Mode of formation

Primary aromatic amines differ from primary aliphatic amines in their reaction with nitrous acid. Whereas the latter yield the corresponding alcohols (RNHj — ROH) without formation of intermediate products see Section 111,123, test (i), primary aromatic amines 3neld diazonium salts. Thus aniline gives phcnyldiazonium chloride (sometimes termed benzene-diazonium chloride) CjHbNj- +C1 the exact mode of formation is not known, but a possible route is through the phenjdnitrosoammonium ion tlius ... 

F. L. Galeener, in R. A. Weeks and D. L. Kinser, eds.. Effects of Modes of Formation on the Structure of Glasses, Trans Tech PubHcations Ltd., Brookfield,... 

One useful classification of graphite depends on the mode of formation that leads to three physically distinct common varieties dake, lump, and amorphous. The term dake is self-explanatory dake forms occur disseminated in rock. Lump graphite occurs in fissure-filled veins in pegmatite dikes, also associated with chip and the rarer needle forms. Amorphous graphite occurs in beds that were once coal, but fine-grained, easily ground vein graphite is also classified as amorphous. 

A number of subdivisions of the maceral groups have been developed and documented by the International Commission on Coal Petrology (14). Table 1 Usts the Stopes-Heeden classification of higher rank coals. Periodic revisions include descriptions of the macerals, submacerals, morphology, physical properties, and chemical characteristics. Theories on the mode of formation of the macerals and their significance in commercial appUcations are also included of Reference 14. 

Beyond the scope of this chapter, but similar in mode of formation and reactivity to the title compounds, are some three-membered rings with three heteroatoms. Oxadiaziridine... 

In view of its possible interest as the mode of formation of harman, harmine and harmaline in plants, Kermack, Perkin and Robinson investigated the conversion of tryptophan (II) into harman (I) and nor-harman (IV). The latter is produced when tryptophan is condensed with formaldehyde in presence of dilute sulphuric acid and the product (III) oxidised by potassium dichromate. Harman is formed when formaldehyde in this process is replaced by acetaldehyde. 

Irradiation of a benzene solution of (267) containing a sixfold excess of l-acetoxybut-l-en-3-one leads to the formation of the two cyclobutane adducts [(278) 47% yield of converted starting material] and [(279) 20% yield], and the acetylcyclobutene [(280) 9 % yield]. The mode of formation of the product (280) is not yet established unambiguously, although it is not formed during workup. 

Several products other than 2,2 -biaryls have been isolated following reaction of pyridines with metal catalysts. From the reaction of a-picoline with nickel-alumina, Willink and Wibaut isolated three dimethylbipyridines in addition to the 6,6 -dimethyl-2,2 -bipyridine but their structures have not been elucidated. From the reaction of quinaldine with palladium-on-carbon, Rapoport and his co-workers " obtained a by-product which they regarded as l,2-di(2-quinolyl)-ethane. From the reactions of pyridines and quinolines with degassed Raney nickel several different types of by-product have been identified. The structures and modes of formation of these compounds are of interest as they lead to a better insight into the processes occurring when pyridines interact with metal catalysts. 

During this work the presence of small quantities of piperidine and -picoline were also noticed. The exact mode of formation of these products remains to be elucidated, but the formation of piperidine shows that sufficient hydrogen remains on the catalyst to bring about some hydrogenation of the pyridine. 

Bildungs-geschwindigkeit,/. speed of formation or development, -gleichung, /. equation of formation structural equation, -schicht, /. formative layer specif.. (Bot.) cambium, -warme, /. heat of formation, -weise, /. mode of formation, bildwerfen, v.t. project (trtctures). 

Another internal acetal, methyl 2-0-benzoyl-3,4-0-benzylidene-/ -D-arabinopyranoside 103 (84), behaves in an analogous manner, except that the isomeric 4-bromo (104) and 3-bromo (105) benzoate derivatives are formed in a ratio of 1 1. The identity of 104 (l-xylo) can be deduced from its mode of formation from a presumed benzoxonium ion (106)... 

The azuleno[l, 8-rc/]azepine 35 is formed as a byproduct from the reaction of excess benzonitrile with 7-isopropyl-l,4-dimethylazulene (guaiazulene, 34) in the presence of a strong base.111 The mode of formation of this unexpected fully conjugated 14jt system has been discussed. 

Scheme 13 Possible mode of formation of the cyclopentadiene 61 isomeric with 60a by 1,2-migration of the dimethylamino group via a bridged zwitterionic intermediate 62 [44]...

The formation of the tricarbonylchromium-complexed fulvene 81 from the 3-dimethylamino-3-(2 -trimethylsilyloxy-2 -propyl)propenylidene complex 80 and 1-pentyne also constitutes a formal [3+2] cycloaddition, although the mechanism is still obscure (Scheme 17) [76]. The rf-complex 81 must arise after an initial alkyne insertion, followed by cyclization, 1,2-shift of the dimethylamino group, and subsequent elimination of the trimethylsilyloxy moiety. Particularly conspicuous here are the alkyne insertion with opposite regioselectivity as compared to that in the Dotz reaction, and the migration of the dimethylamino functionality, which must occur by an intra- or intermo-lecular process. The mode of formation of the cyclopenta[Z ]pyran by-product 82 will be discussed in the next section. 

Recently, Akiyama et al. reported an enantiocontrolled [3+2] cycloaddition of chirally modified Fischer alkenylcarbene complexes 180 with aldimines 181 under Lewis-acid catalysis (Sn(OTf)2) to afford enantiomerically pure 1,2,5-trisubstituted 3-alkoxypyrrolines 182 (Scheme 40) [121]. The mode of formation of these products 182 was proposed to be a [4+2] cycloaddition, with the complexes 180 acting as a 1-metalla- 1,3-diene with subsequent reductive elimination. Upon hydrolysis under acidic conditions, the enol ethers give the enantiomerically pure 3-pyrrolidinones 183 (Table 9). 

Figure 5. The nature of the product ions from ethylene as a function of the energy absorbed by the molecule during the charge exchange (20). (A dotted line has been used where the mode of formation is uncertain)...

In all experiments, unless otherwise stated, approximately 5% oxygen was added to the reaction mixture to remove free radicals from the system and thereby simplify the derivation of the modes of formation of the hydrocarbon products. 

There is much evidence that the mechanism" of the 1-pyrazoline reactions generally involves diradicals, though the mode of formation and detailed structure (e.g singlet vs. triplet) of these radicals may vary with the substrate and reaction conditions. The reactions of the 3 f-pyrazoles have been postulated to proceed through a diazo compound that loses N2 to give a vinylic carbene." ... 

Figure 1. Structural series of vanadium borides and mode of formation VnB + i (n - 1) VB + VB2 n = 1,2,3,5. The structures are projeeted along [100] large eireles are metal atoms small eircles are B atoms filled circles are atoms in x — 1/2, open eireles are atoms in x = 0.

Figure 2. Structural series of Cr-AI borides and mode of formation Crn. AlB2 = CrAI + nCrB2, n = 1,2. The structures are projected along [001] the B net and Al atoms in z = 1 /2 Cr atoms are in z = 0.

Mode of formation Binuclear species Specific decomposition rate at 25.0 °C (sec ) log k for formation of SCN complex Ref... 

In a similar study, Gray et al. (60) investigated the possible formation of N-nitrosamines in heated chicken frankfurters which been prepared with various levels of nitrite (0-156 mg/kg). As expected, apparent N-nitrosamine levels increased with increasing concentrations of nitrite, but did not exceed 4 yg/kg except for two samples which contained 8 and II yg/kg of NMOR. The presence of these relatively high levels of NMOR was confirmed by mass spectrometry and raised the question as to its mode of formation. It was shown to be due to the morpholine present in the steam entering the smokehouse, as this amine is commonly used as a corrosion inhibitor in steam process equipment ( ). The detectable levels of NMOR in the Canadian study ( ) were also attributed in part to the use of morpholine as an anti-corrosion agent in the steam supply (62). 

In the last fifteen years there has been considerable interest in the analysis of volatile N-nitrosamines in foods. The primary focus has been on meat cured with nitrite (3 ) although nitrosamines have been shown to occur occasionally in other foods such as fish and cheese (, 3) Recently, attention has been directed to volatile nitrosamines in beer and other alcoholic beverages. The purpose of this paper is to review current information on the presence of nitrosamines in beer, and to discuss work done in our laboratory and elsewhere on the mode of formation of nitrosamines in beer. 

Figure 6. Proposed mode of formation for Pt multipods in the presence of silver species.

Fischer1-2 decided that the mode of formation, the reactions with hydrazines, aromatic diamines, and oxidizing agents, and the reduction to D-fructose could be explained by attributing to the open-chain form of D-glucosone the a-ketoaldehyde structure L. 

The starting materials for the chemical synthesis of kojic acid are also carbohydrates, but only hexoses and their derivatives have been used for this purpose. Maurer and his coworkers studied the synthesis extensively in order to clarify the mode of formation of the 7-pyrone system from carbohydrates. They succeeded in preparing di-O-acetylkojic acid (XLIII) by purely chemical means, first from D-glucose54 and then from D-galac-tose.67 The mechanism of formation of XLIII, which does not contain any asymmetric carbon atoms, was apparently not dependent on the configura-... 

Concerning the mode of formation of ES, we prefer the concept that the substrate in a monolayer is chemisorbed to the active center of the enzyme protein, just as the experimental evidence pertaining to surface catalysis by inorganic catalysts indicates that in these reactions chemisorbed, not physically adsorbed, reactants are involved. Such a concept is supported by the demonstration of spectroscopically defined unstable intermediate compounds between enzyme and substrate in the decomposition by catalase of ethyl hydroperoxide,11 and in the interaction between peroxidase and hydrogen peroxide.18 Recently Chance18 determined by direct photoelectric measurements the dissociation con-... 

Montgomery and Wiggins47 have studied the reaction of D-mannitol with hydrochloric acid in detail and the results throw some light on the mode of formation of isomannide from D-mannitol. When D-mannitol is heated under reflux with hydrochloric acid for several days, isomannide results in about 35-40% yield. But when D-mannitol is heated under pressure with fuming hydrochloric acid l,6-dichloro-l,6-didesoxy-D-mannitol (40% yield) and very little isomannide are formed. On examination of the residues after separation of isomannide from the first reaction mentioned above, no fewer than two monoanhydrohexitol derivatives and three new dianhydrohexitol derivatives were encountered. The products isolated are summarized in Table II. 

Dolomite is one of the most abundant sedimentary carbonate minerals but its mode of formation and its surface properties are less well known than for most other carbonate minerals. As we have mentioned, the nucleation of dolomites and its structural ordering is extremely hindered. There is a general trend for the "ideality" of dolomite to increase with the age of dolomite over geological time (Morse and Mackenzie, 1990). Most dolomites that are currently forming in surfacial sediments and that have been synthesized in the laboratory are calcium-rich and far from perfectly ordered. Such dolomites are commonly referred to as "protodolomites . Morse and Mackenzie (1990) have reviewed extensively the geochemistry (including the surface chemistry of dolomites and Mg-calcites. 

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