J. Phys. Chem. 1992,96,9250-9254 1972; Vol. 3, pp 91-274. (b) Hargittai, I. The Structure of Volatile Sulphur Compounds; Reidel: Dordrecht, 1985. (4) (a) Kato, K. Acta Crystallogr. 1972, B28, 55-59. (b) Penn, R. E.; Block, E.; Revelle, L. K. J . Am. Chem. SOC.1978, 100, 3622-3623. (c) Hamilton, W. C.; La Placa, S.J. J . Am. Chem. Soc. 1964,86,2289-2290. (d) Wallmeier, H.; Kutzclnigg, W. J . Am. Chem. Soc. 1979,101,2804-2814. (5) (a) Steiger, T.; Steudel, R. J. Mol. Struct. ( T H E W H E M ) 1992, 257, 313-323. (b) Fender, M. A.; Sayed, Y.M.; Prochaska, F. T. J . Phys. Chem. 1991, 95, 2811-2814. (6) Baumeister, E.; Oberhammer, H.; Schmidt, H.; Steudel, R. Heteroatom Chem. 1991, 2, 633-641. (7) Dietrich, H.:, Diercks, H. Messtechnik (Braunschweig) 1970, 78,184. (8) Luger, P.; Buschmann, J. J . Am. Chem. Soc. 1984,106,7118-7121. (9) Luger, P. KAPCOR,An endless cylinder volume correction program; Freie Universitlt Berlin: Berlin, 1984. (IO) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467-473. (1 1) Hall, S.R., Stewart, J. M., Eds.XTAL 2.2 User's Manual; University of Westem Australia: Nedlands, WA, and University of Maryland: College Park, MD, 1987. (12) Cromer, D. T.; Mann, J. B. Acta Crysfullogr.,Sect. A 1968, A24, 321-328. (13) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J. Chem. Phys. 1965, 42, 3175-3186. (14) International Tables for X-ray Crystallography IF Ibers, J. A,, Hamilton, W. C., Eds.; The Kynoch Press: Birmingham, England, 1974; p 148. (15) Hansen, N. K.; Coppens, P. Acta Crystallogr. 1978, A34,909-921.
(16) Hehre, W. J.; Stewart, R. F.; Pople, J. A. J . Chem. Phys. 1%9,51, 2657-2664. (17) Kurki-Suonio, K. Isr. J . Chem. 1977, 16, 1 15-123. (18) Schwarz, W. H. E.; Valtazanos, P.; Ruedenterg, K. Theor. Chim. Acta 1985, 68, 471-506. (19) Seiler, P.; Schweizer, W. B.; Dunitz, J. D. Acta Crystullogr. 1984, 840, 319-327. (20) Schwarz, W. H. E.; Mewching, L.; Valtazanos, P.; Von Niessen, W. Int. J . Quantum Chem. 1986, 29,909-914. (21) Frisch, M., Ed. GAUSSIAN86, User's Guide; Carnegie-Mellon University: Pittsburgh, PA, 1984. (22) Donohue, J.; Schomaker, V. J . Chem. Phys. 1948,16, 92-96. See also: Jug, K.; Iffert, R. J. Comput. Chem. 1987, 8, 1004-1015. (23) Blukis. U.: Kasai. P. H.: Mvers. R. J. J . Chem. Phvs. 1963. 38. 2753-2760. See also the structure of-CH;OH: Lees, R. M.; Baker, J. G.J: Chem. Phys. 1968,48, 5299-5318. (24) Keller, E. SCHAKAL88. Graphics program for molecular and crystallographic models; Albert-Ludwigs-Universitlt,Freiburg, Germany, 1988. ~. (25) Bondi, A. J. Phys. Chem. 1964,68,441-451. (26) Kucsman, A.; Kapvits. I. In Organic Sulfur Chemistry: Theoretical and Experimental Advances; Bernardi, F., Csizmadia, I. G., Mangini, A., Eds.; Elsevier: Amsterdam, 1985; pp 191-245. (27) Rasenfield, R. E.; Parthasarathy, R.;Dunitz, J. D. J . Am. Chem. Soc. 1977, 99,4860-4862. (28) For a discussion of similar examples, see: Kunze, K. L.; Hall, M. B. J . Am. Chem. SOC.1986, 108, 5122-5127. ~~
Oxywater (Water Oxide): New Evidence for the Existence of a Structural Isomer of Hydrogen Peroxide Cynthia Meredith3 Tracy P. Hamilton,t and Henry F. Schaefer III* Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602 (Received: May 28, 1992)
Ab initio molecular electronic structure theory has been applied in an investigation of the oxywater-hydrogen peroxide isomerization. Oxywater, hydrogen peroxide, and the transition state connecting them have been located using the selfconsistent-field (SCF), configuration interaction including all single and double excitations (CISD), and coupled cluster with single and double excitations (CCSD) methods with several basis sets, the largest being of triple-zeta plus double-polarization (including f functions on the oxygen atoms) quality (TZ2P+O. Harmonic vibrational frequencies have been evaluated at the SCF, CISD, and CCSD levels of theory and the stationary points characterized as minima or transition states. The CCSD method with connected triple excitations [CCSD(T)] also has been used to obtain oxywater's equilibrium geometry and frequencies as well as to compute singlepoint energies of all CCSD-optirmzed structures. A classical barrier to isomerization of 5.7 kcal mol-' has been predicted at the highest level of theory. After correction for zero-point vibrational energies, the comparable ground-state activation energy is 3.2 kcal mol-'. Although these ab initio predictions could be decreased by 1 or 2 kcal mol-' at yet higher levels of theory, there can be little doubt that oxywater is a genuine minimum on the H202 potential energy hypersurface.
Introduction Oxywater (H200) is a proposed structural isomer of hydrogen peroxide (HOOH) that may serve as a transient intermediate in oxidation reactions initiated by the latter species.'J This molecule has been described by Pople, Raghavachari, Frisch, Binkley, and Schleyer' as an "abnormal" valent form of H2O2, Le., a neutral H202isomer in which the formal charges on some nuclei are nonzero. Of course, any neutral molecule involving a trivalent oxygen atom must be considered hypervalent and therefore contrary to the normal rules of qualitative valence theory? Oxywater, if it exists, is likely to be formed from a [1,2]-hydrogen shift of hydrogen peroxide. Although hydrogen peroxide has been well studied both experimentallys-I3and theoreti~ally,'~~' oxywater has never been observed an&? seldom been considered in the literature. To our knowledge, the first reference to oxywater appeared in 1955 'Charles A. Coulson Graduate Fellow. *Present address: Department of Chemistry, University of Alabama, Birmingham, AL 35294.
0022-3654/92/2096-9250$03.00/0
in a paper by Bain and Gigu6re.28 These investigators analyzed the infrared (IR) spectrum of H202using isotopically substituted species. Because they were unable to observe an oxygen-oxygen stretching fundamental other than that which is characteristic of hydrogen peroxide, they ruled out the existence of "any tautomeric form of the molecule such as H20-0". The first theoretical study to investigate the existence of oxywater was the aforementioned 1983 paper of Pople et al.3in which they examined several [1,2]-hydrogen shifts and concluded that singlet isomers resulting from rearrangement to an "abnormalvalence coordination" either have shallow potential minima or do not correspond to minima at all. Oxywater was found to exist as a stable minimum at the HF/6-31G* level of theory with a rearrangement barrier (A@ of 21.2 kcal mol-'. However, addition of correlation corrections at the MP4SDQ/6-31GS* level reduced the barrier to 2.0 kcal mol-', and subsequent addition of a triple substitution correction eliminated the barrier entirely. Since Pople et al. did not optimize the geometries of oxywater, hydrogen peroxide, and the transition state connecting them at high levels of theory but merely evaluated MP4 single-point energies at the 0 1992 American Chemical Society
New Evidence for the Existence of Oxywater HF/6-3 lG* geometries, their contention that oxywater cannot exist as a stable minimum is tenuous. Two additional theoretical studies of oxywater were published recently. The first was a communication concerning the role of electron correlation in oxygen atom transfer. Of particular interest was the oxidation of ammonia by hydrogen peroxide. Using methods similar to those of Pople et a1.3 but optimizing structures at these higher levels of theory, Bach, McDouall, Owensby, and Schlegel' reached a dramatically different conclusion-that oxywater does indeed exist as a local minimum lying 6.3 kcal mol-I below the energy of the transition structure for the [1,2]-hydrogen shift (although with the zero-point vibrational energy correction this barrier drop to 3.1 kcal mol-'). In addition, Bach et al. discuss in some detail the mechanism for the gas-phase reaction of ammonia with hydrogen peroxide, which appears to involve both a [ 1,2]-hydrogen shift and the simultaneous transfer of the oxygen by an SN2-likecleavage of the 0-0 bond. However, since the overall gas-phase barrier to oxygen transfer from H 2 0 2to NH3 (51.4 kcal mol-') is too high to be compatible with oxygen-transfer chemistry in aqueous solution or in the presence of a protic solvent, it is proposed that oxygen atom transfer from Hz02under typical experimental conditions must occur via an ionic pathway involving protonation of peroxide followed by a nucleophilic attack on the resultant oxy-oxonium ion and subsequent deprotonation from the adjacent oxygen atom. This ionic mechanism is, in effect, a [ 1,2]-hydrogen shift. One year later (1991), Bach, Owensby, Gonzalez, Schlegel, and McDoual12 published another theoretical study of the mechanism of oxygen transfer from hydrogen peroxide. They optimized structures at the complete active space (CAS) SCF, CISD, and QCISD levels of theory and confirmed the previous findings of Bach et al. concerning the gas-phase mechanism. However, they also noted that the high barrier for the H202[ 1,2]-hydrogen shift can be lowered dramatically by adding one or two molecules of solvent water and on this basis suggested that oxywater, though it may have only a fleeting existence in the gas phase, is a viable entity in protic solvent. Moreover, they noted that oxywater can serve as a model for theoretical studies of oxygen transfer from alkyl peroxides. The current study applies advanced theoretical methods up through the TZZP+f/CCSD(T) level to the question of the existence of oxywater in an attempt to verify the chemically and biologically significant findings of Bach et al. Both the thermodynamic and kinetic stability of oxywater are examined, and a ground-state activation energy for the rearrangement of oxywater to hydrogen peroxide is estimated. Theoretical Methods Geometries for all three stationary points were optimized using selfconsistent-field,B configuration interaction (CI),Mand coupled cluster with single and double excitations (CCSD)" analytic gradient methods. At the SCF level of theory, harmonic vibrational frequencies were obtained from analytic second-derivative methods,'2 and at correlated levels of theory they were found by finite central differencesof analytic gradients. SCF level zeropoint vibrational energies (ZPVES) were scaled by a factor of 0.91 to account for anharmonicity and electron ~orrelation,3~ and CISD ZPVEs were scaled by 0.95 to correct primarily for anharmonicityqu Singlepoint energies for all three structures were evaluated using the CCSD with connected triple excitations [CCSD(T)IS5 method at the respective CCSD-optimized structures using both the DZP and the TZ2P+f basis sets. The configurations in the CI expansion included single and double substitutions with respect to the Hartree-Fcck reference determinant (CISD). In the CISD, CCSD, and CCSD(T) calculations, two frozen core and two deleted virtual molecular orbitals were used. The effect of unlinked quadruple excitations on the CISD energies was estimated by incorporating the Davidson correcti~n,'~ and the corresponding energies are denoted CISD+Q. The ground-state activation energies were estimated in the following manner. The scaled DZP zero-point energies were added to the TZZP+f/CCSD(T) relative energies for each structure,
The Journal of Physical Chemistry, Vol. 96, No. 23, 1992 9251
Hd
Loop = 70.9'
T = 103.8'
H3
.H4
p Q
o . 9 6 + y o
01
o"2
2=
111.2O
1.442 Figure 1. Structural parameters (bond lengths in angstroms) for oxywater, the transition state for rearrangement,and hydrogen peroxide at the TZZP+f/CCSD level of theory. The torsional angles are defined as Hd-02-0 I-Hg.
and the relative energies were recalculated from these scaled energy differences. The resulting Mais defined as the activation energy for the H 2 0 0 to HOOH isomerization. The smallest basis set used was of double-zeta (DZ) quality, namely, the 0(9s5p/4s2p) and H(4s/2s) of Huzinaga3' and Dunning,38with one set of polarization functions added with exponents of ad(0) = 0.85 and a,(H) = 0.75. Also employed was the Huzinaga-Dunning triple-zeta basis set,39designated O(lOs6p/5s3p) and H(5s/3s), with two sets of polarization functions (TZZP) on all the nuclei. The polarization function exponents for orbitals of I = 1, + 1 (where 1, represents the 1 angular momentum value for the outermost valence shell) were a,(H) = 1.50, 0.375 and = 1.70, 0.425. The exponents for 1, 2 orbitals were ad(H) = 1.OO and ado) = 1.40. The 0(10~6p2dlf/5~3p2dlf) and H(5s2pld/3s2pld) basis set will be referred to as TZZP+f. The d functions in the DZP calculations were the five-component spherical harmonic functions, and the f functions in the TZ2P+f calculations were the seven-component spherical harmonics. The TZ2P+f CISD wave functions for C, oxywater, C2 hydrogen peroxide, and the CI transition state connecting them include 77535,77006, and 153735 configuration state functions, respectively.
+
Results and Discussion The equilibrium geometries for oxywater, hydrogen peroxide, and the transition state for the [1,2]-hydrogen shift were predicted at the SCF, CISD, and CCSD levels of theory using both DZP and TZ2P+f basis sets. In addition, the oxywater structure was examined further at the CCSD(T) level of theory. Figure 1 shows the geometrical parameters obtained at the TZ2P+f/CCSD level of theory for both the minima and the transition state as well as the atomic numbering scheme employed here. The predicted geometries for the stationary points are given in Table I. The harmonic vibrational frequencies, reported in Table 11, support our characterization of the stationary points as minima and transition states on the potential energy surface. Hydrogen peroxide unscaled and scaled DZP/CISD frequencies are compared with experimentally obtained fundamentals in Table 111. Absolute energies for all levels of theory are shown in Table IV, while energies of hydrogen peroxide and the transition state relative to that of oxywater are given in Table V.
9252 The Journal of Physical Chemistry, Vol. 96, No,23,I992
Meredith et al.
TABLE I: Structural Parameters (Bond Lengths in A and Angles in deg) for Oxywater, the Tramitisn State for Rerrrmgemeat, rad Hydrogen
Peroxidea
Oxvwatcr DZP CCSD CCSD(T)
“*-.“+..-*l
DLIUCIULLLL
parameters
SCF
CISD
r(OO)
1.602 0.949 108.1 65.1
1.549 0.966 106.6 70.2
LHOH LOOP
1.564 0.973 106.0 72.3
1.578 0.974 105.8 74.4
SCF
TZ2P+f CISD
CCSD
1.567 0.944 108.5 64.1
1.515 0.957 107.3 68.4
1.534 0.964 106.7 70.9
Transition State structural parameters r(0102) r(O2H4) r(OiH3) r(O#J L0102H4 T
SCF
DZP CISD
CCSD
SCF
TZ2P+f CISD
CCSD
1.598 0.949 1.184 1.085 101.3 106.1
1.615 0.966 1.331 1.038 99.1 104.1
1.637 0.973 1.38 1 1.034 98.1 103.7
1.588 0.944 1.188 1.080 101.7 105.6
1.588 0.957 1.307 1.040 99.9 104.2
1.614 0.964 1.349 1.038 98.7 103.8
SCF
DZP CISD
CCSD
SCF
TZ2P+f CISD
CCSD
1.392 0.948 102.7 111.9
1.440 0.965 100.5 112.7
1.461 0.972 99.8 113.4
1.386 0.942 103.1 110.5
1.420 0.954 101.3 110.7
1.442 0.961 100.5 111.2
Hydrogen Peroxide structural oarameters r(OO)
r(OH) fOOH 7
‘For oxywater the out-of-plane (oop) angle is defined as the angle between the 00 vector and the HOH plane. The torsional angle for the transition state is defined as H&-O,-fi3. TABLE Ik H a d c Vibrational Frequencies (in em-’) for Oxywater, the Transition State for Rearrangement, and Hydrogen Peroxide
symmetry a” a‘ a’ a” a’ a’
symmetry a
vibrational frequencies *I *2 *3 0 4
*5 *6
vibrational freuuencies
a
*I *2
a a a
*3 *4 w5
a
*6
symmetry a
vibrational frequencies 0 1
w2 w3 *4 WS w6
SCF
CISD
4218 4103 1740 854 810 512
3997 3887 1668 883 873 689
Oxwater DZP CCSD
~
SCF 4157 2842 1369 998 737 18151’
3948 3063 1447 977 702 1317i
4156 4153 1597 1478 1162 419
3888 3772 1636 792 8 30 636
4180 408 1 1742 90 1 846 548
3907 3791 1645 835 850 663
Transition State DZP CISD CCSD
SCF
CCSD(T)
TZ2P+f SCF
3847 3070 1460 924 672 1156i
3946 3941
3839 3838
1483
1440
1370 1010 402
1327 937 389
assignment 0-H asym str 0-H sym str HQH bend 0 4 - H asym bend out-of-plane 0-0 str
assignment 0-H exocyclic str OI-H3 cyclic str out-of-plane (H,-02-Ol-H3) H 4 - 0 exocyclic bend
4139 2830 1374 1016 730 18221
Hydrogen Peroxide DZP CISD CCSD
Although the present investigation is concerned primarily with oxywater and secondarily with the transition state for the [ 1,I]-hydrogen shift, hydrogen peroxide also was characterized. This was deemed naxssary largely because this species has been well studied both experimentally and theoretically whereas oxywater, as mentioned previously, has never been observed. It was expected that the extent to which our theoretical results match the experimental results for hydrogen peroxide would provide a measure of the likely succc8s of our methods for characterizing oxywater and the elusive transition state.
TZ2P+f SCF
~~
00 str
Oz-H, cyclic str
TZ2P+f SCF 4144 4142 1606 1494 1159 424
assignment 0-H sym str O-H asym str 0-0-H sym bend
0 4 - H asym bend 0-0 str torsion
Though the experimental geometrical parameters of hydrogen peroxide have been studied extensively by means of molecular spectroscopy, there still is no consensus on the equilibrium geometry of this species. The reasons for this unfortunate circumstance are as follows. Hydrogen peroxide’s skew configuration (and consequently low C, symmetry) precludes unequivocal determination of four internal parameters from three rotational constants; thus, a full set of internal coordinates can be obtained only by selecting a value for one coordinateusually the 0-H bond length-and evaluating the other three accordingly. In
The Journal of Physical Chemistry, Vol. 96, No. 23, 1992 9253
New Evidence for the Existence of Oxywater TABLE IIk Compuison of Both Ulrserled rad Scaled TheoreticaI Freqwncles with Experimeatd Frequencies (in cm-I) for Hydrogen
PerOXiW ~
~~
vibrational freq VI
v2 vj v4 v5 v6
assignment 0-H sym str 0-H asym str 0-0-Hsymbend O-O-H asym bend 0-0 str torsion
DZPICISD unscaled scaled 3946 3749 3744 3941 1409 1483 1370 1302 960 1010 382 402
expt 3599b 3611b 1387c 1265d 864d 550(?)c
'Scaling factors are 0.91 for SCF and 0.95 for CISD, as discussed in the Methods section. bReference 48. cReference 49. dRefercnce 13. e Reference 5.
addition, the weakly hindered internal rotation about the 0-0 bond permits the equilibrium geometry to vary considerably depending on the environment. The most commonly cited equilibrium geometry for hydrogen peroxide is that obtained from the IR data of Redington, Olson, and Crossm on the assumption that r(OH) = 0.950 A. 09 this basis, Redington et al. obtain an r(OO) of 1.475 A and an angle LOOH of 94.8O. Using these parameters-which are consistent with the microwave spectrum of H O O H - a torsional angle of T = 119.8O was obtained by Oelfke and Gordy.4' However, in 1986 K o p ~ addressed t~~ the controversy over H202)s geometry (particularly in dispute is the torsional angle T ) by employing an ab initio/empirical harmonic force field determined by Botschwina, Meyer, and Semk0w,4~solving the corresponding SchrMinger equation, and fitting the experimental data directly in terms of the molecular parameters. In this manner, Koput obtained the following structure based on the assumption that the 0-H bond length is 0.965 A: r(O0) = 1.464 A, LOOH = 99.4O, and T = 111.8O. As can k seen from Table I, the latter two experimental angles match our theoretical results much more closely than do those of Redington et al. Our best structure also agrees qualitatively with the highest level equilibrium geometry reported in Harding's careful study?' For oxywater, our DZP/SCF 0-0 bond is predictedto be 1.602 A,a value that is similar to the 1.606 A obtained by Pople et al. at the HF/6-31G* level of theory.' Electron correlation, rather than (as is usually the case) lengthening the 0-0 bond, shortens it subetantially (-0.05 A at the CISD level). This fmding suggests that this structure is more tightly bound at higher levels of theory. Moreover, it is consistent with the fact that the inclusion of correlation is essential to the proper description of chemical bonds between atoms such as oxygen that are rich in lone pairs. The 0-H bond, on the other hand, increases progressively from the SCF to the CISD and the CCSD levels for each basis set, and the LOOH decreases concomitantly. The out-of-plane angledefined as the angle between the 0-0 vector and the HOH
p l a n e a l s o widens moderately with increasing levels of theory. The 0-0bond of the transition state, as expected, is lengthened (compared to oxywater) considerably by the [ 1,2]-hydrogen shift, but only at correlated levels of theory. In addition, the increasing O2-H' bond length is consistent with the migration of a hydrogen atom from the central oxygen of oxywater to the terminal oxygen. While the 0-Hbond lengths among the three species are similar, the critical 0-0bond length of the transition state is significantly closer to that of oxywater than of hydrogen peroxide. This latter observation is consistent with Hammond's postulate, which states that for an endothermic reaction (cf. Table V) the transition state resembles the products more closely than the reactants.u The theoretically predicted harmonic vibrational frequencies obtained for the three stationary points may be evaluated roughly according to the agreement between the theoretical frequencies for hydrogen peroxide and those obtained from experiment. A comparison of the experimental values with our most reliable theoretical harmonic vibrational frequencies (cf. Table 111) shows that, with the exception of the highly anharmonic torsional oscillation frequency, the experimental values are considerably lower. Scaling of the frequencies as discussed in the Methods section brings the 0-H stretches to within 4% of the experimental values, but the other frequencies (except for the torsion) still range from 2 to 11% too high. As made clear by Harding's high-level theoretical study2' of the H202vibrational frequencies, the experimental 550-cm-' torsional vibrational frequencySnow appears dubious. It is reasonable to assume that our unscaled theoretical harmonic vibrational frequencies for oxywater and the transition state are too high. Taking this factor into account, we note that, with the exception of the imaginary frequency of the transition state, all of the theoretical frequencies for both molecules still are sufficiently positive that increasing levels of theory would not be expected to eliminate them entirely; i.e., oxywater is a genuine minimum. In general, the theoretical frequencies are consistent with the geometry changes that occur over the course of the [ 1,2]-hydmgen shift. A notable exception to this trend is the 0-0 stretch, which increases by 13 cm-l (DZP/CISD) in forming the transition state even though the 0-0 bond in the latter is 0.066 A longer. The large imaginary frequency w6 of the transition state corresponds to the attenuation of the bond between the migrating hydrogen and the central oxygen of oxywater. The relative energetics for the three stationary points (cf. Table V) are reasonably consistent at correlated levels of theory and confirm that hydrogen peroxide, as expected, lies well below the "abnormal valent" oxywater (AE = 46.7 at the TZ2P+f/ CCSD(T) level). It is also observed that, even at our highest level of theory, the classical barrier to H200-HOOH isomerization is a substantial 5.7 kcal mol-'. The addition of scaled ZPVEs, however, lowers this barrier to 2.9 kcal mol-' (with SCF amection) or 3.2 kcal mol-' (with CISD correction). This latter value is estimated to be no more than 2 kcal mol-' above the true
TABLE I V Absolute Energies (in au) for Oxywater, Tramition State, and Hydrogen Peroxide' DZP TZ2P+f species SCF CISD CISD+Q CCSD CCSD(T) SCF CISD CISD+Q CCSD CCSD(T) oxywater -150.755 34 -151.094 89 -151.126 38 -151.124 87 -151.13426 -1 50.781 26 -151.225 44 -151.267 43 -151.265 82 -151.283 73 Ts -150.724 36 -1 5 1.08068 -151 . I 16 75 -1 51 . I 14 66 -1 51.127 13 -1 50.749 79 -1 51.208 32 -1 5 1.25467 -1 51.252 94 -1 51.274 71 peroxide -150.818 73 -151.170 33 -151.202 87 -151.201 44 -151.21049 -150.845 81 -1 51.299 59 -151.342 12 -151.34029 -151.358 21
"The CCSD(T) energy is at the optimized CCSD geometry obtained with the same basis set. TABLE V E"ka (in kerl mol-') for the T d t i o a State aod Hydronea Peroxide, Relative to Oxwater" DZP TZZP+f - -~ spccies SCF CISD CISD+Q CCSD CCSD(T) SCF CISD CISD+Q 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 oxywater 8.0 19.7 10.7 6.4 4.5 8.9 6.0 Ts 19.4 46.9 -40.5 -46.5 -48.0 -48.0 -47.8 -39.8 -47.3 peroxide
CCSD 0.0 8.1 -46.7
CCSD(T) 0.0 5.7 -46.7
'The CCSD(T) energy is at the optimized CCSD geometry obtained with the same basis set. Zero-point vibrational energy corrections arc not included in this table.
9254 The Journal of Physical Chemistry, Vol. 96, No. 23, 1992
Meredith et al.
(6) Massey, J. T.; Bianco, D. R. J. Chem. Phys. 1954,22, 442. (7) Massey, J. T.;Hart, R. W. J. Chem. Phys. 1955,23, 942. (8) Hunt, R. H.; Leacock, R. A,; Peters, C. W.; Hecht, K. T. J. Chem. Concluding Remuks Phys. 1965,42,1931. The results of our high-level theoretical study are internally (9)Busing, W. R.; Levy, H. A. J. Chem. Phys. 1%5,42, 3054. (10)Hunt, R. H.; Leacock, R. A. J. Chem. Phys. 1966,45,3141. consistent and lend solid support to the findings of Bach et al.'.2 (1 1) GiguCre, P. A,; Srinivasan,T. K. K. J. Mol. Specrrosc. 1977,66,168. concerning the existence and kinetic stability of oxywater, a hy(12) Cremer, D.;Christen, D. J . Mol. Spectrwc. 1979,74,480. pervalent isomer generated from the [ 1,2]-hydrogen shift of hy(13)Hillman, J. J.; Jennings, D. E.; Olson, W. B.; Goldman, A. J . Mol. drogen peroxide. However, while the differencesbeween our work Spectrosc. 1986,I 17,46. (14)Dunning, T.H.,Jr.; Winter, N. W. Chem. Phys. Lerr. 1971,II, 194. and that of Bach et al. are minor, the present study of the mo(15) Ranck, J. P.; Johansen, H. Theor. Chim. Acta 1972,24, 334. lecular structures and energetics of the hydrogen peroxide (16)Ryan, P. B.; Todd, H. D. J. Chem. Phys. 1977,67,4787. [ 1,2]-hydrogen shift has been carried out at significantly more (17) Cremer, D. J . Chem. Phys. 1978,69,4440. trustworthy levels of approximation. Moreover, this study is the (18) DeFrees, D. J.; Levi, B. A,; Pollack, S.K.; Hehre, W. J.; Binkley, J. S.;Pople, J. A. J. Am. Chem. Soc. 1979,101, 4085. first to predict harmonic vibrational frequencies, which should (19) Bair, R. A.; Goddard, W. A., 111J. Am. Chem. Soc. 1982,101,2719. greatly facilitate identifkation. Thus, given this new information, (20) Hout, Jr., R. F.; Levi, B. A.; Hehre, W. J. J . Compur. Chem. 1982, the experimentalist may now proceed to search for oxywater with 3, 234. confidence. (21) Block, R.; Jansen, L. J . Chem. Phys. 1985,82,3322. Oxywater is predicted to lie 46.7 kcal mol-' above hydrogen (22)Hougen, J. T.Can. J . Phys. 1984,62,1392. (23)Aida, M.; Nagata, C. Theor. Chim. Acta 1986, 70,73. peroxide and on this basis must be regarded as thermodynamically (24)Politzer, P.; Bar-Adon, R.; Miller, R. S.J. Phys. Chem. 1987,91, unstable with respect to HOOH. The classical barrier for the 3191. oxywater-hydrogen peroxide isomerization is 5.7 kcal mol-' at (25)Christen, D.; Nack, H.-G.; Oberhammer, H. Tetrahedron 1988,44, the TZZP+f/CCSD(T) level of theory. The analogous ground7363. (26)Valtazanos, P.;Simandiras,, E. D.; Nicolaides, C. A. Chem. Phys. state activation energy for this isomerization is 3.2 kcal mol-'. Lett. 1989,156, 240. Oxywater may be compared with k 'Al vinylidene (H,CC) in (27)Harding, L. B. J . Phys. Chem. 1989,93,8004. that both are tetratomic species generated from a [ 1.21-hydrogen (28)Bain. 0.; Giguare, P. A. Can. J . Chem. 1955,33,527. (29)Pulay, P. Modern Theoretical Chemistry; Schaefer, H. F., Ed.; Pleshift of a stable and well-characterized structural isomernum: New York, 1977;pp 153-185. hydrogen peroxide in the former case and acetylene in the latter. (30)Brooks, B. R.; Laidig, W. D.; Saxe, P.; Goddard. J. D.; Yamaguchi, On the basis of rigorous geometry optimizations at the TZZP/ Y.;Schaefer, H. F. J. Chem. Phys. 1980,72,4625.Rice, J. E.;Amos, R. D.; CCSD level of theory, Gallo, Hamilton, and S ~ h a e f e recently r~~ Handy, N. C.; Lee., T. J.; Schaefer, H. F. J . Chem. Phys. 1986,85, 963. (31) Scheiner, A. C.;Scuseria, G. E.; Lee, T. J.; Rice, J. E.; Schaefer, H. predicted a classical barrier to rearrangement of 6.1 kcal mol-' F. J. Chem. Phys. 1987,87,5361. for the vinylideneacetylene [ 1,2]-hydrogen shift. Evaluation of (32) Pople, J. A.; Krishnan, R.; Schlegel, H. B.; Binkley, J. S. h t . J. TZZP/CCSDT- 1 single-point energies at the TZ2P/CCSD geQuantum Chem. 1975,S13,225.Saxe, P.; Yamaguchi, Y.; Schaefer, H. F. ometries lowered the barrier to 4.9 kcal mol-', a value 0.8 kcal J . Chem. Phys. 1982, 77, 5647. Osamura, Y.; Yamaguchi, Y.; Saxe, P.; mol-' below that obtained for the oxywater rearrangement. InVincent, M. A.; Gaw, J. F.; Schaefer, H. F. Chem. Phys. 1982, 72, 131. (33) Grev, R. S.;Janssen, C. L.; Schaefer, H. F. J. Chem. Phys. 1991,95, corporation of mepoint energy corrections for both isomerizations 5128. yields ab initio activation energies of -2.0 kcal mol-'; conse(34) Besler, B. H.;Scuseria, G. E.; Scheiner, A. C.; Schaefer, H. F. J . quently, we may conclude that oxywater should be about as tightly Chem. Phys. 1988.89, 360. (35) Scuseria, G. E. Chem. Phys. Lerr. 1991, 176, 27. bound as vinylidene. Given that Lineberger and co-w~rkers~.~' (36)Langhoff, S.R.; Davidson, E. R. Inr. J . Quantum Chem. 1974,8,61. were able to observe k 'Al vinylidene by means of ultraviolet (37)Huzinaga, S.J. Chem. Phys. 1965,42,1293. photoelectron spectroscopy, it indeed seems likely that oxywater, (38)Dunning, Jr., T.H. J . Chem. Phys. 1970. 53, 2823. the [1,2]-hydmgen-~hiftedisomer of hydrogen peroxide, may soon (39)Dunning, Jr., T.H. J . Chem. Phys. 1971,55, 716. (40)Redington, R. L.; Olson,W. B.; Cross, P. C. J. Chem. Phys. 1962, be detected as well. 36, 1311. Acknowledgment. This research was supported by the US. (41) Oelflte, W. C.; Gordy, W. J . Chem. Phys. 1969,51,5336. (42) Koput, J. J. Mol. Spectrosc. 1986,115, 438. National Science Foundation, Grant CHE-8718469. We thank (43) Botschwina, P.;Meyer, W.; Semkow, A. M. Chem. Phys. 1976,15, Charlene L. Collins and Dr. Geoffrey E. Quelch for helpful 25. discussions. (44)Hammond, G. S.J . Am. Chem. Soc. 1955,77, 334. (45)Gallo, M. M.; Hamilton, T. P.; Schaefer, H. F. J . Am. Chem. Soc. References and Notes 1990, 112,8714. (46) Burnett, S. M.; Stevens, A. E.; Feigerle, C. S.;Lineberger, W. C. (1) Bach, R. D.; McDouall, J. J. W.; Owensby, A. 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ground-state activation energy for this isomerization.
