The structure and conformation of N,N'-bis[(2-hydroxy)phenyl]oxamide (1 ); N,N'-bis[(2-methoxy)phenylloxamide (2); NN-bis(pheny1)oxamide (3); N,N'-bis[(l R,2S)-( -)-norephedrineloxamide (4); N,N'-bis[ (1 R,2R)-( -)-norpseudoephedrine]oxamide ( 5 ) ; N-[(2-hydroxy)phenyl]methylamide (6); N-[ (2-methoxy)phenyl]methylamide (7); N-phenylmethylamide (8); N-[ ( -) -norephedrine1methylamide ( 9 ) and N-[( -) -norpseudoephedrine]methylamide (1 0) were unambiguously established by 'H, 13C, 15N, 2 0 and variable temperature NMR spectroscopy. A careful NMR investigation of the conformational behaviour in these systems was relevant. It has been found that the dicarbonylic group in compounds 1-5 has a trans geometry, stabilized by intramolecular hydrogen bonding and that they possess a C2 axis. Compounds 1 and 2 are planar and compounds 1,2,4 and 5 present the amidic proton coordinated by two oxygen atoms.

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Protic-fluoride interactionsThe preparation, NMR and X-ray diffraction studies of a series of azolylboron hydrides derived from pyrrole, indole, and carbazole coordinated with tetrahydrofuran, pyridine, and imidazole are reported. The azolyl substituents are very electroattractive leading to a n acidic boron atom which strongly coordinates with the Lewis bases. The stabilization of the -BH2-groups against disproportionation could be explained in terms of the interactions found between the acidic hydrogen atoms of the heterocycles (C-H'+ acceptor) and the hydrides (B-H6-donors).There are few examples of aminoboron hydrides NBH2 derived from aromatic nitrogen heterocycles [',2], in part because free XBH2 boron dihydrides are not stable compounds, the XBH2 group disproportionating to BH3 and BX,; however, the acidic boron atom of these compounds can be stabilized in a cycle by coordination as in the case of pyrazaboles[2c-dl and other XBH2 compounds (X = O)w. It is relevant to understand the nature of the N-B bondC4] and the structural factors for stabilization of the N -BH2 group which could include the donating ability of the nitrogen atoms, the ring aromaticity and the charge distribution. The (dialky1amino)boranes derived from pyrrole, indole, and carbazole were studied by "B-NMR spectro~copy[~>~1.Herein, the preparation and the study by NMR and Xray diffraction analyses of a series of azolylboron hydrides derived from pyrrole, indole, and carbazole coordinated with tetrahydrofuran, pyridine, and imidazole is reported (Scheme 1). The imidazole-BF, adduct was also prepared in order to compare it with the azolylborane-irnidazole adducts. We wanted to know the structural and electronic reasons for the stability of these boron compounds and how coordination affects their behaviour. Results and DiscussionThe azolylborane-THF complexes (Scheme 1) were synthesized from the equimolar reaction of the azole (1-3) and BH3 . THE The reactions were followed by measuring the hydrogen evolution. When the reactions had finished the coordinating nitrogen heterocycles were added. The adducts were isolated by crystallization or precipitation from saturated THF solutions.

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The synthesis and NMR spectra of the N‐borane adducts of two diimines, N‐borane‐bis(α‐phenylethylidene)ethylenediamine and N‐borane‐bis(α‐phenylbenzylidene)ethylenediamine, and four imines, N‐borane‐α‐methylethylidene‐2‐phenylethylamine, two N‐borane‐α‐phenylethylidene‐n‐butylamines and N‐borane‐α‐phenylbenzylidene‐n‐butylamine, are reported. The NMR spectra of the N‐borane adducts of these imines can be used to determine their configuration.

An NMR titration method has been used to simultaneously measure the acid dissociation constant (pK a ) and the intramolecular NHO prototropic constant ΔK NHO on a set of Schiff bases. The model compounds were synthesized from benzylamine and substituted ortho-hydroxyaldehydes, appropriately substituted with electron-donating and electron-withdrawing groups to modulate the acidity of the intramolecular NHO hydrogen bond. The structure in solution was established by

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