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 CH₂OH 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.

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H键对脱氧己糖糖酸度的影响

不寻常的单糖，例如脱氧己糖，包括甲基戊糖和醛糖，是生命科学中很有希望的重要糖。但是，关于这些系统中氢键相互作用的研究很少。醛戊糖具有质子而不是C ₅上的CH ₂ OH基团；相反，甲基戊糖在C ₅上有一个CH ₃基团。本研究的目的是研究分子内氢键对CH ₃戊糖（L-岩藻糖和L-鼠李糖）和醛基戊糖（D-木糖，L-lyxose，D）的酸度的作用和性质。核糖和L-阿拉伯糖）使用B3LYP / 6-311 ++ G（d，p）水平。计算出的酸度值（ΔH_酸）这些Dexoy-hexose的分子量为343至369 kcal.mol ^-1，表明它们比乙醇和2-丙醇更强酸，酸度值为378.3和375.1 kcal.mol ^-1， 分别。这与通过分子内氢键稳定这些糖的共轭碱基有关，在本研究中使用分子中原子（AIM）和天然键合轨道（NBO）方法对其进行了分析。AIM和NBO分析表明，在L-糖和L-阿拉伯糖的共轭碱基中存在一个分叉的分子内H键，在D-核糖的共轭碱基中存在两个分叉的H键，而L-岩藻糖，L的共轭碱基存在鼠李糖和D-木糖呈现一种正常的分子内氢键。根据拓扑参数和电荷转移数据，正常和分叉的分子内氢键的存在可大大增加脱氧己糖的酸度。醛糖-戊糖糖的共轭碱基中的H键强度高于甲基戊糖糖包括CH的共轭碱基中的H键强度C ₅上的_3个基团，使戊戊糖的酸度比甲基戊糖的酸强。