Linking groups acetylene

HiPtCI Cross-linked polystyrene substituted with cyanomethyl groups Acetylene with H5iCI3 63, 75... 

Polyphenylquinoxalines were cross-linked by acetylenic end-groups (Fig. 3.52), giving Tg = 321°C and good resistance to hot humid aging, but the addition of aliphatic hydrocarbon structure apparently sacrificed heat-aging resistance. Propargyl ether of bisphenol A (Fig. 3.53) was cured to a thermoset plastic with = 360°C. 

The core is not of the usual type but has a hollow centre surrounded by alternating benzene rings and acetylene-linking groups conventional ether and ester units have been used as the peripheral moieties. The materials were designed to exhibit columnar mesophases that would self-organise into molecular channels which could be used for transportation of electrons in applications such as molecular wires and membranes. However, as can be seen from compounds 26 and 27, they exhibit the phase, probably... 

When additional substituents are introduced in the 2- and/or 4-position, the thermal rearrangement gives products in which the substituents that were originally located in the 1- and 5-position of the quadricyclane are then located at C4 and C5 of the oxepin 7.30,123 In order to trap intermediates of this rearrangement reaction by intramolecular cycloaddition vinyl and acetylene groups were linked with different spacer groups to C2 of quadricyclane.123 In this manner two different intramolecular cycloadducts were isolated in addition to oxepin derivatives.123... 

Simple acetylenic allylic alcohols can be cyclized easily by tarf-butoxide, and since this base initiates prototropic shifts the vinylic link may.be E or Z such cyclizations proceed via exomethylene furans similar to 15.65 If necessary, UV irradiation can effect both the isomerization of an to a Z-alkene and the cyclization, leaving only the final adjustments to be made chemically.66 In a variation, methoxide plays the role of leaving group allowing very good yields to be attained (Scheme 10).67... 

The oxygen transfer from an ortho nitro group to a carbon-carbon triple bond has been studied by high-resolution mass spectrometry, linked scan techniques and chemical substitution81. Oxygen transfers to both acetylenic carbons were detected as parallel fragmentation pathways81. 

Silicones can be prepared in such a way that they contain only one percent or less of vinyl groups and silicon hydrides, which undergo a catalytic hydrosilylation reaction to give the desired cross-linking (Figure 18.3). Vinyl silanes are made by Si-H addition to acetylene, and thus two hydrosilylations are involved. 

The extent of acetylene insertion can be limited by the control of reaction conditions, such as the ratio of reactant acetylene to the number of Si-Si bonds or reaction time. In addition, if an organic substrate with two alkyne functional groups is used, cross-linked polymers are formed. Other palla-... 

These reactions, which have provided a means of inhibiting the flavin-linked monoamine oxidases, enable us to end on a clinical note. The monoamine oxidases are responsible for the deamination of monoamines such as adrenaline, noradrenaline, dopamine, and serotonin, which act as neurotransmitters. Imbalances in the levels of monoamines cause various psychiatric and neurological disorders Parkinson s disease is associated with lowered levels of dopamine, and low levels of other monoamines are associated with depression. Inhibitors of monoamine oxidases may consequently be used to treat Parkinson s disease and depression. The flavin moiety is covalently bound to the enzyme by the thiol group of a cysteine residue (equation 9.17). The acetylenic suicide inhibitor N,N-dimethyl-propargylamine inactivates monoamine oxidases by alkylating the flavin on N-5.25 A likely mechanism for the reaction is the Michael addition of the N-5 of the reduced flavin to the acetylenic carbon 2... 

The synthesis of optically active polymers is an important area in macromolecular science, as they have a wide variety of potential applications, including the preparation of CSPs [31-37]. Many of the optically active polymers with or without binding to silica gel were used as CSPs and commercialized [38]. These synthetic polymers are classified into three groups according to the methods of polymerization (1) addition polymers, including vinyl, aldehyde, isocyanide, and acetylene polymers, (2) condensation polymers consisting of polyamides and polyurethanes, and (3) cross-linked gels (template polymerization). The art of the chiral resolution on these polymer-based CSPs is described herein. 

An example of the enhanced cross-linking approach involves the pyrolysis of cyclic and linear oligosilane precursors that bear vinyl or acetylenic side groups.34 These are... 

The most efficient system of this type is obtained by the reduction of bovine serum albumin in the presence of molybdate. Apparently disulfide links in the peptide are broken and form thiolate groups which then bind molybdenum. In a borate buffer, this system will reduce dinitrogen and acetylene, although not using dithionite as an electron source. The turnover is similar to that of the iron-molybdenum cofactor (see Section XII), and dinitrogen reduction is inhibited by carbon monoxide and stimulated by ATP. The yield of ammonia is linearly dependent upon PN2, and the yield is also depressed in the presence of fumarate and, more surprisingly, succinate. It is calculated that the... 

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