Metastable ion studies. III—composite metastable peaks in fragmentations of some small hydrocarbon cations

Composite metastable peaks are generated in the unimolecular fragmentations (i) [C₃H₅]⁺ → [C₃H₃]⁺ + H₂ (flat-top upon flat-top) and (ii) [C₄H₉]⁺ → [C₃H₅]⁺ + CH₄ (flat-top and gaussian). The measurement of appearance potentials and kinetic energy releases lead us to conclude, in agreement with earlier proposals, that in (i) the components can arise from the generation of the isomeric cyclopropenium and propargyl daughter cations. In (ii) the components are proposed to arise from the fragmentation of tert- and sec-butyl cations yielding allyl as the common daughter ion. The composite peak observed in the fragmentation (iii) [C₃H₄]⁺· → [C₃H₃]⁺ + H· is shown to be present only if the decomposing molecular ion is large enough to also produce [C₆H₈]²⁺ ions. The second component in (iii) then arises from the reaction [C₆H₈]²⁺ → [C₆H₆]²⁺ + H₂.     

The role of angular momentum in collision-induced vibration-rotation relaxation in polyatomics

Vibrational relaxation of the 6(1) level of S(1)((1)B(2u)) benzene is analyzed using the angular momentum model of inelastic processes. Momentum-(rotational) angular momentum diagrams illustrate energetic and angular momentum constraints on the disposal of released energy and the effect of collision partner on resultant benzene rotational excitation. A kinematic "equivalent rotor" model is introduced that allows quantitative prediction of rotational distributions from inelastic collisions in polyatomic molecules. The method was tested by predicting K-state distributions in glyoxal-Ne as well as J-state distributions in rotationally inelastic acetylene-He collisions before being used to predict J and K distributions from vibrational relaxation of 6(1) benzene by H(2), D(2), and CH(4). Diagrammatic methods and calculations illustrate changes resulting from simultaneous collision partner excitation, a particularly effective mechanism in p-H(2) where some 70% of the available 6(1)-->0(0) energy may be disposed into 0-->2 rotation. These results support the explanation for branching ratios in 6(1)-->0(0) relaxation given by Waclawik and Lawrance and the absence of this pathway for monatomic partners. Collision-induced vibrational relaxation in molecules represents competition between the magnitude of the energy gap of a potential transition and the ability of the colliding species to generate the angular momentum (rotational and orbital) needed for the transition to proceed. Transition probability falls rapidly as DeltaJ increases and for a given molecule-collision partner pair will provide a limit to the gap that may be bridged. Energy constraints increase as collision partner mass increases, an effect that is amplified when J(i)>0. Large energy gaps are most effectively bridged using light collision partners. For efficient vibrational relaxation in polyatomics an additional requirement is that the molecular motion of the mode must be capable of generating molecular rotation on contact with the collision partner in order to meet the angular momentum requirements. We postulate that this may account for some of the striking propensities that characterize polyatomic energy transfer.     

A new strategy for the construction of the imidazo[1,5-a]quinoxalin-4-one ring system and its application to the efficient synthesis of BMS-238497, a novel and potent Lck inhibitor

A new efficient strategy was developed for the construction of the imidazo[1,5-a]quinoxalin-4-one ring system. The new method involves condensation of o-nitroaniline with glyoxylate in methanol followed by treatment of the resulting alpha-(o-nitroanilino)-alpha-methoxy acetate with tosylmethyl isocyanide (TosMIC) reagent to give 1-(o-nitrophenyl)imidazole-5-carboxylate. Reductive cyclization of the nitro imidazole carboxylate afforded imidazo[1,5-a]quinoxalin-4-one in three steps and 60% overall yield. The new method was successfully applied to the synthesis of BMS-238497, a novel and potent Lck inhibitor.     

Aerobic catalytic photooxidation of olefins by an electron-deficient Pacman bisiron(III) mu-oxo porphyrin

The synthesis and oxygen atom transfer (OAT) photoreactivity of a diiron(III) mu-oxo meso-tripentafluorophenyl bisporphyrin appended to a dibenzofuran spacer are presented. Reaction of 4,6-diformyldibenzofuran under standard Lindsey conditions furnishes the parent cofacial porphyrin architecture in a single step. These cofacial porphyrins photocatalyze the oxidation of sulfides and olefins using visible light and molecular oxygen as the terminal oxidant. High turnover numbers reflect the enhanced stability of the electron-deficient diiron(III) mu-oxo bisporphyrin core appended to a dibenzofuran spacer under aerobic conditions.     

The effect of amino acid deletions and substitutions in the longest loop of GFP

Background  

The effect of single and multiple amino acid substitutions in the green fluorescent protein (GFP) from Aequorea victoria has been extensively explored, yielding several proteins of diverse spectral properties. However, the role of amino acid deletions in this protein -as with most proteins- is still unknown, due to the technical difficulties involved in generating combinatorial in-phase amino acid deletions on a target region.     

Synthetic and structural studies on some 1,3-diselena- and 1,3-dithia-[3]ferrocenophanes of germanium and tin. crystal and molecular structure of 1,3-diselena-2,2- dichlorogermyl-[3]ferrocenophane

A series of [3]ferrocenophanes of general formula Fe(C₅H₄X)₂YCl₂ and the spiro compounds [Fe(C₅H₄X)₂]₂Ge (X = S, Se; Y = Ge, Sn) have been prepared by the reaction of ferrocene 1,1′-dithiol and ferrocene 1,1′-diselenol with tetrahalides of germanium and tin. Spectroscopic properties of the compounds are reported. In solution, the compounds are fluxional by a bridge reversal process. The crystal structure of 1,3-diselena-2,2-dichlorogermyl-[3]ferrocenophane at 163 K. has been determined by X-ray diffraction methods. At that temperature, crystals have space group P2₁/n with a 6.222(3), b 16.156(13), c 12.968(4) Å, β 97.53(1)° and Z = 4. Least-squares refinement gave R = 0.033 for 2834 unique significant reflections whose intensities were measured by counter diffractometry. The two SeGe bond lengths are 2.323 and 2.325(1) Å, with GeCl 2.148 and 2.161(1) Å. The SeGeSe bond angle is 118.2(1)°, ClGeCl 104.7(1)°, and SeGeCl angles range from 106.2 to 109.8(1)°. The SeC bond lengths are 1.901 and 1.904(5) Å, with CSeGe angles of 95.8 and 96.5(2)°. The cyclopentadienyl rings are in an eclipsed conformation with a mean twist angle of 2.7°, and are inclined to one another at 6.1°. The Se atoms are displaced from the ring planes by 0.17 and 0.20 Å yielding a non-bonded intramolecular Se…Se contact of 3.99 Å.     

Stabilization of a high energy molecular conformation by specific intermolecular forces, a novel planar benzylideneaniline system

The system containing six benzylideneanilines (BA) has been studied: Group 1:

The preparation of dimolybdenum(V,V) complexes from molybdenum quadruply bonded metal-metal dimers

Oxidation of quadruply bonded metal-metal dimers in the presence of good π-accepting ligands results in the formation of Mo^V---Mo^V compounds of the type [MO₂(μ-X)₂(Y)(Y′)]²⁺ (X = O or S; Y,Y′ = O,O; S,S; O,S). Reaction of MO₂(O₂CCH₃)₄ with oxygen in the presence of Na₂mnt (mnt = 1,2-dicyanoethylene-2,2-dithiolate) gives [MO₂(μ-S)₂(O)(S)(mnt)₂]²⁻ (1). The compound crystallizes in the monoclinic space group P2₁/c, with cell dimensions a = 19.547(4), b = 15.210(4), c = 18.754(6) Å, β = 101.69(2)°, V= 5460(2) ų, and Z = 4. Similarly, oxidation of o-dichlorobenzene solutions of Mo₂Cl₄(CH₃CN)₄ and 4,4′-dimethyl-2,2′-dipyridyl (dmpby) or, more directly, the reaction of Mo₂Cl₄(dmbpy)₂ with oxygen leads to the formation of a red solid, which was characterized by X-ray crystallography to be Mo₂(μ-O)₂(O)₂(Cl)₂(dmbpy)₂ (2). Red diamond crystals, prepared by slow evaporation of CH₃CN solutions of 2, are trigonal and in the space group P3₁21 with cell dimensions a = 16.135(4), b = 16.135(4), c = 10.709(3) Å, V = 2414.4(13) ų and Z = 3. In both structures, the geometry about each of the molybdenum atoms is a distorted square pyramid with terminal oxygen or sulphur atoms at the apices and in a syn conformation. The molybdenum-molybdenum bond distances of 2.858(1) Å and 2.562(2) Å in structures of 1 and 2, respectively, are typical of other Mo^V---Mo^V dimers and indicative of a single Mo---Mo bond.     

Studies in qualitative inorganic analysis. XX

Summary Existing tests for differentiating carbonate and hydrogen carbonate are shown to be unreliable. New tests have been developed which enable carbonate and hydrogen carbonate to be differentiated readily; cyanate and other anions may also be tested for in the mixture. The recommended tests are applicable in the presence of other anions.Preliminary water extraction is done to remove hydrogen carbonates and soluble carbonates and cyanates. The insoluble portion is then treated with hydrochloric acid; the evolution of carbon dioxide confirms insoluble carbonates or cyanates. The latter are confirmed by making the solution alkaline and testing for ammonia. Insoluble carbonate is tested for by extracting another portion of the sample with water and treating the residue with acetic acid. Cyanates do not react under these conditions.The original water extract is divided into three parts: one portion is treated with hydrochloric acid; the evolution of carbon dioxide indicates that any of the three ions may be present. A further portion is treated with phenolphthalein. The red colour indicates soluble carbonate. Barium chloride is added until the colour is discharged; slow evolution of carbon dioxide in the cold or on gently warming indicates the presence of hydrogen carbonate. The third portion is made alkaline and boiled to expel any ammonia present from ammonium salts. The solution is then acidified, made alkaline again and then tested for ammonia. A positive test indicates that soluble cyanates are present.

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Zusammenfassung Bekannte Reaktionen zur Unterscheidung von Carbonat und Hydrogencarbonat erwiesen sich als ungeeignet. Daher wurden neue Tests ausgearbeitet; Cyanat und andere Anionen können dabei gleichfalls nachgewiesen werden.Zunächst wird zur Entfernung von Hydrogencarbonat, löslichen Carbonaten und Cyanaten mit Wasser extrahiert. Der unlösliche Anteil wird mit Salzsäure behandelt; die Freisetzung von Kohlendioxid zeigt unlösliche Carbonate oder Cyanate an. Letztere werden nachgewiesen, indem man alkalisiert und auf Ammoniak prüft. Unlösliche Carbonate sind durch Extraktion einer weiteren Probe mit Wasser und Ansäuern des Rückstandes mit Essigsäure nachweisbar. Cyanate reagieren unter diesen Bedingungen nicht.Der wäßrige Extrakt wird in drei Teile geteilt. Ein Teil wird mit Salzsäure behandelt; Kohlendioxidentwicklung zeigt die Gegenwart einer der drei Ionenarten an. Ein weiterer Teil gibt mit Phenolphthalein Rotfärbung, wenn lösliche Carbonate vorliegen. Man setzt Bariumchlorid bis zur Entfärbung zu: langsame Kohlendioxidentwicklung in der Kälte oder bei leichtem Erwärmen zeigt Hydrogencarbonat an. Der dritte Teil wird alkalisiert und durch Kochen vollständig von Ammoniak aus Ammoniumsalzen befreit. Dann säuert man an, alkalisiert wieder und prüft auf Ammoniak. Ein positives Ergebnis zeigt das Vorhandensein löslicher Cyanate an.

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Résumé On montre que les procédés de recherche qui existent actuellement pour différencier le carbonate de l'hydrogéno-carbonate ne sont pas exacts. On a mis au point de nouvelles réactions permettant de distinguer rapidement un carbonate d'un hydrogéno-carbonate; on peut aussi rechercher les cyanates et d'autres anions dans le mélange. Les procédés de recherche que l'on recommande peuvent s'appliquer en présence d'autres anions.On effectue l'extraction préliminaire par l'eau pour séparer les hydrogénocarbonates, les carbonates solubles et les cyanates. La partie insoluble est alors traitée par l'acide chlorhydrique; le dégagement de gaz carbonique indique la présence de carbonates ou de cyanates insolubles. On confirme l'existence de ces derniers en rendant la solution basique et en faisant l'essai á l'ammoniac. On caractérise les carbonates insolubles en extrayant par l'eau une autre portion de l'échantillon et en traitant le résidu par l'acide acétique. Les cyanates ne réagissent pas dans ces conditions.L'extrait par l'eau initial est divisé en trois parties: l'une est traitée par l'acide chlorhydrique; le dégagement de gaz carbonique indique que l'un des trois ions peut être présent. Une autre est traitée par la phénolphtaléine. L'apparition d'une coloration rouge indique un carbonate soluble. On ajoute du chlorure de baryum jusqu'á disparition de la coloration; un faible dégagement de gaz carbonique á froid ou sous chauffage doux montre la présence d'un hydrogéno-carbonate. La troisiéme partie est rendu alcaline et soumise á l'ébullition pour éliminer l'ammoniac des sels d'ammonium. On acidifie alors la solution, on la rend de nouveau alcaline et on fait ensuite l'essai á l'ammoniac. Une réaction positive indique la présence de cyanates solubles.

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Part XIX: Mikrochim. Acta [Wien]1964, 179.