Additivity rules pyridine

Six-membered conjugated heterocycles which contain nitrogen atoms (azines) have also been extensively examined by nitrogen NMR methods (ref. Id, pp. 218-219). Additivity rules for their nitrogen chemical shifts, relative to that of pyridine, have been reported (113) in terms of 1,2-(—73 4 ppm), 1,3- (+22 3 ppm), and 1,4-interactions (—20 6 ppm) in the six-membered ring. The observed shift for 1,2,4,5-tetrazine (113)... 

A regression analysis has been performed (45) on the chemical shifts of some azine-N-oxides in terms of 10 parameters which include interactions between the N-0 moiety and the nitrogen atoms at positions 2, 3, and 4 in the six-membered ring. Effects due to additional fused rings in the system and corrections for interactions between pyridine-type nitrogen atoms are also included. The additivity rules for the shifts are then used to predict those for a number of azine N-oxides which have been hitherto unknown or not examined by nitrogen NMR spectroscopy. (45)... 

Aroma2 Rule C-replaced benzenoids are more aromatic than substituted benzenoids, e.g.. Pyridine and Pyiimidine vs. Phenol and Aniline ordering aromaticity in Table 4.5 this rule extends the substituted versus addition rules in aromaticity historical definition (see Introduction) AromaS Rule double-C-replaced annulens have greater aromaticity than mono-C-replaced annulenes, e.g., this is... 

Once the above system of I in solvent HS has been studied, one can determine the properties of an additional base B (e.g. pyridine) in this medium. Here the electroneutrality rule yields... 

Halofluorinations take place, as a rule, regioselectively (Markovnikov addition), the olefinic carbons can be substituted with a variety of substituents ranging from alkyl or aryl groups to different electron-withdrawing functions see for example refs 31 and 178-180. Bromo-fluorination of 4-/m-butyl-l-methylcyclohexene with /V-bromosuccinimide in 70% hydrogen fluoride/pyridine gave two stereoisomers 1 and 2.181... 

Furan and acetyl nitrate give an addition product which is converted by pyridine into 2-nitrofuran (Scheme 10). The positions in which substituted furans undergo nitration with acetyl nitrate are shown in diagrams (59)-(63) and illustrate the rules of orientation. 

As expected, nucleophilic substitution of quinoline occurs in the hetero ring, as a rule in the 2- or 4-position. S Ar processes proceed faster in quinoline than in pyridine, because the fiised benzene ring stabilizes the addition products by conjugation. 

As a rule, the formation of macromolecular metallocomplexes include a special design of macroligand, their functional groups, and MX with its own and frame ligands, which are retained in the inner coordination sphere of metal after immobilization. In addition to the halides, carbonyls, nitrosyls, phosphines, acetylacetonates and CH3COO-, pyridine and Dipy can also be used as frame ligands [35]. 

Additionally, almost 10% of acetate was found as adsorbed acetic acid. The incubation of radio-labeled sample with non-radio active acetic acid in pyridine caused a 10% decrease in the amount of acetate groups. The exchange of 0-1-l C-acetate or N-l-l C-acetate with acetic acid was ruled out since 2-naphthyl-l-l C-acetate and carbazole-l- C-acetate had the same specific activity after incubation with non-radio active acetic acid in pyridine. 

Intramitochondrial hydrolysis of pyridine nucleotides and release of nicotinamide from mitochondria exposed to hydroperoxide [9] suggested the existence of an intramitochondrial NAD" glycohydrolase. Subsequent studies [12] located the enzyme on the inner side of the inner mitochondrial membrane. Activity was also present in the matrix fraction of mitochondria, but release from the iiuier membrane into the matrix fraction during isolation of the membrane was not ruled out. The activity in iimer mitochondrial membranes (submitochondrial particles, SMP) is inhibitable by ATP [11]. In addition, ATP-sensitive covalent modification of SMP concomitant with enzymatic hydrolysis of NAD was indicated. 

In contrast, it has been suggested that the reaction proceeds via a pyridyne. The available evidence, some of which was mentioned above, is sufficient to rule out this as a general mechanism . In addition, when a mixture of pyridine and pyridine-3D is partially aminated with sodamide, the unreacted material has the same isotopic composition as the starting material,... 

When 1 was treated with pyridine (1.5 equiv) in dry diethyl ether or chloroform, addition of water (1.2 equiv) afforded a new complex (9) that was converted to 7 over 1-2 hours (Scheme II). H NMR indicated a formulation involving a 1 1 1 ratio of bis(trimethylsilyl)cyclopentadienyl, acetylacetonate, and pyridine ligands. The infrared spectrum did not show O-H absorotions, which ruled out an aquo or hydroxo complex. The oxo-bridged dimer 9 is proposed based on these data and on the facile hydrolysis of 9 to 7. Other structures for 9 are possible. Unfortunately, the limited thermal and hydrolytic stability of 9 precluded its further characterization. 

As mentioned earlier, in catalyses by elemental iodine or perfluorinated iodoaUcanes [86-88, 124] it is sometimes difficult to rule out that traces of acid contribute at least partially to the observed reactivity. Thus, in this study our goal was to show as unambiguously as possible that halogen bonding is indeed responsible for the activation of the substrate. In the solvolysis reaction of benzhydryl bromide, accidental acid catalysis by impurities can safely be ruled out as the use of even 1 equiv. of the strong acid HOTf (trifluoromethanesulfonic acid) yields only 25% of 22 under otherwise identical conditions. Furthermore, trace amounts of acid can be quenched by the addition of 10 mol% of pyridine to the reaction, whereas the effect of the bis(iodoimidazohum) activators is only marginally affected by this additional component. 

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