Experimental and theoretical study of the intramolecular C–H···N and C–H···S hydrogen bonding effects in the 1H and 13C NMR spectra of the 2‐(alkylsulfanyl)‐5‐amino‐1‐vinylpyrroles: a particular state of amine nitrogen. (22nd May 2013)

• Record Type: Journal Article
• Authors: Afonin, Andrei V.; Pavlov, Dmitry V.; Albanov, Alexander I.; Tarasova, Ol'ga A.; Nedolya, Nina A.
• Is Part Of: Magnetic resonance in chemistry. Volume 51:Number 7(2013:Jul.)
• Page Start: 414
• Page End: 423
• Publication Date: 2013-05-22
• Subjects: Nuclear magnetic resonance spectroscopy -- Periodicals; Chemistry, Organic -- Periodicals; Magnetic resonance -- Periodicals; 538.36
• DOI: 10.1002/mrc.3967
• Languages: English
• ISSNs: 0749-1581

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>In the <sup>1</sup>H NMR spectra of the 1‐vinylpyrroles with amino‐ and alkylsulfanyl groups in 5 and 2 positions, an extraordinarily large difference between resonance positions of the H<sub>A</sub> and H<sub>B</sub> terminal methylene protons of the vinyl group is discovered. Also, the one‐bond <sup>1</sup><italic>J</italic>(C<italic><sub>β</sub></italic>, H<sub>B</sub>) coupling constant is surprisingly greater than the <sup>1</sup><italic>J</italic>(C<italic><sub>β</sub></italic>, H<sub>A</sub>) coupling constant in pyrroles under investigation, while in all known cases, there was a reverse relationship between these coupling constants. These spectral anomalies are substantiated by quantum chemical calculations. The calculations show that the amine nitrogen lone pair is removed from the conjugation with the <italic>π</italic>‐system of the pyrrole ring so that it is directed toward the H<sub>B</sub> hydrogen. These factors are favorable to the emergence of the intramolecular C–H<sub>B</sub>N hydrogen bonding in the s‐<italic>cis</italic>(N) conformation. On the other hand, the spatial proximity of the sulfur to the H<sub>B</sub> hydrogen provides an opportunity of the intramolecular C–H<sub>B</sub>S hydrogen bonding in the s‐<italic>cis</italic>(S) conformation. Presence of the hydrogen bond critical points as well as ring critical point for corresponding chelate ring revealed by a quantum theory of atoms in molecules (QTAIM) approach confirms the existence of the weak intramolecular C–HN and C–HS hydrogen bonding. Therefore, an unusual high‐frequency shift of the H<sub>B</sub> signal and the increase in the <sup>1</sup><italic>J</italic>(C<italic><sub>β</sub></italic>, H<sub>B</sub>) coupling constant can be explained by the effects of hydrogen bonding. Copyright © 2013 John Wiley & Sons, Ltd.</p> </abstract>