Donor groups

The cyclization reactions discussed here either involve the intramolecular reaction of a donor group D with an acceptor group A or a cyclizing dimerization of two molecules with two terminal acceptors and two donors. A polymerization reaction will always compete with cyclization. For macrolides see p. 146 and p. 319 — 329. 

EthylenediaminetetraaceticAcid. Ethylenediaminetetraacetic acid (EDTAH has six potential donor groups two nitrogen atoms and four carboxylate groups. If EDTA 4— acts as a hexadentate ligand to a metal, the resulting complex contains five five-membered chelate rings and has a charge that is four less than that of the metal ion. 

Donors a.ndAcceptors. Table 3 Hsts common electron—donor groups, and electron—acceptor groups selected from a large number capable of evoking fluorescence. 

Sulfonation increases the water solubiUty of dyes. A sulfonic group is electron withdrawing but has a weakening effect on the fluorescence only if it is ortho to the donor group. For example, in Brilliant Sulfoflavine FF [2391-30-2] (17), where R = p-tolyl, —it has a weakening effect, although the cleanness of the fluorescent color is somewhat improved compared to that of the unsulfonated compound. 

The conjugated chromophore (color-causing) system can be extended by electron-donor groups such as —NH2 and —OH and by electron-acceptor groups such as —NO2 and —COOH, often used at opposite ends of the molecule. An example is the aromatic compound alizarin [72-48-0], also known since antiquity as the ted dye madder. 

The strength of electron-donor groups iacrease ia the order OH < NH < NHR < HNAr. Tetra-substituted anthraquiaones (1,4,5,8-) are more bathochromic than di- (1,4") 01 trisubstituted (1,2,4-) anthraquiaones. Thus, by an appropriate selection of donor groups and substitution patterns, a wide variety of colors can be achieved (see Dyes, anthraquinone). 

Oxadiazoles are difficult to alkylate, unless the ring contains a strong electron donor group such as an amino substituent. 

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. 

This is a term introduced by Gokel and co-workers only very recently. The compounds included in this class are those which have single macrorings like crowns but additional pendant donor groups which make them similar in some respects to crytands. The presumption from which the name derives is that a complexed cation will be bound by both the macroring and the sidechain in much the same fashion as a lasso binds an animal. The compounds are named as simple crown derivatives and are illustrated as 16 a 17 below. 

The name lariat ethers has recently been suggested by Gokel and coworkers to describe a class of compounds which are based on crown ethers and have secondary donor groups bound to the macrormg by flexible arms (see Sect. 1.3 5). The name lariat is suggested by the analogy to the lassoes used to rope and tie animals since it is hoped that the more successful molecules of this class will be able to do likewise with sundry cationic species. 

One heterocyclic subunit which is an excellent donor group is the 2,6-pyrido-sub-stitutent - ". However, when 4-chloro-2,6-dicarboxypyridine was utilized as precursor to the macrocycle, the product apparently was less stable than was the corresponding nonchlorinated ester The decomposition was apparently initiated by complexation of either Sr or Ba " but the mechanism by which this degeneration occurred was not suggested nor is it obvious to the present authors, especially in the absence of any commentary concerning the products of decomposition. The synthesis of the apparently unstable system is illustrated below. 

In later work, Vogtle and his coworkers prepared analogs of both crown ethers and cryptands. These molecules are designed to have a terminal donor group which is capable of offering a complexed cation additional binding sites. Numerous... 

It follows from the preceding discussion that the unbranched H bond can be regarded as a 3-centre 4-electron bond A-H B in which the 2 pairs of electrons involved are the bond pair in A-H and the lone pair on B. The degree of charge separation on bond formation will depend on the nature of the proton-donor group AH and the Lewis base B. The relation between this 3-centre bond formalism and the 3-centre bond descriptions frequently used for boranes, polyhalides and compounds of xenon is particularly instructive and is elaborated in... 

The LUMO in benzenium ion reveals where electron donor groups are likely to be most effective. 

First examine the geometry of methyl radical. Is it planar or puckered Examine the geometries of 2-methy 1-2-propyl radical, trifluoromethyl radical, trichloromethyl radical and tricyanomethyl radical. Classify each of the substituents (methyl, fluoro, chloro and cyano) as a n-electron donor or as a Tt-electron acceptor (relative to hydrogen). Does replacement of the hydrogens by 7t-donor groups make the radical center more or less puckered Does replacement by Jt-acceptor groups make the radical center more or less puckered Justify your observations. 

This type of tautomerism pertains to azole systems which contain exo-cyclic amino, hydroxy, thiol, and other proton donor groups. 

Hypercoordinated derivatives of P,0-heterocycles with intramolecular coordination by donor groups 98EJI1847. 

EDTA, leading to a postulate that more than one equivalent of Ca2+ can be captured by X (e.g. one Ca2+ sequestered by the three amines and the three carboxylates and another Ca2 + by the remaining half the donor groups), as the Dreiding model suggests. The fact that there was no interaction at neutral pH of X with phosphate or oxalate anions was separately confirmed. Thus, the dissolution of Ca3(P04)2 and Ca(C204) is entirely due to the cation complexation mechanism. 

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