摘要:

Spectroscopic Properties of Silicon‐Sulfur‐Compounds with at least one Si‐S‐bound – A ReviewBond lenghts, bond angles and29Si‐NMR data are tabulated. If possible this parameters are discussed on the bases of covalent radii, electronegativities and other general properties.Qualitative estimations of29Si‐NMR shifts as a function of series of compounds, as a function of ring‐size and by comparison with homologous Si‐O compounds are suggested. Observations of contrarotating effects of29Si‐NMR shifts in organosubstituted Si‐O and Si‐S molecules as compared to their hydrogensubstituted counterpart

ISSN:0941-1216    

DOI:10.1002/prac.19923340302

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Chemoenzymatical Synthesis of N6‐Carbamoyl‐D‐4‐thialysine and N7‐Carbamoyl‐D‐homo‐5‐thialysineThe combination of classical chemical and enzymatical methods opens a way to highly functionalized chiral molecules like N6‐carbamoyl‐D‐4‐thialysine (5) or N7‐carbamoyl‐D‐homo‐5‐thialysine (6). The biotransformation of the corresponding hydantoines withAgrobacterium radiobacter

ISSN:0941-1216    

DOI:10.1002/prac.19923340303

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Synthesis of 4,4‐Bis(trifluoromethyl)‐1‐oxabuta‐1,3‐dienesSilyl enol ethers(1)and hexafluoroacetone(2)react to give O‐silylated aldol adducts3which, after desilylation with methanol/hydrochloric acid, are transformed into 4.4‐bis(trifluoromethyl)‐1‐oxabuta‐1,3‐dienes(5)on treatment with trifluoroacetic ac

ISSN:0941-1216    

DOI:10.1002/prac.19923340304

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Regio‐ and Stereospecific Addition of Diazomethane to Gibberellic Acid: A New Effective Pathway to 1α,2α‐MethylenegibberellinsA new pathway to 1α,2α‐methylenegibberellines via pyrazoline intermediates is reported. In contrast to the addition of diazomethane to the Δ1‐double bond of corresponding enones in the case of1“Umpolung” of the regioselectivity with cis‐addition from the α‐side to give pyrazoline ester4is observed. Subsequent photolysis of4leads to the 1,2‐cyclopropyl derivative6.The structures of the key compounds4and6are confirmed especially by n.

ISSN:0941-1216    

DOI:10.1002/prac.19923340305

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Abstract1‐Benzyl‐4‐phenyl‐1,2,4‐triazolium chloride(1)is cleaved by aqueous sodium hydroxide to form 4‐benzyl‐1‐formyl‐1‐phenyl‐amidrazone (5), the structure of which is proved by mass spectroscopy. The kinetics of the cleavage reaction are studied by UV spectroscopy in methanol/water 1:1 (v/v) in the presence of Na2CO3/HCl buffer at pH values from 11.64 to 12.61. The reaction obeys a first‐order kinetic law. The rate constants do not depend linearly on the hydroxide concentration. This is in coincidence with fast formation of the pseudobase from1, followed by fast deprotonation to the pseudobase anion, and slow decay to the amidrazone. The pseudobase anion is proved spectroscopically, and its spectroscopically determined pKQOH= 12.7 coincides with that from the kinetic experiments. The equilibrium constant of pseudobase formation pKA= 10.99 is two orders of magnitude higher than that from the azocoupling of1[1] which shows that in the azocoupling not the pseudobase but its methyl ether (pKQOMe= 8.7) is active.4‐Benzyl‐1‐formyl‐1‐phenyl‐amidrazone (5) re‐cyclizes in the presence of HCl in MeOH/H2O to form1. The kinet

ISSN:0941-1216    

DOI:10.1002/prac.19923340306

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Quantum Chemical Calculations on the Addition of CH3–XFX(X = 0,…,3) to Ethene. I. Semiempirical Investigations by Means of the AM1 MethodAM1 calculations are reported for the homolytical addition of CH3–XFX(X = 0,…,3) to ethene. The structures of the reactants, the products and the transition states, as well as the reaction enthalpies are described reasonably. The calculated activation barriers are significantly different from the experimental activation energies, probably because the parametrisation is not well suited for the energetics of radical species, especially radical transition states. MNDO gives similar results, MINDO/3 fails com

ISSN:0941-1216    

DOI:10.1002/prac.19923340307

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

1,2,3‐Triazabutadienes. XXII. Photochemistry of 1‐(Carbmethoxy‐aryl)‐ and 1‐(Carboxy‐aryl)‐3‐(3‐alkyl‐benzthiazolinyliden‐(2))‐triazenes as potential CEL‐dyes1‐(Carbmethoxy‐aryl)‐3‐(3‐alkyl‐benzthiazolinyliden‐(2))‐triazenes (ester‐triazenes) (1) were synthesized by coupling of substituted 3‐alkyl‐2‐imino‐benzthiazolines‐(1,3) with 2‐, 3‐ and 4‐carbmethoxy‐benzenediazonium salts. The Z‐isomers obtained can be transformed into the E‐isomers2photochemically or by heating. In the presence of acids the E‐ester‐triazenes are protonated. From the E‐ester‐triazenes the potassium‐salts (4) can be produced by alkaline ester hydrolysis. With hydrochloric acid the E‐triazene‐potassium salts (4) can be transformed into the protonated (at the N(1)‐Atom) E‐acid‐triazenes (5). Their photochemical properties are identical with those of the protonated E‐ester‐triazenes (3). The 1‐(carboxy‐aryl)‐3‐(3‐alkyl‐benzthiazolinyliden‐(2))‐triazenes (E‐acid‐triazenes) (6) can be obtained from the protonated derivates by deprotonation in the presence of water. The photochemical behaviour of the E‐acid‐triazenes (6) and of the E‐triazene‐potassium‐salts (4) depends on the position of the carboxy‐group (2‐position: photolysis, 3‐ and 4‐position: photoisomerization). The

ISSN:0941-1216    

DOI:10.1002/prac.19923340308

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

The Connection between1JSiHCoupling Constants and Group Electronegativities in SilanesFrom n.m.r. coupling constants in silanes of the type HSiMe3‐n(X)n(X = CH2SiMe3, NHSiMe3, N(SiMe3)2, OSiMePhCH2CH3, OSiMePhCH2Cl; n = 0…3) substituent parameters α for the groups X were deduced showing distinct dependencies not only on the atoms directly bonded to the silicon atom but also on the atoms which are separated by two or more bonds from the silicon atom. These parameters supplement an excisting body of substituent parameters. They can be used to predict coupling constants. The good correlation of the parameters α with the electronegativities χ has been used to estimate group electronegativities of the above mentioned groups and, additionally, of the group

ISSN:0941-1216    

DOI:10.1002/prac.19923340309

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractProducts of the reaction of propane‐2‐sulphonic acid p‐cresylester with sodium butoxide in butanol are the sodium salt of propan‐2‐sulphonic acid, di‐n‐butyl ether, p‐cresyl‐n‐butyl ether and p‐cresol. The reaction proceeds via propane‐2‐sulphonic acid n‐butylester which is formed from the starting compound by an elimination‐addition (sulphene) mechanism. The eliminat

ISSN:0941-1216    

DOI:10.1002/prac.19923340310

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Synthesis of Substituted 2‐Nitrophenylhydrazones of 2‐Oxodicarboxylic Acid Esters and Investigation of Their Tautomerism and Absorption Behaviour32 Substituted 2‐nitrophenylhydrazones of diethyl oxalacetate, 2‐oxoglutaric acid and its 1‐mono‐ and 1,5‐dialkyl esters, resp., have been synthesized from substituted 2‐nitrophenylhydrazines and 4,6‐dinitro‐1,3‐dihydrazinobenzene and the carbonyl compounds named above.1H‐n.m.r. spectra prove all products to have the constitution of hydrazones and not that of azo compounds or enhydrazines and also allow the assignation of the E‐ and Z‐configuration, resp., to the hydrazone diastereomers. The absorption behaviour of all hydrazones is discussed with comparison of the different substitution patterns. Unexpectedly, the 4,6‐dinitro‐1,3‐bishydrazones27 – 32show very high lg ϵmaxvalues (at about 4.8) due to th

ISSN:0941-1216    

DOI:10.1002/prac.19923340311

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY