Protonation intermolecular

In the dihapto mode the pyridine ring can be protonated intermolecularly at nitrogen, or even intramolecularly deprotonated at carbon. The first evidence for metal C—N insertion is the reaction of the metallaaziridine complex (111) with homogeneity LiHBEt3 in THF at low temperature that yields (112) (Scheme 49).251-254 Experiments with carbon nucleophiles (RMgCl, MeLi) in place of LiHBEt3 have provided valuable information to allow discrimination between... 

As with fumarate hydratase, the enzyme holds the abstracted proton (for up to 7 x 10 5 s) long enough so that a ds-aconitate molecule sometimes diffuses from the enzyme and (if excess ds-aconitate is present) is replaced by another. The result is that the new ds-aconitate molecule sometimes receives the proton (intermolecular proton transfer). The proton removed... 

Hydroalkoxylation. The cycloisomerization of unactivated unsaturated alcohols has been achieved using Al(OTf)3 (eq Reaction with unsaturated oximes also led to 1,2-oxaza heterocycles with five-, six-, and seven-membered rings. This catalyst provided a straightforward route to cyclic ethers with a Markovnikov-type regioselectivity. Notably, these conditions were used for efficient synthesis of olfactory-active rose oxide derivatives. Mechanistic studies showed that Al(OTf)3 coordinates to the oxygen atom of the alcohol, leading to strong acidification of the hydroxyl proton. Intermolecular hydroalkoxylation with methanol has also been reported. ... 

MHz H NMR spectrum of benzyl alcohol The hydroxyl proton and the methylene protons are vicinal but do not split each other because of the rapid intermolecular exchange of hydroxyl protons... 

Aldehydes can undergo an intermolecular oxidation—reduction (Canni22aro reaction) in the presence of base to produce an alcohol and a carboxyUc acid salt. Any aldehyde is capable of participating in such a reaction, however, it is more common for those containing no protons on the alpha carbon, for example... 

The acid-catalyzed rearrangements of substituted pyrroles and thiophenes consequent on ipso protonation have been referred to previously (Section 3.02.2.4.2). There is some evidence that these rearrangements are intramolecular in nature since in the case of acid-induced rearrangement of 2-acylpyrroles to 3-acylpyrroles no intermolecular acylation of suitable substrates could be demonstrated (Scheme 10) (8UOC839). 

The imbalance between and NMR studies in the solid state (Section VI,F) partly reflects the fact that it is easier to introduce N than into heterocyclic compounds, particularly azoles (DNMR in the solid state usually requires isotopic enrichment). Compared to solution studies, solid-state intermolecular proton transfer between tautomers has the enormous advantage that the structure of the species involved is precisely defined. 

The first observation of the proton transfer in pyrazoles in the solid state was made for the intermolecular tautomerism in 3,5-dimethylpyrazole 10b (85JA5290). The degenerate rearrangement was recorded using the... 

A. Side view of channel spanning the lipid layer of a planar lipid bilayer, The structure is comprised of two monomers, each in a left-handed, single stranded p -helical conformation, and joined together at the head or formyl end by means of six, intermolecular hydrogen bonds. The two formyl protons are seen at the center of the structure in this view. Replacement of these protons by methyls destabilizes the conducting dimer as shown with N-acetyl desformyl Gramicidin A (Fig. 3D). 

CT) complex with absorption maxima at 470 and 550nm, was produced. These species were formed only in polar solvents with relatively high proton affinity. The data suggested an intermolecular proton transfer, from electronically excited TNB to the solvent forming the anion... 

However, the aminoazo product is formed via two pathways. The first is through the 1 1 addition complex (HAArNj )n as side-equilibrium and an intermolecular rearrangement involving redissociation of this complex into the reagents followed by formation of another 1 1 addition complex (HAArNJ )c and the classical C-o-complex (oc in Scheme 13-13). The second pathway starts from the first mentioned 1 1 complex (HAArNJ )N to which a second molecule of amine is added. This complex forms the aminoazo product by proton transfer to a base. The base may be the second amine molecule of the 1 2 complex. 

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