Schiff bases structure

Scanning force morphology (SFM), 490 Schiff base structures, 152 Schrock alkylidenes, 433 Schrock-type alkylidene catalysts, 438 Sealants... 

In order to test this very simple idea, the MHOC tail was incorporated into the prototypical bent-core double-Schiff-base structure, providing as target the mesogen (Rac)-MHOBOW (9),53 whose structure and phase sequence is shown in Figure 8.30. The racemate was prepared in order to avoid complications in the interpretation of the results caused by molecular enantiomeric... 

Ir and nmr analysis of the condensation products of primary amines with aldehydes and ketones are in favor of the Schiff-base structure (46a). Nevertheless, these substances react with aryl azides in chloroform solution in the tautomeric enamine form (46b) yielding aminotriaiolines.206 225- 227 It proves that the dipolarophilic activity of an enamine olefin bond is much greater than that of an azomethine bond. 

Huisgen has stated that the driving force behind the 1,3-dipolar addition is stronger the more the loss of T-bond energy in the reactants is overcompensated by the energy of the two new bond energy is O-N < N-N < C-N, azides do not add at all to aldehydes and ketones and add with more difficulty to nitriles than to olefins. Phenyl azide, for instance, adds preferentially to the C-C double bond of acrylonitrile.194 103 This is also the reason why the condensation products of aldehydes and primary amines, which essentially exist in the Schiff-base structure 46a, react in the tautomeric enamine form 46b.2 ... 

The principles of the above reactions form the basis of a series of important metabolic interconversions involving the coenzyme pyridoxal phosphate (structure 2.41). This condenses with amino acids to form a Schiff base (structure 2.42). The pyridine ring in the Schiff base acts as an electron sink which very effectively stabilizes a negative charge. 

As discussed in Chapter 2, section C2, pyridoxal phosphate condenses with amino acids to form a Schiff base (structure 8.44). Each of the three groups around the chiral carbon at the top of structure 8.44 may be cleaved to give an anion that is stabilized by delocalization of the electrons over the 7r orbitals. 

The infrared spectra of solid M-2-naphthyl- and AT-o-tolyl-n-glucosyl-amine are considered by Legay as giving evidence for these compounds having a Schiff-base structure. Both give a peak at 6.05 n, usually caused by ... 

However, he did find an absorption band at 6.05 n for solid A -o-tolyl-o-glucosylamine, and also for fV-2-naphthyl-D-glucosylamine, indicating for the first time the existence of a Schiff-base structure for A -substituted glucosylamines in the solid state. For the other A -substituted o-glucosyl-amines tested (A-phenyl, A-p-nitrophenyl, and A-m-nitro-p-tolyl), no Schiff-base structure was indicated. All compounds exhibited a band at 2.88 n which could have been given by either an NH or an OH grouping. 

Likewise, triazoloquinazolinium iodides, prepared from 150 as outlined in Scheme 47, lead to tetrahydrotriazoloquinazolines (e.g., 151) the latter are generally difficult to isolate, probably because of the ring-chain tautomeric Schiff base structures 152 (76ACH419). 

The enrichment in nitrogen of humic substances extracted in EDA (Table 5) suggests that solvents containing this compound, or any other primary amine, would not be appropriate for use with humic substances. EDA readily reacts with carbonyl groups to form Schiff base structures. Such reactions are rapid when the protonated carbonyl group reacts with the nonpro-tonated amine. Thus the maximum reaction rate occurs when the product of the concentrations of the protonated carbonyl groups and free amines is maximum. The reaction continues, but at a rate which decreases in an exponential manner, as the pH is raised or lowered from the optimum value for the reaction. 

The same was observed for the following two polymers (3.44) and (3.45) with the mesogenic units of a schiff base structure (Frosini et al, 1981). The polyacrylate is a smectic liquid crystal from 93 °C to 258 °C. The polymethacrylate does not form any liquid crystalline phase. 

The SchifF-base structure (XXVI) was proposed (Legay, 1952) for N-o-tolyl-o-glucosylamine, because it exhibited a C=N band at 1653 cm . However, the pure compound shows no band (Ellis, 1966) at 1653 cm , indicating that the structure is cyclic, probably the pyranoid form (XXVII). All the spectra of N-substituted glycosyl-amines examined by Ellis (1966) indicated the compounds to be cyclic. 

The presence of the l,ll-diamino-6-oxoundecane in hydrolysates of heat-treated nylon-6 [359] thus is obviously the result of the hydrolysis of the Schiff base moiety. The absence of the corresponding oxo-structure in the hydrolysates of gelled nylon-6,6 may be indicative of an analogous decarboxylation mechanism entailing intramolecular acid amide interaction Hydrolysis of the Schiff base structure yields, as indicated, hexamethylene diamine and cyclopentanone, both of which have been found. 

When the reaction was first applied to the sugars, amorphous products were obtained which were considered to have the Schiff base structure. By heating glucose or fructose in an alcoholic solution of aniline, Sorokin 10) was able to prepare crystalline products, although the crystallinity of iV-phenyl-D-glucosylamine is in doubt 10, 11). Many other crystalline glycosylamines are known at present in the aliphatic 5, 12) and aromatic 13,14) series of amines. 

Infrared spectroscopic data (28) for solid A-o-tolyl- and iV-jS-naphthyl-D-glucosylamine shows peaks at 6.05 /x- Such peaks are usually due to a —C=N— grouping, indicative of a Schiff base. The compounds p-tolyl-and p-nitrophenyl-D-glucosylamine, however, do not show such a peak. In the reaction between 2,3,4,5-tetra-0-acetyl-aZde%do-D-ribose and aniline in ethanol or methanol, crystalline compounds corresponding to the Schiff base type (V) were isolated these contained one molecule of ethanol or methanol. The infrared absorption spectra of these compounds, however, showed that they did not have the Schiff base structure (V), but were of... 

Methacrylate monomers having a Schiff-base structure... 

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