De la chimie des ptérines. 19e communication [1]. Essai d'interprétation des propriétés chimiques des ptérines au moyen de calcul d'orbitales moléculaires

HMO and semi-empirical SCF calculations on pterine systems of biochemical interest have been performed. The most basic center of each molecule has been determined by correlating the perturbation effect on the transition energy and the spectroscopic data. Additional calculations attempt to show why the redox-system which interfers in hydroxylation reactions consists of 5,6,7,8-tetrahydropterine and a quinoidic form. Finally the formation of radicals in the oxidation step of hydrogenated pterines is discussed.     

De la chimie des ptérines. 15e communication. Hydroxylation non-enzymatique de la phénylalanine en tyrosine à l'aide de ptérines tétrahydrogénées

The non-enzymatic hydroxylation of phenylalanine to tyrosine has been effected by atmospheric oxygen in aqueous solution in the presence of 5,6,7,8-tetrahydropterines, Fe^II or Fe^III, and EDTA, in a phosphate buffer at pH 6,9. A possible reaction mechanism is discussed.     

Action d'organolithiens sur la méthyl-2 quinoxaline. Etude de la réactivité des adduits

The action of organolithium reagents such as phenyllithium or n-bulyllithium on 2-methylquinoxaline gave lithiation of the methyl group which upon reaction with electtropholesphiles produce side chain alkenyl derivatives. On the other hand organolithium reagents react with the quinoxaline azomethine bond to give I-lithio-2-alkyl)or ary-1)-3 methylquinoxalines which can be further loithiated on the methyl group to give 2-alkyl(or aryl)-3-alkenylquinoxaline derivatives. The adducts can be condensed with clectrophiles such as benzonitrile or methlyl benzoate but only methyl benzoate leads to N condensed derivatives. Furthermore substituted 1,2,3,4-terahydroqinoxalines are available via the above lithio intermediates.     

Calorimètre pour la mesure des chaleurs de mélange des liquides

A calorimeter has been designed for measuring the heat of mixing of liquid systems, which eliminates the need to correct for changes in the composition of the vapour phase on mixing. Improved accuracy has been obtained. It permits the measurements of thermic effects of the order of 0.005 joule, corresponding to temperature differences of 10^?4 of a degree. Heats of mixing have been measured for the system hexadecane-hexane, the results of which are highly satisfactory.     

Thermodynamique des mélanges liquides binaires. Chaleurs de mélange des cycloalcanes

Heats of mixing were measured between 10° and 80°C for all binary systems formed with cycloalcanes C_nH_2n, n = 5, 6, 7, 8.     

Etude des mécanismes de réarrangement dans la fragmentation des benzoyloxy-cyclopentànes par impact électronique

The fragmentation modes of 3-benzoyloxy-cyclopentene and of 4-benzoyloxy-cyclopentene have been studied on deuterium-labelled analogues. A mathematical model is proposed for the study of the rearrangement reactions which occur during the expulsion of H₂O and of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CO}_2 {\rm H}^. $\end{document} from the molecular ion of 3-benzoyloxy-cyclopentene.     

Sur le mécanisme de la réaction de meth-cohn-tarnowski de préparation des thiocoumarines

Reaction of 2-t-butylthiobenzaldehyde with N-(2-dialkylaminoethyl)-cyanacetamides followed by heating of the resulting 3-(2-t-butylthiophenyl)-2-cyanoacrylamides in polyphosphoric acid leads to the formation of 3-carboxamido-2-imino-2H-benzo[b][l]thiopyrann intermediates which afford thiocoumarins on hydrolysis. The authors postulate the intermediate formation of a thiophenate ion by an electronic mechanism involving six centers.     

Analyse Conformationnelle de Pseudoprotoberbérines Naturelles. II. Etude Structurale par RMN de 13C des Tétrahydropseudoprotoberbérines provenant de I'Isopyrum thalictroïdes

The four pseudoprotoberberins extracted from Isopyrum thalictroides L. were reduced with sodium borohydride to the corresponding tetrahydropseudoprotoberberins. Comparison between the ¹³C NMR spectra of these and of synthetic protoberberins allowed us to assign a trans-1 configuration to the four reduced alkaloids and also to provide for this particular configuration an unequivocal criterion for the differentiation (based on the chemical shift of C-8) between tetrahydroprotoberberins (9, 10 substituted) and tetrahydropseudoprotoberberins (10, 11 substituted).     

Analyse en spectroscopie infrarouge, de la structure des complexes BF3 du méthanol, des méthanols deutériés et de l'acide acétique Comparaison de la liaison hydrogène et de la liaison donneur-accepteur

A study of the infrared spectra led to the conclusion that the 2-1 complexes formed from two molecules of methyl alcohol or acetic acid and one molecule of BF₃ have an open structure. One methyl alcohol molecule is linked by hydrogen bonding to a second molecule which is attached to BF₃. The consequences of the addition of BF₃ to the OH (OD) vibrators are similar to those of the formation of a hydrogen bond: elevation of the wave number of the in-plane bending vibration and lowering of the wave number of the stretching vibration compared with the monomer.     

Extension de la méthode du «logarithme limite» [1] pour la détermination de la composition et de la constante de stabilité des complexes

A study of the conditions of applicability to weak complexes of the relation log x = v log V + log (β_v,cC^c) = f(logV), where V and C are variable and constant total concentrations of the constituants of the complexe, shows that for conditions other than C ? V, another function φ(log V) accounts better for the formation equilibrium of the complexe. From f(log V) and φ (log V) a relation t(log V) is derived whose simple analysis permits the determination of the composition and the stability constant of weak complexes. Applications are given to 1:1, 1:2, 2:2 composition.     

Étude thermochimique des méthylnaphtalènes

Calorimetric measurements of enthalpies of change of state (sublimation or vaporization) of methylnaphthalenes gave the following results:

1-methylnaphthalene: (ΔH√_vap)_m=(57.32±0.42) kJ mol⁻¹

2-methylnaphthalene: (ΔH√_sub)_m=(65.69±0.84) kJ mol⁻¹

Combination of these values with those obtained by Speros and Rossini¹ for enthalpies of combustion of these compounds makes it possible to determine their energy of isomerization more accurately. This energy is (2.97±2.41) kJ mol⁻¹ and should be attributed to steric hindrance in the 1-methylnaphthalene molecule.

The comparison of energies of conjugation, theoretical as well as experimental, which we have determine for both molecules studied, confirms the present result.     

Etude comparative des méthyl-borazines par RMN

A comparative study of borazine ( 0 ) and six methyl borazines ( 1 to 6 ) has been conducted by NMR. It becomes evident that the chemical shift of N? CH₃ protons hardly varies between mono-, di- and tri-N-methyl borazines, whereas this parameter undergoes a strong change (in all 0·21 ppm, to high field) when one passes from N-trimethyl borazine (HB? NCH₃)₃ to hexamethyl borazine (CH₃B? NCH₃)₃ through a gradual substitution on the three boron atoms ( 3, 4, 5 and 6 ). Moreover, a systematic variation of the parameter δ has been found between compounds 3, 4 and 5 for the protons which keep precisely the same immediate environment. A qualitative interpretation of this experimental result is proposed in terms of electronic effects general to the hexagonal planar boron/nitrogen ring which characterises these molecules.     

Propriétés themodynamiques des mélanges binaires. Chaleurs de mélange des n-alcanes ainsi que de leurs isomères

The following heats of mixing have been measured: the five isomers of hexane with n-dodecane at 10°, 20° and 30°C, and with n-hexadecane at 20°C, as well as the systems dodecane-hexene-1 at 20°C, and dodecane-methyl-2-pentene-1 at 10° 20° and 30°C.     

Le mécanisme de l'hydrolyse acide des aryl-diazométhanes

In the acid catalysed hydrolysis of three monoaryl-diazomethanes (p)-nitrophenyl-diazométhane (I), p-chlorophenyl-diazomethane (II), phenyl-diazomethane (III), absence of exchange H-D, solvent isotope effects about 2,6, and general acid catalysis prove that proton transfer is rate determining (A-S_E2 mechanism). Like other A-S_E2 reactions, the hydrolysis of I is shown to obey the Brønsted catalysis law with a variety of carboxylic acids; for eight of these acids, α_B was found to be 0,69 ± 0,06.