halon是什么意思on在线翻译读音例句

UnimolecularRateConstantandThresholdEnergyfortheHFEliminationfrom

ChemicallyActivatedCF

3

CHFCF

3

,,BrookeSibilaStiles,*

DepartmentofChemistry,UniVersityofNorthCarolinaatAsheVille,OneUniVersityHeights,

AsheVille,NorthCarolina28804-8511

ReceiVed:January8,2010;ReVisedManuscriptReceiVed:May18,2010

CombinationofCF

3

CHFandCF

3

radicalsatroomtemperaturegeneratedchemicallyactivatedCF

3

CHFCF

3

moleculeswith95(3kcal/molofinternalenergythatdecomposebylossofHF,initiallyattachedtoadjacent

carbons,withanexperimentalunimolecularrateconstantof(4.5(1.1)yfunctionaltheory

wasusedtomodeltheunimolecularrateconstantforHFelimination,k

HF

,todetermineathresholdenergyof

75(2kcal/mol.

uction

ThereactionsofCF

3

CHFCF

3

inthegasphaseareofgreat

interestbecauseCF

3

CHFCF

3

isusedasafiresuppressantin

placeofHalon1301,CF

3

Br;1–6asaworkingfluidinrefrigeration

andairconditioningapplications;7–9asafoamblowingagent

withfireretardantcapabilities;10andasapropellantinmedical

sprays.11–13Modelingstudiesoflow-pressureandatmospheric

pressurecombustionrelyuponaccuratekineticdataforthe

unimoleculardecompositionofCF

3

CHFCF

3

anditsbimolecular

-

mentalandcomputationalstudies14–26oftheproductprofilefor

combustionofCF

3

CHFCF

3

andofthereactionsbetween

CF

3

CHFCF

3

andOHradicalsoratomicspecies(F,Cl,H,O,

etc)haveappeared.

Ashocktubepyrolysis26ofCF

3

CHFCF

3

overthetemperature

range1200-1500Kconcludedthatthermaldecomposition

dominatedtheremovalprocessesofCF

3

CHFCF

3

andthatHF

eliminationpredominatesoverC-Cbondfideled

thecombustionprofileusinganassumedArrheniusactivation

energy,E

a

,for1,2-HFlossof69.6kcal/

a

was

estimatedbyadding38.8kcal/moltotheenthalpychangefor

theHFeliminationreactionandcorrespondstoathreshold

energy,E

0

(HF),of67.4kcal/mol;theA-factorwasassumedto

be7.9ingstudy1usinglaser-induced

fluorescencedetectionofradicalspeciesintheCF

3

CHFCF

3

inhibitedCH

4

+O

2

flameagreedthatunimolecularHF

decompositionwasdominant,butconcludedthatC-Cbond

rupturewasincreasinglyimportantastheflametemperature

increased,anditappearedthatthesameArrheniusparameters

ecentthermal

decompositioninvestigation19busingUVphotoelectrondetection

alsofoundthat1,2-HFeliminationwasfavoredbutsuggested

thatformationofHCF

3

+CF

2dCF2

,ratherthanC-Cbond

rupture,becamemoreimportantathighertemperatures.A

modelingstudyoftheproductprofilefromthereactionbetween

CF

3

CHFCF

3

andeitheratomichydrogenorO(3P)usedE

a

)

69.5kcal/mol23forHFelimination,butasimilarapproach27

fortheinhibitionbyCF

3

CHFCF

3

onshockheatedethane-

oxygen-argonmixturesusedE

a

)75.6kcal/mol.

AtheoreticalinvestigationattheQCISD(T)levelrecom-

mended28E

0

)79.2kcal/mol,butfivedifferentlevelsoftheory

predictedanE

0

intherange82.3-89.1kcal/molandB3LYP

with6-31G(d)gaveabarrierof75.4kcal/

0

is

typicallytwoorthreekcal/mollowerthanE

a

athightemper-

ature;thus,thetheoreticalworksuggestedanactivationenergy

between75and90kcal/flameprofilemodeling

studies1,26agreedthatunimoleculareliminationofHFfrom

CF

3

CHFCF

3

isanimportantstepinthecomplexreaction

chemistryofinhibitedflamesand,becauseaprecisethreshold

energyisessentialtoaccuratelymodelthecombustionsystem,

anexperimentalinvestigationofthe1,2-HFeliminationreaction

fromCF

3

CHFCF

3

seemswarranted.

WewillmeasuretheunimolecularrateconstantforHFloss

fromCF

3

CHFCF

3

chemicallyactivatedbythecombinationof

CF

3

andCHFCF

3

rageenergy,〈E〉,ofthe

chemicallyactivatedCF

3

CHFCF

3

isestimatedas95kcal/mol

fromtheCF

3

CHF-CF

3

bonddissociationenergy,D

0

(CF

3

CHF-

CF

3

),plustheaveragethermalenergyofthecombiningradicals.

TheRRKMtheory29willbeusedtocalculatetherateconstant

forHFeliminationfromCF

3

CHFCF

3

,withanenergyequalto

〈E〉,andthethresholdenergy,E0

,willbevarieduntilthe

computedunimolecularrateconstantmatchestheexperimental

arametersneededfortheRRKMcomputationof

therateconstant(vibrationalfrequenciesandmomentsofinertia)

willbecalculatedwithdensityfunctionaltheory(DFT)using

maticstudy31ofDFT

andabinitiomethodsforthe1,2-HF(DF)eliminationfrom

CF

3

CH

3

(CF

3

CD

3

)determinedthatB3LYPorB3PW91together

witheithera6-31G(d′,p′)oracc-PVDZbasissetgavethebest

agreementbetweencomputedandexperimentalrateconstants

ecentwork,32–34DFTusing

theB3PW91methodwitha6-31G(d′,p′)ora6-311+G(2d,p)

basissetwasfoundtogivecloseagreementbetweenthe

computedandexperimentalassignedE

0

(HF)forninehalopro-

panesandonehalobutane.

Therearethreemainsourcesofuncertaintyinmatchingthe

computedrateconstanttotheexperimentalmeasurementto

determinetheE

0

forHFelimination:(1)Theenthalpyof

formationforCF

3

CHFCF

3

,theCF

3

CHFradical,andtheCF

3

radicalareusedtodetermineD

0

(CF

3

CHF-CF

3

).Theexperi-

mentaluncertaintyinthermochemistryforthesefluorocarbon

speciesisoften(1-2kcal/molleadingtoanuncertaintyof

*Towhomcorrespondenceshouldbeaddressed.E-mail:bholmes@

.

.A2010,114,6996–70026996

10.1021/jp100195e2010AmericanChemicalSociety

PublishedonWeb06/10/2010

(2-4kcal/molforthe〈E〉.Thisuncertaintywillberepresented

asthehorizontaledgesofaboxinFigure2.(2)Thereissome

errorinmeasuringtheexperimentalrateconstant,butthisis

frequentlylessthantheuncertaintyassociatedwiththecolli-

certaintywillberepre-

sentedbytheheightofaboxinFigure2.(3)Theelectronic

structurecalculationsgivevibrationalfrequenciesandmoments

ofinertiaforthemoleculeandthetransitionstatethatareneeded

toevaluatetherateconstant,k

E

,ataspecificenergyEaccording

ion3.3wewilldemonstrate

thatdifferentDFTmethodsandbasissets,foracommonE

0

,

givenearlyidenticaldependenceofk

E

r,the

twoCF

3

torsionalfrequenciescanbetreatedasavibration,

sanddensities

ofstatescanbesensitivetothespecificmodelusedtodescribe

thetorsionalmotion,andwewilltestdifferentmodelsforthe

CF

3

torsionalmotionfortheeffectonk

E

.Thebestcalculated

rateconstantsaresubjecttotheassumptioninherentintransition

E

curvein

Figure2thattouchestheboxillustratingtheuncertaintyin〈E〉

andintheexperimentalrateconstantwillbecriteriaforan

acceptableE

0

.Agreementbetweenthecomputedandthe

experimentalrateconstantsshouldreducethewidevariation

inthecurrentlypublishedE

0

value(67-89kcal/mol)23,26–28to

(2kcal/mol.

ThechemicallyactivatedCF

3

CHFCF

3

,denotedwithan

asterisk(*),wasformedbythecombinationofCF

3

CHFand

CF

3

radicals,eq1andtheotherradicalcombinationreactions

are2and3.

PhotolysisofCF

3

CHFIandCF

3

Iinpyrexvesselscontaining

smallamountsofmercury(I)iodide(toscavengeatomic

iodine)on5

showsthatchemicallyactivatedCF

3

CHFCF

3

*maybestabilized

bycollisionwithbathgasmolecules,M,mainlytheiodide

precursors,oratsufficientlylowpressuresitmaydecompose

via1,2-HFelimination,afluoroethane,reaction3,

andmeso-andd,l-CF

3

CHFCHFCF

3

,reaction2,arestabilized

atthepressuresoftheseexperiments.

Therateratioforeqs4and5equalstheproductratiosowe

canwriteeq6.

whichisoftheformy)mx+b(y)[CF

2dCFCF3

]/[CF

3

-

CHFCF

3

],m)k

1,2-HF

/k

M

,x)1/[M],andb)0).The

concentrationofthecollisionpartner,[M],equalsthepressure,

P;thus,aplotof[CF

2dCFCF3

]/[CF

3

CHFCF

3

]versus1/Pwould

belinearwithaslopeofk

1,2-HF

/k

M

andaninterceptofzero.

mentalSection

Pyrexvesselswithvolumesrangingfrom552to4900mL

containingnormally0.182molof1-iodo-1,2,2,2-tetrafluoro-

ethaneand0.547moltrifluoromethyliodide,andsmall

amountsofmercury(I)iodide,werephotolyzedwithahigh-

pressureOriel68811arclampoperatingwitha500Wmercury

ctionvesselwasplacedatleast25cmfromthe

presenceofmercury(I)iodideinthevesselsduringphotolysis

aidsinformationofthetrifluoromethyland1,2,2,2-tetrafluo-

roethylradicals.35Photolysistimeswerebetween10and20min,

atroomtemperature,resultingintheconversionof12-22%

plepreparation,apressureofeither

1.00or3.00Torrofaniodidewasmeasuredinasmall,

calibratedvesselwithaMKS270electronicmanometerand

al

pressureinthereactionvesselwasdeterminedbyadding

togethertheresidualpressurepriortoadditionoftheiodides,

typicallybetween(2and4)10-4Torr,andthepressuredue

totheiodidesthathadbeentransferredfromthecalibrated

ingadditionoftheCF

3

CHFIandCF

3

Isamples

tothereactionvesselthetotalpressurewasbetween(0.22and

3.0)10-2Torr.

Productidentificationwasbasedoncomparisonofmass

spectralfragmentationpatternsandretentiontimeswithau-

dzuQP5000GC/MSwitha0.25mm

by105mRtx-200columnwasusedformassanalysis,aGC/

icaldatawere

collectedusinga0.53mmby210mRtx-200combination

columninaShimadzuGC-14Awithflameionizationdetector

andaShimadzuCR501ChromatopacIntegratorforintegration

sothermalGCanalysisat35Cthetypical

retentiontimeswereasfollows:C

2

F

6

,19.4min;CF

2dCFCF3

,

20.4min.;CF

3

CHFCF

3

,21.2min.;CF

3

I,22.1min,meso-and

d,l-CF

3

CHFCHFCF

3

,26minand29min.;andCF

3

CHFI,33

cdatawerecollectedusinga210mGCcolumnto

ensurebaselineseparationofC

2

F

6

,CF

2dCFCF3

,CF

3

CHFCF

3

,

andCF

3

ticsamplesofallproductswereavailable

exceptCF

3

CHFCHFCF

3

.Theflameionizationdetectorcalibra-

tionfactorwas[CF

2dCFCF3

]/[CF

3

CHFCF

3

])0.685(0.007

basedonfourreplicatesfromfivedifferentmixturesofauthentic

samples.

sandDiscussions

mentalChemicalActivationRateConstant.

ThischemicalactivationstudyusingCF

3

CHFIandCF

3

Ito

producetheCF

3

CHFandCF

3

radicalsisacleanchemical

activationsystemwithnoevidenceforsecondaryunimolecular

reactionsandnoevidencefordisproportionationreactionsof

alGC/MStraceofaphotolyzedsample

usedtoidentifyproducts,whichispresentedinSupporting

Information,showsonlyproductsfromeq1-5wereobserved.

Aplotof[CF

2dCFCF3

]/[CF

3

CHFCF

3

]versusinversepres-

sure,seeeq6,ssure

rangeissmallerthandesirable,butwewantedthepressurein

thereactionvesselstobeanorderofmagnitudelargerthanthe

residualpressure;thus,ourvacuumsystemrestrictionedthelow

pressurelimitto210-3Torrwhichis1/P)

CF

3

CHF+CF

3

98

k

cCF

3

CHFCF

3

*(1)

2CF

3

CHF98

k

cmeso-andd,l-CF

3

CHFCHFCF

3

*(2)

2CF

3

98

k

cCF

3

CF

3

*(3)

CF

3

CHFCF

3

*98

k

1,2-HFCF

2

dCFCF

3

+HF(4)

98

k

M

[M]

CF

3

CHFCF

3

(5)

[CF

2

dCFCF

3

]/[CF

3

CHFCF

3

])k

1,2-HF

/k

M

[M](6)

HFEliminationfromChemicallyActivatedCF

3

CHFCF

3

.A,Vol.114,No.26,20106997

anticipatedforaunimolecularreactioninanefficientbathgas,

theplotislinearandtheintercept,-(2.9(4.8)10-4,is

zerowithintheexperimentaluncertainty((1standarddevia-

tion).Theslopeis(3.4(0.2)10-5Torrandequalsk

1,2-HF

/

k

M

.TheuseofthestrongcollisionmodelisdefendedinSection

econstantinpressureunitsisconvertedtouni冬天图片 tsof

s-1bymultiplicationbythecollisionrateconstantk

M

)

d2

A,M

(8kT/

A,M

)1/2Ω2,2(T*).Usingcollisiontheorywithcol-

lisiondiameters,d,and/kvalues(inparentheses)of5.1

(288K),5.2(300K),and6.1(200K)forCF

3

I,CF

3

CFHI,

andCF

3

CHFCF

3

,respectively,k

M

)1.32107(torr-s)-

slopeisconvertedtoarateconstantforHFeliminationfrom

CF

3

CHFCF

3

,k

1,2-HF

)(4.5(1.1)lision

diametersandthe/kvaluesusedforCF

3

CHFIandCF

3

CHFCF

3

areestimatesbasedonvaluesemployedfortheCF

3

CHFCH

3

system.32The6%uncertaintyintheslopeoftheplotFigure1

wasincreasedto(25%toaccountfortheuncertaintyin

convertingtherateconstantfrompressureunitstos-1units.

ationofnonequilibriumrate

constantsforcomparisonwiththeexperimentalchemical

activationresultsrequirestheaverageenergy,〈E〉,depositedin

theCF

3

CHFCF

3

nenergyofthechemically

activatedCF

3

CHFCF

3

isgivenbyeq7,whereD

0

(CF

3

CHF-

CF

3

)isthebonddissociationenergyfortheC-Cbondformed

byradicalcombination,anditequals-∆H

rxn,0

meanvibrationalenergyoftheradicalsisdeterminedfromtheir

vibrationalfrequencies〈E

vib

(CF

3

)〉)0.4kcal/moland〈E

vib

-

(CHFCF

3

)〉)1.7kcal/mol,and3RTistherotationalenergyof

theradicals.

The∆H

f,0(CF3

))-111.7kcal/molisestablished.36Weadopt

∆H

f,298(CF3

CHF))-166.7kcal/mol,whichisanaverageof

fourrecentvalues(-168,37-167.4,38-166.7,39and-164.5

kcal/mol26)andcorrectionto0Kgives∆H

f,0(CF3

CHF))-165

kcal/ports(-371.1,40-374.2,41-374.5,38-370.6,2

and-365.626b)for∆H

f,298(CF3

CHFCF

3

)wereaveragedtogive

-371.2kcal/molandcorrectedto0Ktogive∆H

f,0(CF3

-

CHFCF

3

))-368.0kcal/∆H

rxn,0forreaction1is

-91.3kcal/molwithacombineduncertaintyof(3kcal/mol.

PetersonandFrancisco28calculatedD

0

(CF

3

CHF-CF

3

))92.3,

ingoodagreementwithour91.3(3kcal/ingthese

valuesintoeq7gives95.2(3kcal/mol,andwewilluse〈E〉

)95(3kcal/rnativemethodtocompute〈E〉will

begiveninSection3.4.

vibrationalfrequenciesandmomentsofinertiaforthemolecule

andthetransitionstate,usedinthestatisticalrateconstant

calculations,weredeterminedbyDFTusingGaussian03,30see

CF

3

torsionalmotionsweretreatedaseither

torsionvibrations(TOR),hindered-internalrotors(HIR)oras

freerotorsforcalculations42oftheharmonicdensityorsumof

ctionpathdegenercieswere4forthe

’smethod

wasusedtocalculatethereducedmomentsofinertia,shown

inTable1,fortheCF

3

groupforthemoleculeandforthe

transitionstatestructure;thetorsionalpotentialenergybarrier

forrotationofaCF

3

group,V(CF

3

),wascalculated,using

B3PW91orB3LYPwiththefivebasissetslistedinTable2,

tobe3kcal/molfortheCF

3

CHFCF

3

,independentofmethod

andbasisset,anditwasassumedtheV(CF

3

)didnotchangein

〈E〉)100kcal/molwithanE

0

(HF))

74kcal/mol,theHIRrateconstantwasjust6.8%lowerthan

therateconstantcalculatedusingafree-rotormodel;thus,Figure

2willonlyshowtheenergydependenceofrateconstants

calculatedusingtheHIRorTORmodels.

TwoDFTmethods(B3PW91andB3LYP)andthefivebasis

setsshowninTable2wereusedtoillustratethatthecalculate

E

0

(HF)candecreasebymorethan6kcal/molfromthesmallest

r,thetwoDFTmethodsgive

explorewhetherrateconstantscomputedusingdifferentmethods

orbasissetsexhibiteddifferentmagnitudeandenergydepen-

dencetheB3LYP/6-31G(d),B3PW91/6-31G(d′,p′),andB3PW91/

6-311+G(2d,p)DFTmethodswereusedtocomputek

E

versus

E,methodwasusedforallcalculations.

TherateconstantsatE

0

(HF))74kcal/molwithB3LYP/6-

31G(d)wereindistinguishablefromtherateconstantscalculated

usingfrequencyandmomentsofinertiadatacomputedusing

B3PW91/6-31G(d′,p′),eresultwasfound

atE

0

(HF))76kcal/molwhenrateconstantswerecompared

fortheB3PW91/6-31G(d′,p′),andB3PW91/6-311+G(2d,p)

oughtheE

0

(HF)valuesvariedsignificantly

fordifferentDFTmethods,thecomputedrateconstantsfora

,wecan

computek

E

atspecificenergies,E,usingjustoneDFTmethod

withconfidencethatotherbasissetswouldgivesimilarresults.

TheremainingcalculationswilluseB3PW91/6-31G(d′,p′),

whichhasbeenverysuccessfulinourpreviouswork.32–34

Bycontrast,useofTORversusHIRmodelsgavecalculated

rateconstantsdifferingbyaboutafactorof2,dependingon

thespecific〈E〉,CF

3

torsionalmotions

appeartobestronglycoupledbecausethefrequenciesare

significantlydifferent:oneinthe10-25cm-1rangeandthe

othernear85cm-1,,theHIRmodelis

preferredandjusttheHIRmodelbasedonB3PW91/6-

31G(d′,p′)nstantcalculationswere

doneforarangeofE

0

(HF)valuesfortheHIRmodelto

determinewhichthresholdenergiesproducedcomputedrate

constantsthatencompassedtheuncertaintiesinboththe

experimentalrateconstantandthe〈E〉shownastheboxin

ioof[CF

2dCFCF3

]/[CF

3

CHFCF

3

]vsreciprocal

pressureforthe1,2-eliminationofHFfromchemicallyactivated

CF

3

CHFCF

3

,peis(3.4(0.2)10-5

Torr,theinterceptis-(2.9(4.8)10-4,andthecorrelationcoefficient

is0.96.

〈E〉

)D

0

(CF

3

CHF-CF

3

)+3RT+〈E

vib

(CF

3

)〉+

〈E

vib

(CHFCF

3

)〉(7)

.A,Vol.114,No.26,2010Duncanetal.

〈E〉)95kcal/mol,thek

〈E〉

)170s-1foranE

0

)

76kcal/molandk

〈E〉

)660s-1foranE

0

)74kcal/

heHIR

modelanE

0

(HF)from73to77kcal/molwouldjusttouchthe

box,seeFigure2;thus,weareconfidentinassigningE

0

(HF)

)75(2kcal/mol.

ingtheSpecificRateConstant,k

〈E〉

,atan

AverageEnergy〈E〉totheAverageRateConstant,〈k

E〉.The

previoussectionusedthespecificrateconstant,k

〈E〉

at〈E〉to

determineacceptablevaluesforthethresholdenergyforthe

anapproximationbecausethe

radicalcombinationreaction,eq1,producesCF

3

CHFCF

3

with

adistributionofenergies,f(E),andtheaveragerateconstant,

〈kE〉canbecalculatedoncef(E)helarge

uncertaintyin〈E〉,itisnotreasonabletoattemptafurther

refinementofE

0

,butitwouldbeofinteresttoknowhowk

〈E〉

comparesto〈k

E〉.Thef(E)canbecalculated29onceamodelfor

ociation

complexconsistsofthevibrationalfrequenciesforthetwo

radicals,fourbendingfrequencies(twoat50cm-1andtwoat

100cm-1),sionalmotionabout思念却不能相见的句子

theC-CbondfortheCF

3

CHFradicalwastreatedasafree

culatedenergydistributionfunctionisshownin

hef(E)andthek

E

values

forHIRatE

0

)74kcal/molthe〈k

E〉)a

factorof2.2largerthank

〈E〉

)660s-1for〈E〉)95kcal/mol.

TheE

0

forthe〈k

E〉calculationwouldneedtoberaisedbyabout

1kcal/moltogiveagreementwiththek

〈E〉

.

erimentalrate

constantwasevaluatedwiththeassumptionthateachcollision

betweenthebathgasandCF

3

CHFCF

3

*(seeeq5)removed

sufficientenergysuchthatfurtherreactionwasnegligible

r,in

caseswherethediffer空谷足音的意思 encebetween〈E〉andE

0

islargeand/or

thecollisionpartnerisinefficient,amultistepdeactivation

rtocalculatearate

constantformultistepdeactivationtheaverageenergyremoved

percollisionandthemodel(stepladder,exponential,orsome

othermodel)fortheenergyremovalmechanismmustbeknown

thisinformationisavailablefor

CF

3

CHFCF

3

*collidingwithabathgasthatisamixtureofCF

3

I

andCF

3

mentalevidenceofmultistepdeactivation

wouldbetheupwardcurvatureofaD/Svs1/Pplotatlower

pressureswhereD/S>a,seeFigure1,doesnot

extendbeyondD/S)0.02,andnoevidenceformultistep

tion,wehavestudied32,33several

chemicallyactivatedhydrohalocarbonswithCF

3

Iandother

TABLE1:CalculatedFrequencies,MomentsofInertia,andReducedMomentsofInertiaforCF

3

CHFCF

3

andtheHF

EliminationTransitionStateatB3PW91/6-31G(d′,p′),B3LYP/6-31G(d),andB3PW91/6-311+G(2d,p)

CF

3

CHFCF

3

transition

6-31G(d′,p′)6-31G(d)6-311+G(2d,p)6-31G(d′,p′)6-31G(d)6-311+G(2d,p)

frequencies(cm-1)9.389a16.66a24.06a

83.56a87.52a85.12a52.44a54.13a51.09a

149.6153.6149.777.5679.1280.38

213.5215.3214.9156.2159.1153.1

234.5233.6239.2200.9199.7204.9

288.8288.5288.4240.7238.3235.7

322.3322.1319.7268.9263.9260.4

342.1341.1341.2287.1279.6271.1

454.9450.5449.9346.0344.6344.7

519.3512.0512.4374.7371.9368.9

537.4530.1531.6420.5419.3403.0

552.8546.3547.5504.0498.5499.6

608.1606.9602.5547.9544.6532.7

688.0683.7684.9599.4596.7595.2

743.4742.3739.8621.7618.7612.3

868.7875.9859.6716.1718.1694.7

917.0923.4910.1777.0775.8763.5

1145.21158.51114.8812.0813.4787.7

1156.81166.81141.71029.91033.21025.0

1212.31224.11168.91146.11142.31141.7

1246.01257.81212.51207.91217.11181.0

1273.61286.31225.01226.61232.81198.7

1297.11310.11273.01245.41257.31237.5

1330.01341.11305.11363.01368.91347.3

1394.51410.81377.31455.61468.71446.9

1407.91426.61394.31575.21580.81554.5

3106.43121.23097.61736.31733.21738.7

amu(2)I

x

242.1242.4241.5263.8265.0265.8

I

y

479.5478.5481.8510.9510.8513.6

I

z

544.1543.0545.9558.2556.9556.5

ReducedMomentofInertiaoftheCF

3

Group(I

red

)

I

red

(amu2)60.961.160.662.162.362.1

aFrequencyreplacedwithI

red

inhinderedinternalrotorandfreerotorratecalculations.

TABLE2:ComputedThresholdEnergiesusingDFTfor

HFEliminationfromCF

3

CHFCF

3

thresholdenergy(kcal/mol)

basisSetB3PW91B3LYP

6-31G(d)75.275.4

6-31G(d′,p′)71.771.7

cc-PVDZ69.769.7

6-311+G(2df,2p)69.769.7

6-311+G(2d,p)69.069.0

HFEliminationfromChemicallyActivatedCF

3

CHFCF

3

.A,Vol.114,No.26,20106999

hydrofluoroalkyliodidesasbathgasesandhavenotfound

evidenceforinefficientbehaviorintheD/eless,

theuseofthestrongcollisionassumptionforCF

3

CHFCF

3

*

collidingwithabathgascomparabletoourmixtureofCF

3

I

andCF

3

stionofmultistep

deactivationhasbeeninvestigatedfortwochemicallyactivated

molecules,CF

3

CH

3

43and1,1,2,2-tetrafluorocyclopropane,44with

astructureanalogoustoCF

3

CHFCF

3

.Forcyclo-CF

2

CF

2

CH

2

*

collidingwithCF

2dCF2

theaverageenergyremovedper

collisionwas9kcal/mol.44Themoreexhaustivestudy43of

CF

3

CH

3

*withnumerouscollisionpartnersshowedthatfor

moleculessimilartoourbathgastheaverageenergyremoved

percollisionwouldbe6-10kcal/mol.

TheHIRk

E

vsEcurvewithE

0

)74kcal/molinFigure2

willbeusedtoexaminewhetherthestrongcollisionassumption

isvalidforoursystem,andwewillassumethatourbathgas

mixtureremovesanaverageof6kcal/molfromCF

3

CHFCF

3

*

evethisistheworst-casescenariobecause

thestudieswithCF

3

CH

3

*andcyclo-CF

2

CF

2

CH

2

*suggestthat

eachcollisionwilllikelyremovemorethan6kcal/molof

〈E〉)95kcal/molthek

E

)660s-1,andif6kcal/

molisremovedbyonecollisiontherateconstantdeclinesto

34s-1at〈E〉)89kcal/ingjustonecollisionthat

removes6kcal/molofenergy,therateconstantisonly5%of

thevalueat〈E〉)95kcal/lativelylargedeclinein

k

E

isaconsequenceofthesteepslopeofthek

E

versusEcurve

portanttonotethatforthelowestpressures

inFigure1theD/S<0.02;thus,thecollisionrateisatleast50

timeslargerthank

E

asisofthis

analysis,thestrongcollisionassumptiondoesnotintroduceany

significantadditionalerrorintheassignmentofthethreshold

energy.

smodelingthe

productprofileforcombustionofCF

3

CHFCF

3

useArrhenius

utedk(T)fortheHIRmodel

withV(CF

3

))3kcal/molandI

red

)61amuhenius

parametersat1000Kforthefullreactionpathdegeneracyare

14.21013s-1andE

a

)77.2kcal/-exponential

factorforV(CF

3

))6kcal/molis20.4ange

arisesbecausetheHIRinthetransitionstateiscanceledby

oneinthemolecule,andthepartitionfunctionissmallerfor

oneremovesafactorof6forreactionpathdegeneracythepre-

exponentialfactoris“normal”foratighttransitionstate.31–34If

thepre-exponentialfactorfordissociationoftheC-Cbondis

1016s-1,thenHFeliminationisdominantat1000Kbut

dissociationwouldbecomecompetitivewithHFeliminationat

highertemperatures,consistentwiththeexperimentalfindings.1,26

edStructuresfortheReactant,Transition

State,3hasthebonddistanceandbond

anglesforthestructurescomputedusingB3PW91/6-31G(d′,p′)

forCF

3

CHFCF

3

,thetransitionstatestructureforHFlossand

theCF

2dCFCF3

followingdiscussionthe

carbonlosingthehydrogenisdesignatedC

H

,andC

F

represents

reeofsp2characterofthe

carbonsinthefour-centeredringofthetransitionstateis

illustratedbythe14.7angleatC

F

(theangledefinedbythe

triangularplanebetweentheCF

2

andanimaginaryline

extendingalongtheCdC)andthecorrespondingangleatC

H

is37.8,erence,theangleis55forasp3

carbonand0reeofplanaritydiffers

atthetwocarbonsinthetransitionstateringwiththecarbon

losingtheFbeingsignificantlymoreplanarthatthecarbon

artrend34ghasbeenobservedfor

interestingtonotethattheout-of-ringC-Fbonddistanceat

C

F

isshorterinthetransitionstate(1.29)thanineitherthe

reactant(1.34)ortheCF

2dCFCF3

product(1.31),sug-

gestingthatthefluorinesubstituentsaredonatingelectron

densitytoC

F

.Bycontrast,theout-of-ringC-Fbonddistance

(1.36)atC

H

isnearlythesameasintheCF

3

CHFCF

3

molecule

(1.37).TheC-Cbonddistanceinthering(1.43)isexactly

halfwaybetweenthebonddistanceofthereactant(1.53)

andproduct(1.33).

isonwithPreviousStudiesInvolvingHF

ecularrateconstantsforHFelimination

fromotherchemicallyactivatedfluoropropanes32(CF

3

CH

2

CF

3

,

CF

3

CHFCH

3

,andCF

3

CH

2

CH

3

)

previouslynoted32thegoodagreementbetweenthresholdenergy

valuesforthesehydroflrisonwouldbe

usefulbetweenCF

3

CHFCF

3

andCF

3

CH

2

CF

3

becauseforboth

fluoropropanesanHonthecentralcarboniseliminatedtogether

withanFatomfromeitherendCF

3

3

CH

2

CF

3

the

〈E〉)104kcal/mol,kHF

)1.2105s-1,andE

0

)73kcal/

molcomparedto〈E〉)95kcal/mol,k

HF

)4.5102s-1,and

E

0

)75kcal/molforCF

3

CHFCF

3

.33Theexperimentalrate

constantisafactorof270smallerforCF

3

CHFCF

3

compared

toCF

3

CH

2

CF

3

.Adifferenceof9kcal/molin〈E〉accountsfor

afactorof30intherateconstant,forexample,for〈E〉)95

kcal/molthecalculatedk

HF

)8.8102s-1forCF

3

CHFCF

3

andat〈E〉)104kcal/molthek

HF

)2.90104s-1,whichis

ionpathdegeneracyof6for

flogk

E

vsEforhinderedinternalrotor(HIR)and

torsional(TOR)modelsforvariousE

0

usingresultsfromtheB3PW91/

6-31G(d′,p′)calculationsunlessspecifiedasG(d)orG(2d,p)forthe

B3LYP/6-31G(d)ortheB3PW91/6-311+G(2d,p)calculations,respec-

tively.[HIR,E

0

)74kcal/molwithtwodifferentbasissets:O-

B3PW91/6-31G(d′,p′)andb-B3LYP/6-31G(d)];[0-TOR,E

0

)74

kcal/molusingB3PW91/6-31G(d′,p′)];[HIR,E

0

)76kcal/molusing

twodifferentmethodsandbasissets:[[-B3PW91/6-31G(d′,p′)and

4-B3LYP/6-31G(d)]and[2-HIR,E0

)77kcal/molusingB3PW91/

6-31G(d′,p′)].

.A,Vol.114,No.26,2010Duncanetal.

CF

3

CHFCF

3

versus12forCF

3

CH

2

CF

3

accountsforanad-

ditionalfactorof2.33Atwokcal/mollowerthresholdenergy

willincreasetheunimolecularrateconstantbyaboutafactor

of4,eefactorscombinedcontributeafactor

ofover240tothedifferenceinrateconstants,showingthat

theRRKMmodelsforthetwomoleculesareactuallyquite

consistentdespitethelargedifferenceintheactualrateconstants.

PetersonandFrancisco28computationallyinvestigatedthe

possibledecompositionpathwaysforCF

3

CHFCF

3

usingabinitio

methodsandbasissetstestedthey

foundE

0>95kcal/molforthe2,2-HFeliminationreaction

formingtheCF

3

CCF

3

dnoevidencefor

1,2-

HFeliminationreactionPetersonandFranciscopredictedan

E

0

rangingfrom75.4[B3LYP/6-31G(d)]to89.1kcal/mol

[QCISD(T)/6-31G(d)]andrecommended79.5kcal/molbased

uponQCISD(T)/6-311G(d,p).Ourresultsusing〈E〉)95kcal/

molareconsistentonlywiththesmallestE

0

calculatedby

PetersonandFrancisco.

AcomparisonofthevariousE

0

valuescanalsobeusefulto

ngthat

CF

3

CH

3

withE

0

)69kcal/molistheselectedforcomparison32

thenE

0

)73kcal/mol33forCF

3

CH

2

CF

3

suggeststhatreplace-

mentofoneHofCF

3

CH

3

withaCF

3

groupraisesE

0

by4

kcal/sentworkwithE

0

)75kcal/molfor

CF

3

CHFCF

3

suggestedthatreplacementofasecondHwith

atomicFmayincreaseE

0

byanadditional2kcal/mol.

sions

TheunimolecularrateconstantforHFeliminationfrom

CF

3

CHFCF

3

chemicallyactivatedat95kcal/molwask

HF

)4.5

ngcomputedrateconstantstotheexperimental

measurementforHFeliminationfromchemicallyactivated

CF

3

CHFCF

3

at〈E〉)95kcal/molgivesE

0

(HF))75(2kcal/

oldenergiesfor1,2-HFel七夕图片浪漫唯美图片 iminationfromfluoro-

propanesspan20kcal/molfromthesimplestmemberofthe

seriesCH

3

CHFCH

3

45,46(E

0

)55kcal/mol)33aandCH

3

CH

2

CH

2

F46,47

(E

0

)57kcal/mol)33atoCF

3

CHFCF

3

,themosthighlyfluori-

ral,32,33a

replacementofHbyFonacarbonincreasestheE

0

by2-4

kcal/ationofFfromthecentralcarbonhasalower

E

0

thanlossofFfromtheendcarbonifthetotalnumberofF

substituentsgenerallydecrease32,33a

theE

0

,buttheeffectismorepronouncedatC

F

thanwhen

attachedtoC

H

.

ialsupportfromtheNational

ScienceFoundation(CHE-0647582)

for

sorSetserkindlyassistedincomput-

ingtheArrheniusA-factorandtheenergydistributionforthe

chemicallyactivatedCF

3

CHFCF

3

.

SupportingInformationAvailable:Theenergydistribution

computedfromanassociationcomplexforthechemically

activatedCF

3

CHFCF

3

andaGC/MStraceofaphotolyzed

formationisavailablefreeofcharge

viatheInternetat.

ReferencesandNotes

(1)Williams,B.A.;L’Esperance,D.M.;Fleming,t.

Flame2000,120,160.

(2)Lee,E.P.F.;Dyke,J.M.;Chau,F.-T.;Chow,W.-K.;Mok,

.2003,376,465.2005,402,32.

(3)Bundy,M.;Hamins,A.;Lee,2003,133,

299,andreferencestherein.

(4)Fleming,.1999,16.

(5)Robin,.1995,611,85.

(6)Jiang,Z.;Chow,W.K.;Li,.2007,24,

663.

(7)Froeba,A.P.;Botero,C.;Leipertz,phys.2006,

27,1609.

(8)Coquelet,C.;Rivollet,F.;Jarne,C.;Valtz,A.;Richon,

.2006,47,3672.

(9)Yousefi,F.;Moghadasi,J.;Papari,M.M.;Campo,.

.2009,48,5079.

(10)Zatorski,W.;Brzozowski,Z.K.;Kolbrecki,.

Stab.2008,93,2071.

atedstructuresforCF

3

CHFCF

3

,thetransitionstate

forHFelimination,andCF

2dCFCF3

attheB3PW91/6-31G元旦王安石的诗 (d′,p′)

method.

HFEliminationfromChemicallyActivatedCF

3

CHFCF

3

.A,Vol.114,No.26,20107001

(11)Saso,Y.;Seki,T.;Chono,S.;Morimoto,liVerySci.

Technol.2006,16,147.

(12)Engstrom,J.D.;Tam,J.M.;Miller,M.A.;Williams,R.O.,III;

Johnston,.2009,26,101.

(13)Auwaerter,V.;Proquitte,H.;Schmalisch,G.;Wauer,R.;Pragst,

logy2005,29,574.

(14)Sanogo,O.;Delfau,J.L.;Akrich,R.;Vovelle,.

Technol.1997,122,33.

(15)Hsu,K.-J.;DeMore,.1995,99,1235.

(16)Nelson,D.D.,Jr.;Zahniser,M.S.;Kolb,.

1993,20,197.

(17)Ritter,.1997,209.

(18)Hynes,R.G.;Mackie,J.C.;Masri,Fuels1999,13,

485.

(19)(a)Lee,E.P.F.;Dyke,J.M.;Chow,W.-K.;Chau,F.-T.;Mok,

.2006,417,.2007,28,

1582.(b)Copeland,G.;Lee,E.P.F.;Dyke,J.M.;Chow,W.K.;Mok,

D.K.W.;Chau,.A2010,114,3540.

(20)Zhang,Z.;Padmaja,S.;Saini,R.D.;Huie,R.E.;Kurylo,M.J.J.

.1994,98,4312.

(21)Urata,S.;Takada,A.;Uchimaru,T.;Chandra,.

Lett.2002,368,215.

(22)Liu,J.;Li,Z.;Dai,Z.;Huang,X.;Sun,.2002,

362,39.

(23)Yamamoto,O.;Takahashi,K.;Inomata,.A2004,

108,1417.

(24)DeMore,iol.A2005,176,129.

(25)Tokuhashi,K.;Chen,L.;Kutsuna,S.;Uchimaru,T.;Sugie,M.;

Sekiya,neChem.2004,125,1801.

(26)(a)Hynes,R.G.;Mackie,J.C.;Masri,.A

1999,103,54.(b)Hynes,R.G.;Mackie,J.C.;Masri,t.

Flame1998,113,554.

(27)Ikeda,E.;Mackie,2001,215,997.

(28)Peterson,S.D.;Francisco,.A1999,103,54.

(29)Holbrook,K.A.;Pilling,M.J.;Robinson,40不惑50知天命60花甲70 ecular

Reactions,2nded.;JohnWileyandSons:NewYork,1996.

(30)Frisch,M.J.;Trucks,G.W.;Schlegel,H.B.;Scuseria,G.E.;Robb,

M.A.;Cheeseman,J.R.;Montgomery,J.A.,Jr.;Vreven,T.;Kuden,K.N.;

Burant,J.C.;Millam,J.M.;Iyengar,S.S.;Tomasi,J.;Barone,V.;

Mennucci,B.;Cossi,M.;Scalmani,G.;Bega,N.;Petersson,G.A.;

Nakatsuji,H.;Hada,M.;Ehara,M.;Toyota,K.;Fukuda,R.;Hasegawa,J.;

Ishida,M.;Nakajima,T;Honda,Y.;Kitao,O.;Adamo,C.;Jaramillo,J.;

Gomperts,R.;Stratman,R.E.;Yazyev,O.;Austen,A.J.;Cammi,R.;

Pomelli,C.;Ochterski,J.W.;Ayala,P.Y.;Morokuma,K.;Voth,G.A.;

Salvador,P.;Dannenberg,J.J.;Zakrzewksi,V.G.;Dapprich,S.;Daniels,

A.D.;Strain,M.C.;Farkas,O.;Malik,D.K.;Rabuck,A.D.;Raghavachari,

K.;Foresman,J.B.;Ortiz,J.V.;Cui,Q.;Baboul,A.G.;Clifford,S.;

Cioslowski,J.;Stefanov,B.B.;Liu,G.;Liashenko,A.;Piskorz,P.;

Komaromi,I.;Martin,R.L.;Fox,D.J.;Keith,-Laham,M.A.;Peng,

C.Y.;Nanayakkara,A.;Challacombe,M.;Gill,P.M.W.;Johnson,B.;

Chen,W.;Wong,M.W.;Gonzalez,,an03,ReVision

B.04;Gaussian,Inc.:Pittsburg,PA,2003.

(31)Martell,J.M.;Beaton,P.J.;Holmes,.A2002,

106,8471.

(32)Holmes,D.A.;Holmes,.A2005,109,10726.

(33)(a)Ferguson,J.D.;Johnson,N.L.;Keknes-Husker,P.M.;Everett,

W.C.;Heard,G.L.;Setser,D.W.;Holmes,.A2005,

109,4540.(b)Zhu,L.;Simmons,J.G.,Jr.;Burgin,M.O.;Setser,D.W.;

Holmes,.A2006,110,1506.

(34)(a)Burgin,M.O.;Simmons,J.G.,Jr.;Heard,G.L.;Setser,D.W.;

Holmes,.A2007,111,2283.(b)Beaver,M.R.;

Simmons,J.G.,Jr.;Heard,G.L.;Setser,D.W.;Holmes,.

Chem.A2007,111,8445.(c)Lisowski,C.E.;Duncan,J.R.;Heard,G.L.;

Setser,D.W.;Holmes,.A2007,111,8445.(d)

Zaluzhna,O.;Simmons,J.G.,Jr.;Heard,G.L.;Setser,D.W.;Holmes,B.

.A2008,112,6090.(e)Zaluzhna,O.;Simmons,J.G.,Jr.;

Setser,D.W.;Holmes,.A2008,112,12117.(f)

Ferguson,H.A.;Parworth,C.L.;Holloway,T.S.;Midgett,A.G.;Heard,

G.L.;Setser,D.W.;Holmes,.A2009,113,10013.

(g)Duncan,J.R.;Solaka,S.A.;Setser,D.W.;Holmes,.

Chem.A,2010,114,794.

(35)Holmes,B.E.;Paisley,S.D.;Rakestraw,D.J.;King,.

.1986,18,365.

(36)Chase,M.W.,-JANAFThemochemicalTables,Fourth

,Monograph91998,1.

(37)Zachariah,M.R.;Westmoreland,P.R.;Burgess,D.R.,Jr.;Tsang,

W.;Melius,.1996,100,8737.

(38)Zhang,X.-.1998,63,3590.

(39)Haworth,N.L.;Smith,M.H.;Bacskay,G.B.;Mackie,J.C.J.

.A2000,104,7600.

(40)Krespan,C.G.;Dixon,.1998,63,36.

(41)Orlov,Y.D.;Zaripov,R.K.;Lebedev,.

1998,47,621.

(42)(a)Barker,.2001,33,232.(b)Barker,

.2009,41,748.

(43)(a)Marcoux,P.J.;Setser,.1979,83,3168.

(b)Chang,H.W.;Craig,N.L.;Setser,.1972,76,

954.(c)Marcoux,P.J.;Siefert,E.E.;Setser,.

1975,7,473.

(44)Arbilla,F.G.;Ferrero,J.C.;Staricco,.1983,

87,3906.

(45)Kim,K.C.;Setser,.1973,77,2021.

(46)Cadman,P.;Day,M.;Trotman-Dickenson,.A

1971,248.

(47)Cadman,P.;Day,M.;Trotman-Dickenson,.A

1970,2498.

JP100195E

.A,Vol.114,No.26,2010Duncanetal.