摘要:

AbstractConventional organic molecules for applications in second‐order non‐linear optics are donor–acceptor substituted π systems that show only one intense charge‐transfer (CT) transition. Thus, only a single element of the second‐order polarizability tensor, β, is significant in these one‐dimensional systems. The advantages and optimization strategies for two new classes of molecules with multiple CT transitions and two‐dimensional second‐order polarizability are reviewed. These are donor–acceptor substituted π systems that lack a dipole and have a molecular symmetry ofC3or higher, and dipolar molecules of symmetryC2v. A basic introduction to the

ISSN:0941-1216    

DOI:10.1002/prac.19983400202

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

Monofunctionalized Dendrons of Different Generations – as Reagents for the Introduction of Dendritic SubstituentsIn recent years dendrimers become more and more important not only in organic chemistry. They represent a new class of molecules with unique characteristic features. But dendrimers represent not only designed molecular architecture. They stand for a new concept in chemistry. They can be used to alter the properties of already existing molecular skeletons or they can be used to transfer new properties to a classical functional unit. This means that functionalized dendrimers and dendrons (dendritic building blocks) can be regarded as reagents for the preparation of new compounds with dendritic properties. In this article the synthesis and the practical use of appropriate dendritic reagents is explained. Furthermore we introduce the new technical terms „{n} dendryl‐”︁ for dendritic substituents of n generations and „dendriagent”︁ which stands for dendritic reagents. Moreover we give a short outlook on futu

ISSN:0941-1216    

DOI:10.1002/prac.19983400203

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractSeveral new push‐pull azobenzene dyes were synthesized by diazonium salt coupling of electron‐poor anilines withN,N‐dialkylanilines. Their dipole moments and first‐order hyperpolarizabilities were evaluated respectively from the concentration dependence of the dielectric constant of solutions in apolar solvents and by the electric‐field‐induced‐second‐harmonic‐generation (EFISH) technique. Investigation of the influence of both nature and steric hindrance of the electron‐withdrawing group allowed to highlight a significant deviation from linearity in the relationship between dipole moments and first‐order hyperpolarizabilities. This effect was particularly noticeable when multiple electron withdrawing groups pointing in different directions were present on

ISSN:0941-1216    

DOI:10.1002/prac.19983400204

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe addition ofN‐chlorophthalimide (1b) to alkenes3viaphthalimidyl radicals introduces a chlorine atom and an imidyl moiety to vicinal C‐atoms of a carbon chain. The yields depend on the substituents of the alkene3. The regioselectivity can be explained by steric and electronic effects; differences in the behavior of the addition ofN‐chlorophthalimide (1b) andN‐bromophthalimide (1a) can be explained by a reversible attack of the phthalimidyl radical to the doub

ISSN:0941-1216    

DOI:10.1002/prac.19983400205

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

A Novel Synthetic Route to Open‐Chained and Cyclic OligoetherketonesOligoetherketones of the structure2a,bcan be generated by repetitive insertion reactions of terminal biscarbenoids4a,b, into the OH bonds of diols like5. The formation of the corresponding ring systems7aand the involved carbene dimerization leading to8bare processes which compete with the linear polyinsertion. A related one‐component reaction can be performed with ω‐hydroxy‐1‐diazo‐2‐alkanon

ISSN:0941-1216    

DOI:10.1002/prac.19983400206

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractA new synthesis of the title crownviaisoxazolo crown ether7and macrocyclic bis‐β‐eneaminoketone10is described.7can be synthesized in 14% yield by a non‐template double‐[3+2] cycloaddition of dinitrileoxide5preparedin situfrom dinitropolyether19by dehydration with Ph–NCO and alkyne6. The compounds16, 17and18are synthesized by the same synthetic strategy. Comparable IR and1H NMR spectroscopic data of macrocyclic and non‐cyclic compounds show, that macrocyclic conformation stabilizing effects can be ruled out. The structures of the macrocycles1, 7, 10and that of the Hg(II)‐complex25, synthesized by reaction of1with Hg(OAc)2were established by single‐crystal X‐ray structure analyses. Both inter‐ and intramolecular hydrogen bonds are observed for the macrocyclic bis‐β‐eneaminoketone10, whereas only intramolecular hydrogen bonds are formed by1.In the Hg(II)‐complex of1the mercury is bonded to two methylene groups. CHgC is almost linear [177(1)°], the mean HgC distance amounts to 215(1) pm. In addition to the HgC bonds, each Hg makes a short contact to a carbonyl oxygen in a neighbouring molecule in the plane perpendicular to the CHgC axis [Hg(1)

ISSN:0941-1216    

DOI:10.1002/prac.19983400207

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe 1‐aza‐2‐azoniaallene salt8prepared from 3‐acetyl coumarinviathe hydrazone6and the (chloroalkyl)azo derivative7reacts with nitriles to afford the 3‐(3‐chromenyl)‐1,2,4‐triazolium salts11a–d. With diisopropylcarbodiimide the triazolium salt13and with norborene a tricyclic pyrazolium salt14are obtained. Concurrent to these cycloadditions the by‐product12is formed by intramolecular cyclization of the cumulene8. Similarly, the intramolecular cyclization product18is isolated as the sole product when the 1‐aza‐2‐azoniaallene salt17a(prepared from the ethyl carbazone of camphor by chlorination and treatment of the product16awith SbCl5) was treated with nitriles, carbodiimides or alkenes. In contrast, 1,2,4‐triazolium salts20a–c,23c, respectively pyrazolium salts20d–f, and 1,3,4‐thiadiazolium salts23a,bare obtained by reaction of the 1‐aza‐2‐azoniaallene salt17bwith nitriles, respectively alkenes, alkynes, diisopropylcarbodiimide, and isothiocyanates. The constitutions of two of these products (20e, 23a) we

ISSN:0941-1216    

DOI:10.1002/prac.19983400208

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe acid dissociation constants (Ka) of a series of 3,4‐diaryl‐1H‐1,2,4‐triazole‐5‐thiones (1) were determined and were found to correlated linearly with Hammett substituent constants; logKa= 1.06 σx− 11.01. Such a result indicates that1exists essentially in one tautomeric form namely the thione form. Reactions of1with hydrazonoyl chlorides2gave the thiohydrazides5. Similiar reaction of 3‐phenyl‐1H(4H)‐ 1,2,4‐triazole‐5‐thione1gwith2agave the thiohydrazide5hwhich was converted into 1,3,5‐triphenyl‐1,2,4‐triazolo[3,4‐c]‐1,2,4‐triazole (9). The latter was also prepared from 3‐phenyl‐5‐methylthio‐4H‐1,2,4‐triazole (6) and2a.

ISSN:0941-1216    

DOI:10.1002/prac.19983400209

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

Synthesis and Transport Investigations of Dioxapolyazacalix[4]arenes and Triazino Crown EthersSynthesis and characterisation of new dioxapolyazacalix[4]arenes5a–cand triazino crown ethers9a–iare described. The structures and conformations of these novel macrocyclic ring systems have been investigated by various NMR methods. Transports of metal ions across a liquid membrane are also repor

ISSN:0941-1216    

DOI:10.1002/prac.19983400210

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractBase‐catalyzed cyclization of the naphthoquinone5afforded the 1,2‐dihydroanthraquinone6a. The bisalkylation products9and10were obtained by Stille‐type chain elongation of the corresponding triflate6bwith the stannanes7or8. The dihydroanthraquinone9is a potential precursor for the SS‐228 Y‐type angucyclinones, where as the diketone10can be converted to 8‐deoxytetrang

ISSN:0941-1216    

DOI:10.1002/prac.19983400211

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY