Influence of H‐bonds on acidity of deoxy‐hexose sugars. (9th June 2020)

• Record Type: Journal Article
• Authors: Kotena, Zahrabatoul Mosapour; Fattahi, Alireza
• Is Part Of: Journal of physical organic chemistry. Volume 33:Number 10(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-06-09
• Subjects: acidity -- deoxy‐hexoes sugars -- hydrogen bonding; Chemistry, Physical organic -- Periodicals; 547.1
• DOI: 10.1002/poc.4094
• Languages: English
• ISSNs: 0894-3230

Abstract

Abstract: The unusual monosaccharaides such as deoxy‐hexose sugars, including methyl‐pentose and aldo‐pentose, are promising and important sugars in life science. However, little research on H‐bond interactions in these systems has been reported. The aldo‐pentose has a proton instead of the CH2 OH group on C5 ; conversely, methyl‐pentose has a CH3 group on C5 . The aim of the present study is to investigate the role and nature of intramolecular H‐bonds on acidity of CH3 ‐pentose sugars (L‐fucose and L‐rhamnose) and aldo‐pentose sugars (D‐xylose, L‐lyxose, D‐ribose, and L‐arabinose) using B3LYP/6‐311++G (d, p) level. The calculated acidity values ( ΔH acid ) of these Dexoy‐hexose were found to be from 343 to 369 kcal.mol −1, indicating they are stronger acid than ethanol and 2‐propanol with the acidity values of 378.3 and 375.1 kcal.mol −1, respectively. This is related to the stabilization of the conjugate bases of these sugar through intramolecular H‐bonds, which were analyzed in this study using atoms in molecules (AIM) and natural bonding orbital (NBO) methods. AIM and NBO analyses indicate the presence of one bifurcated intramolecular H‐bond in the conjugate bases of L‐lyxose and L‐arabinose and two bifurcated H‐bonds in conjugate base of D‐ribose, whereas the conjugate bases of L‐fucose, L‐rhamnose, and D‐xylose present one normal intramolecular H‐bond. According to the topological parameters and charge transfer data, existence of normal and bifurcated intramolecular H‐bonds could greatly increase acidity of deoxy‐hexose sugars. The H‐bond strength in the conjugate bases of aldo‐pentose sugars is higher than that in the conjugate bases of methyl‐pentose sugars including CH3 group on C5, making aldo‐pentose sugars stronger acid than methyl‐pentose sugars. Abstract : The calculated acidity values of Dexoy‐hexose were found to be from 343 to 369 kcal.mol‐1, indicating they are stronger acid than ethanol and 2‐propanol with the acidity values of 378.3 and 375.1 kcal.mol‐1, respectively. The existence of normal and bifurcated intramolecular H‐bonds could greatly increase acidity of Deoxy‐hexose sugars. The H‐bond strength in the conjugate bases of aldo‐pentose is higher than that in the conjugate bases of methyl‐pentose including CH3 group on C5, making aldo‐pentose stronger acid than methyl‐pentose.