Nucleophile reactions with

If the dye contains no mobile substituents ia the chain, nucleophiles attack primarily the end carbon atoms (changing of terminal residues). Streptocyanines can be hydroly2ed ia aqueous alkaline solution to form the corresponding merocyanines and then the oxonoles (71,72). These processes are reversible. Nucleophilic reactions with the methylene bases of the corresponding heterocycles result ia polymethines containing new end groups (Fig. 

Cobalt(II) complexes of three water-soluble porphyrins are catalysts for the controlled potential electrolytic reduction of H O to Hi in aqueous acid solution. The porphyrin complexes were either directly adsorbed on glassy carbon, or were deposited as films using a variety of methods. Reduction to [Co(Por) was followed by a nucleophilic reaction with water to give the hydride intermediate. Hydrogen production then occurs either by attack of H on Co(Por)H, or by a disproportionation reaction requiring two Co(Por)H units. Although the overall I easibility of this process was demonstrated, practical problems including the rate of electron transfer still need to be overcome. " " ... 

B. Nucleophilic Reactions with Metal Isocyanide Complexes... 

The subjects of structure and bonding in metal isocyanide complexes have been discussed before 90, 156) and will not be treated extensively here. A brief discussion of this subject is presented in Section II of course, special emphasis is given to the more recent information which has appeared. Several areas of current study in the field of transition metal-isocyanide complexes have become particularly important and are discussed in this review in Section III. These include the additions of protonic compounds to coordinated isocyanides, probably the subject most actively being studied at this time insertion reactions into metal-carbon bonded species nucleophilic reactions with metal isocyanide complexes and the metal-catalyzed a-addition reactions. Concurrent with these new developments, there has been a general expansion of descriptive chemistry of isocyanide-metal complexes, and further study of the physical properties of selected species. These developments are summarized in Section IV. 

Xanthobacter sp. strain Py2 may be grown with propene or propene oxide. On the basis of amino acid sequences, the monooxygenase that produces the epoxide was related to those that catalyzes the monooxygenation of benzene and toluene (Zhou et al. 1999). The metabolism of the epoxide is initiated by nucleophilic reaction with coenzyme M followed by dehydrogenation (Eigure 7.13a). There are alternative reactions, both of which are dependent on a pyridine nucleotide-disulfide oxidoreductase (Swaving et al. 1996 Nocek et al. 2002) ... 

The nucleophilic reaction with the solvent is of crucial importance. Monomers with lower oxidation potentials (aniline and pyrrole) can easily be polymerized even in aqueous electrolytes. For monomers with higher oxidation potentials, aprotic solvents must be used, such as acetonitrile... 

Nucleophilic reactions with coordinated NO are illustrated by the well known reversible reaction of hydroxide ion with the nitrosyl ligand of... 

Calculations of the nucleophilic reactions with MeO" were performed for the carbocations 4H+, 5H+ and 6H+ in order to simulate the crucial step of aza-PAH/adduct formation. These reactions were considered as models for evaluation of the reactivity trend for these carbocations toward nucleophiles. Thus, the thermodynamical tendency of each carbocation to react with the nucleophilic sites of DNA was estimated. 

Figure 4. Calculated nucleophilic reactions with MeO. Adaptedfrom reference 26.

Diamines of varying structure show rate enhancements of 20-200 fold, compared to monofunctional aliphatic amines, in nucleophilic reactions with N-acetylimidazole (Page and Jencks, 1972). These were attributed to intramolecular general base catalysis of proton removal from the attacking nitrogen, viz.. 

In the absence of nucleophile, neither the 412 nm species nor the formation of the radical anion, nor that of the photosubstitution product is found. It is concluded therefore that the 412 nm species results from some kind of interaction between the (excited) aromatic compound and the nucleophilic reagent. The character of this aromatic compound-nucleophile-complex is as yet unknown. However, in our present view, the nature of the complex has to allow for the formation of both the radical anion and the photosubstitution product(s). An attractive possibility for this complex remains the a-complex, in formal analogy with the Meisenheimer complexes in the thermal nucleophilic reactions with aromatic compounds. An exciplex forms another possibility. 

Thiols undergo the same types of nucleophilic reaction with carboxylic acid derivatives as do alcohols. However, reactivity tends to be increased for two reasons. First, sulfur, because of its larger size, is a better nucleophile than oxygen (see... 

Section 6.1.2) second, RS is a better leaving group than RO (see Section 6.1.4), again because of size and the less localized electrons. Simple nucleophilic reactions with H2S parallel those with H2O, and those with RSH parallel those with ROH. This gives rise to carboxylic acid derivatives containing sulfur, such as thioacids and thioesters. 

Hydroxylamines, as potentially ambident nucleophiles, can utilize either the basic N atom or the O atom in nucleophilic reaction with a variety of electrophilic centers . This is illustrated in Scheme 2 through the box on the left hand side of the diagram. Also shown in Scheme 2 are the dissociation equilibria K,, K a, and K 2- The equilibrium denoted as... 

Af-Acetoxy-Af-butoxybenzamide (145, R = Bu, = Me) reacted with glutathione in DMS0-t/6/D20 and with (L)-cysteine methyl and ethyl esters in methanol-tij. NMR studies indicated a bimolecular process, with thiol consumed at twice the rate of Af-acyloxy-A-alkoxyamide. Like the Al-aminohydroxamic esters described in the previous section, the intermediate A-thioalkylhydroxamic ester (146) is also unstable, being susceptible to a non-rate-determining, secondary nucleophilic reaction with the reactive thiol . ... 

The speculative mechanism(20-21) as outlined in Equation 2 involves initial reaction between palladium(II) and butadiene to form a -complex 2 followed by a nucleophilic reaction with carbon monoxide and methanol to give 3. 

Dimethyl-2-vmyl-5(4/i/)-oxazolone (VDMO) 140 and 4,4-dimethyl-2-isopro-penyl-5(4//)-oxazolone 328 have been extensively investigated as monomers (Fig. 7.32). Copolymeiization of 140 or 328 with other monomers, for example, acrylates or acrylamides produces reactive polymers that are conveniently further modified by nucleophilic reaction with alcohols, amines, or other nucleophiles. ""... 

Problem 14.44 Since (CH,)2S==0 is an ambident nucleophile, reaction with CHjI could give ((CH,),s =oir or [(CH3)jS=0—CH,]I. (a) What type of spectroscopy can be used to distinguish between the two products (b) Predict the major product. <... 

We have compared three different polymer samples in the molecular weight range of 600 to 60,000 but only in regard to the nucleophilic reaction with nitrophenyl esters. The differences are small, less than a factor of 10. 

Most main group organometallic compounds undergo nucleophilic reactions with carbonyl groups, whereas 1,4-conjugate addition to enones... 

The possible ambiguities that may arise in ring syntheses based upon nucleophilic reactions with a-halo ketones are also exemplified by the reactions with a-lithioaldimines leading to pyrrole formation, as shown in Scheme 73a (73TL3517). A similar problem could well arise in the related carbazole synthesis indicated in Scheme 73b if a less symmetrical substrate was employed (81TL1475). 

Interestingly, treating (>/4-cyclooctatetraene)Fe(CO)3 with acetyl chloride under Friedel-Crafts reaction conditions yielded unexpectedly222-223 the (>/2,>/3-8-e.x0-acetyl bicy-clo[3.2.1]octadienylium)Fe(CO)3 cation complex, presumably by rearrangement of the intermediate bicyclo[5.1.0]octadienylium isomer (Scheme 8). The structure of the rearranged cation was confirmed from the X-ray crystal structure and from the typical 1,3-cr.ji-allylic products obtained upon nucleophilic reaction with LiAlD4 and NaCN. The nucleophilic reaction of the more bulky iodide occurs, however, on the metal. 

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