-dimethylpentane.GiveIUPACnamesofthemonosubstitutedchlorinatedcompounds.
ais1-chloro-2,4-dimethylpentanebis3-chloro-2,4-dimethylpentanecis2-chloro-2,4-dimethylpentane
StatisticalFactorxReactivityFactorPrimaryHydrogenAtomAbstraction12x1.0=12SecondaryHydrogenAtomAbstraction2x3.8=7.6TertiaryHydrogenAtomAbstraction2x5.0=10Percentof1-chloro-2,4-dimethylpentane
Percentof3-chloro-2,4-dimethylpentane
Percentof2-chloro-2,4-dimethylpentane
1229.6
x 100 = 40.5%
7.629.6
x 100 = 25.7%
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10. Thefreezingpointof3.5gramsofanunknownorganiccompoundin100mL
ofbenzeneis5.0oC.Calculatethemolecularweightoftheunknownorganiccompound.
Thedensityofbenzeneis0.8765g/mL
1029.6
x 100 = 33.8%
ΔTf = Kf m
d = massvolume
0.8765 gmL
= mass100 mL
0.8765 gmL
x 100 mL = mass
87.65 g = mass
(278.7 − 278.2) K = 5.12 K kgmol
x
3.5 gMW
0.08765 kg
0.5 K
5.12 K kgmol
x 0.08765 kg = 3.5 gMW
0.00856 mol = 3.5 gMW
MW = 3.5 g0.00856 mol
= 410 g/mol