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O-O Bond Dissociation Enthalpy In Perfluoromethyl Fluorocarbonyl Peroxide, CF3OOC(O)F. A Density Functional Quantum Chemical Analysis
Erben1, M. F.; Della Védova, C. O.1,2
1CEQUINOR
Centro de Química Inorgánica (CONICET-UNLP). Departamento de Química. Facultad de Ciencias Exactas. Universidad Nacional de La Plata, 47 esq. 115 (1900) La Plata, Argentina.
2LaSeISiC,
Laboratorio de Servicios a la Industria y al Sistema Científico (UNLP-CIC-CONICET) Camino Centenario, Gonnet, Argentina
FAX: +54 221 425 9485; email: carlosdv@quimica.unlp.edu.ar
Received March 16, 2004. In final form April 17,
2004
Dedicated to Prof. Pedro J. Aymonino on
the occasion of his 75th birthday
Abstract
Density functional at the
B3LYP levels of theory using the Pople's 6-311+G(3df) basis sets and the
Dunning's aug-cc-pVTZ correlation consistent basis sets have been employed to
determine the enthalpy of formation (DHf0(298)) of CF3OOC(O)F
at 298 K, using the isodesmic reaction CF3OOCF3 +
FC(O)OOC(O)F ® 2 CF3OOC(O)F.
Thus, the B3LYP/6-311+G(3df) and B3LYP/aug-cc-pVTZ methods yield DHf0(298) values of –273.3 and –273.2 kcal mol-1, respectively. From the reported DHf0(298) for CF3O·
and FC(O)O· radicals, bond energy dissociation (DO-O) values of 38.3
and 38.2 kcal mol-1 are deduced for CF3OOC(O)F, which are
in agreement with the reported value for related peroxides. Also, calculations
for the enthalpy change in the peroxide bond excision reaction were performed
at the B3LYP and B3PW91 using several basis sets. The corresponding DO-O
values obtained using these enthalpy changes are too low independently of both
basis sets and method of calculation used for the calculation.
Resumen
El método B3LYP de los funcionales de la densidad con
la base de Pople 6-311+G(3df) y con la base de correlación consistente de
Dunning aug-cc-pVTZ, fue empleado para determinar la entalpía de formación a
298 K (DHf0(298)) del CF3OOC(O)F,
utilizando la reacción isodésmica CF3OOCF3 + FC(O)OOC(O)F
® 2 CF3OOC(O)F. Es así que se obtienen
valores de DHf0(298)
de –273.3 y –273.2 kcal mol-1 para los métodos B3LYP/6-311+G(3df) y
B3LYP/aug-cc-pVTZ respectivamente. A partir de los valores de DHf0(298) reportados para los
radicales CF3O· y FC(O)O·, se obtienen valores de energía de
disociación de enlace DO-O igual a 38.3 y 38.2 kcal mol-1,
que acuerdan con los valores reportados para peróxidos similares. El cambio de
entalpía en la reacción de escisión del enlace peróxido fue calculado a los
niveles B3LYP y B3PW91 utilizando varias funciones bases. Los correspondientes
valores de DO-O obtenidos utilizando estos cambios de entalpía son
demasiado bajos, con independencia tanto del conjunto de funciones base, como
del método utilizados en el cálculo.
Introduction
CF3OOC(O)F was synthesized for the first
time in 1967 by Cauble and Cady by photochemical reaction of FC(O)OOC(O)F with
fluorine [1] with a yield of about 5% (based upon the amount of peroxide
consumed). In a separated [2] article these authors reported some physical and
spectroscopic characteristic of CF3OOC(O)F. At the same time, Talbot [3] reported the synthesis of CF3OOC(O)F by photochemical reaction
of a mixture containing FC(O)OOC(O)F and CF2N2 in a yield
close to 18%. Later, in 1970 Anderson and Fox [4] and DesMarteau [5] synthesized CF3OOC(O)F using the reaction between CF2(OF)2
and C(O)F2 catalyzed by CsF. At the same time, Blesa and Aymonino [6] reported in this journal an improved method for the preparation of CF3OOC(O)F
by photolysis of gaseous mixtures of perfluorocyclobutanone, fluorine and
oxygen, upon UV irradiation, with the yield being ca. 35%.
Species containing only carbon, oxygen and fluorine
atoms have renewed its attraction and many of them are being investigated or
even re-investigated since they have shown to play an important role in
atmospheric chemistry [7].
Recently [8], we have reported a structural and conformational study of CF3OOC(O)F
structural and conformational features, which included the use of gas electron
diffraction (GED) technique, vibrational spectroscopy (IR of both gas phase and
isolated in Ar-matrix, and liquid Raman) and quantum chemical calculations. The
dihedral angle around the peroxide bond in CF3OOC(O)F (d(COOC) = 111(5)°) with one sp2-
and one sp3- hybridized carbon substituent is intermediate between
those found in FC(O)OOC(O)F (83.5(14)°) [9] with two sp2- hybridized
carbon substituents and in CF3OOCF3 (123(4)°) [10] with two
sp3- hybridized carbon substituents. Furthermore, syn orientation of
the C=O double bond relative to the O-O single bond is preferred in CF3OOC(O)F.
The MP2 DG° (G0anti – G0syn)
value (DG° = 2.03 kcal/mol) is in excellent agreement with the experimental DG° value of
2.09(22) kcal/mol as derived from the matrix IR experiment. The O-O bond length
in CF3OOC(O)F (1.422(15)Å) is within experimental uncertainties
equal to those in CF3OOCF3 (1.419(20) Å) and FC(O)OOC(O)F
(1.419(9) Å).
Furthermore, when Ar/CF3OOC(O)F mixtures
are passed thought the spray-on nozzle held at temperatures higher than 300 °C, new bands
appear in the IR spectra superposed to those belonging to the parent CF3OOC(O)F
peroxide. These bands belong to CF3O· and FC(O)O· radicals [11]. No
characteristic bands of CF3OO· nor FC(O)OO· peroxi radicals [12]
were found in the IR spectra. These features agree with the previous finding of
Argüello and Willner [11]. Quantum chemical calculations performed at the
B3LYP/6-311G* level of the theory for bond energy dissociations predict the
peroxide bond weaker than the C-O bonds. Thus, the computed values for DO-O,
DC(sp2)-O and DC(sp3)-O are 21.3, 70.2 and 75.5 kcal mol-1,
respectively. However, this computed DO-O bond energy dissociation
is too low, as compared with reported values for related peroxides [8].
In the present contribution, we report a theoretical study
concerning thermodynamic properties of CF3OOC(O)F, specially those
related with the DO-O bond energy dissociation.
Quantum Chemical Calculations
Electronic structure calculations using Becke's
three-parameters functional [13] with the correlation functional of Lee, Yang
and Parr (B3LYP) hybrid functional were performed with the GAUSSIAN 98 program
[14]. The Pople's triple-zeta split valence 6-311+G(3df) basis sets which include
diffuse and polarization function [15] and the Dunning's triple-zeta diffuse
function augmented correlation consistent basis sets, denoted as aug-cc-pVTZ,
[16] were used to calculate fully optimized equilibrium geometries and harmonic
vibrational frequencies of the molecules under investigation. The syn conformer
was taken as the more stable conformation for CF3OOC(O)F [8] (syn
with respect to C=O and O-O bonds) and C2 molecular symmetry with
syn conformation was adopted in FC(O)OOC(O)F [17] (syn with respect to C=O and
O-O bonds). A good agreement was found between calculated and experimental
geometrical parameters and fundamental vibrational frequencies [18], [19].
The enthalpy of formation of the CF3OOC(O)F
molecule was estimated using the following isodesmic reaction:
CF3OOCF3 + FC(O)OOC(O)F ® 2 CF3OOC(O)F
In a isodesmic reaction, reactants and products
contain the same number of the same type of bonds and errors due to inherent
limitations in the basis set and electron correlation energy nearly cancel [20]. Total energies are corrected by zero-point vibration energies (ZPVE)
(without any scaling factor). Thermal corrections, 0 K to 298.15 K, are
calculated to estimate the reaction enthalpy at 298.15 K (DHr0(298)).
DHf0(298)
values for CF3OOCF3 and FC(O)OOC(O)F were taken from the
literature [21], [22].
A second model was employed for the calculation of
bond dissociation enthalpies taking into account the difference between the
corrected enthalpies at 298 K for reactants and products. Thus, the bond
dissociation enthalpy for the CF3OOC(O)F ® CF3O· + FC(O)O· dissociation, is then determined by: DO-O = (H0298(CF3O·)
+ H0298(FC(O)O·)-H0298(CF3OOC(O)F).
B3LYP and B3PW91 hybrid functionals with Pople's type basis sets up to
6-311+G(3df) and the Dunning's cc-pVDZ and aug-cc-pVTZ basis sets were applied.
These results are listed in Table 1.
Table 1. Calculated DO-O bond energy dissociations, in kcal mol-1, for CF3OOC(O)F as the enthalpy reaction change at 298 K for the process CF3OOC(O)F ® CF3O· + FC(O)O·.a
|
6-31G* |
6-31+G*b |
6-311+G* |
6-311+G(3df) |
cc-pVDZ |
aug-cc-pVTZ |
B3LYP |
28.8 |
- |
24.0 |
26.8 |
28.1 |
26.8 |
B3PW91 |
29.2 |
26.9 |
25.0 |
28.2 |
28.1 |
28.1 |
a CF3O· was optimized assuming Cs geometry. b The convergence criteria are not reach for CF3OOC(O)F at the B3LYP/6-31+G* level of calculation.
Results and Discussion.
The enthalpy of formation of CF3OOC(O)F was
evaluated using the calculated isodesmic reaction enthalpies DHr0(298)
and the experimental enthalpy of formation of CF3OOCF3 of
-343±3 kcal mol-1 [21] and the computed enthalpy of formation
for FC(O)OOC(O)F of -202.9 kcal mol-1 [22]. From the
B3LYP/6-311+G(3df) and B3LYP/aug-cc-pVTZ levels of calculations, DHf0(298)
values of –273.3 and –273.2 kcal mol-1 were calculated for CF3OOC(O)F.
According to the experimental uncertainties, an error level of ±4 kcal mol-1 is estimated for the above value [21].
The predicted DHf0(298)
values, in conjunction with the DHf0(298) values of –149±2 kcal mol-1
for CF3O· [23] and of -86.0 kcal mol-1 for FC(O)O· [24],
lead to reaction enthalpies values of 38.3 and 38.2 kcal mol-1 for
CF3OOC(O)F ® FC(O)O·+CF3O· at the B3LYP/6-311+G(3df) and
B3LYP/aug-cc-pVTZ, respectively. The mean DO-O value for CF3OOC(O)F
of 38.2 kcal mol-1 lies in between of the experimentally determined
bond dissociation energy values for the symmetrically substituted peroxides,
which are 47.5±0.5 kcal mol-1 for CF3OOCF3
[25], and 31±3 [26] and 29.5 kcal mol-1 for FC(O)OOC(O)F [27]. In
addition, the experimental DO-O value for CF3OOC(O)OCF3
is 34 kcal mol-1 [27]. It is interesting to note that this molecule
displays a similar DO-O value as calculated in this work for CF3OOC(O)F.
Thus, our previously calculated DO-O
value at the B3LYP/6-311G* level of calculation of 21.3 kcal mol-1 [8] seem to be low. It should be noted that this value was calculated by using
the enthalpy change in the dissociation reaction CF3OOC(O)F ® CF3O·
+ FC(O)O·. In order to study both the role of the basis set and the calculation
method in the computed DO-O value, several basis sets at the B3LYP
and B3PW91 methods were used (Table 1). DO-O values depend strongly
on the basis sets. With the two levels of approximation used in this work, both
6-311+G(3df) and aug-cc-pVTZ, (351 and 414 basis function for CF3OOC(O)F,
respectively) basis sets display better results than the previously reported [8] B3LYP/6-311G* method (162 basis function for CF3OOC(O)F), but
are still too low (ca. 10 kcal mol-1) as compared with the value
obtained by using an isodesmic reaction scheme and experimental data reported
for related peroxides [25], [28]. Similar discrepancies were reported for the
computed thermodynamic properties of FC(O)OOC(O)F. Strong dependencies on the basis
set were calculated for the DO-O value obtained as enthalpy
differences (FC(O)OOC(O)F ® 2 FC(O)O·) by using the B3LYP level of approximation [22], [29].
Even at higher level of calculations (B3LYP/6-311+G(3df)//B3LYP/6-311+G*), the
DO-O value is around 14 kcal mol-1 lower that the
experimental one. The use of a scheme of isodesmic reactions leads to a DO-O which agrees fairly well with that determined experimentally. In the Reference [22], it was suggested that for the description of a non-isodesmic reaction the
B3LYP method results inadequate probably due to deficiencies in the treatment
of electron correlation effects. In the present study for CF3OOC(O)F
a coincidence with the reported result was found. In addition it is shown that
the B3PW91 hybrid method has similar limitations even by using larger basis
sets. Therefore, the use of an isodesmic reaction scheme for a reliable
description of these systems can be considered as necessary.
Acknowledgements
The authors thank
ANPCYT-DAAD for the German-Argentine cooperation Awards. They also thank the Consejo Nacional
de Investigaciones Científicas y Técnicas (CONICET) and the Comisión de
Investigaciones Científicas de la Provincia de Buenos Aires (CIC), Argentina.
They are indebted to the Facultad de Ciencias Exactas, Universidad Nacional de
La Plata, Argentina for financial support.
They also thank the FONCyT (Agencia Nacional de
Promoción Científica y Tecnológica) and to the following institutions: LNLS
(Brazil), British Council (U.K), Jesus College (Oxford), DAAD, AvH and VW
Stiftung (Germany)
References
[1] Cauble, R.; Cady, G. H. J. Am. Chem. Soc. 1967, 89, 5161.
[2] Cauble, R.; Cady, G. H. J. Org. Chem. 1968, 33, 2099.
[3] Talbott, R. L. J. Org. Chem. 1968, 33, 2095.
[4] Anderson, L. R.; Fox, W. B. Inorg. Chem. 1970, 9, 2182.
[5] DesMarteau, D. D. Inorg. Chem. 1970, 9, 2179.
[6] Aymonino, P. J.; Blesa, M. A. An. Asoc. Quím. Argent. 1970, 58, 27.
[7] Francisco, J. S.; Maricq, M. M., Atmospheric photochemistry of alternative halocarbons. In Advances in Photochemistry, vol 20, Eds. Neckers, D. C.; Volman, D. H., von Bünau, G.. John Wiley & Sons, 1995.
[8] Trautner, F.; Gholivand, K.; García, P.; Willner, H.; Erben, M. F.; Della Védova, C. O.; Oberhammer, H. Inorg.Chem. 2003, 42, 3079.
[9] Mack, H.-G.; Della Védova, C. O.; Oberhammer, H. Angew. Chem. Int. Ed. Engl. 1991, 30, 1145.
[10] Marsden, C. J.; Bartell, L. S.; Diodati, F. P. J. Mol. Struct. 1977, 39, 253.
[11] Argüello, G. A.; Willner, H. J. Phys. Chem. A 2001, 105, 3466.
[12] Sander, S.; Pernice, H.; Willner, H. Chem. Eur. J. 2000, 6, 3645.
[13] Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
[14] Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.; Stratman, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Menucci, B.; Pomelli, C.; Adamo, C.; Clifford, S;. Ochterski, J.; Petersson, G. A.; Ayala, P.Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A.D.;. Raghavachari, K.; Foresman, J. B.; Cioslovski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzales, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzales, C.; Head-Gordon, M.; Replogle, Pople, J. A. GAUSSIAN 98 (Revision A.7), Gaussian, Inc. Pittsburgh PA, 1998.
[15] Raghavachari, K.; Trucks, G. W.; Pople, J. A.; Head-Gordon, M. Chem. Phys. Lett. 1989, 157, 479.
[16] a) Dunning, Jr. T. H. J. Chem. Phys. 1989, 90, 1007 b) Kendall, R. A.; Dunning, Jr. T. H.; Harrison, R. J. J. Chem. Phys. 1992, 96, 6769.
[17] Mack, H.-G.; Della Védova, C. O.; Oberhammer, H. Angew. Chem. Int. Ed. 1991, 30 , 1145.
[18] Della Védova, C. O.; Mack, H.-G. J. Mol. Struct. 1992, 274, 25.
[19] Marsden, C. J.; Bartell, L. S.; Diodati, F. P. J. Mol. Struct. 1977, 39, 253. Hehre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. Ab Initio Molecular Orbital Theory, Wiley, New York, 1986.
[20] Hehre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. Ab Initio Molecular Orbital Theory, Wiley, New York, 1986.
[21] DeMore, W. B.; Sander, S. P.; Golden, D. M.; Hampson, R. F.; Kurylo, M. J.; Howard, C. J.; Ravishankara, A. R.; Kolb, C. E.; Molina, M. J. Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling. Evaluation Number 12, JPL Publ. 97-4, 1997.
[22] Badenes, M. P.; Castellano, E.; Cobos, C. J.; Croce, A. E.; Tucceri, M. E. Chem. Phys. Lett. 1999, 303, 482.
[23] Schneider, W. F.; Wallington, T. J. J. Phys. Chem. 1994, 98, 7448.
[24] Dibble, T. S.; Francisco, J. S. J. Phys. Chem. 1994, 98, 11694.
[25] Reints, W.; Pratt, D. A.; Korth, H. G.; Mulder, P. J. Phys. Chem. A 2000, 104, 10713.
[26] Arvia, A. J.; Aymonino, P. J.; Schumacher, H. J. Z. Physik. Chem. NF 1961, 28, 393.
[27] Burgos Paci, M. Tesis Doctoral "Estudios teóricos y experimentales de compuestos fluorados de importancia atmosférica", 2003, Fac. de Ciencias Químicas, U.N.C.
[28] Burgos Paci, M.; Argüello, G. A.; García, P.; Willner, H., Int. J. Chem. Kinet. 2003, 35, 15.
[29] McKee, M. L.; Webb, T. R. J. Phys. Chem. 1996, 100, 11292.