摘要:

AbstractWhereas diverse and highly refined fiber optics have long been in technical use for the conduction of visible light, traditional but expensive silica glass lenses and prisms have had to be utilized until quite recently for the transmission of ultraviolet light. The reason for this was the lack of suitable materials. UV light cannot be transported to any technically useful extent either with pure glass‐glass (core and sheath materials) light guides or with plastic‐plastic light guides. UV light guides for wavelengths down to 200 nm can be produced by combination of a silica glass as the core material with a tetrafluoroethylene‐hexafluoropro pylene copolymer or methylpolysiloxane as the sheath material. Fiber optics of this type constitute a new aid for medical technology, medicine, and many technical and scientific fields, whose range of applications cannot yet be fully envi

ISSN:0570-0833    

DOI:10.1002/anie.197304391

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

摘要:

AbstractSurprisingly little is still known about many aspects of the system “elemental sulfur”, in spite of its being one of the longest known and common “chemical substances” and today available cheaply and in great purity. This paper summarizes some of the newer investigations that have increased our understanding of this

ISSN:0570-0833    

DOI:10.1002/anie.197304451

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

摘要:

AbstractThis report reviews the preparation of hydrazidinyls and their chemical and physical properties.

ISSN:0570-0833    

DOI:10.1002/anie.197304551

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

摘要:

AbstractThe Bredt rule, which proved useful in earlier decades mainly as an exclusion criterion in the assignment of structures, has in recent years become the stimulus for efforts to synthesize strained bicyclic systems with a bridgehead double bond. On the basis of the ring‐strain forces operating in such systems, an extended Bredt rule is discussed. The “Bredt comgounds” to which this rule applies, which include bicyclic systems not prevoously consodered from this point of view (e.g. bridged methylenecyclopropanes), form a clearly circumscribed, interesting field within the chemistry of highly‐strained hydrocarbons with ring unsat

ISSN:0570-0833    

DOI:10.1002/anie.197304641

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

摘要:

AbstractIn contrast to carbon, silicon fails to form multiple bonds that are stable at room temperature. Consequently molecules in which silicon exhibits coordination numbers (CN) of 1, 2, and 3 may only be obtained at very high or low temperatures. Under these conditions their structural features, including multiple bonds, resemble those of carbon. On the other hand, silicon is capable of forming various hexacoordinated compounds making use of its d orbitals. Nitrogen and oxygen bonded to silicon develop an unusual stereochemistry: planar nitrogen, nearly or completely linear oxygen, and considerable shortening of SiN, SiO, and SiF bonds are specific examples. N(SiR3)2and CH2SiR3ligands permit stabilization of unusually low CNs of many metals and give rise to amino and alkyl derivatives of unexpectedly high stability due to the particular electronic, the R3Si group.

ISSN:0570-0833    

DOI:10.1002/anie.197304741

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

摘要:

AbstractThe polymerizability of compounds such as 1,l‐disubstituted ethylenes, aldehydes, ketones, isocyanates, and five‐ and six‐membered ring compounds is determined largely by thermodynamic considerations. The transition from non‐polymerizability to polymerizability, correspondlng to a change in the sign of ΔG, is often quite sharp. Factors which generally make the free energy of polymerization more negative, and which therefore favor polymerization, are low temperature, high pressure, and high monomer concentration. Additional driving force is sometimes available if the monomer is in the supercooled (glassy) state rather than the crystalline state, or if the polymer crystallizes on formation. Alkyl substituents have an unfavorable effect on polymerizability; halogen substituents have a favorable effect. Many monomers which do not homopolymerize for thermodynamic reasons will copolymerize with a second monomer to the extent of forming copolymers containing 50 or even 66 mol per cent of the first

ISSN:0570-0833    

DOI:10.1002/anie.197304871

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197304952

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197304971

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197304991

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197305001

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY