Theoretical Stud ies on Thermal D ecom position of Benzoyl Perox ide in Ground State 3

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1 CH EM. R ES. CH IN ESE U. 2003, 19 (3), Theoretical Stud ies on Thermal D ecom position of Benzoyl Perox ide in Ground State 3 SUN Cheng2ke 1, 2, YAN G Si2ya 2, L IN Xue2fei 2, M A Si2yu 1 and L I Zong2he D ep a rtm en t of Chem istry, B eij ing N orm a l U n iversity, B eij ing , P. R. Ch ina; 2. D ep a rtm en t of Chem istry, Q uj ing N orm a l Colleg e, Q uj ing , P. R. Ch ina R eceived O cṫ 21, 2002 System atic studies of the therm al decompo sition m echanism of benzoyl peroxide (BPO ) in ground state, leading to various interm ediates, p roducts and the po tential energy surface (PES) of po ssible dissociation re2 actions w ere m ade com putationally. T he structures of the transition states and the activation energies fo r all the path s causing the fo rm ation of the reaction p roducts m entioned above w ere calculated by the AM 1 sem i2 emp irical m ethod. T h is m ethod is show n to to be one p redict co rrectly the p referred pathw ay fo r the title re2 action. It has been found that in ground state, the therm al decompo sition of benzoyl peroxide has tw o k inds of path s. T he first pathw ay PhC (O )O OC (O ) Ph PhC (O )O Ph + CO 2 p roduces finally phenyl radicals and carbon dioxide. A nd the second pathw ay PhC (O ) OO C (O ) Ph PhC (O ) OO + PhC (O ) PhC (O ) + O 2 Ph + CO + O 2, v ia w h ich the reaction takes p lace only in tw o step s, p roduces oxygen and PhC (O ) radicals, and the further therm al dissociation of PhC (O ) is quite difficult because of the h igh acti2 vation energy in ground state. T he calculated activation energies and reaction enthalp ies are in good agree2 m ent w ith the experim ental valueṡ T he research results also show that also the therm al dissociation p rocess of the tw o bonds o r the th ree bonds fo r the benzoyl peroxide doesn t take p lace in ground state. Ke yw o rds Benzoyl peroxide, T herm al decompo sition, R adical, UAM 1 A rtic le ID (2003) In troduction T he chem istry of diacyl perox ide radicals has a long h isto ry, w h ich can be traced back to the early days of the 20th cen tu ry [1, 2 ]. Benzoyl perox ide is the mo st rep resen tative one ex ten sively studied ex2 perim en tally [3 6 ] becau se of its w idely comm ercial u se as a po lym erization in itiato r, especially the u s2 age in m ed icine, food stuffs, co sm et ics and rubber indu stries [7 11 ]. In comparison w ith its w idesp read u sage and experim en tal study, its theo retics has re2 ceived relatively little atten tion. To ou r know l2 edge, no theo ret ica l system a t ic stud ies have been repo rted on the therm al dissociation m echan ism of benzoyl p erox ide in g round sta te. T herefo re, the m echan ism studied fo r the title thermo lysis reaction is p resen ted here w ith the view s of settling ground2 w o rk fo r a fu rther study of radical s p ro tection and app lication, and also help ing the experim en ts and the relevan t indu stries. Com puta tiona l M ethods A ll the calcu lation s described in th is w o rk w ere imp lem en ted on an Pen tium g 2GH z computer w ith the Guassian 98 package [12 ]. T he po ten tial en2 ergy su rface (PES) [13 ] of the variou s dissociation s, the geom et ries and the energ ies of the reactan t s, p roducts, in term ediates and tran sition states w ere fu lly op tim ized by m ean s of the AM 1 m ethod [14 ], w h ich appears to be the best availab le sem iemp iri2 cal p rocedu re fo r the study of the thermo lysis reac2 tion s becau se the m ethod leads to reasonab le ge2 om etries, en thalp ies of fo rm ation and activation en2 ergies to compare w ith experim en tal values [15, 16 ]. A ll the structu res w ith the m in im um energy w ere found v ia the Berny algo rithm [17 ]. A ll the station2 ary po in ts w ere fu rther confirm ed by the analytical computation of the fo rce con stan ts and character2 ized by the num ber of im aginary vib rational fre2 quencies [18 ]. Results and D iscuss ion T he traditional view po in t ho lds that the disso2 ciation of benzoyl perox ide (BPO ) based on the ex2 perim en t is a symm etrical homo lytic cleavage reac2 tion, the in term ediate dissociated is free radical 3 Suppo rted by N ationaln atural Science Foundation of Ch ina (N o ) and the N atural Science Foundation of Q u2 jing N o rm al Co llege (N o ). 3 3 To w hom co rrespondence should be addressed.

2 3 56 CH EM. R ES. CH IN ESE U. V o l. 19 PhC (O )O, and it is fu rther dissociated in to free radical Ph and CO 2 [19 ]. How ever, w hether o ther decompo sition w ays ex ist, too, such as asymm etri2 cal homo lytic cleavage, ion ic hetero lytic cleavage, the tw o bonds dissociation o r the tree bonds disso2 ciation etc. is unknow n. To understand fu lly tho se p rob lem s, the variou s p robab le dissociation m echa2 n ism s o r the cu tting m ethods of benzoyl perox ide are detailed in Schem es 1 5. Scheme 1 Pathway 1. Scheme 2 Pathway 2. Scheme 3 Pathway 3. Scheme 4 Pathway 4. Schem es 1 3 show th ree k inds of reaction pathw ays w ith single bond dissociation respective2 ly, and Schem e 4 is the pathw ay of the tw o bonds d issocia t ion and Schem e 5 is hypo thet ica lly reac2 tion of the th ree bonds dissociation. 1 Com par ison of PES for D ifferen t K inds of D issoc ia tion W ays in the Ground Sta te To iden t ify w ha t k ind of react ion invo lved above can take p lace likely and its reaction m echa2 n ism s w e firstly m ade an investigation in detail, all the PES of Schem es 1 4 dissociation u sing AM 1 w ith op tim ization, as show n in F igs11 4. A ll the F igu res, draw n directly by Excel 2000, are derived from the real values w ith the AM 1 calcu lation ṡ F irst ly, under the cond it ion of keep ing the sp in con servation ( 2s + 1) and ground state, the PES of dissociation s fo r 1a cleavage w ay and 2a cleavage w ay w ere calcu lated by u sing restricted AM 1 (RAM 1 ) and un restricted AM 1 (UAM 1 ) m ethods respectively (F ig. 1 and T ab le 1). T he re2 Scheme 5 Pathway 5. su lts show clearly that the energy increases w ith e2 longating the bond distance fo r the PES (ion ic het2 ero lytic cleavage) of RAM 1 calcu lating w hether 1a F ig. 1 Compar ison of PES prof iles of RAM 1 and UAM 1 scanned for 1a and 2a decom position ways in ground state. o r 2a cleavages ex ist o r no ṫ But the energy cu rve of PES (free radical homo lytic cleavage) w h ich has been calcu lated w ith UAM 1 p resen ts the m ax im um value, and the to tal energy of PES (w ith UAM 1) is low er than that of PES (w ith RAM 1). T he conclu2

3 N o. 3 SUN Cheng2ke et al. 357 sion indicates that the therm al dissociation of BPO in g round sta te takes p lace v ia free rad ica l ho2 m o lyt ic cleavage, bu t the react ion of ion ic het2 ero lytic cleavage is impo ssib le. T he resu lt is in rea2 sonab le agreem en t w ith the experim en tal m echa2 n ism. Table 1 Change of energ ies (e igenvalues) with bond length E longated bond length for 1a and 2a dissoc iation ways in ground state by mean s of RAM 1 and UAM 1 scan s respectively 3 RAM 1 UAM 1 1a 2a 1a 2a a: PhC (O ) O OC (O ) Ph; 2a: PhC (O ) OO C (O ) Ph. Bond lengthgnm; energygh artree. Second ly, the deta iled stud ies of the d issocia2 tion s of BPO v ia the w ays of 1a to 4a w ere carried ou t w ith the computational model of the free radi2 ca l hom o lyt ic cleavage in g round sta te by un re2 stricted UAM 1, as show n in F ig. 2 ( the detailed da ta a re listed in T ab le 2). Com p a ring the PES p rofiles of the fou r differen t k inds of dissociation F ig. 2 Compar ison of PES prof iles for four differen t k inds of decom position ways in ground state (UAM 1). w ays in ground state show s that the PES of 1a w ay of the sing le bond hom o lyt ic cleavage is the low 2 est, and that of 4a w ay of the tw o bonds decompo2 sition is the h ighesṫ T he PES p rofile cu rves of 1a and 2a w ays show the located po in t of ex trem um, and their to tal energies are relatively low er, w h ich show s that reaction s 1a and 2a cou ld take p lace v ia the tran sition states w h ich have low er po ten tial barriers. But the PES p rofiles of reaction s 3a and 4a do no t have the located po in t of ex trem um, and they are relatively h igher than tho se of 1a and 2a in to tal energy, w h ich increase as the bond length in2 creases. T herefo re, the dissociation s v ia 3a and 4a w ays are qu ite difficu lt in ground state. Table 2 Change of energ ies (e igenvalues) with the change of bond length for the four differen t k inds of dissoc iation ways in ground state 3 E longated bond length 3 UAM 1 1a 2a 3a 4a a: PhC (O )O OC (O ) Ph; 2a: PhC (O )OO C (O ) Ph; 3a: PhC (O )OOC (O ) Ph; 4a: Ph C (O )OOC (O ) Ph. Bond lengthgnm; energygh artree. To confirm fu rther tha t the d issocia t ion s of the tw o bonds of 4a do no t take p lace sim u ltane2 ou sly, w e also computed its tw o2dim en sional po2 ten tial energy su rface TD 2PES w ith UAM 1 (F ig. 3). A cco rding to the TD 2PES, it indicates clearly that the dissociating energy of the tw o bonds at the sam e tim e is on the saddle po in t diagonal of h igher po ten t ia l energy. M o reover, the doub le2bond cleavage reaction w ill p roduce tw o Ph free radi2 ca ls and a doub le2free2rad ica l C (O )OOC (O ), w h ich is in a h igher energy state ( the calcu lated

3 58 CH EM. R ES. CH IN ESE U. V o l. 19 value is 592164 kj gmo l) and leads to disadvan ta2 geou s dissociation. So the 4a w ay doesn t take p lace.

4 3 58 CH EM. R ES. CH IN ESE U. V o l. 19 value is kj gmo l) and leads to disadvan ta2 geou s dissociation. So the 4a w ay doesn t take p lace. F rom the TD 2PES, o therw ise, the 3a w ay w ith the single2bond dissociation does no t have any ex trem um value and also is no t the tran sition sate. Indeed, in the computing w e didn t find the tran si2 tion state fo r 3a w ay. But as a w ho le, the energy of 3a w ay isn t h igher, w h ich is in the energy val2 ley. So m ay be the single2bond dissociation by on ly heat vib rating. been fu rther studied. T he computed data are listed in T ab le 3 and show n in F ig. 4. F ig. 3 TD -PES of the two bonds decomposition (PhC C2O 4 CPh) of benzoyl perox ide in ground state (UAM 1). Table 3 Change of Energ ies with bond length for the three E longated bond length differen t k inds of in termediates dissoc iation ways in ground state UAM 1 1b 2b 2c b: Ph CO ; 2b: PhOC O 2 ; 2c: Ph CO. Bond lengthgnm; energygh artree. F inally the PES of the decom po sit ion reac2 tion s of the in term ediates in the ground state have F ig. 4 Compar ison of PES prof ile for the three differen t k inds of in term ed iates decom position in ground state (UAM 1). T he resu lts show that the PES have a m ax i2 m um va lue, and the d issocia t ion energ ies of 1b (Ph CO 2 ) and 2b (PhOC O 2 ) a re low er than that of 2c (Ph CO ), w h ich m ean s that the de2 compo sition s of 1b and 2b take p lace v ia the tran si2 tion state, bu t the therm al decompo sition of 2c that has a h igher energy is mo re difficu lt than tho se of 1b and 2b. If the decom po sit ion of 2c cou ld p roceed, it m u st be heat vib ration dissocia2 tion becau se of no t being the tran sition state. T he PES of the th ree2bond d issocia t ion of BPO has also been scanned. U sing the resu lts can p redict that the energy p rofile is h igher than that of the tw o2bonds dissociation. T herefo re th is dis2 sociation reaction by 5a w ay cou ldn t take p lace. 2 AM 1 Optim ized Geom etr ies, Energy and Imaginary Frequenc ies A cco rd ing to the above invest iga ted conclu2 sion s on the po ten tial energy su rface of the decom 2 po sition reaction by variou s cu tting m ethods, the m echan ism s of the therm al decompo sition reaction of BPO in ground state v ia Schem es 1 and 2 have been investigated system atically. Becau se all the react ion s a re free rad ica l react ion s, so the un re2 stricted UAM 1 is u sed as the computational algo2 rithm. T he op tim ized geom etry configu ration s, the p a ram eters, the energ ies and the im ag ina ry fre2 quencies of the tran sition states, and som e selected geom etries of the in term ediates and the p roducts are listed in T ab le 4, w here the special geom etry configu ration s tran sfered directly by Gau ssview 211 [20 ], are derived from the computational real values w ith UAM 1. A ll the stationary po in ts w ere fu rther confirm ed by the computation s of the fo rce con stan t s ana lyt ica lly and cha racterized by the num ber of im aginary vib rational frequencies. T he

N o. 3 SUN Cheng2ke et al. 359 system s w ere characterized as the tran sition states by the p resence of one and on ly one negative eigen2 value.

sition state of its 1a dissociation is a p lanar structu re, and the tran sition state of its 2a dissociation is a cro ssbeding structu re (T ab le 4).

T he o ther selected geom etry param eters are also listed in T ab le 4.

va lues, w e found tha t the o ther bond leng th s, bond ang les and d ihed ra l ang les w ere in good agreem en t w ith the experim en tal values [15, 16 ].

Param eters of geom etries Spacial geom etry configuration b decompo sition a [Bond lengthgnm, angleg( ) ] Reactant PhC (O )OOC (O ) Ph (2s+ 1= 1) TS (1a) PhC (O )O OC (O ) Ph (2s+ 1= 1) TS (1b) Ph C

5 N o. 3 SUN Cheng2ke et al. 359 system s w ere characterized as the tran sition states by the p resence of one and on ly one negative eigen2 value. T he resu lts of the op tim ized structu res w ith UAM 1 indicate that the reactan t show ed a spacial geom etry, that is, the tw o benzoyl group s w ere perpendicalar to each o ther, bu t the tran sition state of its 1a dissociation is a p lanar structu re, and the tran sition state of its 2a dissociation is a cro ssbeding structu re (T ab le 4). T he distances R s of the dissociated bonds fo r tran sition states T S (1a), T S (1b), T S (2a) and T S (2b) are , , and nm resp ect ively. T he o ther selected geom etry param eters are also listed in T ab le 4. Excep t that the bond length of the per2 oxyl bond R (O 13 O 15 ) = nm is sligh tly sho rter than that of the ob served value, comparing tho se calcu lated param eters w ith their experim en t va lues, w e found tha t the o ther bond leng th s, bond ang les and d ihed ra l ang les w ere in good agreem en t w ith the experim en tal values [15, 16 ]. So Table 4 UAM 1 optim ized geometr ies and parameters, energ ies and imag inary frequenc ies of the tran sition states for the two k inds of homolytic cleavages of benzoyl perox ide System s of Param eters of geom etries Spacial geom etry configuration b decompo sition a [Bond lengthgnm, angleg( ) ] Reactant PhC (O )OOC (O ) Ph (2s+ 1= 1) TS (1a) PhC (O )O OC (O ) Ph (2s+ 1= 1) TS (1b) Ph C (O )O TS (2a) PhC (O )OO C (O ) Ph (2s+ 1= 1) TS (2b) PhC (O ) OO IM (1b) PhC (O )O IM (2b) PhC (O )OO IM (2c) PhCO R (C 12 O 13 ) = R (C 12 O 14 ) = R (O 13 O 15 ) = C 12 O 13 O 15 = O 13 O 15 C 16 = R (O 13 O 15 ) = R (C 12 CO 13 ) = R (C 12 O 14 ) = O 13 C 12 O 14 = O 13 O 15 C 16 = R (C 3 C 12 ) = R (C 12 O 13 ) = R (C 12 O 14 ) = O 13 C 12 O 14 = C 2 C 3 C 12 O 13 = R (O 15 C 16 ) = R (C 12 O 14 ) = R (C 12 O 14 ) = C 12 O 13 O 15 = C 12 O 13 O 15 C 16 = R (C 12 O 13 ) = R (C 12 O 15 ) = R (O 13 O 14 ) = C 3 C 12 O 15 = C 3 C 12 O 13 O 14 = R (C 3 C 12 ) = R (C 12 O 13 ) = R (C 12 O 14 ) = O 3 C 12 O 14 = C 2 C 3 O 12 O 13 = R (C 12 O 15 ) = R (C 12 O 13 ) = R (O 13 O 14 ) = C 12 O 13 O 14 = C 3 C 12 O 13 O 14 = R (C 2 C 3 ) = R (C 3 C 12 ) = R (C 12 O 13 ) = C 3 C 12 O 13 = C 2 C 3 C 12 O 13 = EnergiesgH artree; im aginary frequenciesgcm - 1 H f= E ZPE= H f= E ZPE= Im a. freq. = i Rel. inten. = H f= E ZPE= Im a. freq. = i Rel. inten. = H f= E ZPE= Im a. freq. = i Rel. inten. = H f= E ZPE= Im a. freq. = i Rel. inten. = H f= E ZPE= H f= E ZPE= H f= E ZPE= a. T S rep resents transition states, IM rep resents interm ediates; b. all geom etry configurations are directly cited from Gaussview conver2 sion.

6 3 60 CH EM. R ES. CH IN ESE U. V o l. 19 the UAM 1 m ethod is show n to be one to p redict co rrectly the reasonab le configu ration s fo r the de2 compo sition reaction of benzoyl perox ide, w h ich is very impo rtan t to the reliab ility of calcu lating ener2 gy. 3 The M echan ism s of Therma l D ecom position of BPO in Ground Sta te Based on the analysis of computed PES and the system atical calcu lation s of 1a and 2a pathw ays of BPO therm al dissociation in ground state, the energ ies of the reactan t, the in term ed ia tes, the p roducts and the variou s tran sition states w ere computed, and the energy p rofiles fo r the reaction pathw ays w ere draw n, as show n in F ig. 5. A cco rd ing to the energy p rofiles w e can see clearly that the activation energies E a (1a), E a (1b), and H (1a) of the dissociation reaction s of 1a and 1b by p a thw ay 1 a re , and kj gmo l respectively, and are in good agree2 m en t w ith the experim en tal values ( , and kj gmo l ) [21 ], w h ich indiacates that UAM 1 leads to reasonab le resu lts. In F ig. 5, the activation energies E a (2a) and E a ( 2b ) of 2a and 2b dissociation reaction s are and kj gmo l respectively, w h ich are reasonab le resu lts [22 ]. T he fact that the activation energies of 1a and 1b dissociation s are low er than tho se of 2a and 2b indicates that the reaction pathw ay of Schem e 1 takes p lace mo re easily than pathw ay 2 in Schem e 2. How ever, as a w ho le, the activation energies of 2a and 2b are also no t too h igh. So at the h igher temperatu re it can be carried ou t po ssib ly. But the activation energy of 2a reaction is h igher than that of 1a after all. M ak ing u se of the A rrhen iu s fo rm u2 la can lead to the ratio of the rate con stan ts of the tw o reaction s [23, 24 ], i. e., k 1a = exp k 2a H 2a - R T H 1a exp S 1a - R S 2a (1) A s sub stitu ting the calcu lated thermodynam ic data fo r the variab les, w e can ob tain the ratio as fo llow s: k 1agk 2a = T herefo re, as a w ho le, the m ain reaction is the pathw ay of 1a. In regard to 2c reaction, the therm al dissocia2 tion of it cou ldn t take p lace in g round sta te be2 cau se of the h igh energy of radical Ph w h ich is in2 stab le, so that the final p roducts can on ly be radi2 cal PhC (O ) and O 2. But the dissociation energy ( Jgmo l) of PhC (O ) is in the energy range of visib le ligh t to u ltravio let radiation [25 ], so under the condition of visib le radiation o r u ltravio let radi2 ation illum inating etc., 2c can fu rther dissociates to p roduce Ph and CO. Conclus ion s T he therm al decompo sition m echan ism of ben2 zoyl p erox ide in g round sta te, lead ing to va riou s in term ediates, p roducts and the po ten tial energy su rface (PES) of the po ssib le dissociation reaction have been studied system atically by m ean s of the AM 1 sem i2emp irical m ethod. T h is m ethod is show n to be u sed to p redict co rrectly the p referred pathw ay fo r the reaction of the title compound. T he p resen ted calcu lated resu lts based on the as2 sump tion of five k inds of dissociation pathw ays show that in ground state, the therm al decompo si2 tion of benzoyl perox ide has tw o k inds of path s. N o t on ly ex ists the symm etrical homo lytic cleavage reaction w h ich is held traditionally, e. g., pathw ay

7 N o. 3 SUN Cheng2ke et al , PhC (O )O OC (O ) Ph PhC (O ) O Ph + CO 2 p roduces fina lly the p henyl free rad ica l and carbon diox ide, bu t also the asymm etrical ho2 mo lytic cleavage reaction ex ists, e. g., pathw ay 2, PhC (O )OO C (O ) Ph PhC (O )OO + PhC (O ) PhC (O ) + O 2 Ph + CO + O 2 is carried ou t on2 ly in tw o step s, that is, the dissociation p roduces oxygen and free radical PhC (O ). A nd the fu rther therm al dissociation of PhC (O ) is qu ite difficu lt becau se of the h igh act iva t ion energy in g round state. But in the condition of visib le radiation o r u ltravio let radiation illum inating etc., 2c dissociat2 ing m ay be po ssib le, fu rther p roducing free radical Ph and CO. T he research resu lts also indicate that the therm al dissociation p rocess of the tw o bond s o r the th ree bond s of benzoyl p erox ide doesn t take p lace in ground state. T he calcu lated geom et ries, the therm odynam ic da ta and the act i2 vation energies are in good agreem en t w ith the ex2 perim en tal values, w h ich show s that the AM 1 m ethod is reasonab le fo r BPO decompo sition lead2 ing to the reliab le m echan ism put fo rw ard in the article. In addition, the studied resu lts show that w hen the temperatu re is low er, pathw ay 1 is the m a in react ion to p roduce the p henyl free rad ica l and CO 2, bu t w hen the temperatu re is h igher, pathw ay 2 takes p lace sim u ltaneou sly to fo rm free radical PhC (O ) and O 2, even fu rther to p roduce the phenyl free radical and CO. So in the experi2 m en ts and indu strial p rocesses, w hen BPO is u sed as the in itiato r of po lym erization reaction s, it shou ld operate at a low er temperatu re, to fo rm in2 ert CO 2 and phenyl free radicals rather than active O 2 and CO leading to danger. Re fe re nce s [ 1 ] C rich D., Kom atsu M., Ryu İ, Chem. R ev., 1999, 99, 1991 [ 2 ] M ekarbane P. G., T abner B. J., J. Chem. S oc., Perk in T rans, 2000, 2, 1465 [ 3 ] H ammond G. S., J. A m. Chem. S oc., 1950, 72, 3737 [ 4 ] H ammond G. S., Soffer L. M., J. A m. Chem. S oc., 1950, 72, 4711 [ 5 ] B raun W., Rajbenback L., E irich F. R., J. P hy ṡ Chem., 1962, 66, 1591 [ 6 ] Edge D. J., Koch i J. K., J. A m. Chem. S oc., 1973, 95, 2635 [ 7 ] Sanchez J., M yers T. N., K irk2o thm er E ncy clop ed ia of Chem ical T echnology, V o l. 18, 4th Edn., John W iley & Sons Inc., N ew Yo rk, 1996, 230 [ 8 ] W alling C., F ree R ad icals in S olu tion, John W iley & Sons Inc., N ew Yo rk, 1957, 273 [ 9 ] Sanchez J., M yer T. N., K irk2o thm er E ncy clop ed ia of Chem ical T echnology, V o l. 14, 4th edn., John W iley & Sons Inc., N ew Yo rk, 1995, 431 [ 10 ] M oad G., So lomon D. H., Comp rehensive P olym er S cience, Pergamon P ress, O xfo rd, 1989, 3, 97 [ 11 ] Chateauneuf J., L usztyk J., Ingo ld K. U., J. A m. Chem. S oc., 1988, 110, 2877 [ 12 ] F risch M. J., T ruck s G. W., Sch legel H. B., et al., Gaussian 98, P ittsburgh PA, Gaussian Inc., 1998 [ 13 ] Sch legel H. B. ; Ed., Yarkony D. R., M od ern E lectronic S tructure T heory, W o rld Scientific Publishing, 1995 Singapo re, [ 14 ] D ew ar M. J. S., Zoebisch E. G., H ealy E. F., J. A m. Chem. S oc., 1985, 107, 3902 [ 15 ] L ide D. R., H and book of Chem istry and P hy sics, 73rd Edn., CRC P ress Inc., L ondon, , 921 [ 16 ] Karch N. J., Koh E. T., W h itsel B. L., et al., J. A m. Chem. S oc., 1975, 97, 6729 [ 17 ] Sch legel H. B., J. Comp. Chem., 1982, 3, 214 [ 18 ] Fo resm an J. B., F risch M. J., E xp loring Chem istry w ith E lectronic S tructure M ethods, 2nd Edn., Gaussian Inc., P ittsburgh, PA, 1996, 61 [ 19 ] H uang R. L., Goh S. H., O ng S. H., T he Chem istry of F ree R ad icals, Edw ard A rno ld, L ondon, 1974, 61 [ 20 ] Gaussv iew 2. 1, Sem ichem Inc., Gaussian, P ittsburgh PA, 2000 [ 21 ] V an Sick le D. E., J. O rg. Chem., 1969, 34, 3446 [ 22 ] W alling C., Savas E. S., J. A m. Chem. S oc., 1960, 82, 1738 [ 23 ] Sun C. K., Gong S. Y., L i Z. H., et al., Chem. J. Ch i2 nese U niversities, 2000, 21 (6), 912 [ 24 ] Sun C. K., Yang S. Y., M a S. Y., et al., Chem. J. Ch i2 nese U niversities, 2002, 23 (1), 109 [ 25 ] H uang R. L., Goh S. H., O ng S. H., T he Chem istry of F ree R ad icals, Edw ard A rno ld, London, 1974, 27, 58, 62

V o l. 21, N o. 2 M ar., 2002 PRO GR ESS IN GEO GRA PH Y ,, 2030, (KZ9522J 12220) E2m ail: w igsnrr1ac1cn

21 2 2002 3 PRO GR ESS IN GEO GRA PH Y V o l. 21, N o. 2 M ar., 2002 : 100726301 (2002) 022121209 30, (, 100101) : 30,, 2030 16, 3,, 2030,,, 2030, 13110 6 hm 2 2010 2030 420 kg 460 kg, 5 79610 8 kg7 36010