b1Σ+ Emissions from group V–VII diatomic molecules. b 0+ → X1 0+, X2 1 emissions of AsI and SbI

Chemiluminescence from the b 0⁺ → X₁ 0⁺ band system of AsI and of the b 0⁺ → X₁ 0⁺, X₂ 1 systems of SbI in the near-infrared spectral region has been observed in a discharge flow system. Analysis of the spectra led to the spectroscopic constants (in cm^?1) of AsI: ω_e(X₁, X₂) = 257 ± 2, ω_ex_e(X₁, X₂) = 0.82 ± 0.2, T_e(b 0⁺) = 11738 ± 5, ω_e(b 0⁺) = 271 ± 2, ω_ex_e(b 0⁺) = 0.66 ± 0.2, and of SbI: T_e(X₂ 1) = 965 ± 10, ω_e(X₁, X₂) = 206 ± 6, T_e(b 0⁺) = 12328 ± 10, ω_e(b 0⁺) = 211 ± 6. The intensity ratio of the two sub-systems b 0⁺ → X₂ 1 and b 0⁺→ X₁ 0⁺ was found to be ≈0.013 in the case of SbI and ? 0.01 for AsI.     

Initial distribution of vibration of the OH radicals produced in the H + O3 → OH(X2Π1/2,3/2) + O2 reaction. Chemiluminescence by a crossed beam technique

The chemiluminescence in the H + O₃ → OH(X²Π_1/2,3/2) + O₂ reaction was observed using a crossed beam technique. The initial population of the OH radicals in the vibrational state v (4 ⩽ v ⩽ 9) were found to be N(9) = 1.0, N(8) = 0.95 ± 0.1, N(7) = 0.9 ± 0.2, N(6) = 0.2 ± 0.1 and N(5) = N(4) = 0.2 ± 0.2. The total cross section of the formation of OH(4 ⩽ v ⩽ 9) was estimated to be of the order of 10⁻² nm². No chemiluminescence was observed in the reaction D + O₃ → OD(X²Π_1/2,3/2) + O₂ under the present experimental conditions.     

Photo valence isomerization of sterically strained aromatic hydrocarbons: 8,9-dicarbethoxy[6]paracyclophane

Irradiation of 8,9-dicarbethoxy[6]paracyclophane (1) in the long-wavelength band with λ ≈ 310 nm in dilute fluid solutions gives the 1,4-Dewar isomer (2) with 2.4% quantum yield. The thermal back reaction 2 → 1 follows an Arrhenius law (E_a = 88.3 ± 3.6 kJmol^-1, logA = 9.3 ± 0.6). By calorimetry an enthalpy of this reaction was determined as δH = -19.8 ± 3.8 kJmol^-1. This is significantly smaller than in unstrained systems with a planar aromatic ground state. No other products were detected in this thermoreversible photoreaction. The photochemical rearomatization 2 → 1 occurs with a quantum yield of 0.12 ± 0.02 with light of λ ≈ 288 nm. Only by irradiation of 2 with λ < 270 nm the prismane isomer (3) is formed.     

Rate constants for the reactions of C2H5O,i‐C3H7O,and n‐C3H7O with NO and O2 as a function of temperature

The rate constants of the reactions of ethoxy (C₂H₅O), i‐propoxy (i‐C₃H₇O) and n‐propoxy (n‐C₃H₇O) radicals with O₂ and NO have been measured as a function of temperature. Radicals have been generated by laser photolysis from the appropriate alkyl nitrite and have been detected by laser‐induced fluorescence. The following Arrhenius expressions have been determined: (R₁) C₂H₅O + O₂ → products k₁ = (2.4 ± 0.9) × 10⁻¹⁴ exp(−2.7 ± 1.0 kJmol⁻¹/RT) cm³ s⁻¹ 295K < T < 354K p = 100 Torr (R₂) i‐C₃H₇O + O₂ → products k₂ = (1.6 ± 0.2) × 10⁻¹⁴ exp(−2.2 ± 0.2 kJmol⁻¹/RT) cm³ s⁻¹ 288K < T < 364K p = 50–200 Torr (R₃) n‐C₃H₇O + O₂ → products k₃ = (2.5 ± 0.5) × 10⁻¹⁴ exp(−2.0 ± 0.5 kJmol⁻¹/RT) cm³ s⁻¹ 289K < T < 381K p = 30–100 Torr (R₄) C₂H₅O + NO → products k₄ = (2.0 ± 0.7) × 10⁻¹¹ exp(0.6 ± 0.4 kJmol⁻¹/RT) cm³ s⁻¹ 286K < T < 388K p = 30–500 Torr (R₅) i‐C₃H₇O + NO → products k₅ = (8.9 ± 0.2) × 10⁻¹² exp(3.3 ± 0.5 kJmol⁻¹/RT) cm³ s⁻¹ 286K < T < 389K p = 30–500 Torr (R₆) n‐C₃H₇O + NO → products k₆ = (1.2 ± 0.2) × 10⁻¹¹ exp(2.9 ± 0.4 kJmol⁻¹/RT) cm³s⁻¹ 289K < T < 380K p = 30–100 Torr All reactions have been found independent of total pressure between 30 and 500 Torr within the experimental error. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 860–866, 1999     

Conformational equilibria in N-chloropiperidines

Nitrogen inversion equilibria in the anancomeric piperidines 3–6, 8 and 9 have been studied by variable temperature ¹H NMR in order to determine free energy differences ΔG_e→a⁰ for one class of N-substituted piperidines by an unequivocal method, i.e. direct integration of separate NMR signals for conformers whose interconversion is slow on the NMR timescale at an easily accessible temperature. Using 6 as a model ΔG_e→a⁰ (N-chloropiperidine) has been found to be 5·3±0·1 kJ mol^-1 at 193 K; similarly a study of 10 leads to ΔG_e→a⁰ (N-chloromorpholine) = 4·2±0·1 kJ mol^-1 at 203 K.     

Quenching of O2(1Δg) by aliphatic amines

The quenching rate constants of O₂(¹Δ_g) with n-butylamine, diethylamine, dipropylamine, dibutylamine, and tripropylamine have been determined in a discharge flow system. The rate constants are found to be (1.6 ± 0.2) × 10³, (8.5 ± 0.6) × 10⁴, (9.8 ± 0.5) × 10⁴, (2.1 ± 0.1) × 10⁵, and (8.6 ± 0.5) × 10⁵ 1 mol^?1 s^?1, respectively. The rate constants are found to increase in the order, tertiary amine → secondary amine → primary amine. The “inductive effect” of alkyl substitution is also found to increase the rate constant in a given series of amines.     

The synthesis of a natural product family: from debromoisolaurinterol to the aplysins

Total syntheses of (±)-aplysin 1, (±)-debromoaplysin 2, (±)-isoaplysin 3, (±)-aplysinol 4, (±)-debromoaplysinol 5, (±)-aplysinal 6, (±)-isolaurinterol 7 and (±)-debromoisolaurinterol 8 are described. Key features are a diastereoselective, sulfur mediated radical cyclisation of diene 12 to give 35; a new radical to polar crossover sequence mediated by Bu₃Sn that transforms diene 12 into (±)-debromoisolaurinterol 8; and a series of biomimetic cyclisation and oxidation reactions.     

Synthesis,characterization and reactivity of pentacarbonyl(η1-2,4-pentadienyl)manganese

Reaction of NaMn(CO)₅ with trans-1-bromopenta-2,4-diene in tetrahydrofuran at −78°C gives (η¹-2,4-pentadienyl)Mn(CO)₅ (1) in excellent yield. Compound 1 undergoes η¹ → syn-η³ → η⁵ transformation and, yields (syn-η³-2,4-pentadienyl)Mn)(CO)₄ (2) and (η⁵-pentadienyl)Mn(CO)₃ (3), respectively. The reactions of 1 with the electrophiles tetracyanoethylene (TCNE) and sulfur dioxide (SO₂) were investigated. Compound 1 undergoes a [4 + 2] cycloaddition with TCNE and an insertion reaction with SO₂. The product are characterized by elemental analysis and spectroscopic data.     

Preparation and Diels-Alder Reactivity of 2,3,5,6,7,8-Hexamethylidenebicyclo [2.2.2]octane (‘[2.2.2]Hericene’). Force-field calculations of exocyclic dienes as a moiety of bicyclic skeletons

The [2.2.2]hericene ( 6 ), a bicyclo[2.2.2]octane bearing three exocyclic s-cis-butadiene units has been prepared in eight steps from coumalic acid and maleic anhydride. The hexaene 6 adds successively three mol-equiv. of strong dienophiles such as ethylenetetracarbonitrile (TCE) and dimethyl acetylenedicarboxylate (DMAD) giving the corresponding monoadducts 17 and 20 (k₁), bis-adducts 18 and 21 (k₂) and tris-adducts 19 and 22 (k₃), respectively. The rate constant ratio k₁/k₂ is small as in the case of the cycloadditions of 2,3,5,6-tetramethylidene-bicyclo [2.2.2]octane ( 3 ) giving the corresponding monoadducts 23 and 27 (k₁) and bis-adducts 25 and 29 (k₂) with TCE and DMAD, respectively. Constrastingly, the rate constant ratio k₂/k₃ is relatively large as the rate constant ratio k₁/k₂ of the Diels-Alder additions for 5,6,7,8-tetramethylidenebicyclo [2.2.2]oct-2-ene ( 4 ) giving the corresponding monoadducts 24 and 28 (k₁) and bis-adducts 26 and 30 (k₂). The following second-order rate constants (toluene, 25°) and activation parameters were obtained for the TCE additions: 3 +TCE→ 23 : k₁ = 0.591±0.012 mol^?1·l·s^?1, ΔH^≠=10.6±0.4 kcal/mol, and ΔS^≠ = ?24.0±1.4 cal/mol·K (e.u.); 23 +TCE→ 25 : k₂=0.034±0.0010 mol^?1·l·s^?1, ΔH^≠ = 10.6±0.6 kcal/mol, and ΔS^≠ = ?29.7±2.0 e.u.; 4 +TCE→ 26 : k₁ = 0.172±0.035 mol^?1·l·s^?1, ΔH^≠ 11.3±0.8 kcal/mol, and ΔS^≠ = ?24.0±2.8 e.u.; 24 +TCE→ 26 : k₂ = (6.1±0.2)·10^?4 mol^?1·l·s^?1, ΔH^≠ = 13.0±0.3 kcal/mol, and ΔS^≠ = ?29.5±0.8 e.u.; 6 +TCE→ 17 : k₁ = 0.136±0.002 mol^?1·l·s^?1, ΔH^≠ = 11.3±0.2 kcal/mol, and ΔS^≠ = ?24.5±0.8 e.u.; 17 +TCE→ 18 : k₂ = 0.0156±0.0003 mol^?1·l·s^?1, ΔH^≠ = 10.9±0.5 kcal/mol, and ΔS^≠ = ?30.1 ± 1.5 e.u.; 18 +TCE→ 19 : k₃=(5±0.2) · 10^?5 mol^?1 mol^?1 ·l·s^?1, ΔH^≠ = 15±3 kcal/mol, and ΔS^≠ = ?28 ± 8 e.u. The following rate constants were evaluated for the DMAD additions (CD₂Cl₂, 30°): 6 +DMAD→ 20 : k₁ = (10±1)·10^?4 mol^?1 · l·s^?1; 20 +DMAD→ 21 : k₂ = (6.5±0.1) · 10^?4 mol^?1 ·l·^?1; 21 +DMAD→ 22 : k₃ = (1.0±0.1) · 10^?4 mol^?1 ·l·s^?1. The reactions giving the barrelene derivatives 19, 22, 26 and 30 are slower than those leading to adducts that are not barrelenes. The former are estimated less exothermic than the latter. It is proposed that the Diels-Alder reactivity of exocyclic s-cis-butadienes grafted onto bicycle [2.2.1]heptanes and bicyclo [2.2.2]octanes that are modified by remote substitution of the bicyclic skeletons can be affected by changes inthe exothermicity of the cycloadditions, in agreement with the Dimroth and Bell-Evans-Polanyi principle. Force-field calculations (MMPI 1) of 3, 4, 6 and related exocyclic s-cis-butadienes as a moiety of bicyclo [2.2.2]octane suggested single minimum energy hypersurfaces for these systems (eclipsed conformations, planar dienes). Their flexibility decreases with the degree of unsaturation of the bicyclic skeleton. The effect of an endocyclic double bond is larger than that of an exocyclic diene moiety.     

Cavity ring‐down study of BrO radicals: Kinetics of the Br + O3 reaction and rate of relaxation of vibrationally excited BrO by collisions with N2 and O2

Cavity ring‐down (CRD) techniques were used to study the kinetics of the reaction of Br atoms with ozone in 1–205 Torr of either N₂ or O₂, diluent at 298 K. By monitoring the rate of formation of BrO radicals, a value of k(Br + O₃) = (1.2 ± 0.1) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ was established that was independent of the nature and pressure of diluent gas. The rate of relaxation of vibrationally excited BrO radicals by collisions with N₂ and O₂ was measured; k(BrO(v) + O₂ → BrO(v − 1) + O₂) = (5.7 ± 0.3) × 10⁻¹³ and k(BrO(v) + N₂ → BrO(v − 1) + N₂) = (1.5 ± 0.2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. The increased efficiency of O₂ compared with N₂ as a relaxing agent for vibrationally excited BrO radicals is ascribed to the formation of a transient BrO–O₂ complex. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 125–130, 2000     

Thermal properties of dimethylgold(III) 8-hydroxyquinolinate and 8-mercaptoquinolinate

Dimethylgold(III) complexes with 8-hydroxyquinoline Me₂Au(Ox) (I) and 8-mercaptoquinoline Me₂Au(Tox) (II) were synthesized and studied. Complex II obtained for the first time was identified from the elemental analysis, IR, ¹H NMR, and mass spectrometry data. The thermal properties of complexes I, II in condensed state were investigated by thermography. The temperature dependences of the saturated vapor pressure over crystals were measured by the Knudsen effusion method with mass spectrometric recording of the gas phase composition and the thermodynamic characteristics of the sublimation process were determined: for I, log P[Torr] = (14.6 ± 0.3) ? (6.34 ± 0.10) × 10³/(T, K), Δ H _subl ^o = 121.2 ± 1.9 kJ^?1, Δ S _subl ^o = 224.1 ± 4.6 J mol^?1 K^?1 (the temperature interval under study 80–115°C); for II, log P [Torr] = (13.3 ± 0.2) ? (6.30 ± 0.09) × 10³/(T, K), Δ H _subl ^o = 120.5 ± 1.7 kJmol^?1, ΔS _subl ^o = 199.3 ± 3.0 J mol^?1 K^?1 (86–145°C).     

The ultraviolet absorption spectra of the acetyl radical and the kinetics of the CH3 + CO reaction at room temperature

A continuum-absorption spectrum between 200 and 240 nm is assigned to the acetyl radical. Kinetic measurements using molecular modulation spectroscopy show for the reaction CH₃ + CO (+M) → CH₃CO + M the rate constants are (1.8 ± 0.2) × 10^?18 cm³ molecule^?1 s^?1 at 100 Torr and (6 ± 1) × 10^?18 at 750 Torr. The rate constant for acetyl combination 2CH₃CO → (CH₃CO)₂ is (3.0 ± 10) × 10^?11 at 25°C.     

Kinetic study of the reactions of Br2 with OH and OD

The kinetics of the reactions OH + Br₂ → HOBr + Br (1) and OD + Br₂ → DOBr + Br (3) have been studied in the temperature range 230–360 K and at total pressure of 1 Torr of helium using the discharge‐flow mass spectrometric method. The following Arrhenius expressions were obtained either from the kinetics of product formation (HOBr, DOBr) in excess of Br₂ over OH and OD or from the kinetics of Br₂ consumption in excess of OH and OD: k₁ = (1.8 ± 0.3) × 10⁻¹¹ exp [(235 ± 50)/T] and k₃ = (1.9 ± 0.2) × 10⁻¹¹ exp [(220 ± 25)/T] cm³ molecule⁻¹ s⁻¹. For the reaction channels of the title reactions: OH + Br₂ → BrO + HBr and OD + Br₂ → BrO + DBr, the upper limits of the branching ratios were found to be 0.03 and 0.02 at T = 320 K, respectively. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 698–704, 1999     

Flash photolysis studies of the reaction of NH2 radicals with NO

The kinetics of the reaction NH₂ + NO → N₂ + H₂O were studied, using a conventional flash photolysis system. A value of k₁ = (1.1 ± 0.2) × 10¹⁰ & mole^?1 s^?1 was obtained at room temperature and in the pressure range 2–700 torr in the presence of nitrogen. A slight negative temperature coefficient was observed between 300 and 500 K, equivalent to a negative activation energy of 1.05 ± 0.2 kcal mole^?1.     

Heat capacity of polynuclear Fe(HTrz)3(B10H10)·H2O and trinuclear [Fe3(PrTrz)6(ReO4)4(H2O)2](ReO4)2 complexes (HTrz=1,2,4-triazole, PrTrz=4-propyl-1,2,4-triazole) manifesting 1A1⇔5T2 spin transition

Low-temperature heat capacity of polynuclear Fe(HTrz)₃(B₁₀H₁₀)·H₂O (I) and trinuclear [Fe₃(PrTrz)₆(ReO₄)₄(H₂O)₂](ReO₄)₂ (II) spin crossover coordination compounds was measured in 80–300 K temperature range using a vacuum adiabatic calorimeter. For I, an anomaly of heat capacity with a maximum at T _trs=234.5 K (heating mode) was observed, Δ_trs H=10.1±0.2 kJ mol^?1 Δ_trs S=43.0±0.8 J mol^? K^?1. For II, a smooth anomaly between 150 and 230 K was found, Δ_trs H=2.5±0.25 kJ mol^?1 Δ_trs S=13.6±1.4 J mol^? K^?1. Anomalies observed in both compounds correspond to ¹A₁?⁵T₂ spin transition.     

A practical chemoenzymatic process to access (R)-quinuclidin-3-ol on scale

(±)-3-Butyryloxyquinuclidinium butyrate 6 (2 M, 571 g/L), prepared from (±)-quinuclidin-3-ol 1 and butyric anhydride, undergoes enantioselective hydrolysis by an Aspergillus melleus protease {1.0% (w/v)} in water in the presence of Ca(OH)₂ to keep the reaction at pH 7 and trap butyric acid that is introduced as part of (±)-6 and generated by the enzymatic hydrolysis. After a 24 h period, extraction with n-heptane provides (R)-quinuclidin-3-yl butyrate 5a, which, on methanolysis with Na₂CO₃, is converted into (R)-1, a common pharmacophore of neuromodulators acting on muscarinic receptors, in 96% ee and 42% overall yield from (±)-1. The unwanted antipode (S)-1, which is extracted into n-butanol and purified via its hydrochloride salt in 89% ee and 40% overall yield from (±)-1, can be racemized by the catalysis of Raney Co at 140°C under an atmosphere of H₂ (5 kg/cm²) to regenerate (±)-1 in 97% yield.     

Gas‐phase reactions of Cl atoms with propane,n‐butane,and isobutane

Using the relative kinetic method, rate coefficients have been determined for the gas‐phase reactions of chlorine atoms with propane, n‐butane, and isobutane at total pressure of 100 Torr and the temperature range of 295–469 K. The Cl₂ photolysis (λ = 420 nm) was used to generate Cl atoms in the presence of ethane as the reference compound. The experiments have been carried out using GC product analysis and the following rate constant expressions (in cm³ molecule^?1 s^?1) have been derived: (7.4 ± 0.2) × 10^?11 exp [‐(70 ± 11)/ T], Cl + C₃H₈ → HCl + CH₃CH₂CH₂; (5.1 ± 0.5) × 10^?11 exp [(104 ± 32)/ T], Cl + C₃H₈ → HCl + CH₃CHCH₃; (7.3 ± 0.2) × 10^?11 exp[?(68 ± 10)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃ CH₂CH₂CH₂; (9.9 ± 2.2) × 10^?11 exp[(106 ± 75)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃CH₂CHCH₃; (13.0 ± 1.8) × 10^?11 exp[?(104 ± 50)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CHCH₃CH₂; (2.9 ± 0.5) × 10^?11 exp[(155 ± 58)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CCH₃CH₃ (all error bars are ± 2σ precision). These studies provide a set of reaction rate constants allowing to determine the contribution of competing hydrogen abstractions from primary, secondary, or tertiary carbon atom in alkane molecule. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 651–658, 2002     

Aryl-oxadiazole Schiff bases: Synthesis, α-glucosidase in vitro inhibitory activity and their in silico studies

α-Glucosidase enzyme is a therapeutic target for diabetes mellitus and its inhibitors play a vital role in the treatment of this disease. A new series of aryl-oxadiazole Schiff bases (1–18) were synthesized and evaluated for α-glucosidase inhibitory potential. Fifteen compounds 1–8, 11–13, and 15–18 showed excellent inhibition with IC₅₀ values ranging from 0.30 ± 0.2 to 35.1 ± 0.80 µM as compared to the standard inhibitor acarbose (IC₅₀ = 38.45 ± 0.80 µM), nonetheless, the remaining compounds were found to have moderate activity. Among the series, compounds 7 (IC₅₀ = 0.30 ± 0.2 μM) with hydroxy groups at phenyl rings on either side of the oxadiazole ring was identified as the most potent inhibitor of α-glucosidase. The molecular docking studies were conducted to understand the binding mode of active inhibitors with the active site of enzyme and results supported the experimental data.     

Mixtures obtained by reacting trans-(±)-1,2-diaminocyclohexane with acetylacetone in the presence of simple cobalt(II) salts

In the absence of a metal ion, racemic trans-1,2-diaminocyclohexane (trans-(±)DCH) reacts with acetylacetone (acacH) (1:2.5 mole ratio) to form the bisoxoenamine condensation product, boe (1). CoCl₂·6H₂O and Co(ClO₄)₂·6H₂O each react with trans-(±)DCH in air to give complexes containing the oxidised Co(III) ion, [Co((±)DCH)₃]³⁺, which does not subsequently react with added acacH to give a Schiff base complex. Mixtures of complexes are obtained from one-pot reactions involving trans-(±)DCH, a simple Co(II) salt and acacH (1:1:2.5 mole ratio). When CoCl₂·6H₂O is used, the mixed-ligand Co(II) complex [Co((±)DCH)Cl₂] (4) precipitates first and, after a period of weeks, the Co(II) complex (diazH)₂[CoCl₄] (5) (diazH⁺ is a diazepinium cation), the Co(II) complex [Co(boe)Cl₂]_n (6) and the Co(III) complex [Co(acac)₃] (7), co-crystallise from the mother liquor. Using Co(ClO₄)₂·6H₂O in the reaction with trans-(±)DCH and acacH also gives a mixture of products. Complexes 7, the Co(II) complex [Co₂(acac)₄(H₂O)₂][Co(acac)(H₂O)₄]ClO₄·EtOH (8) and the Co(III) complex [Co(acac)₂(±)DCH]ClO₄ (9) co-crystallise. Complexes 1, 5, 7, 8 and 9 were characterised using X-ray crystallography. The major difference between using CoCl₂·6H₂O and Co(ClO₄)₂·6H₂O in reactions involving (±)DCH and acacH is that no DCH/acacH condensation products are identified in the product mixtures when the perchlorate salt is employed.     

b 1Σ+ Emissions from group V–VII diatomic molecules: bO+ → X1 O+ emission of Pl

Chemilluminescence of the bO⁺ → X₁O⁺ band system of P1 has been observed in a discharge flow system. Thirty-eight bands of the sequences, δν = +2, +1, 0, ?1, ?2 and ?3 were recorded photoelectrically at medium resolution. Evidence is presented that the vibrational numering assigned to the bands in the recently published first analysis of this system has to be modified. The re-analysis leads to the new constants (in cm ^?1) T_e = 11135 ± 5, ω′_e 400 ± 2, ω_e′_e = 1.4 ± 0.3, ω″_e = 372 ±2 and ωχ″_e, 1.4 ± 0.3 for the bO⁺ and χ₁ states, respectively. An upper limit of 0.01 was found for the ratio of the (0.0) band intensifies of the two sub-systems bO⁺ → χ₂ 1 and bO⁺ → χ₁O⁺.