Complexes of amides

The interpretation of the infrared and Raman spectra of solid salts of amides has been the subject of much disagreement. One must first distinguish solid complexes of amides with carboxylic acids from salts with strong mineral acids. In the first, the interaction is... 

G Dollo, P Le Corre, F Chevanne, R Le Verge. Inclusion complexation of amide-typed local anaestetics with /3-cyclodextrin and its derivatives. II. Evaluation of affinity constants and in vitro transfer rate constants. Int J Pharm... 

The preparation of fulvene enamines by the reaction of sodium cyclopent-adienide with dimethyl sulfate complexes of amides or lactams has recently been reported by several investigators [77, 78] (Eq. 22). 

Amide deprotonation is normally observed in copper(II), nickel(II) or cobalt(II) complexes of amides, but it has now been demonstrated that [Zn(LH)2]2 (H3L = H2NC0CH2N(CH2C02H)2) may be further deprotonated, and that the equilibria in Scheme 1 are established. The ability of the d10 zinc(II) ion to promote such equilibria suggests that a major requirement for deprotonation of an amide is a positively charged centre, since the d10 ion cannot show ligand field effects.390... 

The structure found in salts like Na2[Gd(dtpa)(H20)] is thought to represent the species found in solution - data from a number of measurements on solutions containing [Ln(dtpa)(H20) ] species, such as luminescence spectra of the Eu and Tb analogues, indicate that one water molecule is coordinated. A wide variety of complexes of amide derivatives of DTPA have also been synthesised, in order to create neutral species. Using [Gd(DTPA)(H20)] it has been shown that these complexes get absorbed by the DNA of the cell they have been used to locate and that they could act as an agent for neutron capture cancer therapy. 

Table 2.46 Binding energetics of complexes of amide with water or another amide (see Fig. 2.23 for definitions). All data computed with aug-cc-pVDZ basis set and corrected for BSSE, in kcal/moF .

Figure 3. Complexation of amide portion ofNY66 with aq. CaCl2 solution.

In the early proton nuclear magnetic resonance ( H NMR) studies with the O2 complexes of amide functionalized, basket-handle porphyrins (5, Fig. 2), a pronounced downfield shift of the amide C(0)—NH was observed in apolar solvent, indicating the C(0)—NH 02 hydrogen bonding (14a,16). This hydrogen bond, however, was weak, since the estimated nitrogen-02 distance is 4 A. 

Numerous complexes of amides and alkoxides involving Li+, Na+ or K+ as the cations were described by Canber, Lecolier et al.443), who stressed their versatility in affecting the rate and stereochemistry of polymerization. 

O vs. N Protonation.—Controversy over the site of protonation of amides has been raised anew by Liler. Using u.v. spectroscopy, she has suggested that benzamide is 50 50 O N protonated in 80 % sulphuric acid. However, a considerable weight of evidence has been produced to indicate that protonation or Lewis acid complexation of amides consistently occurs by co-ordination with oxygen. Studies have included the acidity-dependent changes in the tt-tt and n-it u.v. absorption bands of aliphatic amides kinetic evidence based on rate data for acid-catalysed amide hydrolysis in both dilute and concentrated acid an n.m.r. study of proton exchange rates, where for A -methylacetamide the molar ratio of 0 N protonated species exceeds 10 a n.m.r. study of adducts of boron trifluoride and antimony pentachloride with N-labelled ureas, where the hybridization-dependent —H coupling constants were inconsistent with N-co-ordination ... 

Meot-Ner, M. (1984) The ionic hydrogen bond. 4. Intramolecular and multiple bonds. Protonation and complexes of amides and amino acid derivatives. J. Am. Chem. Soc., 106, 278-283. 

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