The cyclodimerisation of 3-methyl-2-butenenitrile

3-Methyl-2-butenenitrile (1) cyclodimerised on treatment with lithium diisopropylamide in dimethoxyethane at temperatures between ?78°C and 0°C to 3-amino-4-cyano-1,5,5-trimethyl-1,3-cyclohexadiene (2) the structure of which was established by acid hydrolysis to the known 4-cyano-1,5,5-trimethyl-1-cyclohexene-3-one (3).     

β-lithiations of carboxamides. Synthesis of β-substituted-α,β-unsaturated amides

N-Methyl-2-methyl-3-(benzotriazol-l-yl)propanamide, on treatment with butyllithium forms a dianion which on treatment with alkyl and benzyl halides, aldehydes and ketones affords monosubstituted products; with ethyl p-toluate, a lactam is formed. The alkylated derivatives eliminate benzotriazole in the presence of base to afford trisubstituted α,β-unsaturated amides.     

Conical parametric scattering of a single extraordinary beam in BaTiO3 crystal

In this paper, the parametric scattering of a single extraordinary polarized beam of laser in BaTiO₃ photorefractive crystal has been investigated experimentally and theoretically. The resulting pattern consists of beam fanning, isotropic ring, and anisotropic one. Among all parts of scattering pattern, isotropic ring has not been studied as much as beam fanning and anisotropic ring, and there still are some differences in reports about it. Therefore, the study has mainly focused on this part. In this experimental configuration, isotropic ring is just visible in positive angles although the other parts of parametric scattering pattern can be visible from behind and in front of the crystal. In addition to steady state pattern in forward and backward directions, its transient behavior with the rotation of crystal has been studied. The results of experiments have been analyzed carefully, and their theoretical explanations have been presented based on the standard theory of parametric scattering in photorefractive crystals. It has been shown that this configuration corresponds to the so called parametric B-process scattering.     

Die Bildung von kristallinem Böhmit in gemeinsam gefällten AlFe(III)-Hydroxiden unter hydrothermalen Bedingungen

Under mild hydrothermal conditions originally amorphous aluminium hydroxide coprecipitated with iron(III)ions as Al_0,5Fe_0,5(OH)₃ transforms into aluminium hydroxide crystalline phases which are not observed in products of ageing of pure aluminium hydroxide.By X-ray diffraction analysis, IR spectroscopic studies and microscopic observations it has been found that due to the presence of iron(III) hydroxide it is possible to stabilize the trihydoxide of aluminium i.e. bayerite until 130–140°C. Moreover, with increasing temperature well crystallized boehmite is obtained instead of the usually formed pseudoboehmite.Experiments revealed that the formation of crystalline boehmite does not take place as a process of pseudoboehmit crystallites growth but only as a result of bayeriteboehmite transformation.

     

Self-chemical ionization of diethylzinc

The self-chemical ionization of diethylzinc is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and semiempirical molecular orbital calculations. Electron impact of diethylzinc neutral produces the radical cation, C(4)H(15)Zn(+) (m/z x 122), which reacts further with the neutral (C(2)H(5))(2)Zn to give the following product ions: Zn(+) (m/z x 64), C(2)H(5)Zn(+) (m/z x 93), C(4)H(9)Zn(+) (m/z x 121), C(4)H(11)Zn(2)(+) (m/z x 187), and C(6)H(15)Zn(2)(+) (m/z x 215). To determine the structure and pathways for production of these ions, monoisotopic (12)C(4)H(15)(64)Zn(+), (64)Zn(+) and (12)C(2)H(5)(64)Zn(+) were individually isolated and reacted with the neutral background. We also performed semiempirical molecular orbital calculations (ZINDO/1). The molecular orbital calculations and experimental data are consistent in predicting that the ethyl group on the diethylzinc cation carries the positive charge. Copyright 1999 John Wiley & Sons, Ltd.     

Temperature effects on coprecipitated Al,Fe-hydroxides during hydrothermal transformations

Studies of the hydrothermal behaviour of coprecipitated Al, Fe-hydroxides with aluminium contents from 5 to 50 mol% reveal that the temperature of the hydrothermal process strongly affects the reciprocal influence of Al(III) and Fe(III) ions on the direction of transformation of the initially amorphous gels.It has been found by X-ray diffraction analysis and IR spectroscopic investigations that at 373 K, up to 10 mol% Al, well-crystallized Al-substituted hydrohematite is formed; at 15–25 mol% Al the crystallinity falls off and the products are amorphous; and at 27.5–50 mol% Al the poorly-crystallized hydrohematite appears, accompanied by different crystalline aluminium trihydroxides, the equilibria of which depend essentially on the AlFe ratio and on the pH of the medium.The hydrothermal process carried out at 413 K yields the Al-substituted protohematite for samples with 15–50 mol% Al, whereas the unique crystalline phase of Al-hydroxide is a well-crystallized boehmite.

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Zusammenfassung Untersuchungen des hydrothermalen Verhaltens von kopräzipierten Al, Fe-Hydroxiden mit Aluminiumgehalten von 5–50 mol% haben ergeben, daß die Temperatur des hydrothermalen Prozesses den gegenteiligen Effekt von Al(III)- und Fe(III)-Ionen auf die Richtung der Umwandlung der anfänglich amorphen Gele wesentlich beeinflußt. Durch Röntgendiffraktion und IR-Spektroskopie wurde ermittelt, daß bei 373 K bis zu 10 mol% Al gut kristallisierter, Al-substitutierter Hydrohämatit gebildet wird. Bei 15–25 mol% Al sind die Produkte amorph und bei 27,5–50 mol% Al liegt schlecht kristallisierter Hydrohämetit vor, begleitet von verschiedenen kristallinen Aluminiumtrihydroxiden, deren Gleichgewicht im wesentlichen vom Al/Fe-Verhältnis und vom pH des Mediums abhängt. Der bei 413 K. ausgeführte hydrothermale Prozeß ergibt Al-substituiertes Protohämatit für Proben mit 15–50 mol% A, während ein gut kristallisierter Boehmit die einzige kristalline Al-Hydroxidphase ist.

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5 50 , . , 373 10 , . 15 25 , , 27,5–50 — . , , , AlFe pH . , 413 15–50 , , .

     

Mechanisms of solvolyses of acid chlorides and chloroformates. Chloroacetyl and phenylacetyl chloride as similarity models

[reaction: see text] Rate constants and product selectivities (S = ([ester product]/[acid product]) x ([water]/[alcohol solvent]) are reported for solvolyses of chloroacetyl chloride (3) at -10 degrees C and phenylacetyl chloride (4) at 0 degrees C in ethanol/ and methanol/water mixtures. Additional kinetic data are reported for solvolyses in acetone/water, 2,2,2-trifluoroethanol(TFE)/water, and TFE/ethanol mixtures. Selectivities and solvent effects for 3, including the kinetic solvent isotope effect (KSIE) of 2.18 for methanol, are similar to those for solvolyses of p-nitrobenzoyl chloride (1, Z = NO(2)); rate constants in acetone/water are consistent with a third-order mechanism, and rates and products in ethanol/ and methanol/water mixtures can be explained quantitatively by competing third-order mechanisms in which one molecule of solvent (alcohol or water) acts as a nucleophile and another acts as a general base (an addition/elimination reaction channel). Selectivities increase for 3 as water is added to alcohol. Solvent effects on rate constants for solvolyses of 3 are very similar to those of methyl chloroformate, but acetyl chloride shows a lower KSIE, and a higher sensitivity to solvent-ionizing power, explained by a change to an S(N)2/S(N)1 (ionization) reaction channel. Solvolyses of 4 undergo a change from the addition/elimination channel in ethanol to the ionization channel in aqueous ethanol (<80% v/v alcohol). The reasons for change in reaction channels are discussed in terms of the gas-phase stabilities of acylium ions, calculated using Gaussian 03 (HF/6-31G(d), B3LYP/6-31G(d), and B3LYP/6-311G(d,p) MO theory).     

怀孕期头发中一些元素含量的变化趋势

用同步辐射激发X射线荧光分析,对11个产妇怀孕期间头发内一些元素含量的变化趋势进行了测量,在各自对比的基础上,得到了一些结果。     

Conjugated systems derived from piperazine-2,5-dione

The preparation of mono- and of symmetrical and unsymmetrical bis-ylidine derivatives of piperazine- 2,5-dione is described. The uv-visible absorption of the products is correlated with acceptor/donor character of the substituents.