Alkyl peroxyls form in the atmospheric oxidation of hydrocarbons and in their combustion. When NO concentration is low, they can appreciably react with themselves. This reaction has both propagation and termination channels. Multireference second-order perturbative energy calculations CAS(16,12)-PT2/6-311G(2df,p) have been carried out on the CAS(8,8)-MCSCF/6-311G(d,p) geometries pertaining to the reaction pathways explored. The tetroxide intermediate put forward first by Russell in 1957 is found as a stable energy minimum, but the calculations indicate that, as the system moves from atmospheric to combustion temperatures, its formation becomes problematic. A concerted synchronous transition structure, apt to connect it with the termination products, formaldehyde, methanol, and dioxygen, is not found. The concerted dissociation of the two external O–O bonds in the tetroxide leads to the (CH23O)233O2 complex, with overall singlet spin multiplicity. Both termination via H transfer, to give H2CO,CH3OH, and O2, or dissociation to 2 CH3O+O2 (possible propagation) are feasible. The former could occur in principle with production of either excited O21 or excited H23CO. However, if a sufficiently easy intersystem crossing (ISC) could take place in the complex, the process would end up with all ground-state molecules. The (possible) propagation channels are favored by higher temperatures, while lower temperatures favor the ISC mediated termination channel. A fairly good qualitative agreement with experimental T dependence of the relevant branching ratio is found. From the tetroxide over again, dissociation of a single external O–O bond leads to CH3O and CH3O3, or possibly to a (CH3OCH3O3)1 complex, but further transformations along this line are not competitive.

1.
(a) R. Lesclaux, in Peroxyl Radicals, edited by Z. B. Alfassi (Wiley, New York, 1997), Chap. 6;
(b) T. J. Wallington and O. J. Nielsen, ibid., Chap. 15.
2.
B. J. Finlayson-Pitts and J. N. Pitts, Jr., Chemistry of the Upper and Lower Atmosphere (Academic, New York, 2000), Chap. 6.
3.
G. A.
Russell
,
J. Am. Chem. Soc.
79
,
3871
(
1957
).
4.
(a)
J. A.
Howard
and
K. U.
Ingold
,
J. Am. Chem. Soc.
90
,
1056
(
1968
);
(b)
J. A.
Howard
and
K. U.
Ingold
,
J. Am. Chem. Soc.
90
,
1058
(
1968
).
5.
T. J.
Wallington
,
P.
Dagaut
, and
M. J.
Kurylo
,
Chem. Rev.
92
,
667
(
1992
).
6.
J. E.
Bennet
and
J. A.
Howard
,
J. Am. Chem. Soc.
95
,
4008
(
1973
).
7.
B. Plesnicar, in Organic Peroxides, edited by W. Ando (Wiley, New York, 1992), pp. 491–494, 526, 527.
8.
P. D.
Lightfoot
,
R.
Lesclaux
, and
B.
Veyret
,
J. Phys. Chem.
94
,
700
(
1990
).
9.
O.
Horie
,
J. N.
Crowley
, and
G. K.
Moortgart
,
J. Phys. Chem.
94
,
8198
(
1990
).
10.
Q.
Niu
and
G. D.
Mendenhall
,
J. Am. Chem. Soc.
112
,
1656
(
1990
);
Q.
Niu
and
G. D.
Mendenhall
,
J. Am. Chem. Soc.
112
,
1657
(
1990
).
11.
P.
Ase
,
W.
Bock
, and
A.
Snelson
,
J. Phys. Chem.
90
,
2099
(
1986
).
12.
J. R.
Kanofsky
,
J. Org. Chem.
51
,
3386
(
1986
).
13.
S. P.
Sander
and
R. T.
Watson
,
J. Phys. Chem.
85
,
2960
(
1981
).
14.
M.
Nakano
,
K.
Takayama
,
Y.
Shimizu
,
Y.
Tsuji
,
H.
Inaba
, and
T.
Migita
,
J. Am. Chem. Soc.
98
,
1974
(
1976
).
15.
S.-H.
Lee
and
G. D.
Mendenhall
,
J. Am. Chem. Soc.
112
,
1656
(
1990
).
16.
H. B. Schlegel, in Computational Theoretical Organic Chemistry, edited by I. G. Csizsmadia and R. Daudel (Reidel, Dordrecht, 1981), pp. 129–159;
J. Chem. Phys.
77
,
3676
(
1982
);
H. B.
Schlegel
,
J. S.
Binkley
, and
J. A.
Pople
,
J. Chem. Phys.
80
,
1976
(
1984
);
H. B.
Schlegel
,
J. Comput. Chem.
3
,
214
(
1982
).
17.
B. O. Roos, in Ab Initio Methods in Quantum Chemistry-II, edited by K. P. Lawley (Wiley, New York, 1987);
D.
Hegarty
and
M. A.
Robb
,
Mol. Phys.
38
,
1795
(
1979
);
M. A.
Robb
and
R. H. A.
Eade
,
NATO Adv. Study Inst. Ser., Ser. C
67
,
21
(
1981
).
18.
W. J.
Hehre
,
R.
Ditchfield
, and
J. A.
Pople
,
J. Chem. Phys.
56
,
2257
(
1972
);
P. C.
Hariharan
and
J. A.
Pople
,
Theor. Chim. Acta
28
,
213
(
1973
);
T.
Clark
,
J.
Chandrasekhar
,
G.
Spitznagel
, and
P. v. R.
Schleyer
,
J. Comput. Chem.
4
,
294
(
1983
);
M. J.
Frisch
,
J. A.
Pople
, and
J. S.
Binkley
,
J. Chem. Phys.
80
,
3265
(
1984
).
19.
B. O.
Roos
,
K.
Andersson
,
M. P.
Fülscher
,
P.-Å.
Malmqvist
,
L.
Serrano-Andres
,
K.
Pierloot
, and
M.
Mercham
,
Adv. Chem. Phys.
93
,
219
(
1996
);
K.
Andersson
,
P.-Å.
Malmqvist
, and
B. O.
Roos
,
J. Chem. Phys.
96
,
1218
(
1992
).
20.
C.
Gonzalez
and
H. B.
Schlegel
,
J. Chem. Phys.
90
,
2154
(
1989
);
C.
Gonzalez
and
H. B.
Schlegel
,
J. Phys. Chem.
94
,
5523
(
1990
), and references therein.
21.
Reaction enthalpies were computed as outlined, for instance, in J. B. Foresman and Æ. Frisch, Exploring Chemistry with Electronic Structure Methods (Gaussian, Inc., Pittsburgh, PA, 1996), pp. 166–168;
D. A. McQuarrie, Statistical Thermodynamics (Harper and Row, New York, 1973), Chap. 8.
22.
G. A.
Petersson
,
T. G.
Tensfeldt
, and
J. A.
Montgomery
,Jr.
,
J. Chem. Phys.
94
,
6091
(
1991
);
J. W.
Ochterski
,
G. A.
Petersson
, and
J. A.
Montgomery
, Jr.
,
J. Chem. Phys.
104
,
2598
(
1996
), and references therein.
23.
L. A.
Curtiss
,
K.
Raghavachari
,
G. W.
Trucks
, and
J. A.
Pople
,
J. Chem. Phys.
94
,
7221
(
1991
).
24.
M. J. Frisch, G. W. Trucks, H. B. Schlegel et al., GAUSSIAN98, Gaussian, Inc., Pittsburgh, PA, 1998.
25.
MOLCAS 4: K. Andersson, M. R. A. Blomberg, M. P. Fülscher, K. Karlström, R. Lindh, P.-Å. Malmqvist, P. Neogrády, J. Olsen, B. O. Roos, A. J. Sadlej, M. Schütz, L. Seijo, L. Serrano-Andrés, P. E. M. Siegbahn, and P.-O. Windmark, MOLCAS VERSION 4 (University of Lund, Sweden, 1997).
26.
MOLDEN:
G.
Schaftenaar
and
J. H.
Noordik
,
J. Comput.-Aided Mol. Design
14
,
123
(
2000
).
27.
E.
Henon
,
F.
Bohr
,
A.
Chakir
, and
J.
Brion
,
Chem. Phys. Lett.
264
,
557
(
1997
).
28.
W. Koch and M. C. Holthausen, A Chemist’s Guide to Density Functional Theory (Wiley VCH, Weinheim, 2000), Chaps. 8, 9, and 13.
29.
R.
Seeger
and
J. A.
Pople
,
J. Chem. Phys.
66
,
3045
(
1977
).
30.
R.
Bauernschmitt
and
R.
Ahlrichs
,
J. Chem. Phys.
104
,
9047
(
1996
).
31.
H. B. Schlegel and J. J. McDouall, in Computational Advances in Organic Chemistry, edited by C. Ogretir and I. G. Csizmadia (Kluwer Academic, Dondrecht, 1991), p. 167.
32.
A.
Maranzana
,
G.
Ghigo
, and
G.
Tonachini
,
J. Am. Chem. Soc.
122
,
1414
(
2000
);
F. Motta, Tesi di Laurea, Università di Torino, 2000;
A. Maranzana, G. Ghigo, and G. Tonachini, Chem. Eur. J. (in press). As already noted in these previous studies, unrestricted DFT (UDFT) calculations on diradicals, diradicaloid structures, homolysis processes, and radical coupling converge on incorrect closed-shell type solutions, with zero spin densities. To get a qualitatively correct picture in terms of nonzero spin densities, the UDFT monodeterminantal wave function has to be handled in a way already described, and the energy values so obtained need to be refined by using the formula suggested by Yamaguchi:
S.
Yamanaka
,
T.
Kawakami
,
K.
Nagao
, and
K.
Yamaguchi
,
Chem. Phys. Lett.
231
,
25
(
1994
);
K.
Yamaguchi
,
F.
Jensen
,
A.
Dorigo
, and
K. N.
Houk
,
Chem. Phys. Lett.
149
,
537
(
1988
).
See also
C. J.
Cramer
,
F. J.
Dulles
,
G. J.
Giesen
, and
J.
Almlöf
,
Chem. Phys. Lett.
245
,
165
(
1995
);
E.
Goldstein
,
B.
Beno
, and
K. N.
Houk
,
J. Am. Chem. Soc.
118
,
6036
(
1995
).
33.
The interaction energy between the (CH23O)23 complex and O23 is −1.5 kcal mol−1, at the CAS(16,12)-PT2/6-311G(2df,p)//CAS(8,8)/6-311G(d,p) level.
34.
T. P. W.
Jungkamp
and
J. H.
Seinfeld
,
Chem. Phys. Lett.
257
,
15
(
1996
);
T. P. W.
Jungkamp
and
J. H.
Seinfeld
,
Chem. Phys. Lett.
259
,
683
(
1996
);
T. P. W.
Jungkamp
and
J. H.
Seinfeld
,
Chem. Phys. Lett.
263
,
371
(
1996
).
This content is only available via PDF.
You do not currently have access to this content.