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Influence of H‐bonds on acidity of deoxy‐hexose sugars
Author(s) -
Kotena Zahrabatoul Mosapour,
Fattahi Alireza
Publication year - 2020
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.4094
Subject(s) - pentose , chemistry , intramolecular force , hexose , rhamnose , arabinose , stereochemistry , natural bond orbital , xylose , conjugate , ribose , molecule , organic chemistry , galactose , fermentation , enzyme , mathematical analysis , mathematics
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 CH 2 OH group on C 5 ; conversely, methyl‐pentose has a CH 3 group on C 5 . The aim of the present study is to investigate the role and nature of intramolecular H‐bonds on acidity of CH 3 ‐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 CH 3 group on C 5 , making aldo‐pentose sugars stronger acid than methyl‐pentose sugars.