Study of unconventional sulfur and selenium hydrogen bonding using FTIR and NMR spectroscopy combined with quantum chemical calculations

Abstract

The hydrogen bond plays a crucial role in various biomolecules, supramolecules, and materials. Despite having weak strength, it shows excellent applications and explanations of many structures. Even after 100 years of its discovery, it is still fascinating to the scientific community. According to the recent definition of the hydrogen bond, it is no more restricted to atoms having strong electronegativity. Thus, there is recent interest in understanding the nature and strength of unconventional hydrogen bonds where the hydrogen bond donor and acceptor are weak in electronegativity. This study attempts to explore the nature and strength of sulfur and selenium in the solution phase using FTIR and NMR spectroscopy combined with quantum chemical calculations. FTIR spectroscopy has been exploited with quantum chemical calculations to compare the strength of oxygen, sulfur, and selenium as hydrogen bond acceptors while having oxygen as a conventional hydrogen bond donor. NMR spectroscopy has been exploited to explore the physical nature of unconventional hydrogen bonds. On hydrogen bond formation, deshielding of proton and carbon occurs, resulting in a downfield shift. Our study found an upfield shift in both proton and carbon NMR, indicating the shielding behavior of hydrogen bonding. We attempted to explain this phenomenon by comparing various interactions, where oxygen, sulfur, and selenium acted as hydrogen bond acceptors while having only oxygen and sulfur as hydrogen bond donors.