Protonation of N-alkenylacrylamides

Protonation of N-alkenylacrylamides and medium effects on the protonation direction were studied theoretically (DFT calculations) and experimentally (IR spectroscopy). In crystal, N-alkenylacrylamide hydrochlorides exist in the O-protonated form in contrast to acrylamide hydrochloride which exists in the N-protonated form.     

均三溴氯磺酚离解与质子化作用的研究

本文报道测钪新试剂均三溴氯磺酚在水溶液中的离解与质子化作用，用电位法和光度法测得了它的逐级离解常数与质子化常数，以及热力学参数，并由分布函数获得试剂主要存在形式和ｐＨ值的关系。     

Protonation of carbethoxypyrroles

The PMR and UV spectra of the bases and conjugate acids of carbethoxy derivatives of pyrrole were investigated. The conjugate acids of 3-carbethoxypyrroles in 22–25 N H₂SO₄ have the -pyrrolene structure, which corresponds to protonation of these compounds at the 5-C atom of the pyrrole ring. The protonation of 2-carbethoxypyrroles under the same conditions proceeds through the formation of an intermediate form, which is converted to the stable cation form in several hours. The stable form of the conjugate acid of 3,4-dimethyl-2-carbethoxypyrrole has the -pyrrolene structure, which corresponds to the addition of a proton to the unsubstituted 5-C ring carbon atom. The structures of the stable forms of the conjugate acids of 2-carbethoxypyrroles that are substituted in the 5 position of the methyl group correspond to protonation of these compounds at the nitrogen atom of the pyrrole ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 336–341, March, 1972.     

Hydrogen bond formations between pyrazine and formic acid and between pyrazine and trichloroacetic acid

The hydrogen bond formations between pyrazine and formic acids and between pyrazine and trichloroacetic acids were studied through observation of the Raman and infrared spectra for mixture of pyrazine and formic acid and also mixture of pyrazine and trichloroacetic acid at 77 K. It was observed that the mutual exclusion principle held for the Raman and infrared spectra of both mixtures, even for the spectra of the samples whose mixing mole ratio of acids was very low. This fact clearly indicates that the hydrogen bonded molecule does not exist in the form of formic acid-pyrazine or trichloroacetic acid-pyrazine whose geometry belongs to the Cs point group, but exists in the form of formic acid-pyrazine-formic acid or trichloroacetic acid-pyrazine-trichloroacetic acid belonging to the C(i) point group.     

Protonation of 3-aminopyrroles

The protonation of 3-aminopyrroles has been investigated using H and ¹³C n.m.r. spectroscopy. The spectral data are compatible with predominant protonation of the amino group with no evidence for protonation of the pyrrole ring.     

Protonation equilibria and solubility of l-cystine

l-Cystine is the natural least soluble of the naturally occurring amino acids. Its solubility is a function of the hydrogen ion concentration depending on its protonation. This paper presents an investigation on properties of l-cystine in a constant ionic medium of NaCl at different concentrations (3.00,2.00,1.00,0.500,0.150 mol dm(-3)) and at 25 degrees C. In such experimental conditions, solubility and its changes as a function of hydrogen ion concentration were determined. Protonation of cystine was studied in acid and basic solution, by measuring the electromotive force of galvanic cell involving a glass electrode. Four protonation constants for l-cystine were determined in all the selected concentrations of ionic medium. The different values obtained for the constants in ionic medium of different concentration could be explained both with the variation of activity coefficients or with the complex formation between l-cystine and sodium ions. Variations of solubility for different concentration of NaCl were observed as well.     

Protonation thermochemistry of aminoacetonitrile

The gas-phase basicity (GB) of aminoacetonitrile (NH2CH2CN, 1) has been determined from measurement of proton transfer equilibrium constants in an ion cyclotron resonance mass spectrometer (GB(1) = 789.3 +/- 1.0 kJ x mol(-1)). Molecular orbital calculations up to the G2 level demonstrate that protonation occurs preferentially on the nitrogen atom of the NH2 group, and provide a theoretical proton affinity (PA(1)) of 824.0 kJ x mol(-1). Exact calculation of the entropy associated with hindered rotations and consideration of Boltzman distribution of conformers allow a theoretical estimate of the molar protonation entropy S degrees (1H+) - S degrees (1) = 8.6 J x mol(-1) x K(-1). Combining this value with experimental GB(1) leads to an 'experimental' proton affinity of 819.2 kJ x mol(-1), in close agreement with the G2 expectation.     

Enantioselective Protonation of Enolates and Enols

Enantioselective protonation, until recently a largely overlooked reaction, has, in the last five years, developed into a field of intense research activity. The progress achieved parallels or complements that obtained in the understanding of enolate structures and reactivities. The conceptual simplicity and attractiveness of enantioselective protonation results from the fact that after reaction, the chiral proton donor is regenerated in its original protonated form by an extractive workup. Enantioselective protonation has been applied to the synthesis of amino acids, antiinflammatory agents (2-arylpropanoic acids), and fragrance compounds such as (S)-α-damascone, for which its industrial feasibility has been demonstrated.     

Mass spectra of pyrazine N-oxides. Studies on pyrazine derivatives. III

The mass spectra of pyrazine 4- and 1-oxides, their di-N-oxides and corresponding pyrazines have been determined. The fragmentations induced by electron impact were examined by means of deuterium labeling and high-resolution measurements. The most pronounced feature of the spectra was the appearance of M-16 ion peaks. In the case of the methyl and methoxy derivatives of 1-oxides, the intensity ratio of M-17/M-16 was larger than in the 4-oxides.     

二溴对甲基偶氮羧质子化及其离解

用萃取法对二溴对甲基偶氮羧进行了纯化,并用分光光度法研究了二溴对甲基偶氮羧的质子化和五级离解作用,测定了其质子化常数和逐级离解常数,获得满意的效果。     

Reactivity of aminopyrroles: Protonation

The behaviour of 2- and 3-aminopyrroles towards protonation is similar. In dimethyl sulphoxide/trifluoroacetic acid they are protonated at the exocyclic nitrogen, whereas in pure trifluoroacetic acid, protonation at the 5- and/or 3-position of the ring takes place.     

Protonation of isomeric angular pyrroloquinolines

The protonation (deuteration) rate, K_D, for the β-position of the pyrrole ring has been measured for several angular pyrroloquinolines. A relationship has been found between the K_D values and the PMR spectral parameters characterizing the structural features of the isomers, enabling the relative reactivities of the latter towards electrophilic substitution reactions to be determined.     

Protonation of manganese phosphonioallenyl complexes

The addition of phosphines to the manganese allenylidene complexes Cp(CO)₂MnCCC(Ph)R (R = H, Ph) proceeds selectively at the C_α atom to result in the α-phosphonioallenyl complexes Cp(CO)₂Mn⁻-C(⁺PR₃¹)CC(Ph)R. The protonation of the latter affords the η²-(1,2)-phosphonioallenes Cp(CO)₂Mn{η²-(1,2)-HC(⁺PR₃¹)CC(Ph)R}, rather than the phosphoniovinylcarbenes Cp(CO)₂MnC(⁺PR₃¹)-HCC(Ph)R. All complexes obtained are stereochemically rigid and do not isomerize into the η²-(2,3)-phosphonioallene isomers.