Papers by Joseph Bozzelli
Thermo, Mar 2, 2021
Structures, thermochemical properties, bond energies, and internal rotation potentials of acetic ... more Structures, thermochemical properties, bond energies, and internal rotation potentials of acetic acid hydrazide (CH 3 CONHNH 2 ), acetamide (CH 3 CONH 2 ), and N-methyl acetamide (CH 3 CONHCH 3 ), and their radicals corresponding to the loss of hydrogen atom, have been studied. Gas-phase standard enthalpies of formation and bond energies were calculated using the DFT methods B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p) and the composite CBS-QB3 methods employing a series of work reactions further to improve the accuracy of the ∆H f • (298 K). Molecular structures, vibration frequencies, and internal rotor potentials were calculated at the DFT level. The parent molecules' standard formation enthalpies of CH 3 -C=ONHNH 2 , CH 3 -C=ONH 2, and CH 3 -C=ONHCH 3 were evaluated as -27.08, -57.40, and -56.48 kcal mol -1 , respectively, from the CBS-QB3 calculations. Structures, internal rotor potentials, and C-H and N-H bond dissociation energies are reported. The DFT and the CBS-QB3 enthalpy values show close agreement, and this accord is attributed to the use of isodesmic work reactions for the analysis. The agreement also suggests this combination of the B3LYP/work reaction approach is acceptable for larger molecules. Internal rotor potentials for the amides are high, ranging from 16 to 22 kcal mol -1 .
Combustion Science and Technology, 2018
Several chemical reactions related to the oxidation and combustion of sulfur are investigated usi... more Several chemical reactions related to the oxidation and combustion of sulfur are investigated using a number of computational chemistry methods with the objective of determining appropriate methods for use in developing an elementary reaction mechanism for oxidation of sulfur. Calculations are focused on thermochemical properties and reaction energetics for reactive species and transition state structures for reactions in the oxidation/combustion of sulfur. Reactions involving several intermediates resulting from the reactions of S 2 with oxygen were investigated with the density functional theory B3LYP (with several basis sets) and BB1K/GTLarge. The composite ab-initio methods G2, G3, G3MP2, G3B3, G3MP2B3 and CBS-QB3 were also used. Enthalpies of a series of sulfur compounds and transition state structures are calculated using the ab-initio and DFT calculations. The calculations were combined with isodesmic reaction analysis, whenever possible, in order to cancel error and improve the accuracy of the calculations. Results show that all B3LYP DFT calculations including the 6-311++G(3df,2p) basis set show poor outcome in estimating the enthalpy of reactions involving S 2 . The six composite methods have all shown consistency with each other and their calculated reaction energies/bond energies are in good agreement with the available literature. Kinetic parameters for calculation of the kinetic parameters on SO 3 dissociation to SO 2 and O using the canonical transition state theory are reported.
The Journal of Physical Chemistry A, 1998
Ab initio calculations are performed on nine fluorinated ethane compounds and thermodynamic prope... more Ab initio calculations are performed on nine fluorinated ethane compounds and thermodynamic properties (S°2 98 and C p (T)'s 300 < T/K < 1500) are calculated. Geometries of stable rotational conformers and transition states for internal rotation are optimized at the RHF/6-31G* (6-31G(d)) and MP2/6-31G* levels of theory. Harmonic vibrational frequencies are computed at the RHF/6-31G* level of theory. Potential barriers for internal rotations are calculated at the MP2/6-31G*//MP2/6-31G* level. Parameters of the Fourier expansion of the hindrance potential are tabulated. Standard entropies (S°2 98 ) and heat capacities (C p (T)'s, 300 < T/K < 1500) are calculated using the rigid-rotor-harmonic-oscillator approximation with direct integration over energy levels of the intramolecular rotation potential energy curve. Heats of formation are adopted from literature evaluation and BAC-MP4 ab initio calculations. Thermodynamic properties for fluorinated carbon groups C/C/F/H2, C/C/F2/H, and C/C/F3 are determined by existing thermodynamic group parameter of C/C/H3 and data on CH 2 FCH 3 , CHF 2 CH 3 , and CF 3 CH 3 , respectively: no fluorine or other halogen is on the methyl carbon adjacent to the carbon bonded to the fluorine(s). Six interaction terms in addition to the above groups are developed to account for repulsion and steric effects. Interaction terms are required to accurately estimate ∆H f °298 , S°2 98 , and C p (T)'s (300 < T/K < 1500) for fluoroethanes where fluorine(s) are on carbons adjacent to a carbon bonded to fluorine(s). entropies (S°2 98 ) and heat capacities (C p (T)'s, 300 < T/K < 1500) are calculated using the rigid-rotor-harmonic-oscillator approximation on the basis of the information obtained from the ab initio studies.
The Journal of Physical Chemistry A, 1999
are calculated using ab initio methods. Enthalpies of formation (∆H f °298 in kcal/mol) for the a... more are calculated using ab initio methods. Enthalpies of formation (∆H f °298 in kcal/mol) for the above eight compounds are estimated using the G2MP2 composite calculation method and isodesmic reactions. Entropies (S°2 98 in cal mol -1 K -1 ) and heat capacities (C p (T) in cal mol -1 K -1 ) are estimated using HF/6-31G(d) determined frequencies and MP2(full)/6-31G(d) determined geometries. ∆H f °298 for the above compounds
We analyze the iso-propyl + O2 reaction system using thermochemical ki Transition State Theory (T... more We analyze the iso-propyl + O2 reaction system using thermochemical ki Transition State Theory (TST), molecular thermodynamic properties, qua analysis (quantum RRK) for k(E) and modified strong collision analysis Cyclic transition states for both hydrogen transfer and concerted elimi propylene from isopropylperoxy are calculated using semi-empirical (MOP theory in addition to transition states for HO2 elimination and epoxid from hydroperoxy-isopropyl. Computed rate constants are compared to th constant measurements of Gulati and Walker (1988) for isopropyl + O2 => HO2.
The Phenyl + Oâ association results in a chemically activated phenyl-peroxy radical which can dis... more The Phenyl + Oâ association results in a chemically activated phenyl-peroxy radical which can dissociate to phenoxy radical + O, undergo intramolecular addition of the peroxy radical to several unsaturated carbon sites or react back to phenyl + Oâ. The intramolecular addition channels further react through several paths to ring opening (unsaturated + carbonyl moieties) as well as cyclopentadieny radical
ChemInform Abstract: Hydrocarbon Radical Reactions with O2: Comparison of Allyl, Formyl, and Vinyl to Ethyl
ChemInform, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The Journal of Physical Chemistry A, 2000
Kinetics for the reactions of allylic isobutenyl radical (C-C(C)-C) with molecular oxygen are ana... more Kinetics for the reactions of allylic isobutenyl radical (C-C(C)-C) with molecular oxygen are analyzed by using quantum Rice-Ramsperger-Kassel (QRRK) theory for k(E) and master equation analysis for falloff. Thermochemical properties and reaction path parameters are determined by ab initio-Møller-Plesset (MP2-(full)/6-31g(d) and MP4(full)/6-31g(d,p)//MP2(full)/6-31g(d)), complete basis set model chemistry (CBS-4 and CBS-q with MP2(full)/6-31g(d) and B3LYP/6-31g(d) optimized geometries), and density functional (B3LYP/6-31g(d) and B3LYP/6-311+g(3df,2p)//B3LYP/6-31g(d)) calculations. An elementary reaction mechanism is constructed to model the experimental system, isobutene oxidation. The forward and reverse rate constants for initiation reaction C 2 CdC + O 2 T C-C(C)-C + HO 2 are determined to be 1.86 × 10 9 T 1.301 exp(-40939 cal/RT) (cm 3 mol -1 s -1 ) and 6.39 × 10 8 T 0.944 exp(-123.14 cal/RT) (cm 3 mol -1 s -1 ), respectively. Calculations on 2,5-dimethylhexa-1,5-diene, methacrolein, isobutene oxides, and acetone product formation from reaction of isobutene oxidation mechanism are compared with experimental data. Reaction of allylic isobutenyl radical + O 2 forms an energized peroxy adduct [CdC(C)COO‚]* with a shallow well (ca. 21 kcal/mol), which predominantly dissociates back to reactants. The reaction channels of the CdC(C)-COO‚* adduct include reverse reaction to reactants, stabilization to CdC(C)COO‚ radical, O-O bond fission to CdC(C)CO‚ + O, isomerization via hydrogen shift with subsequent β-scission or R‚O-OH bond cleavage. The CdC(C)COO‚* adduct can also cyclize to four-or five-member cyclic peroxide-alkyl radicals. All the product formation pathways of allylic isobutenyl radical with O 2 involve barriers that are above the energy of the initial reactants. This results in formation of isomers that exist in steady state concentration at early time in oxidation, at low to moderate temperatures. The primary reaction is reverse dissociation back to reactants, with slower reactions from the distributed isomers to new products. The concentration of allylic isobutenyl radical accumulates to relatively high levels and the radical is consumed mainly through radicalradical processes in moderate temperature isobutene oxidation. Reactions of CdC(C)COO‚ cyclization to four or five-member cyclic peroxides require relative high barriers due to the near complete loss of π bond energy for the terminal double bond's twist needed in the transition states. These barriers are calculated as 28. 02 (24.95) and 29.72 (27.98) kcal/mol at CBS-q//MP2(full)/6-31g(d) level with A factors of 2.42 × 10 10 (3.28 × 10 10 ) and 3.88 × 10 10 (6.09 × 10 10 ) s -1 at 743 K, respectively, for four-and five-member ring cyclization. Data in parentheses are calculation at B3LYP/6-311+g(3df,2p)//B3LYP/6-31g(d). A new reaction path is proposed: CdC(C‚)COOH T CdC(C‚)CO‚ + OH T CdY(CCOC) + OH, which is responsible for methylene oxirane formation (Y ) cyclic). The reaction barrier for the CdC(C‚)COOH reaction to CdC(C‚ )CO‚ + OH is evaluated as 42.45 (41.90) kcal/mol with an A factor of 4 × 10 15 s -1 . The reaction barrier of CdC(C‚)COOH f TS5 f CdY(CCOC) + OH is calculated as 42.14 kcal/mol with an A factor of 6.95 × 10 11 s -1 at 743 K.
The Journal of Physical Chemistry A, 2012
Molecular hydrogen plays multiple roles in activation of nitrogen. Among others, it inhibits the ... more Molecular hydrogen plays multiple roles in activation of nitrogen. Among others, it inhibits the overall process of N 2 -reduction catalyzed by nitrogenase enzyme. The H 2 -assisted dehydrogenation and the H-atom transfer reactions (called dihydrogen catalysis, DHC) are suggested as possible mechanisms for the degradation and removal of potential intermediates formed during the reduction of nitrogen. Several iron-organic model reactions associated with the core stereospecific reaction (cis-N 2 H 2 + H 2 → N 2 + H 2 + H 2 ) are examined using a comprehensive density functional theory and ab initio analysis of the corresponding potential energy surfaces. A variety of energetically feasible decomposition pathways are identified for the DHC-oxidation of ironbound [N x H y ]-species. A liberated diazene intermediate (HNNH) is suggested to interact in situ with two proximal hydridic H-atoms of an activated (hydrided) Fe-catalyst to produce N 2 and H 2 with a low or even no activation barrier. The majority of identified pathways are shown to be highly sensitive to the electronic environment and spin configuration of metallocomplexes. The H 2 -assisted transport of a single H-atom from a bound [N x H y ] moiety to either the proximal or distal (Fe, S or N) active centers of a catalyst provides an alternative degradation (interconversion) mechanism for the relevant intermediates. The two types of molecular hydrogen-assisted reactions highlighted above, namely, the H 2 -assisted dehydrogenation and the transport of H-atoms, suggest theoretical interpretations for the observed H 2 -inhibition of N 2 activation and HD formation (in the presence of D 2 ). The DHC reactions of various [N x H y ] moieties are expected to play significant roles in the industrial high-pressure hydrodenitrification and other catalytic processes involving the metabolism of molecular hydrogen.
The Journal of Physical Chemistry A, 1999
There are two different carbon sites in C 2 H 3 Cl where OH addition or abstraction reactions can... more There are two different carbon sites in C 2 H 3 Cl where OH addition or abstraction reactions can occur, R and β to the Cl atom, with several dissociation and isomerization products of each addition adduct. Thirteen elementary reactions and 18 species are included in the analysis of this reaction system. Thermochemical kinetic parameters are developed for each elementary reaction process. Chemical activation kinetic analysis with multifrequency QRRK theory for k(E) and master equation for falloff are used to estimate overall rate constants as functions of temperature and pressure. Thermodynamic parameters, including ∆H f °298 , S°2 98 , and C p °(T) (300 e T/K e 1500), of stable species are from the literature when available or estimated by the group additivity method. Values for CHClOHC 4 H 2 are determined by density functional calculation and isodesmic reactions. Results are compared with the experimental data. Rate constants (300∼2000 K, in cm 3 mol -1 s -1 , E a in cal/mol) for the important addition and abstraction channels at 760 Torr are as follows: k ) 1.22 × 10 84 T -25.5 exp(-15000/RT) for C 2 H 3 Cl + OH f CHClOHC 4 H 2 ; k ) 1.77 × 10 40 T -9.08 exp(-7240/ RT) for C 2 H 3 Cl + OH f C 4 HClCH 2 OH; k ) 9.72 × 10 6 T 2 exp(-3800/RT) for C 2 H 3 Cl + OH f CH 2 dC 4 Cl + H 2 O; k ) 1.69 × 10 7 T 2 exp(-4390/RT) for C 2 H 3 Cl + OH f C 4 HdCHCl + H 2 O.
The Journal of Physical Chemistry A, 1998
Reaction pathways and kinetics for cyclopentadienyl radical association with H, OH, HO 2 , O, and... more Reaction pathways and kinetics for cyclopentadienyl radical association with H, OH, HO 2 , O, and O 2 are presented in the temperature range 900-1300 K and atmospheric pressure. Thermochemical data for reactants, intermediate, and product species are evaluated from literature data and from group additivity with hydrogen bond increments. High-pressure limit rate constants for the radical combination reactions and decomposition of the energized adducts are estimated. Pressure-dependent rate constants for each channel in the reaction systems are calculated using bimolecular quantum Rice Ramsperger Kassel, QRRK, for k(E) with a modified strong collision approach for falloff. A submechanism of important cyclopentadienyl radical reactions is assembled and tested in an elementary reaction model for combustion of benzene, where the cyclopentadienyl radical is a key intermediate in the stepwise (C6 f C5 f C4) decomposition. Modeling results are compared with limited literature data on species profiles for appropriate reaction systems, where benzene, cyclopentadiene, and carbon monoxide are the initial fuel, observed intermediate, and major combustion product, respectively. H atom association with cyclopentadienyl radical (CY13PD5 • ) leads to stabilized cyclopentadiene (CY13PD) as the primary product, with linear pentadienal diradical as a minor product. The hydroxyl association with cyclopentadienyl radical forms an energized adduct, which primarily rearranges to cyclopentadienol isomers, which are stabilized. O (3p) association with cyclopentadienyl radical leads to two main product sets: cyclopentadienone plus H atom or 1,3-butadienyl radical plus carbon monoxide. Hydroperoxy radical combination with cyclopentadienyl radical forms an energized hydroperoxy-cyclopentadiene, which can dissociate to lower energy products cyclopentenoxy radical plus OH, to cyclopentadienone + H 2 O, or back to the initial reactants. Oxygen molecule addition to cyclopentadienyl radical forms an energized cyclopentadiene peroxy radical with a very shallow well (ca. 13 kcal/mol), which predominantly dissociates back to reactants. A small, but important, fraction of the energized peroxy adduct undergoes reactions that lead to ring-opening with formation of resonance-stabilized 2-pentenedialdehyde radical or vinyl ketene and formyl radical. These reactions provide paths for cyclopentadienyl radical conversion to linear, unsaturated, oxyhydrocarbons.
The Journal of Physical Chemistry A, 2002
Thermochemical properties for reactants, intermediates, products, and transition states important... more Thermochemical properties for reactants, intermediates, products, and transition states important in the acetyl radical (CH 3 C • (dO)) + O 2 reaction system are analyzed with density functional and ab initio calculations, to evaluate reaction paths and kinetics in both oxidation and pyrolysis. Enthalpies of formation (∆H°f ,298 ) are determined using isodesmic reaction analysis at the CBSQ composite and density functional levels. Entropies (S°2 98 ) and heat capacities (C°p(T)) are determined using geometric parameters and vibrational frequencies obtained at the HF/6-31G(d′) level of theory. Internal rotor contributions are included in S and C p (T) values. The acetyl radical adds to O 2 to form a CH 3 C(dO)OO • peroxy radical with a 35 kcal/mol well depth. The peroxy radical can undergo dissociation back to reactants, decompose to products, CH 2 CdO + HO 2 via concerted HO 2 elimination (E a ) 34.58 kcal/mol), or isomerize via hydrogen shift (E a ) 26.42) to form a C • H 2 C(dO)OOH isomer. This C • H 2 C(dO)OOH isomer can undergo β scission to products, CH 2 CdO + HO 2 (E a ) 31.41), decompose to a cyclic ketone, YCOC(dO) + OH via OH elimination (E a ) 19.97, Y ) cyclic), decompose to a diradical, C • H 2 CO(O • ) + OH via simple RO-OH bond cleavage (E a ) 27.57), or isomerize back to the CH 3 C(dO)OO • isomer. Rate constants are estimated as function of pressure and temperature using quantum Rice-Ramsperger-Kassel analysis for k(E) and master equation for falloff. Important reaction products are stabilization of CH 3 C(dO)OO • peroxy adduct at low temperature and, at higher temperatures, formation of a diradical, C • H 2 CO(O • ), + OH and CH 2 CdO + HO 2 are dominant. ∆H°f ,298 values are estimated for the following compounds at the CBSQ level: (kcal/mol) CH 3 C • (dO) (-3.08), C • H 2 CHO (3.52), CH 3 C(dO)OOH (-84.80), CH 3 C(dO)OO • (-38.57), C • H 2 C(dO)OOH (-32.95), and YCOC(dO) (-44.42). A mechanism for pyrolysis and oxidation of the acetyl radical is constructed. Reaction of acetyl with O 2 versus unimolecular decomposition is evaluated versus temperature and pressure. Related oxygen bonds in acetyl hydroperoxide are predicted to be stronger than corresponding bonds in alkyl hydroperoxide.
The Journal of Physical Chemistry A, 2010
Acrolein, a β-unsaturated (acrylic) aldehyde, is one of the simplest multifunctional molecules, c... more Acrolein, a β-unsaturated (acrylic) aldehyde, is one of the simplest multifunctional molecules, containing both alkene and aldehyde groups. Acrolein is an atmospheric pollutant formed in the photochemical oxidation of the anthropogenic VOC 1,3-butadiene, and serves as a model compound for methacrolein (MACR) and methyl vinyl ketone (MVK), the major oxidation products of the biogenic VOC isoprene. In addition, acrolein is involved in combustion and biological oxidation processes. This study presents a comprehensive theoretical analysis of the acrolein + OH + O 2 addition reactions, which is a key photochemical oxidation sequence, using the G3SX and CBS-QB3 theoretical methods. Both ab initio protocols provide relatively similar results, although the CBS-QB3 method systematically under-predicts literature heats of formation using atomization enthalpies, and also provides lower transition state barrier heights. Several new low-energy pathways for unimolecular reaction of the acrolein-OH-O 2 radicals are identified, with energy at around or below that of the acrolein-OH isomers + O 2 . In each case these novel reactions have the potential to reform the hydroxyl radical (OH) and form coproducts that include glyoxal, glycolaldehyde (HOCH 2 CHO), formaldehyde (HCHO), CO, and substituted epoxides. Analogous reaction schemes are developed for the photochemical oxidation of MACR and MVK, producing a number of observed oxidation products. The reaction MACR + OH + O 2 f hydroxyacetone + OH + CO is expected to be of particular importance. This study also proposes that O 2 addition to chemically activated acrolein-OH adducts can provide prompt regeneration of OH in the atmospheric oxidation of acrolein, via a double activation mechanism. This mechanism can also be extended to isoprene, MVK, and MACR. The importance of the novel chemistry revealed here in the atmospheric oxidation of acrolein and other structurally related OVOCs and VOCs requires further investigation. Additionally, a critical evaluation of the acrolein heat of formation is presented, and a new value of -16.7 ( 1.0 kcal mol -1 is recommended along with other thermochemical properties, from a W1 level calculation.
The Journal of Physical Chemistry A, 1997
Alkyl peroxides, trioxides, and the corresponding radicals are important in atmospheric chemistry... more Alkyl peroxides, trioxides, and the corresponding radicals are important in atmospheric chemistry, photochemical smog formation, and combustion processes, but accurate and widely accepted enthalpy data for these species are not available. In this work we verify enthalpy data for several compounds and derive the corresponding group values for use in the group additivity method. Isodesmic reactions and ab initio calculations (MP4SDTQ/6-31G*//MP2/6-31G* and G2) are used to determine enthalpies of formation for the following compounds (in kcal mol -1 ): CH 3 OOH (-31.8), C 2 H 5 OOH (-39.9), iPrOOH (iPr ) (CH 3 ) 2 -CH-, -49.0), (CH 3 ) 3 COOH (tBu ) (CH 3 ) 3 C-, -58.4), iPrOO• (-15.1), tBuCOO• (-25.2), CH 3 OOCH 3 (-31.0), C 2 H 5 OOC 2 H 5 (-47.2), iPrOOiPr, (-65.4), tBuOOtBu (-84.2), HOOOH (-23.0), CH 3 OOOH (-22.2), CH 3 OOOCH 3 (-21.4). Our results on isodesmic reactions indicate that group additivity is an accurate method to estimate enthalpies (∆H f °298 ) of alkyl peroxides and trioxides. Bond enthalpies are determined as follows: HOOO-H (82.6), CH 3 O 2 -H (86.6), C 2 H 5 O 2 -H (86.1), iPrO 2 -H (86.0), tBuO 2 -H (85.3), HOO-OH (35.8), CH 3 O-OCH 3 (38.8), CH 3 OO-OH (34.2), CH 3 O-OOH (29.6), CH 3 O-OOCH 3 (28.0), iPr-OO (36.6), tBu-OO (37.5). The recommended enthalpy group values of (O/C/O) and (O/O 2 ) are -5.5 and 9.6 kcal mol -1 , respectively.
The Journal of Physical Chemistry A, 1997
Ideal gas thermodynamic properties (∆H f °298 , S°2 98 , and C p (T), 300 e T/K e 1500) for 34 cy... more Ideal gas thermodynamic properties (∆H f °298 , S°2 98 , and C p (T), 300 e T/K e 1500) for 34 cyclic oxygenated hydrocarbons are calculated using the PM3 method, including 12 species on which data are not previously reported. Enthalpies of formation obtained using PM3 are further corrected by -1.642 + 0.882∆H f °298,PM3 , which is obtained by comparison to experimentally-determined ∆H f °298 of 10 cyclic oxygenated hydrocarbon molecules. Enthalpies of formation (∆H f °298 , in kcal mol -1 ) and entropy (S°2 98 , in cal mol -1 K -1 ) for 12 species are calculated as follows:
The Journal of Physical Chemistry A, 1999
The reaction systems tert-butyl radical + O 2 , isobutene + HO 2 , isobutene + OH, and isobutene-... more The reaction systems tert-butyl radical + O 2 , isobutene + HO 2 , isobutene + OH, and isobutene-OH adducts + O 2 , which are important to understanding the oxidation chemistry of tertiary butyl radical (C 3 C • ), are analyzed. Thermochemical parameters are determined by ab initio-Mφller-Plesset (MP2(full)/6-31g(d)), complete basis set model chemistry (CBS-4 and CBS-q with MP2(full)/6-31g(d) and B3LYP/6-31g(d) optimized geometries), density functional (B3LYP/6-31g(d)), semiempirical MOPAC (PM3) molecular orbital calculations, and by group additivity estimation. Thermochemical kinetic parameters are developed for each elementary reaction path in these complex systems, and a chemical activation kinetic analysis using quantum Rice-Ramsperger-Kassel (QRRK) theory for k(E) and master equation analysis for falloff is used to calculate rate constants as a function of pressure and temperature. An elementary reaction mechanism is constructed to model experimental data for oxidation of tert-butyl radical. Calculations for loss of tert-butyl precursor, 2,2,3,3-tetramethylbutane (C 3 CCC 3 ), and production of isobutene and 2,2-dimethyloxirane from the mechanism are compared with experimental data reported in the literature. Reaction of tert-butyl radical (C 3 C • ) with O 2 forms an energized tert-butyl peroxy adduct C 3 COO • * which can dissociate back to reactants, dissociate to isobutene + HO 2 , or isomerize to tert-butyl hydroperoxide (C 3 • COOH). This isomer can dissociate to either isobutene + HO 2 or 2,2-dimethyloxirane + OH, before it is stabilized. In the tert-butyl radical + O 2 reaction system, dissociation of the [C 3 COO • ]* adduct to isobutene + HO 2 via HO 2 molecular elimination is faster than the hydrogen shift to C 3 • COOH by a factor of 86:1 at 773 K and 60 Torr. The reaction barrier (reaction enthalpy difference between TS4 and C 3 • COOH) for the C 3 • COOH reaction to 2,2-dimethyloxirane + OH is calculated as 17.98 (19.06) kcal/mol at the CBS-q//MP2(full)/6-31g(d) level but is evaluated as 15.58 (18.06) kcal/mol by fitting experimental data. Data in parentheses are thermodynamic properties based on CBS-q//B3LYP/6-31g(d) calculation. Barriers for reactions of HO 2 + isobutene f C 3 • COOH (HO 2 addition at CD/C2 carbon atom of isobutene, CD ) carbon double bond) and HO 2 + isobutene f C 2 C • COOH (HO 2 addition at CD/H2 carbon atom of isobutene) are respectively determined as 7.74 (7.38) and 10.69 (10.82) kcal/mol. 2,2-Dimethyloxirane is formed primarily by HO 2 addition to isobutene. OH addition to isobutene results in adducts which further react with O 2 to form acetone, formaldehyde, and the OH radical (Waddington mechanism) with these pathways also analyzed. O2 B3LYP -150
The Journal of Physical Chemistry A, 2002
Chlorinated formyl methyl radicals (C • CdO) are the stable keto forms of chlorovinoxy radicals f... more Chlorinated formyl methyl radicals (C • CdO) are the stable keto forms of chlorovinoxy radicals formed by cleavage or abstraction of the weak O-H bonds of chlorovinyl alcohols. Thermochemical properties, ∆H f °298 , S°2 98 , and C p °(T) (5 K e T e 6000 K), are computed by density functional B3LYP/6-31G(d,p) and B3LYP/ 6-311+G(3df,2p), ab initio QCISD(T)/6-31G(d,p), and composite CBS-Q calculation methods for chlorinated aldehydes and the corresponding chlorinated acetyl and formyl methyl radicals: CCldO (20). Molecular structures and vibration frequencies are determined at the B3LYP/6-31G(d,p) level of theory. Vibration frequencies are scaled for zero-point energies and thermal corrections. Two to four isodesmic reactions are utilized at each calculation level to determine ∆H f °298 of each species. Contributions to S°2 98 and C p °(T) from translation, vibration, and external rotations are calculated using the rigid-rotor-harmonic-oscillator approximation based on the B3LYP/6-31G(d,p) structures. Hindered internal rotational contributions to entropies and heat capacities are calculated by summation over the energy levels obtained from direct diagonalizations of the Hamiltonian matrix of the internal rotation. The bond energies of C-H and C-Cl in chloroaldehydes are also calculated.
The Journal of Physical Chemistry A, 2000
Chlorinated methyl hydroperoxides are important intermediates in the oxidation, combustion, and a... more Chlorinated methyl hydroperoxides are important intermediates in the oxidation, combustion, and atmospheric photochemistry of chlorocarbons. The thermochemical property data on these oxy-chlorocarbon species are important for understanding their stability, reaction paths, and kinetics. Enthalpy, ∆H f °298 , entropy, S°2 98 , and heat capacities, C p (T) (300 e T/K e 1500), are determined for monochloromethyl hydroperoxide, dichloromethyl hydroperoxide, and trichloromethyl hydroperoxide using density functional B3LYP/6-31 G(d,p), and B3LYP/6-311+G(3df,2p), ab initio QCISD(T)/6-31G(d,p), and the composite CBSQ//B3LYP/ 6-31G(d,p) calculation methods (abbreviated as CBSQ//B3**). The molecular structures and vibration frequencies are determined at the B3LYP/6-31G(d,p) density functional calculation level, with single point calculations for energy at the B3LYP/6-311+G(3df,2p), QCISD(T)/6-31G(d,p) and CBSQ//B3LYP/6-31G-(d,p) levels. The vibration frequencies are scaled for zero point energies and for thermal corrections. The enthalpies of formation (∆H f °298 ) are determined at each calculation level using the ∆H°r xn,298 with known enthalpies of other reactants and products in each of five different reactions. Standard entropy (S°2 98 ) and heat capacity (C p (T)'s, 300 e T/K e 1500) from vibrational, translational, and external rotational contributions are calculated using the rigid-rotor-harmonic-oscillator approximation, based on the vibration frequencies and structures obtained from the density functional studies. Potential barriers for internal rotation are calculated at the B3LYP/6-31G(d,p) level, and hindered internal rotational contributions to entropy and heat capacity are calculated by summation over the energy levels obtained by direct diagonalizations of the Hamiltonian matrix of hindered internal rotations. An evaluation of data from the reactions, several of which are isodesmic, results in ∆H f °298 values for CH 2 ClOOH of -41.41 ( 1.45kcal/mol, CHCl 2 OOH of -44.74 ( 3.25 kcal/mol, and CCl 3 OOH of -45.63 ( 3.14 kcal/mol. The ∆H f °298 values suggest that the electronegative Cl(s) on the methyl increase stability and ROOsH bond energy by several kcal/mol relative to CH 3 OOH. Groups for use in Benson type additivity estimations are determined for the carbon with oxygen and chlorine(s). The enthalpy values for the C/Cl/H 2 /OO, C/Cl 2 /H/OO and C/Cl 3 /OO groups are -17.91, -21.24, and -22.13 kcal/mol respectively with error limits as above. The enthalpy values from reactions that are isodesmic show good agreement at all of the theory levels, suggesting effective cancellation of errors in the reaction sets. CBSQ// B3LYP/6-31G(d,p) calculations are judged to be the most accurate for enthalpies from nonisodesmic reactions, in this study.
The Journal of Physical Chemistry A, 2007
Aldehydes are important intermediates and products in a variety of combustion and gas-phase oxida... more Aldehydes are important intermediates and products in a variety of combustion and gas-phase oxidation processes, such as in low-temperature combustion, in the atmosphere, and in interstellar media. Despite their importance, the enthalpies of formation and bond dissociation energies (BDEs) for the aldehydes are not accurately known. We have determined enthalpies of formation for acetaldehyde, propanal, and butanal from thermodynamic cycles, using experimentally measured reaction and formation enthalpies. All enthalpy values used for reference molecules and reactions were first verified to be accurate to within around 1 kcal mol -1 using high-level ab initio calculations. Enthalpies of formation were found to be -39.72 ( 0.16 kcal mol -1 for acetaldehyde, -45.18 ( 1.1 kcal mol -1 for propanal, and -49.27 ( 0.16 kcal mol -1 for butanal. Enthalpies of formation for these three aldehydes, as well as for pentanal, hexanal, and heptanal, were calculated using the G3, G3B3, and CBS-APNO theoretical methods, in conjunction with bond-isodesmic work reactions. On the basis of the results of our thermodynamic cycles, theoretical calculations using isodesmic work reactions, and existing experimental measurements, we suggest that the best available formation enthalpies for the aldehydes acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal are -39.72, -45.18, -50.0, -54.61, -59.37, and -64.2 kcal mol -1 , respectively. Our calculations also identify that the literature enthalpy of formation of crotonaldehyde is in error by as much as 1 kcal mol -1 , and we suggest a value of -25.1 kcal mol -1 , which we calculate using isodesmic work reactions. Bond energies for each of the bonds in the aldehydes up to pentanal were calculated at the CBS-APNO level. Analysis of the BDEs reveals the RsCH 2 CHdO bond to be the weakest bond in all aldehydes larger than acetaldehyde, due to formation of the resonantly stabilized vinoxy radical (vinyloxy radical/formyl methyl radical). It is proposed that the vinoxy radical as well as the more commonly considered formyl and acetyl radicals are important products of aldehyde combustion and oxidation, and the reaction pathways of the vinoxy, formyl, and acetyl radicals are discussed. Group additivity values for the carbon-oxygen-hydrogen groups common to the aldehydes are also determined. Internal rotor profiles and electrostatic potential surfaces are used to study the dipole induced dipole-dipole interaction in the synperiplanar conformation of propanal. It is proposed that the loss of this dipole-dipole interaction in RC • HCH 2 CHdO radicals causes a ca. 1-2 kcal mol -1 decrease in the aldehyde C-H and C-C bond energies corresponding to RC • HCH 2 CHdO radical formation.
The Journal of Physical Chemistry A, 2010
Recombination of two amidogen radicals, NH 2 (X 2 B1), is relevant to hydrazine formation, ammoni... more Recombination of two amidogen radicals, NH 2 (X 2 B1), is relevant to hydrazine formation, ammonia oxidation and pyrolysis, nitrogen reduction (fixation), and a variety of other N/H/X combustion, environmental, and interstellar processes. We have performed a comprehensive analysis of the N 2 H 4 potential energy surface, using a variety of theoretical methods, with thermochemical kinetic analysis and master equation simulations used to treat branching to different product sets in the chemically activated NH 2 + NH 2 process. For the first time, iminoammonium ylide (NH 3 NH), the less stable isomer of hydrazine, is involved in the kinetic modeling of N 2 H 4 . A new, low-energy pathway is identified for the formation of NH 3 plus triplet NH, via initial production of NH 3 NH followed by singlet-triplet intersystem crossing. This new reaction channel results in the formation of dissociated products at a relatively rapid rate at even moderate temperatures and above. A further novel pathway is described for the decomposition of activated N 2 H 4 , which eventually leads to the formation of the simple products N 2 + 2H 2 , via H 2 elimination to cis-N 2 H 2 . This process, termed as "dihydrogen catalysis", may have significant implications in the formation and decomposition chemistry of hydrazine and ammonia in diverse environments. In this mechanism, stereoselective attack of cis-N 2 H 2 by molecular hydrogen results in decomposition to N 2 with a fairly low barrier. The reverse termolecular reaction leading to the gas-phase formation of cis-N 2 H 2 + H 2 achieves non-heterogeneous catalytic nitrogen fixation with a relatively low activation barrier (77 kcal mol -1 ), much lower than the 125 kcal mol -1 barrier recently reported for bimolecular addition of H 2 to N 2 . This termolecular reaction is an entropically disfavored path, but it does describe a new means of activating the notoriously unreactive N 2 . We design heterogeneous analogues of this reaction using the model compound (CH 3 ) 2 FeH 2 as a source of the H 2 catalyst and apply it to the decomposition of cis-diazene. The reaction is seen to proceed via a topologically similar transition state, suggesting that our newly described mechanism is general in nature.
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Papers by Joseph Bozzelli