摘要:

AbstractEnrichment of the potassium isotopes is achieved by means of the chemical exchange reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ ^{41} {\rm K}^{\rm + } + ^{39} {\rm KL}^{\rm + } \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\longrightarrow\over{\smash{\longleftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} ^{39} {\rm K}^{\rm + } + ^{41} {\rm KL}^{\rm + } $$\end{document}Where L represents a macrocyclic polyether. Dicyclohexyl‐18‐crown‐6 ((cis‐syn‐cis)‐isomer) was investigated. The single stage‐separation factor a=1+ε was determined according to the method ofGlueckauffrom the elution curve and iso‐topic assays. One obtains ε‐values of 1.18, 0.84. and 0.74 × 10−3(±5×10−5) at −10, 0 and 10° respectively, in favor of the heavy isotope, indicating an enthalpy of isotopic exchange of −13 ± 4 Joule mol−1.The technical feasibility of a pre‐enrichment process for40K starling wit

ISSN:0018-019X    

DOI:10.1002/hlca.19820650602

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractIsomers of lysergic acid derivatives (3,22,23and24). analogous to aporphine, have been synthesized from the key intermediate ketone12.

ISSN:0018-019X    

DOI:10.1002/hlca.19820650603

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractThe difficultDiels‐Alderadditions of α‐acetoxy‐ and α‐chloroacrylonitrile to furan can be run at 20–35° and atmospheric pressure in the presence of CuCl. Cu(BF4) · 6 H2O, Cu(OOCCH3)2· H2O or cupric tartrate · 3H2O. Under kinetic control, theexo‐carbonitrile adducts2and8, respectively, are favoured. Saponification of the2endo‐acetoxy‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2exo‐carbonitrile (2) furnished the 7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (4). Basic hydrolysis of the adducts (8+9) of α‐chloroacrylonitrile to furan and its 5exo, 6exo‐isopropylidenedioxy derivatives did not give the corresponding ketones, the carboxam

ISSN:0018-019X    

DOI:10.1002/hlca.19820650604

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

Abstractδ‐Chymotraypsin catalyzes peptide‐bond formation between acylated amino‐acid and peptide esters as the carboxyl component and amino‐acid and peptide amides as the amino component. The conditions under which enzyme‐catalyzed coupling can be used for fragment condensation in peptide synthesis is investigated. To illustrate the method the synthesis of tetra‐, penta‐ and hexapeptides of the structure Ac‐Lxn …︁ LxlLyl …︁ LymNH2with Lxl Tyr, designed as subst

ISSN:0018-019X    

DOI:10.1002/hlca.19820650605

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractThe rate constants for 3‐substituted adamantylp‐toluenesulfonates3a‐3kin ethanol/water 80:20 correlate well with the respective inductive substituent constants σ Iq. The reaction constant ρ for the toluenesulfonates3is 10% larger than for the corresponding bromides2, indicating somewhat more charge separation in the activation of the toluenesulfonates. Evidence is presented that stabilization of the resultant 1‐adamantyl cations by induction involves graded 1,3‐bridging, which is favored when the substituent is an electrofugal group, and that stabilization by n‐electron donors involves C, C‐hyperconjugation. Rate ratios for the toluenesulfonates3and the bromides1exceed 103and are almost independent of the 3‐substituents. The implications of this are discussed in the light of

ISSN:0018-019X    

DOI:10.1002/hlca.19820650606

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

The Preparation and Solvolysis of 3‐substituted 1‐Adamantyl ToluenesulfonatesMethods for the preparation of some hitherto unknown 3‐iubstitutetl 1‐adamantyl toluenesulfonates are evaluated. Their solvolysis products in dioxane/water 70:30 are r

ISSN:0018-019X    

DOI:10.1002/hlca.19820650607

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractThe reduction of a series of 1,2‐dimethyl‐3‐indolyl heteroaryl ketones, where the heteroaryl components are 2‐benzoxazolyl, 2‐behzpthiuzolyl. 1‐methyl‐2‐benz‐imidazolyl, 4‐ and 2‐pyridyl, in aprotic and prone solution are described by means of DC. and AC. polarography, cyclic voltammetry and coulometry.In acetonitrile a two‐step reduction mechanism with a reversible first and an irreversible second one‐electron transfer has been observed, confirmed by AC.‐polarographic and cyclovoltammetric measurements. The reduction potentials, between −1.377 and −1.787 V for the first step, and between −1.937 and −2.250 V (vs.Ag/AgCl) for the second, could not be correlated with the LUMO energies from HMO calculations which was explained as being due to a distorted configuration of the π systems.In protic media (ethanol/water) reduction occurs in an irreversible one‐step mechanism. Measurements of the pH dependence of the half‐wave potential in the pH* range 0–12 and the evaluated transfer coefficients show that the reduction step represents the transfer of two electrons and two protons yielding secondary alcohols and no dimerization products under any condition. These findings are supported by coulometric and macroscale electrolysis of the ketones; the products isolated

ISSN:0018-019X    

DOI:10.1002/hlca.19820650608

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractSome benzobarrelenes were studied by photoelectron (PE.) spectroscopy. The results can be interpreted by considering dominant through‐space interaction of the π‐molecular fragments in aMöbius‐fashion, Some chemical features of the substrates are rationalized on the basis of these f

ISSN:0018-019X    

DOI:10.1002/hlca.19820650609

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractThe silylation of the surface of sodium borosilicate glass was investigated under conditions that might be applied to the fabrication of ion‐selective microelectrodes of the liquid membrane type such as are used in physiology, Silylation was carried out for 15 min at different temperatures and with six different silanes. The hydrophobicity was measured and found to be greatest with reaction temperatures of 200–350°, the effectiveness of the different silylating agents being in the (increasing) order: trimethylchlorosilane, tributylchlorosilane, (dimethylamino)trimethylsilane, hexamethyldisilazane, dimethyldichlorosilane, bis(dimethylamino)dimethylsilane. The results give evidence of a catalytic effect of basic amine groups and show that the reactivity of the surface of freshly drawn glass is increased by acid leac

ISSN:0018-019X    

DOI:10.1002/hlca.19820650610

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractFrom1H‐ and13C‐NMR. data, a crown conformation withtransamide bonds is deduced for 1,6‐diaza‐2,7‐cyclodecadione (1) in solution. Compound1was obtained by reaction of 2‐pyrrolidone

ISSN:0018-019X    

DOI:10.1002/hlca.19820650611

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY