Solid‐State Structure and Tautomerism of 2‐Aminotroponimines Studied by X‐ray Crystallography and Multinuclear NMR Spectroscopy

Abstract

Structural studies in the solid state by X‐ray crystallography and by 13C and 15N CPMAS NMR spectroscopy carried out on a series of 2‐aminotroponimine derivatives 2−5 has allowed to establish the existence of hydrogen bonding and to determine the most stable tautomer. Almost all the structures reflect the classical double‐well potential function for the N−H···N hydrogen bonds. Only in the case of the compound N‐(pyrrol‐1‐yl)‐2‐(pyrrol‐1‐ylamino)troponimine (5) the crystal structure shows two independent molecules, one with a classical hydrogen bond and another with either a single‐well or a low‐barrier hydrogen bond. The structure of this compound is discussed with the use of the solid‐state NMR spectroscopic data. 2‐Aminotropones, as intermediates to the 2‐aminotroponimines, show the oxo‐tautomer as the stable form. B3LYP/6‐31G* calculations are used to rationalise the experimental results. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Theoretical study of bifurcated hydrogen bonding effects on the 1J(N,H), 1hJ(N,H), 2hJ(N,N) couplings and 1H, 15N shieldings in model pyrroles

“…It is the point of importance that the angle ζ between the H· · ·N hydrogen bond and N-H covalent bond (see Scheme 2) changes on going from the simple N-H· · ·N hydrogen bond in 1-and 2-Z,E to the bifurcated N(O)· · ·H· · ·N hydrogen bond in 1-and 2-Z,Z, this angle being larger by [10][11][12][13][14][15][16][17][18][19][20] • in the former compounds.…”

A review with comprehensive data on experimental indirect scalar NMR spin–spin coupling constants across hydrogen bonds

“…[92] To this last field we have contributed with an early and rare study of couplings across HBs involving 31 P, [93 -96] and with others on 6-aminofulvene-1-aldimines [97] and 2-aminotroponimines/2-aminotropones. [98] We will discuss these publications in the following order:…”

“…Claramunt et al [98] studied the case of 2-aminotroponimines 86 and 87 as well as 2-aminotropones 88-91 (Scheme 34) and other similar derivatives. The measured coupling constants are reported in Table 26.…”

Product Class 6: Oxonium Salts

“…Ketones react with trialkyloxonium salts to activate the carbonyl to produce vinyl ethers [59,60] or aromatic or conjugated cations, [61,62] or to increase the electrophilicity of the ketone for attack by various nucleophiles. [63,64] 37.6.2.3.3…”