In unsaturated

Carbon can also form multiple bonds with other carbon atoms. This results in unsaturated hydrocarbons such as olefins (alkenes), containing a carbon-carbon double bond, or acetylenes (alkynes), containing a carbon-carbon triple bond. Dienes and polyenes contain two or more unsaturated bonds. 

In unsaturated molecules electronic effects can be transmitted by mesomerism as well as by inductive effects. As with the latter, the mesomeric properties of a group are described by reference to hydrogen. Groups which release electrons to the unsaturated residue of the molecule are said to exert a +Af effect, whereas groups which attract electrons are said to exert a —Af effect. In aromatic structures the important feature of an M-substituent is that it influences the 0- and p-positions selectively. 

TetrabromophthalicAnhydride. Tetrabromophthalic anhydride [632-79-1] (TBPA) is widely used as a reactive flame retardant in unsaturated polyesters as weU as the precursor to a number of other fine retardants. Polyesters prepared from this compound have relatively poor photochemical stabiUty and tend to discolor upon exposure to light. This tendency to discolor can be reduced, but not eliminated, by the use of uv stabilizers. 

Cyclo acylations leadUy take place in intermoleculai acylations involving bifunctional acylating agents. Both functional groups may be acyl (as in the case of a,CO-diacyl halides) or one may be an alkylating group (as in unsaturated acyl halides or certain haloacyl halides) (18). 

Maleic anhydride itself has few, if any, consumer uses but its derivatives are of significant commercial interest (161). The distribution of end uses for maleic anhydride is presented in Table 9 for the year 1992 (182). The majority of the maleic anhydride produced is used in unsaturated polyester resin (see Polyesters, unsaturated). Unsaturated polyester resin is then used in both glass-reinforced appHcations and in unreinforced appHcations as shown in Table 10 (183). 

Trimethylolpropane (TMP), the reduced crossed aldol condensation product of //-butyraldehyde and formaldehyde, competes in many of the same markets as glycerol (qv) and pentaerythritol. The largest market for TMP is as a precursor in unsaturated polyester resins, short-oil alkyds, and urethanes for surface coatings (see Alkyd resins). 

The presence of ammonia during hydrogenation suppresses formation of secondary amines and inhibits hydrogenation of double bonds in unsaturated nitriles. Eatty amines are used as corrosion inhibitors, flotation agents, quaternary salts for sanitizing agents and textile fabric softeners, and surface-active agents. 

Saturated large rings may form nitrogen radicals by H abstraction from N, or abstraction may occur in the a- or /3-positions in nonnitrogen systems. Oxepane gives the radical in the 2-position, with subsequent cleavage and reclosure of the intermediate carbenoid to cyclohexanol (Section 5.17.2.1.5). In unsaturated large systems a variety of reactions, unexceptional in their nature, are found. Some azepines can be brominated by A -bromosuc-cinimide others decompose under similar conditions (Section 5.16.3.7). 

This apparent characteristic enhancement in the basicity has been used quite frequently for the determination of the position of a double bond with respect to the nitrogen atom in unsaturated amines. The cases such as neostrychnine (134) and dehydroquinuclidine (139) in which the protonation at the 8-carbon atom cannot occur due to the lack of overlap between the electron pair on the nitrogen atom and the tt electrons of the double bond, since this would involve the formation of a double bond at the bridgehead— a violation of Bredt s rule—show a decrease in basicity. For instance the basicities of quinuclidine (140) and dehydroquinuclidine (139) have been shown by Grob et al. (82), to differ by 1.13 pK units in aqueous solution at 25. This decrease in basicity has been attributed to the electron-withdrawing inductive effect of the double bond. 

In addition to unsaturated fatty acids, several other modified fatty acids are found in nature. Microorganisms, for example, often contain branched-chain fatty acids, such as tuberculostearic acid (Figure 8.2). When these fatty acids are incorporated in membranes, the methyl group constitutes a local structural perturbation in a manner similar to the double bonds in unsaturated fatty acids (see Chapter 9). Some bacteria also synthesize fatty acids containing cyclic structures such as cyclopropane, cyclopropene, and even cyclopentane rings. 

Reduction of unsaturated aldehydes seems more influenced by the catalyst than is that of unsaturated ketones, probably because of the less hindered nature of the aldehydic function. A variety of special catalysts, such as unsupported (96), or supported (SJ) platinum-iron-zinc, plalinum-nickel-iron (47), platinum-cobalt (90), nickel-cobalt-iron (42-44), osmium (<55), rhenium heptoxide (74), or iridium-on-carbon (49), have been developed for selective hydrogenation of the carbonyl group in unsaturated aldehydes. None of these catalysts appears to reduce an a,/3-unsaturated ketonic carbonyl selectively. 

Chain transfer reactions involving the monomer could also result in unsaturation of the chain ends according to the following two reactions [Eqs. (3) and (4)]. 

Maleic anhydride is important as a chemical hecause it polymerizes with other monomers while retaining the double bond, as in unsaturated polyester resins. These resins, which represent the largest end use of maleic anhydride, are employed primarily in fiber-reinforced plastics for the construction, marine, and transportation industries. Maleic anhydride can also modify drying oils such as linseed and sunflower. 

When crude oil is refined, some of the processes yield additional gaseous products. The C3 and C4 constituents differ from those released from crude oil or from NGLs, which are saturated hydrocarbons. Refinery gases are high in unsaturates, e.g. propane (propylene) and butane (butylenes). These unsaturated hydrocarbons are a valuable source of chemical process intermediates and enjoy a large market alongside naphtha. 

Pople, J. A., Trans. Faraday Soc. 49, 1375, "Electron interaction in unsaturated hydrocarbons."... 

Murphy, R. C. Mass Spectrometry of Lipids. New York Plenum Press, 1993. An extensive review of techniques for locating double bonds in unsaturated fatty... 

A. Hausberger As we mentioned earlier, the light hydrocarbons do not seem to affect catalyst activity, and they do reform into methane. However, you can increase the hydrocarbon content to levels where they do depress the methanation activity. If the hydrocarbons are high enough in unsaturation, they will form carbon when they get to a certain level. As far as hydrogen cyanide and ammonia are concerned, we don t expect them to affect the nickel methanation catalyst. 

NMHC. A large number of hydrocarbons are present in petroleum deposits, and their release during refining or use of fuels and solvents, or during the combustion of fuels, results in the presence of more than a hundred different hydrocarbons in polluted air (43,44). These unnatural hydrocarbons join the natural terpenes such as isoprene and the pinenes in their reactions with tropospheric hydroxyl radical. In saturated hydrocarbons (containing all single carbon-carbon bonds) abstraction of a hydrogen (e,g, R4) is the sole tropospheric reaction, but in unsaturated hydrocarbons HO-addition to a carbon-carbon double bond is usually the dominant reaction pathway. 

As can be seen from Eqs. 5 and 15, this approach allows the polarizability to be decomposed in terms of its most contributing excited states. In unsaturated polymers, the Ti-symmetry bands and particularly their highest-energy states present the largest contribution to Aa, (oo). This fact has been highlighted several times [28,37-38]. 

A pyrolysis technique was investigated as a method for the chemical recycling of glass fibre-reinforced unsaturated polyester SMC composites. The proeess yielded liquid products and gases and also a solid residue formed in the pyrolysis of glass fibres and fillers. The solid residue was used as a reinforeement/filler in unsaturated polyester BMC composites, and the influenee on mechanical properties was studied in comparison with BMC prepared entirely from virgin materials. 

As in molecular chemistry, an alternative path to compensate for electron deficiency is the formation of multiple bonds, through 7r-interactions, as in unsaturated and aromatic molecular systems. Our work in Houston focuses on probing the efficacy of the ZintI concept in rationaUzing stoichiometries, crystal structures and chemical bonding of complex electron-poof ZintI phases that exhibit novel i-systems. Their chemical bonding is reflected by their unusual crystal structures related to unsaturated hydrocarbons [53]. 

The carbon chains of samrated fatty acids form a zigzag pattern when extended, as at low temperamres. At higher temperatures, some bonds rotate, causing chain shortening, which explains why biomembranes become thinner with increases in temperamre. A type of geometric isomerism occurs in unsaturated fatty acids, depending on the orientation of atoms or groups around the axes of double bonds, which do not allow rotation. If the acyl chains are on the same side of the bond, it is cis-, as in oleic acid if on opposite sides, it is tram-, as in elaidic acid, the tram isomer of oleic acid (Fig-... 

Nickel metal successfully catalyzes the hydrogenation of double bonds in unsaturated hydrocarbons such as propylene and butene. Can this metal also catalyze the dehydrogenation of alkanes such as propane and butane ... 

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