Acceptor classes

The donor and acceptor classes illustrated with hydrocarbons can be directly extended to include hetero-atoms. For example, the alcohol moiety q /H would be a 4e donor, of the same orbital symmetry as the ethane moiety Similarly the carbonyl... 

Table 7.11 lists the predicted BDEs of TM compounds with 7r-donor ligands [4, 54, 55, 68-71], The complexes of W(CO)5 with acetylene, ethylene, and formaldehyde belong to the donor-acceptor class. The compounds of WC14 with the same ligands are metallacyclic molecules. 

Answer We have two problems translating the typed formula into a recognizable structure and doing a correct classification. The first compound is a carboxylic acid, which should tip us off to put it in the acids, the H-L or H-A class. The next compound is an aldehyde conjugated to a pi bond. Since an aldehyde is a polarized multiple bond and also an ewg, we would put this compound in the conjugate acceptor class, C=C-ewg. 

This paper reviews the chemistry of metalloborane derivatives that contain borane or heteroatom borane groups which function as monohapto ligands. These compounds can be divided into three classes according to the number of electrons formally donated by the borane ligand to the metal. The electron pair acceptor class, represented by the compound Na[(OC)5Mn BHg], has received little attention thus far. The one-electron donor class, exemplified by the complex, l,2-(CH3)2-3- (C5H5)Fe(CO)2]-BioC2Ho, has a rich chemistry of metal-carbon and metal-boron derivatives. The third class includes two-electron donor derivatives that are represented by the compound (CHs)f,N[7,8-BoHioCHP - CrfCO),]. 

Fig. 1.7 Depiction of Class I organocatalytic domino processes. Cyclization events occur when the electrophile for the second step is attached to either the initial Michael acceptor (Class lA) or on the initial nucleophile (Class IB). It is also possible for a third component to be involved (Class 1C)...

A wide class of aiyl-based quaternary surfactants derives from heterocycles such as pyridine and quinoline. The Aralkyl pyridinium halides are easily synthesized from alkyl halides, and the paraquat family, based upon the 4, 4 -bipyridine species, provides many interesting surface active species widely studied in electron donor-acceptor processes. Cationic surfactants are not particularly useful as cleansing agents, but they play a widespread role as charge control (antistatic) agents in detergency and in many coating and thin film related products. 

A fuzzier atom type participating in these descriptors has been defined that is pharmacologically relevant - the physicochemical type at near-neutral pH [24], which is one of the following seven binding property classes 1 = cation 2 = anion 3 = neutral hydrogen-bond donor 4 = neutral H-bond acceptor ... 

Analogous to the classification of Lewis acids and bases in hard and soft species, Ahrland et al. have su ested a division of donors and acceptors into classes a and 6. See Ahrland, S. Chatt, J. Davies, N.R. Quart. Rev. 1958, 77, 265... 

Aldolases cataly2e the asymmetric condensation of intermediates common in sugar metaboHsm, such as phosphoenolpymvic acid, with suitable aldehyde acceptors. Numerous aldolases derived from plants or animals (Class I aldolases) or from bacteria (Class II) have been examined for appHcations (81). Efforts to extend the appHcations of these en2ymes to the synthesis of unusual sugars have been described (2,81). 

In Example 1 the solute, acetone, contains a ketone carbonyl group which is a hydrogen acceptor, i.e., solute class 5 according to Table 15-4. This solute is to be extracted from water with chloroform solvent which contains a hydrogen donor group, i.e., solvent class 4. The solute class 5 and solvent class 4 interaction in Table 15-4 is shown to give a negative deviation from Raonlt s law. 

It seems that, as suggested by Ahrland et alP in 1958, this distinction can be explained at least partly on the basis that class-a acceptors are the... 

Class-b acceptors on the other hand are less electropositive, have relatively full d orbitals, and form their most stable complexes with ligands which, in addition to possessing lone-pairs of electrons, have empty n orbitals available to accommodate some charge from the d orbitals of the metal. The order of stability will now be the reverse of that for class-a acceptors, the increasing accessibility of empty d orbitals in the heavier halide ions for instance, favouring an increase in stability of the complexes in the sequence... 

Hie stereodiemical trendi disaissed above carbonyl compounds otlier Micliael acceptor rated pbospbane oxides display sim dar bebavi-nitroalkene class of Micliael acceptors is show [28]. Hie best results were tlius obtained for were niucli less selective, wbicli severely restri... 

Cations with noble gas configurations. The alkali metals, alkaline earths and aluminium belong to this group which exhibit Class A acceptor properties. Electrostatic forces predominate in complex formation, so interactions... 

Cations with completely filled d sub-shells. Typical of this group are copper(I), silver(I) and gold(I) which exhibit Class B acceptor properties. These ions have high polarising power and the bonds formed in their complexes have appreciable covalent character. 

Rhinoviruses, which represent the single major cause of common cold, belong to the family of picornavimses that harbors many medically relevant pathogens. Inhibitors of the 3C protease, a cysteine protease, have shown good antiviral potential. Several classes of compounds were designed based on the known substrate specificity of the enzyme. Mechanism-based, irreversible Michael-acceptors were shown to be both potent inhibitors of the purified enzyme and to have antiviral activity in infected cells. 

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