![]() Nevertheless, some empirical, semiempirical, and ab initio procedures have also been reported in the literature for estimating the IHB energy. Many studies for gauging the strength of the IHB in the literature are based on spectroscopic- and electron density topological approaches. Y interaction present within a molecule than in a dimer or a complex.The main difficulty lies in isolating the X–H On the other hand, quantifying an intramolecular hydrogen bond (IHB) strength is not as straightforward as the intermolecular one. Several methods for estimating the intermolecular interaction energies are reported in the literature (see, e.g., Refs. ♻ is routinely performed using a supermolecular approach, in which the HB energy (E HB) is estimated as E HB = E A.The theoretical estimation of intermolecular X–H Y HB strengths for shedding light on several physicochemical phenomena and life processes.Hence, it is of great importance to reliably estimate these X−H HBs provide a significant driving force for the native structures and functions of biomolecules. It is stipulated in the literature that if HBs in water were 7% stronger or 29% weaker, water would not be a liquid at room temperature. The HB’s in liquid water are central to water’s life-providing properties. Y distances suggested in the literature fall in the range of ~1.2–3.0 Å and X–H.O, etc., in neutral molecular systems, exhibit interaction energies lying between ~1 to 20 kcal/mol.Y, where X–H is the proton donor and Y is a proton acceptor.The former states that “the hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X–H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation.”Īn HB may be generally represented as X–H The recent definition of HB by IUPAC is similar in spirit to that in Ref. Pimentel and McClellan suggested that an HB exists when (i) there is evidence of a bond and (ii) there is evidence that this bond involves a hydrogen atom already bonded to another atom. His later usage of the term “hydrogen-bridge” may have led to the German word “Wasserstoffbrücke.” The concept of HB gained popularity after Pauling published his classic book, The Nature of the Chemical Bond in 1939. ![]() Huggins claimed that he was the first to propose the term “H-bond” in 1919. Barnes, while studying the structure of ice, suggested that the hydrogen atoms were midway between the two oxygen atoms, though he did not explicitly mention the hydrogen bond. ![]() ![]() In 1920, Latimer and Rodebush suggested that the hydrogen nucleus in an aqueous solution of amines is held jointly by two octets, constituting a weak bond. The term “Nebenvalenz” by Werner and “weak union” by Moore and Winmill are other early stipulations of this noncovalent interaction. The dimeric association of molecules with hydroxyl groups was suggested by Nernst in 1892. However, the mention of weak, yet specific interactions involving the hydrogen atom is much older. The term “hydrogen bond” seems to have emerged around 1930, from the works of Pauling and Huggins. The hydrogen bond (HB) is a dominant noncovalent interaction found in chemical and biological systems. ![]()
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