.司
calibratedmicrobalance 1 (METTLER TOLEDO MX5 Microbalance) througha longalumintln Chain at
5.2 Computational Methods
4.2.2 Heat capLFCioT Of constant pressure
The heat capacityat constaJlt Pressure Was Calculated usingthe follodng relation・【9・10】
3〃‑6
C。 ‑ch・cm.・Cqb ‑言R・;R・R∑
J=l
hv/kT
(5)
where Cbans, C,.land Cvibare COnbibution to heat capacitydue to translation, rotationalmotion, and vibrationalnotion, respectively.
4.2.3 Enthalpy and Gl'bbs enerw oJfol.maLion
The following equations are employed to calCulatethe absolute hternaleneqgy (tD, enthalpy (F)and Gibb, energy (G) ofthc molecule at 0 Kandthe specified temperature (I)・[9・m]
UoK ‑ Eelec +Ezp.
UT =U。K +(E.,a.u +E.0. +E曲)T
3〃‑6
‑(Ed∝悔,・(言RT・RT・R ∑ (hv/k)【三・
J=1
HT‑ UT+RT
GT =HT ITS
where Eelec isthe intemalenergy due to electronic notion,and Ezpethe 2:erO point energy of the molecule at o K (a correction to the electromic energy). EBanS, El。t and ELbarethe thernalenergy corrections due to
the eqects of moleculartransladon, rotation andvibration atthe speci丘ed temperattqe, respectively・
Inthis study, E.lee is computed atthe B3LYP level. Et,anS, E..t and Ebb Can be rapidly calculated using statisticalthernodynamics.All the values ofEelec, Ezpe, UT, HTand GTaregiven in Hartrecs (atomic umits,
I Hartree=2625.5 I kJ・no1‑1) bythe output of the program.
Based onthese absolute energy values (U, a H), enthalpyand Gibbs energy of formation canbe calculated by different methods.
110
′
Method I
The enthalpies of formation at 0 K were calculated by subtractlngthc calculated atomizadon
energies (∑か。)fromknown enthalpies of formation of the isolated atoms・ The enthalpies offornation at
298.15 K were calculated by correction tothe enthalpies offornation at 0 K・ This method is the common
theo,etiCalmethodfor calCulatingthe enthalty offornation used by many studies.即ト13]
Forthe computation of enthalpies offornation, Curtiss et all [13] tested seven density funCtional
methods: B3IJYP, BP86, B3P86, BPW91, B3PW91 aJId SVWwith148 molecules・ Ofthese seven DFT
methods,the B3LYP method hasthe smallest average absolute deviation (13・O kJ・mol・1)fromthe
eq)eri皿entalValues.
The calculation procedure is as follows :
AfHo(M,OK) ‑ ∑ xAfHo(X,OK) ‑ ∑ D。(M)
‑ ∑ xAfHo(X,OK) ‑ [∑ xU(X,OK) ‑ U(M,OK)]
AfHo(M,298K) ≡ AfHo(M,OK) + lHo(M,298K) ‑ Ho(M,OK)]
‑ ∑X(H2,BK ‑H。K )x
AfGo(M,298K) = AfHo(M,298K) ‑Tis
= A.Ho(M,298K) ‑ TlSo(M,298K) ‑ ∑ xso(X,298K)】
(10)
(ll)
(12)
where Aガo and ALGoarethe staJldard‑state enthalpyand Gibbs energy of fbrnation of the idealgas,
respecdvely・ M st皿dsforthe molecule of the compound, X identifies each element which consists ofM,
and x isthe stoichiomebic codrlCient of the constituent. (H298K‑HoK)x isthefornation enthalpy correction from OK to 29SKfor elementsinreference state.
AF(A, SQ(X, 298 K),and (H298K‑HoK)Ware tabulated in Table 5.1, cited from the NIST‑JANAF
ThermochemiCalTables.[14】 The absolute standard state entropy So(X 29S K) used for elementalCarbon,
hydrogen, bromine,and oxygen (reference state) should be (5.740, 130.680/2, 152.206/2, aJld 205. 147/2)
J・mol l・K11 respectively, notthe values citedinOchterski's paper 【11】 (not in r曲rence state).
日! il
′
Table5・ I Enthalpies offo‑adonfor gaseous atoms and entropyand (H2粥K‑H.K) Values for elements in
their reference state Bom experiments.A
Atoms State
ANT.芹' Af;.'19.:I.K' shte I::I?.8.KK!1慧K
C Gas 71 I. 19土0.46 716.67j=0.46 Reference state 5.74土0.21 1.05 I
H Gas 216.035土0.006 217.999土0.006 Reference state 65.340土0.017 4.238 Br Gas l 17.92土0.06 1 1 1.86土0.06 Reference state 76. 103 12.255
0 Gas 246.79iO.10 249.17土0.10 Rderence state 102.574土0.018 4.342 N Gas 470.82土0.10 472.68土0.10 Reference state 95.805土0.010 4.335
The也lculatedthernochemisby values using B3LYP/6‑31G(d) for C, H, Br, 0, H2, Br2,
dibenzo‑p‑dioxin (DD)and 2,3,7,8‑tetrabromodibenzo‑p‑dioxin CrBDD)are listedinTable 5.2,all values areinHartrees.
Table 5・2 CalCulatedthermochemiby valuesingas phase at 101.325 kPa by B3LYP/6‑3 1 G(d). (Hartree)
Substance Uo K (‑Ho K) U298 K H2,8 K G2,S K
c H Br 0
H2
‑37.846280 ‑3 7.844864
‑0.500273 .0.498857
‑2571.65691S ‑2571.655502
‑75.060623 ‑75.059207
‑1.165536 ̲1.163175 Br2 ‑5 143.398381 ‑5 143.395626 DD ‑612.362477 ‑612.352659 TBDD ・ 10896. 808498 ̲ 10896.792547
‑37.843920
‑0.497913
‑2571.654558
‑75.058263
‑1.162231
‑5 143.394682
‑612.351714
‑10896.79 1602
137. 860825
‑0.5 10927
‑2571.673748
‑75.075575
・1. 177023
‑5 143.422540
・612.398258 110896.856484
UoKand Ho K arethe absolute hternalenergyand enthalpy of the molecule at 0 K.
U29S K, H298 K肌d G298 Karethe absolute intemalenergy'enthalpyand Gibbs energy of the molecule at 298.15 K, respectively. (1 H山ree=2625.51 kJ・mo1‑I)
Method 1 is illustratedwiththe example calCulatiOns for TBDD (C12H.Br.02) as follows:
∑80(TBDD)‑【12×U(C, 0 K)+4×U(H, 0 K)+4×UtBr, 0 K)+2×U(0, 0 K)]・U(TBDD, 0 K)
=[12×(‑37・846280)+4×(‑0・500273)+4×(・2571 ・6569 1 8)+2×(‑75.060623)]・(‑10896.808498)‑3.903 128
Har廿ee= 1 0247. 7 kJ・morl
AU(TBDD, 0 K)=[12×AU(C, 0 K)+4×Aβ○(H, 0 K)+4×AU(Br, 0 K)+2×AF(0, 0 K)]‑∑po(TBDD)
‑(12×71 1 ・ 19叫×21 6・035+4× 1 1 7.92+2×246.790)‑10247.7‑1 15.9 kJ・mol・l
112
′
AF(TBDD, 298 K)‑ Aβ○(TBDD, 0 K)+lH(TBDD, 29S K)‑H(TBDD, 0
K)H 1 2 × (H2,8KIH.K)C+4 × (H298K‑HoK)オ4 × (H298K‑HoKh,+2 × (H298K‑HoK)01
‑115.9+[(‑10896.791602)‑(‑10896・808498)】×2625・5 1‑(12× I ・05 I+4×4・238+ 4× 12・255+2×4342)=73・O
kJ・mo1‑1
AfGoCrBDD, 29S K)‑ AF(TBDD, 298 K)‑29g・ 15×lS'CrBDD, 29S K)I 12×SD(C, 298 K)4× S'(H, 298
K)・4×S'(Br, 29S K)‑2×So(0, 298 K)]
=73.0‑298. 15 ×(571.3112×5.740‑4×65.340‑4×76・ 103‑2× 102・574)/1000
=153.1 kJ・morl
Method2
Using B3I;YP/6‑31G(d), it wasfoundthatthe enthalpy offormation results for benzene and DD
calCAnted by Method 1 differ greatly from the experimentaldata・ Therefore, a simple method, Method 2,
was proposed here.
Becausethe absolute cnthalpy (H) and Gibbs energy (G) Values of the molecule can be obtained
throughtheoretiCalCalculation, lt lS easy tO Obtainthe reaction erLthalpyand Gibbs energy for any reaction
usingthese energy values by eq・ 13and 15・ hanother way'the reaction enthalpy and Gibbs energy can be calculated by eq. 14 aJld 16, respectively・
A,Ho(298 K) ‑ ∑(H2,8 K)p...ucb ‑∑(H2粥K)卿.mB
A.Ho(298 K) ‑ ∑(A,H20,8 K),.。.UCB ‑∑(AfH20,8 K).地nb
A.Go(298 K) ≡ ∑(G2,8 K),..duck ‑ ∑(G2,8 K).也C.mb
A.Go(298 K) = ∑(A,G20,8 K),..ducb ‑ ∑(AfG,0,8 K).eu..nb
(13)
(14)
(15)
(16)
combiningthese equations and usingthe experimentaldata of enthalpy and Gibbs energy of
formation for H2, Br2,and DD,[14・15]thc unknownenthalpyand Gibbs energy offo‑ation values of
TBDD can be calCulated丘om the reaction (Ⅰ) in Fig 5.I. Figure 5.1 showsthe calCuladon procedtqe of
Method 2 (all reactantsand productsare in gas state)・
113
′
二二二一二三二‥ ‑≡二二/…二丁‑≡;‑二=‑== 二
mweR・ bztree: ‑612351714 2×(‑5143・394682) ‑10896・791602 2X(‑1・16223n → APES60;%0霊㌢Tee
AFT, kJ・nDl・1: 159・2 2×30・9 (AFmD) 2xO 一AV℡DD=68・3 kJ・zTD1‑I
el粥R, Hdree・ ・612・398258 2×(15143・422540) ‑10896・856484 2×(‑1・177023) → A・qsO6・.て憲慧ITree
AP, kJIZTDl・.: 56・2 2×3・l (APTD,,) 2xO 一APmD4148・5 kl・nt'1 1
Fig 5. 1 Calculation proc血e of Method 2・
The of enthalpyand Gibbs energy Offornation values of TBDD calCulated丘otn reaction (Ⅰ)are 68・3
kJ・no1‑land 148.5 kJ・no1‑I, respectively.
Method 3 (BensoTL's method)
The third method for estinatingthe enthalpies offomation is consistentwiththe group additivity teclmique developed by Benson・[16] It is a b・aditionalempiriCalmethod・ Benson goup values have been substantially refined duringthe years, e・g・the CHETAH progranl17] by ASTM hternationalpredicts themochemiCalproperties uslng a nOdem Bcnson application・ The available values of group conbibutions to enthalpy offornadon glVen by CHETAH 7・3 aqTe listedinTable 513・
Table 4.3 Vduesa of group additivib, conbibutions to enthalpy of forznadon of PBDDs・
Gro叩 CbH CbBr Cb‑(0) 0‑(Cb)2
Co汀eCtion
Acは
̲1.255
Arina A。血. A由uChe 13.807 44.769 ‑3.766 ・78.659 8368 3.138 8.368
Ac遥慧究l;I.。21t?.,1807 44・769 ‑3・766 ‑78・659 8368 3'138 8'3嘩
For TBDD :
AUTBDD ‑ 4(CbH) + 4(CbBr) + 4【CbT(0)I+ 2[01Cb)2] +Anne + 2A。.th。
‑ 4×13.807 +4×44.769 + 4×(13.766) + 2×(‑78.659) + 8.368 + 2×3.138
= 76.6 kJ・no1‑1
114
′
5.3 Discrepancy Ana吋sis for the Computation of Thermodynamics
To assess the accuracy of the three methods used to predictthe enthalpy and Gibbs energy of
formation,thethermodymamic properties of 16 compounds O)rominatedarenes) were first calculated, and
comparedwithavailable experinentaldata・For brominated arenes, in fact, onlymiminalexpenmentalthertnodynamic data is available・ Table
5.4 showsthe calCAntion results of U, a H, S, C,, AH弧d AfG for benzene, bromoberLZX)Res, benzoic
acid, bromobenzoic acids, naphthalene,and bromonaphthalenesinthe standard‑state idealgas at 298・ 15 K and 101.325 kPa.
115
′
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′
Asshown,the calCula̲ted results of heat capacityand absolute entropy areingood agreementwith
experinentaldata,althoughlittle such data is available. Onthe properties of heat capacib, and absolute
entropy,the calculation results obtained by B3LYP/6・31G(d) seem to be accurate, Since Gaussian
employs the mature theoretiCal nethods of statiStics thernodynamics to compute these two
the‑odynamic properties,and this conputationallevel is moderate.
In calCulatingthe enthalpy offornationforthose compounds, the results by Method I differ from the experimentalValues. The absolute deviationsarefrom (‑10.5 to 54.0) kJ・mol'1,andthe average
deviation is 28.I kJ・nol 1. The reason isthe model chemiby (B3LYP/6‑3 lG(d)) employed due tothe tradeoffof ̲a.ccuracyand cost is not acctmte enoqghforthe absoluteinternalenergy calculation.
The enthalpy offormation values calculated using method 2 areingood agreementwith the
experimentaldata of refemnce compounds (see Fig 5.2). The average absolute deviation from experimental values by method 2 is 4・2 kJ・norl,andthe largest absolute deviation is 17.3 kJ・no1‑I.
The predicting values using methods 3arealso in reasonable agreementwiththe experimental(see Fig 5・2)・ The average absolute deviadonfrom ekperimentalValuesfor Method 3 is 9.8 kJ・mol 1,and the largest absolute deviation is 27・O kJ・noll1 l Forthe enthalpies offornation of 2,4,6‑bibronoanilineand 2,4,61bibromophenol, bothMethod 2 and 3 have large differencesfromthe sole experimentalValues by Allotand Finch・[23] Unfortunately,there is a lack of experimentaldatafor bromoberLZene; the reference values of dibromoberLZene listedinTable 5・4arealso estimated values by OIesik et al. [20]
118
/
C6E6 0;Ⅱ5Br l3‑C6114Br2 1,3‑(芯Ⅱ4Br2 1,A‑C研14Ⅰ暮L2 (a)
60 40 20 00 名0 釣 棚 20 0
1 ●・・一 一I 1
TqJfrq‑oHlv
C 6I・15Nt・12 2 ,4, 61C6It2 a r3 NII2 C6H501I 2 ,4, 6‑C6H2 B r30I・I
C6E5COOEL 2イ:6fl411rCOOtt 3‑C6t14JlrCOOff 4‑C6tI4BrCOOtI
119
50 00 50 ㈹ 50 0 50 帥 5
2 2 1 ‑1 ● l I
ptyLqI.Ltlv
(C)
仰 ー〜0 訓 別 ㈹ 3
pLqmtoHJV
(d)
訓o 謝 1 50 ㈹ 5
PmJm.ottJv
I ̲tl OE7Dr 2イ:1 0Ⅱ7Br
Fig 5.2 Comparison of enthalpies offortnation by Methods ll3withreference data・
The results show thatthe traditionalBenson's method of group additivity(Method 3) is still one of the most acctJrate methods for estimatingfornation enthalpy,and calculation processare very slmPle and
fast.
However, Benson's method can onlygive a roughcorrection for cis‑(runs isonerization enpiriCalIy・
h estimatingthe enthalpies of isomers, Method 2 is superior to Benson's method,althoughMethod 1 and
2 is farmore conputationally expensive.Comparedwiththe selected experimentaldata, Method 2 hasthe smallest absolute deviation among
the three methodsunderthe condition of B3LYP/6‑31G(d).Asindicated by Foresmanand Frisch,[5]
model chemisbiesthatareknownto be qulte reliablefor optlmlZlng geOmebies can be qulte poor at
predicting absolute thernochemiCalproperties (such as absolute internalenergy U, enthalpy Hand Gibbs energy G of the molecule), but such methods could be quite accurate at predicting other molecular properties, vibrationalfrequencies,and a varieb, of relative energy values: energy differences to similarmolecules, reaction energies (such as AHand A,G) and so on. The main reason for Method 2 call Offer
more accurate results isthat the systematic errors for U, Hand G in the method o鮎n cancel out across
the systems being compared.Another reason is due to its use of experiJnentalvalues as benclmarks.
120
′