苯甲酸在水-乙醇混合物溶剂中的电离焓

本文测定了苯甲酸在水-乙醇混合溶剂中的电离焓, 并就此进行了讨论。     

Enthalpies of reaction of triflouromethanesulphonic acid with various bases

The enthalpies of reaction of Cf₃SO₃H with a series of bases have been measured calorimetrically in nitrobenzene. Conductivity studies have been carried out and these have indicated the complexity of the acid-base products in solution. The failure of attempts to fit the enthalpy data to the Drago E and C equation reinforce the need for caution in its use.     

Ice-catalyzed ionization of hydrochloric acid

Ionization of hydrochloric acid (HCl) on stratospheric ice particles is believed to be a key step in the depletion of stratospheric ozone. Ab initio calculations based on a model HCl-water cluster show that HCl ionization on ice surfaces is a barrierless process. Since this mechanism is rapid and produces chloride anions that are exposed to ambient stratospheric chlorine reservoir molecules, it is likely to be important for stratospheric chemistry. It complements a previously suggested mechanism where HCl forms part of the ice lattice before ionizing. The mechanism proposed here is also consistent with experimentally observed ionization of HCl on ice at low temperatures and under vacuum, where the HCl is not expected to be encapsulated in the ice lattice.     

Synthesis of 2,3-quinolinedicarboxylic acid

A new procedure for making 2,3-quinolinedicarboxylic acid ( 6 ), starting with aniline and maleic anhydride has been developed. Evidence for the formation of 2-anilino-3-formyl-N-phenylmaleimide ( 7 ) in the cyclization of S-phenylimino-4-dimethylaminomethylene-N-phenylsuccinimide ( 4a ) to N-phenylacridinimide ( 5a ) is presented.     

Conformational analyses of 2,3-dihydroxypropanoic acid as a function of solvent and ionization state as determined by NMR spectroscopy

Vicinal (1)H--(1)H coupling constants were used to determine the conformational preferences of 2,3-dihydroxypropanoic acid (1) (DL-glyceric acid) in various solvents and its different carboxyl ionization states. The stereospecific assignments of J(12) and J(13) were confirmed through the point-group substitution of the C-3 hydrogen with deuterium, yielding rac-(2SR,3RS)-[3-(2)H]-1, and the observation of only J(13) in the (1)H NMR spectra. While hydrogen bonding and steric strain may be expected to drive the conformational equilibrium, their role is overshadowed by a profound gauche effect between the vicinal hydroxyl groups that mimics other substituted ethanes, such as 1,2-ethanediol and 1,2-difluoroethane. At low pH, the conformational equilibrium is heavily weighted toward the gauche-hydroxyl rotamers with a range of 81% in DMSO-d(6) to 92% in tert-butyl alcohol-d(10). At high pH, the equilibrium exhibits a larger dependence upon the polarity and solvating capability of the medium, although the gauche effect still dominates in D(2)O, 1,4-dioxane-d(8), methanol-d(4), and ethanol-d(6) (96, 89, 85, and 83% gauche-hydroxyls respectively). The observed preference for the gauche-hydroxyl rotamers is believed to stem primarily from hyperconjugative sigma(C--H) --> sigma*(C--OH) interactions.     

Enthalpies of formation for alkylcarbonyl radicals

The data on enthalpies of formation (Δ_f H ^○) of alkylcarbonyl radicals are expanded to 22 items. The reference value of Δ_f H ^○ for diacetylperoxide in the gas phase (?485.5 kJ/mol) is determined via recalculation from evaporation enthalpy (n-C₅H₁₁C(O)O)₂. The Δ_f H ^○ values of 22 diacylperoxides (gaseous) are calculated and used in combination with the literature data on dissociation energies of D(O-O) bonds in them to determine the Δ_f H ^○ of corresponding radicals. The interrelation between structure and properties (the enthalpy of formation) is considered, and the parameters for the calculated prediction of Δ_f H ^○ are found.     

Matrix-assisted laser desorption/ionization and electrospray ionization mass spectrometric study of 2,3-dihydro-1,4-benzoxazepines

Fragmentations of the protonated adduct ions [M+H](+) of seven 1,4-benzoxazepine derivatives were studied using 'post-source decay' matrix-assisted laser desorption/ionization (PSD MALDI) and electrospray nozzle-skimmer collisionally induced dissociation (ESI-CID) mass spectrometric methods. It was found that both methods generated mainly product ions arising from the cross-ring cleavages of the benzoxazepine ring. Similar product ions were generated under MALDI and ESI conditions; however, it was observed that the loss of the alkylene unit from the N-substituted benzoxazepine, and the loss of a H(2)X molecule (where X = O or S), are more preferred under ESI conditions. Based on the experimental results a mechanism is also proposed for the fragmentation of the oxazepines studied.     

Tautomerism and ionization of carminic acid

Carminic acid exists as an equilibrium mixture of 9,10-, 1,4-, 1,10-, 2,9-, and 1,7-anthraquinoid tautomers. Its anions have 9,10-, 1,4-, 1,10-, and 2,9-anthraquinoid structures. No conformational equilibria were detected for carminic acid anions. Variation of the solvent and pH and ionization are accompanied by displacements of tautomeric equilibria. Shifts of the long-wave absorption maxima due to tautomeric transformations are determined mainly by change in the energy of the ground rather than excited states of molecules.     

Diastereoselective protocols for the synthesis of 2,3-trans- and 2,3-cis-6-methoxy-morpholine-2-carboxylic acid derivatives

Two diastereoselective and straightforward protocols for the high-yielding synthesis of 2,3-trans- and 2,3-cis-6-methoxy-3-substituted morpholine-2-carboxylic esters were realized in few steps, through the condensation between 5,6-diethoxy-5,6-dimethyl-1,4-dioxan-2-one and an appropriate imine, which is the key reaction to control the C2-C3 relative stereochemistry, followed by a methanolysis/ring-closure tandem reaction sequence. In particular, 2,3-trans-morpholines derive from the R*,S*-product of the acid condensation of N-functionalized alkylimines with the silylketene acetal of the above lactone, whereas 2,3-cis-morpholines derive from the R*,R*-product of basic condensation of an N-tosylimines with the lactone.     

Synthesis of 2,3-dihydroxy-3-methylvaleric acid

Summary The synthesis of sodium 2,3-dihydroxy-3-methylvalerate (the 2,3-dihydroxy analog of isoleucine) is described.     

Stereospecific synthesis of azetidine-cis-2,3-dicarboxylic acid

Electrocyclic reaction product of 1-(methoxycarbonyl)-1,2-dihydropyridine was stereospecifically converted by RuO(4) oxidation into azetidine-cis-2,3-dicarboxylic acid.     

The acid dissociation constants of 2,3-quinoxalinedithiol

Sodium salts of 2,3-quinoxalinedithiol have been prepared and used for determination of the acid ionization constants by potentiometric titration. The fully protonated form of the reagent was used in an alternative determination of the first ionization constant by a solubility method. The constants are pK(2), == 6.84 +/- 0.04 and pK(2) = 9.95 +/- 0.03.     

Enthalpies of mixing of acetonitrile with isomeric butanols: Enthalpies of hydrogen-bonded complexes

The enthalpies of mixing of four isomeric butanols with acetonitrile were determined at 30°C by a Calvet type microcalorimeter. All the four systems showed endothermic behaviour. The enthalpies of hydrogen bonded complex formation were determined by means of a thermochemical cycle. 1-butanol formed a stronger bonding (−13kJ/mole) than the other three isomers (−11.20kJ/mole). The strength of the H-bond of alcohol with C ≡ N is much less than that with C-N. NCL communication no. 4883     

Thermochemical properties of benzoic acid derivatives X. Enthalpies of combustion and formation of 2,3-, 2,4-, 2,6-, 3,4-, and 3,5-dimethoxybenzoic acids

The energies of combustion of 2,3-, 2,4-, 2,6-, 3,4-, and 3,5-dimethoxybenzoic acids have been determined by static-bomb calorimetry. The enthalpies of formation in the crystalline state at 298.15 K have been derived for these five acids. The values obtained are:

     

17.

Cyclization of vinyl-o-carboranylacetic acid by sodium amide to 2,3-carboranocyclopentanocarboxylic acid     

L. I. Zakharkin  I. V. Pisareva 《Russian Chemical Bulletin》1976,25(9):1980-1982

Conclusions Vinyl-o-carboranylacetic acid when treated with sodium amide in liquid ammonia undergoes intramolecular cyclization to 2,3-carboranocyclopentanocarboxylic acid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2115–2117, September, 1976.     

18.

Enthalpies of formation of silanes     

Iain M. T. Davidson 《Journal of organometallic chemistry》1979,170(3):365-372

Benson's electrostatic model for calculating enthalpies of formation has been applied to the methylsilanes and some disilanes, conforming recent conclusions from electron-impact measurements that these silanes essentially follow bond additivity rules, with very small interaction corrections. These findings are shown to be consistent with recently measured bond dissociation energies.     

19.

Enthalpies of formation of lactams     

V. N. Emel’yanenko  S. P. Verevkin  V. V. Turovtsev  Yu. D. Orlov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2013,87(6):901-905

Combustion calorimetry is used to measure the enthalpies of combustion and formation of azacyclooctan-2-one (I), azacyclononan-2-one (II), and azacyclotridecan-2-one (III) in the crystalline, liquid, and gaseous states. Conformational analysis is conducted, and quantum chemical calculations of the compounds’ enthalpies of formation in the gas phase for conformers corresponding to the global minima are performed. The experimental findings and published data are used to determine mutually congruent combinations of enthalpy parameters for a number of nonsubstituted lactams. The strain energies are estimated. Trends in their changes are considered for the series of cycloalkanes and lactams.     

20.

2,3-Dimethyl-3H-indole-3-acetic acid     

Paul D. Rosenstock 《Journal of heterocyclic chemistry》1966,3(4):537-539

     

	$\text{?ΔH}{}_{\mathrm{f}}{}^{\mathrm{o}}\text{(c)/kJ mol}{}^{\mathrm{?1}}$
2,3-dimethoxybenzoic acid	687.0 ± 1.4
2,4-dimethoxybenzoic acid	712.2 ± 1.4
2,6-dimethoxybenzoic acid	693.8 ± 1.4
3,4-dimethoxybenzoic acid	714.0 ± 1.4
3,5-dimethoxybenzoic acid	724.0 ± 1.5

Cyclization of vinyl-o-carboranylacetic acid by sodium amide to 2,3-carboranocyclopentanocarboxylic acid

Conclusions Vinyl-o-carboranylacetic acid when treated with sodium amide in liquid ammonia undergoes intramolecular cyclization to 2,3-carboranocyclopentanocarboxylic acid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2115–2117, September, 1976.     

Enthalpies of formation of silanes

Benson's electrostatic model for calculating enthalpies of formation has been applied to the methylsilanes and some disilanes, conforming recent conclusions from electron-impact measurements that these silanes essentially follow bond additivity rules, with very small interaction corrections. These findings are shown to be consistent with recently measured bond dissociation energies.     

Enthalpies of formation of lactams

Combustion calorimetry is used to measure the enthalpies of combustion and formation of azacyclooctan-2-one (I), azacyclononan-2-one (II), and azacyclotridecan-2-one (III) in the crystalline, liquid, and gaseous states. Conformational analysis is conducted, and quantum chemical calculations of the compounds’ enthalpies of formation in the gas phase for conformers corresponding to the global minima are performed. The experimental findings and published data are used to determine mutually congruent combinations of enthalpy parameters for a number of nonsubstituted lactams. The strain energies are estimated. Trends in their changes are considered for the series of cycloalkanes and lactams.