Absolute rate constants for the reactions ofOHradicals withCH3CH2OH, CF2HCH2OHandCF3CH2OH

Summary Pulsed laser photolysis with resonance fluorescence monitoring of OH radicals was applied at T = 300±2 K to obtain the rate constants of k₁= (3.38±0.60)x10^-12, k₂= (2.52±0.44)x10^-13and k₃ = (1.06±0.30)x10^-13cm³molecule^-1s^-1with 2σprecision given for the overall reactions OH + CH₃CH₂OH (1), OH + CF₂HCH₂OH (2) and OH + CF₃CH₂OH (3), respectively. k₂is the first direct kinetic data for the reaction of OH radicals with CF₂HCH₂OH reported in the literature.</o:p>     

Theoretical analysis of the alternative additions of radicals to multiple bonds

The alternative additions of the hydrogen atom and methyl, aminyl, and methoxyl radicals to the double bond of CH₂=Y (Y = CHR, CR₂, CHCH=CH₂, CHPh, NH, O) compounds are theoretically analyzed using the intersecting parabolas method and DFT. The enthalpies, activation energies, and geometric parameters of the transition state in the reactions R^· + CH₂=Y → RCH₂Y^· and R^· + CH₂=Y → RYC^·H₂ are calculated. The results obtained by the two methods are compared with experimental data. The competing alternative radical additions to the multiple bonds are governed by the enthalpies of the reactions.     

Pulse radiolysis study of dithio-oxamide in aqueous solutions

The reactions of e⁻ _aq, H-atoms, OH radicals and some one electron oxidants and reductants were studied with dithio-oxamide (DTO) in aqueous solutions using pulse radiolysis technique. The transient species formed by the reaction of e⁻ _aq with DTO at pH 6.8 has an absorption band with λ _max at 380 nm and is reducing in nature. H-atom reaction with DTO at pH 6.8 also produced the same transient species. The semi-reduced species was found to be neutral indicating that the electron adduct gets protonated quickly. However at pH 1, the species produced by H-atom reaction had a different spectrum with λ _max at 360 and 520 nm. Reaction of acetone ketyl radicals and CO₂ ⁻ radicals with DTO at pH 6.8 gave transient spectra which were identical to that obtained by e⁻ _aq reaction. However at pH 1, the spectrum obtained by the reaction of acetone ketyl radicals with DTO was similar to that obtained by H-atom reaction at that pH. The transient species formed by OH radical reaction with DTO in the pH range 1–9.2 also has two absorption maxima at 360 and 520 nm. This spectrum was identical with the spectrum obtained by H-atom reaction at pH 1. This means that all these radicals viz. OH, H-atom and (CH₃)₂COH radicals react with DTO at pH 1 by H-abstraction mechanism. The transient species produced was found to be sensitive to the presence of oxygen. One-electron oxidizing radicals such as Br₂ ^−· and SO₄ ^−· radicals reacted with DTO at neutral pH to give the same species as produced by OH radical reaction having absorption maxima at 360 to 520 nm. At acidic pHs, only Br₂ ^−· and Cl₂ ^−· radicals were able to oxidize DTO to give the same species as produced by OH radical reaction. The semioxidized species is a resonance stabilized species with the electron delocalized over the-N-C-S bond. This species was found to be neutral and non-oxidizing in nature.     

Reactions of mono- and bimolecular hydrogen transfer in alkyl radicals: analysis using the parabolic model and density functional calculations

Experimental data on monomolecular hydrogen transfer in the reactions of the type RC^·H(CH₂)_nCH₂R¹ RCH₂(CH₂)_nC^·HR¹ (n = 2—4, R and R¹ are alkyl substituents) were analyzed using the parabolic model (PM). The parameters characterizing this class of reactions were calculated. Isomerization of alkyl radicals via cyclic transition states (TS) is characterized by the following energy barriers to thermoneutral reaction E _e0: 53.5, 65.4, and 63.2 kJ mol^–1 for the six-, five-, and seven-membered TS, respectively. The E _e0 energy and the strain energy change in parallel in the series of cycloparaffins C_nH_2n. Density functional calculations of intramolecular hydrogen transfer in the n-butyl and n-pentyl radicals and of the bimolecular hydrogen abstraction from the ethane molecule by the ethyl radical were performed. The activation energies of the intra- and intermolecular hydrogen transfer were compared. The parameters of the PM were compared with the interatomic distances in the reaction center of the TS calculated by the density functional method.     

ESR studies of methallyl monomers with redox systems

The effects of three types of free radical initiators (HO·, H₂N·, and H₃C·) from redox systems, have been studied for four types of methallyl monomers, by use of ESR with a flow system. The structure, the relative concentrations, and the steric conformations of the monomer radical intermediates have been derived from the ESR spectra. In the case of H₂N · and HO · addition to methallyl alcohol (MAA), methallyl amine (MAAm), and sodium methallyl sulfonate (SMAS), the ESR spectra of the reacting species are interpreted as monomer head radicals only (H₂N · and HO · are added to the monomer tail). Methallyl acetate (MAAc) with HO ·, is an exception, giving hydrogen abstraction to form an allyl type radical. This reaction may influence the polymerization behavior of MAAc. The methallyl monomers behave differently from the allyl monomers, where appreciable amounts of monomer tail radicals were found in addition to the head radicals which were the main species. For methallyl monomers, this may be due to steric hindrance caused by the two substituents on the α carbon. The CH₃ radicals add only to positively polarized reactive double bonds, i.e., in SMAS in this study, and allyl alcohol in a previous study. The coupling constants of β CH₂ protons vary considerably with the substituents. For β₁ protons, the coupling constants decrease in the order OH > CH₃ > NH₂. For β₂ protons (allyl hydrogen), the coupling constants decrease in the order CH₂OH > CH₂NH₂ > CH₂OCOCH₃Na, i.e., the constants decrease in the order of increased bulkiness of the groups. Some exceptions are interpreted as due to complex formation with Ti⁴⁺. The effects of pH of the reaction medium are largely those expected.     

Kinetic parameters and geometry of the transition state of acyl radical decarbonylation

Experimental data on acyl radical decomposition reactions (RC^·O → R^· + CO, where R = alkyl or aryl) are analyzed in terms of the intersecting parabolas method. Kinetic parameters characterizing these reactions are calculated. The transition state of methyl radical addition to CO at the C atoms is calculated using the DFT method. A semiempirical algorithm is constructed for calculating the transition state geometry for the decomposition of acyl radicals and for the reverse reactions of R^· addition to CO. Kinetic parameters (activation energy and rate constant) and geometry (interatomic distances in the transition state) are calculated for 18 decomposition reactions of structurally different acyl radicals. A linear correlation between the interatomic distance r ^#(C…C) (or r ^#(C…O)) in the transition state the enthalpy of the reaction (δH _e) is established for acyl decomposition reactions (at br _e = const). A comparative analysis of the enthalpies, activation energies, and interatomic distances in the transition state is carried out for the decomposition and formation of acyl, carboxyl, and formyl radicals.     

Determination of the isomerization rate constant HOCH2CH2CH2CH(OO·)CH3 →HOC·HCH2CH2CH(OOH)CH3. Importance of intramolecular hydroperoxy isomerization in tropospheric chemistry

The rate constant of the title reaction is determined during thermal decomposition of di-n-pentyl peroxide C₅H₁₁O( )OC₅H₁₁ in oxygen over the temperature range 463–523 K. The pyrolysis of di-n-pentyl peroxide in O₂/N₂ mixtures is studied at atmospheric pressure in passivated quartz vessels. The reaction products are sampled through a micro-probe, collected on a liquid-nitrogen trap and solubilized in liquid acetonitrile. Analysis of the main compound, peroxide C₅H₁₀O₃, was carried out by GC/MS, GC/MS/MS [electron impact EI and NH₃ chemical ionization CI conditions]. After micro-preparative GC separation of this peroxide, the structure of two cyclic isomers (3S*,6S*)3α-hydroxy-6-methyl-1,2-dioxane and (3R*,6S*)3α-hydroxy-6-methyl-1,2-dioxane was determined from ¹H NMR spectra. The hydroperoxy-pentanal OHC( )(CH₂)₂( )CH(OOH)( )CH₃ is formed in the gas phase and is in equilibrium with these two cyclic epimers, which are predominant in the liquid phase at room temperature. This peroxide is produced by successive reactions of the n-pentoxy radical: a first one generates the CH₃C·H(CH₂)₃OH radical which reacts with O₂ to form CH₃CH(OO·)(CH₂)₃OH; this hydroxyperoxy radical isomerizes and forms the hydroperoxy HOC·H(CH₂)₂CH(OOH)CH₃ radical. This last species leads to the pentanal-hydroperoxide (also called oxo-hydroperoxide, or carbonyl-hydroperoxide, or hydroperoxypentanal), by the reaction HOC·H(CH₂)₂CH(OOH)CH₃+O₂→O()CH(CH₂)₂CH(OOH)CH₃+HO₂. The isomerization rate constant HOCH₂CH₂CH₂CH(OO·)CH₃→HOC·HCH₂CH₂CH(OOH)CH₃ (k₃) has been determined by comparison to the competing well-known reaction RO₂+NO→RO+NO₂ (k₇). By adding small amounts of NO (0–1.6×10¹⁵ molecules cm⁻³) to the di-n-pentyl peroxide/O₂/N₂ mixtures, the pentanal-hydroperoxide concentration was decreased, due to the consumption of RO₂ radicals by reaction (7). The pentanal-hydroperoxide concentration was measured vs. NO concentration at ten temperatures (463–523 K). The isomerization rate constant involving the H atoms of the CH₂( )OH group was deduced: or per H atom: The comparison of this rate constant to thermokinetics estimations leads to the conclusion that the strain energy barrier of a seven-member ring transition state is low and near that of a six-member ring. Intramolecular hydroperoxy isomerization reactions produce carbonyl-hydroperoxides which (through atmospheric decomposition) increase concentration of radicals and consequently increase atmospheric pollution, especially tropospheric ozone, during summer anticyclonic periods. Therefore, hydrocarbons used in summer should contain only short chains (<C₄) hydrocarbons or totally branched hydrocarbons, for which isomerization reactions are unlikely. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 875–887, 1998     

Kinetic isotope effect in the reaction of oh radical with acetone-D6

The discharge-flow method with resonance fluorescence detection of OH radicals was applied to obtain the rate constant value of k _D = 1.95 ± 0.14 (1σ) 10¹⁰ cm³ mol^-1s^-1 at 298 K. Combination with k _H from our previous study gives the kinetic isotope effect of k _H / k _D = 5.33 ± 0.41. OH + CH₃C(O)CH₃ → Products (H) OH + CD₃C(O)CD₃ → Products(D) This revised version was published online in June 2006 with corrections to the Cover Date.     

Radical addition reactions: factors determining the transition-state geometry

Interatomic distances in the reaction centers of the addition reactions of (i) H^· to the C=C, C=O, N≡C, and C≡C bonds, (ii) ^·CH₃ radical to the C=C, C=O, and C≡C bonds, and (iii) alkyl, aminyl, and alkoxyl radicals to olefin C=C bonds were determined using a new semiempirical method for calculating transition-state geometries of radical reactions. For all reactions of the type X^· + Y=Z → X— Y—Z^· the r ^# _X...Y distance in the transition state is a linear function of the enthalpy of reaction. Parameters of this dependence were determined for seventeen classes of radical addition reactions. The bond elongation, Δr ^# _X...Y, in the transition state decreases as the triplet repulsion, electronegativity difference between the atoms X and Y in the reaction center, and the force constant of the attacked multiple bond increase. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 894–902, April, 2005.     

Mechanism of hydroquinone-inhibited oxidation of acrylic acid and methyl methacrylate

The kinetics of hydroquinone-inhibited oxidation of acrylic acid and methyl methacrylate was studied volumetrically by measuring the oxygen uptake in the presence of an initiator (azobisisobutyronitrile) at T = 333 K and P _{O 2} = 1 and 0.21 atm. The oxidation of acrylic acid inhibited by 4-methoxyphenol was studied under the same conditions for comparison. The rate constants of the reactions of the peroxyl radicals of acrylic acid (∼CH₂CH(COOH)O₂^·) and methyl methacrylate (∼CH₂CMe(COOMe)O₂^·) with hydroquinone (HOC₆H₄OH) (1.20 × 10⁵ and 7.16 × 10⁴ l mol⁻¹ s⁻¹, respectively) and of the reaction of peroxyl radicals of acrylic acid with 4-methoxyphenol (p-CH₃OC₆H₄OH) (3.25 × 10⁴ l mol⁻¹ s⁻¹) were measured. The stoichiometric inhibition factors f were determined. The reaction between the semiquinone radical and oxygen, O₂ + HOC₆H₄O^·, plays an important role, decreasing the factor f and the efficiency of the inhibition effect of hydroquinone. The rate constants of this reaction were calculated from kinetic data: k = 5.72 × 10² (in acrylic acid) and 4.60 × 10² l mol⁻¹ s⁻¹ (in methyl methacrylate).     

Kinetics of the radical reactions in pulse radiolyzed RHF — CO2(SF6)-O2-NO gaseous mixtures; RHF = CH3CH2F, CH3CHF2, CH3CF3, CH2FCF3

The kinetics of the peroxy radicals RHFO₂ reactions with NO has been studied by using pulse radiolysis and UV absorption spectroscopy. The rate constants of interaction of oxygen atoms with NO − k ₂ = 2.2±0.2·10⁻¹² cm³·s⁻¹ and NO₂ − k ₃ = 2.1±0.2·10⁻¹¹ cm³·s⁻¹ were found in agreement with the literature values. The bath gases (SF₆ or CO₂) have got minor effect on the rate constants of RHFO₂+NO→NO₂+prod. reactions; RHFO₂ = CH₃CH₂O₂, CH₃CHFO₂, CH₃CF₂O₂, CF₃CH₂O₂, CF₃CHFO₂. The obtained rate coefficients are in the scope of the literature values, although they are lower than those recommended in NIST database. The reasons are discussed.     

Theoretical study on thermal decomposition of azoisobutyronitrile in ground state

Since the first discovery of azoalkanes in 1909,the studies of the chemistry of azoalkane radicals havegone through a long history and many significativeresults have been gotten during the past 30 years[1,2].These versatile compounds lose nitrogen thermally orphotochemically under a wide variety of conditions:R─N═N─R ? 2R?+ N2; hence, they are probablythe cleanest and most convenient sources of variousradicals and biradicals of nearly any desired structure.Several reviews on the applicati…     

Free radical abstraction of H atom from peroxides with concerted dissociation of O-O bond

Quantum chemical calculations of the dissociation energy of the C-H bond in the ??-hydroperoxide fragment of Me₂CHOOH were carried out. It was shown that abstraction of H atom is accompanied by dissociation of the O-O bond. Density functional calculations of transition states of the reactions of ^·CH₃, CH₃OO^·, and HO₂ ^· radicals with the C-H bond in the ??-hydroperoxide fragment of Me₂CHOOH were carried out. It was established that H atom abstraction is accompanied by concerted dissociation of the O-O bond. For 45 peroxides R¹R²CHOOH, R¹R²CHOOR³, and R¹R²CHOOC(O)R³ (R¹, R² = H, Me, Et, Ph, H₂C=CH), the enthalpies of H atom abstraction from the C-H bond in the a-hydroperoxide fragment with fragmentation of the peroxides at the O-O bond were calculated. The kinetic parameters for 12 classes of radical abstraction reactions with fragmentation of molecules were calculated from experimental data within the framework of the model of intersecting parabolas. The activation energies and reaction rate constants of H atom abstraction from C-H bonds of a-peroxide fragments involving peroxyl and alkyl radicals were determined for 45 peroxides of different structure.     

Laser photoemission generation and electrochemical study of methyl radicals as secondary products of OH radicals capture by dimethyl sulfoxide molecules

Electrode reactions of intermediates formed during capture of OH radicals by dimethylsulfoxide molecules were studied by laser photoemission in aqueous buffer solutions and pH range from acidic to basic. The results were compared with those obtained previously for electrochemical behaviour of methyl radicals generated via photoemission from CH₃Cl. The essential similarity was found for parameters of irreversible one-electron transfer from/to these intermediates, i.e. the potentials E _1/2 on time-resolved voltammograms and rate constants at E = E _1/2. Hence, both active particles were concluded to be equivalent and corresponded to methyl radical. The primary product of OH radicals capture by DMSO molecules, i.e. adduct (CH₃)₂SO·(OH), was spontaneously decomposed to form ·CH₃ with time as low as <2 × 10⁻⁵ s. A simultaneous increase of the reduction wave height was observed at pH transition from low basic to low acidic and at illumination times T _m of an electrode with UV light if T _m ≥ 90–300 ms. The increase exceeded considerably the one-electron reduction level. These features were presumably caused by the rather slow formation of organomercury intermediates as interaction products of the components of the system with a mercury electrode.     

Methyl propionate radical cation

Examination of the reactions of the long-lived (>0.5-s) radical cations of CD₃CH₂COOCH₃ and CH₃CH₂COOCD₃ indicates that the long-lived, nondecomposing methyl propionate radical cation CH₃CH₂C(O)OCH ₃ ^+· isomerizes to its enol form CH₃CH=C(OH)OCH ₃ ^+· (ΔH _{isomerization} ? ?32 kcal/mol) via two different pathways in the gas phase in a Fourier-transform ion cyclotron resonance mass spectrometer. A 1,4-shift of a β-hydrogen of the acid moiety to the carbonyl oxygen yields the distonic ion ^·CH₂CH₂C⁺ (OH)OCH₃ that then rearranges to CH₃CH=C(OH)OCH ₃ ^+· probably by consecutive 1,5- and 1,4-hydrogen shifts. This process is in competition with a 1,4-hydrogen transfer from the alcohol moiety to form another distonic ion, CH₃CH₂C⁺(OH)OCH ₂ ^· , that can undergo a 1,4-hydrogen shift to form CH₃CH=C(OH)OCH ₃ ^+· . Ab initio molecular orbital calculations carried out at the UMP2/6-31G** + ZPVE level of theory show that the two distonic ions lie more than 16 kcal/mol lower in energy than CH₃CH₂C(O)OCH ₃ ^+· . Hence, the first step of both rearrangement processes has a great driving force. The 1,4-hydrogen shift that involves the acid moiety is 3 kcal/mol more exothermic (ΔH _{isomerization}=?16 kcal/mol) and is associated with a 4-kcal/mol lower barrier (10 kcal/mol) than the shift that involves the alcohol moiety. Indeed, experimental findings suggest that the hydrogen shift from the acid moiety is likely to be the favored channel.     

On the kinetic mechanism of reactions of hydroxyl radical with CHF2CH3 − n F n (n = 1–3)

The potential energy surfaces of the reactions CHF₂CH_3 − n F _n (n = 1–3) + OH were investigated by MPWB1K and BMC-CCSD (single-point) methods. Furthermore, with the aid of canonical variational transition state theory including the small-curvature tunneling correction, the rate constants of the title reactions were calculated over a wide temperature range of 220–1,500 K. Agreement between the CVT/SCT rate constants and the experimental values is good. Our results show that the order of rate constants is CHF₂CH₂F + OH > CHF₂CHF₂ + OH > CHF₂CF₃ + OH. For reaction CHF₂CH₂F + OH, the 1-H-abstraction channel dominates the reaction at the whole temperature, while 2-H-abstraction channel appears to be competitive with the increase of temperature.     

Estimation of O-H bond dissociation energies in alcohols and acids from kinetic data

The O-H bond dissociation energies (D _O-H) in five alcohols and six acids have been determined from experimental data (rate constants of radical reactions). The ratio of the rate constants of the reactions R¹O˙+RH→R¹OH+R˙ and R ⁱ O˙+RH→R ⁱ OH+R˙ and the intersecting parabolas method are used in the estimation procedure. The D _O-H values are used to calculate the activation energies and rate constants for hydrogen abstraction from 2-methylbutane, butene-1, and cumene by alkoxyl and carboxyl radicals. The geometric parameters of the transition state are calculated for these reactions.     

Reaction of H + ketene to formyl methyl and acetyl radicals and reverse dissociations

Thermochemical properties for reactants, intermediates, products, and transition states important in the ketene (CH₂?C?O) + H reaction system and unimolecular reactions of the stabilized formyl methyl (C·H₂CHO) and the acetyl radicals (CH₃C·O) were analyzed with density functional and ab initio calculations. Enthalpies of formation (ΔH_f°₂₉₈) were determined using isodesmic reaction analysis at the CBS‐QCI/APNO and the CBSQ levels. Entropies (S°₂₉₈) and heat capacities (C_p°(T)) were determined using geometric parameters and vibrational frequencies obtained at the HF/6‐311G(d,p) level of theory. Internal rotor contributions were included in the S and C_p(T) values. A hydrogen atom can add to the CH₂‐group of the ketene to form the acetyl radical, CH₃C·O (E_a = 2.49 in CBS‐QCI/APNO, units: kcal/mol). The acetyl radical can undergo β‐scission back to reactants, CH₂?C?O + H (E_a = 45.97), isomerize via hydrogen shift (E_a = 46.35) to form the slight higher energy, formyl methyl radical, C·H₂CHO, or decompose to CH₃ + CO (E_a = 17.33). The hydrogen atom also can add to the carbonyl group to form C·H₂CHO (E_a = 6.72). This formyl methyl radical can undergo β scission back to reactants, CH₂?C?O + H (E_a = 43.85), or isomerize via hydrogen shift (E_a = 40.00) to form the acetyl radical isomer, CH₃C·O, which can decompose to CH₃ + CO. Rate constants are estimated as function of pressure and temperature, using quantum Rice–Ramsperger–Kassel analysis for k(E) and the master equation for falloff. Important reaction products are CH₃ + CO via decomposition at both high and low temperatures. A transition state for direct abstraction of hydrogen atom on CH₂?C?O by H to form, ketenyl radical plus H₂ is identified with a barrier of 12.27, at the CBS‐QCI/APNO level. ΔH_f°₂₉₈ values are estimated for the following compounds at the CBS‐QCI/APNO level: CH₃C·O (?3.27), C·H₂CHO (3.08), CH₂?C?O (?11.89), HC·CO (41.98) (kcal/mol). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 20–44, 2003     

Conformational Analysis,Infrared, and Fluorescence Spectra of 1-Phenyl-1,2-propandione 1-oxime and Related Tautomers: Experimental and Theoretical Study

Summary. Conformational analysis and frequency calculation were achieved for 1-phenyl-1,2-propandione 1-oxime and its four tautomers: 1-nitroso-1-phenyl-1-propen-2-ol, 1-nitroso-1-phenyl-2-propanone, 2-hydroxy-1-phenyl-propenone oxime, and 3-nitroso-3-phenyl-propen-2-ol. Calculations were carried out at the Hartree–Fock (HF), Density Functional Theory (B3LYP), and the second-order M?ller–Plesset perturbation (MP2) levels of theory using 6-31G^* and 6-311G^** basis sets. Five conformers with no imaginary vibrational frequency were obtained by free rotations around three single bonds of 1-phenyl-1,2-propandione-1-oxime: Ph–C(NOH)C(O)CH₃, PhC(NOH)–C(O)CH₃, and PhC(N–OH)C(O)CH₃. Similarly, eight structures with no imaginary vibrational frequency were encountered upon rotations around three single bonds of 1-nitroso-1-phenyl-1-propen-2-ol: Ph–C(NO)C(OH)CH₃, PhC(N–O)C(OH)CH₃, and PhC(NO)C(–OH)CH₃. In the same manner, six minima were found through rotations around three single bonds of 1-nitroso-1-phenyl-2-propanone: Ph–CH(NO)C(O)CH₃, PhCH(–NO)C(O)CH₃, and PhCH(NO)–C(O)CH₃. Also, two minima were found through rotations around four single bonds of 2-hydroxy-1-phenyl-propenone oxime: Ph–C(NOH)C(OH)CH₂, PhC(N–OH)C(OH)CH₂, PhC(NOH)–C(OH)CH₂, and Ph-C(NOH)C(–OH)CH₂. Finally, two minima were found through rotations around four single bonds of 3-nitroso-3-phenyl-propen-2-ol: Ph–CH(NO)C(OH)CH₂, PhCH(–NO)C(OH)CH₂, PhCH(NO)–C(OH)CH₂, and PhCH(NO)C(–OH)CH₂. Interconversions within the above sets of conformers were probed through scanning (one and/or two dimensional), and/or QST3 techniques. The order of the stability of global minima encountered was: 1,2-propandione-1-oxime > 1-nitroso-1-phenyl-2-propanone > 1-nitroso-1-phenyl-1-propen-2-ol > 2-hydroxy-1-phenyl-propenone oxime > 3-nitroso-3-phenyl-propen-2-ol. Hydrogen bonding appears significant in tautomers of 1-nitroso-1-phenyl-1-propen-2-ol and 2-hydroxy-1-phenyl-propenone oxime. The CIS simulated λ_max for the first excited singlet state (S₁) of 1-phenyl-1,2-propandione 1-oxime is 300.4 nm, which was comparable to its experimental λ_max of 312.0 nm. The calculated IR spectra of 1-phenyl-1,2-propandione 1-oxime and its tautomers were compared to the experimental spectra.     

Conformational Analysis, Infrared, and Fluorescence Spectra of 1-Phenyl-1,2-propandione 1-oxime and Related Tautomers: Experimental and Theoretical Study

Conformational analysis and frequency calculation were achieved for 1-phenyl-1,2-propandione 1-oxime and its four tautomers: 1-nitroso-1-phenyl-1-propen-2-ol, 1-nitroso-1-phenyl-2-propanone, 2-hydroxy-1-phenyl-propenone oxime, and 3-nitroso-3-phenyl-propen-2-ol. Calculations were carried out at the Hartree–Fock (HF), Density Functional Theory (B3LYP), and the second-order M?ller–Plesset perturbation (MP2) levels of theory using 6-31G^* and 6-311G^** basis sets. Five conformers with no imaginary vibrational frequency were obtained by free rotations around three single bonds of 1-phenyl-1,2-propandione-1-oxime: Ph–C(NOH)C(O)CH₃, PhC(NOH)–C(O)CH₃, and PhC(N–OH)C(O)CH₃. Similarly, eight structures with no imaginary vibrational frequency were encountered upon rotations around three single bonds of 1-nitroso-1-phenyl-1-propen-2-ol: Ph–C(NO)C(OH)CH₃, PhC(N–O)C(OH)CH₃, and PhC(NO)C(–OH)CH₃. In the same manner, six minima were found through rotations around three single bonds of 1-nitroso-1-phenyl-2-propanone: Ph–CH(NO)C(O)CH₃, PhCH(–NO)C(O)CH₃, and PhCH(NO)–C(O)CH₃. Also, two minima were found through rotations around four single bonds of 2-hydroxy-1-phenyl-propenone oxime: Ph–C(NOH)C(OH)CH₂, PhC(N–OH)C(OH)CH₂, PhC(NOH)–C(OH)CH₂, and Ph-C(NOH)C(–OH)CH₂. Finally, two minima were found through rotations around four single bonds of 3-nitroso-3-phenyl-propen-2-ol: Ph–CH(NO)C(OH)CH₂, PhCH(–NO)C(OH)CH₂, PhCH(NO)–C(OH)CH₂, and PhCH(NO)C(–OH)CH₂. Interconversions within the above sets of conformers were probed through scanning (one and/or two dimensional), and/or QST3 techniques. The order of the stability of global minima encountered was: 1,2-propandione-1-oxime > 1-nitroso-1-phenyl-2-propanone > 1-nitroso-1-phenyl-1-propen-2-ol > 2-hydroxy-1-phenyl-propenone oxime > 3-nitroso-3-phenyl-propen-2-ol. Hydrogen bonding appears significant in tautomers of 1-nitroso-1-phenyl-1-propen-2-ol and 2-hydroxy-1-phenyl-propenone oxime. The CIS simulated λ_max for the first excited singlet state (S₁) of 1-phenyl-1,2-propandione 1-oxime is 300.4 nm, which was comparable to its experimental λ_max of 312.0 nm. The calculated IR spectra of 1-phenyl-1,2-propandione 1-oxime and its tautomers were compared to the experimental spectra.