The molecular structure of hydrochars produced from 13C-enriched glucose under various conditions has been elucidated based on advanced one- and two-dimensional (2D) 1H-13C and 13C–13C solid-state nuclear magnetic resonance (NMR) with spectral editing. Regardless of synthesis conditions, hydrochars consist mostly of oxygen-substituted arene rings (including diphenols) and furans connected by alkyl linkers rich in ketones. Cross-linking nonprotonated and methyne (C-H) alkyl carbons have been identified through spectrally edited 2D NMR. Alkenes and ‘quaternary’ C-O are observed only at low synthesis temperature, while some clusters of fused arene rings are generated at high temperature. Hydrochar composition is nearly independent of reaction time in the range from 1 to 5 h. Equilibration of 13C magnetization within 1 s shows that the materials are homogeneous on the 5-nm scale, refuting core–shell models of hydrochar microspheres. While furan C-O carbons bonded to alkyl groups or ketones show distinctive cross peaks in 2D NMR, phenolic C-OH is observed unambiguously by hydroxyl-proton selection. While methylene-linked furan rings are fairly common, the signal previously assigned to furan Cα-Cα linkages is shown to arise from abundant, stable catecholic ortho-diphenols, whose HO-C=C-OH structure is proved by 2D13C–13C NMR after hydroxyl-proton selection. Quantitative 13C NMR spectra of low- and high-temperature hydrochars have been matched by chemical-shift simulations for representative structural models. Mixed phenol and furan rings connected by ketones and alkyl linkers provide good fits of the experimental spectra, while literature models dominated by large clusters of fused rings and with few phenols or alkyl-linked ketones do not.

中文翻译：

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葡萄糖水合炭由先进的固态核磁共振揭示的键合酚、呋喃、芳烃、烷基和酮结构组成


基于先进的一维和二维 （2D） 1H-13C 和 13C-13C 固态核磁共振 （NMR） 和光谱编辑，阐明了在各种条件下由 13C 富集葡萄糖产生的水炭的分子结构。无论合成条件如何，水炭主要由氧取代的芳烃环（包括二酚）和呋喃组成，这些呋喃由富含酮的烷基接头连接。交联非质子化和甲基炔 （C-H） 烷基碳已通过光谱编辑的 2D NMR 鉴定。烯烃和“四元”C-O 仅在低合成温度下观察到，而一些熔融芳烃环簇是在高温下产生的。Hydrochar 组成在 1 至 5 小时范围内几乎与反应时间无关。1 s 内 13C 磁化的平衡表明，材料在 5 nm 尺度上是均匀的，反驳了水炭微球的核壳模型。虽然呋喃 C-O 碳与烷基或酮键合在二维 NMR 中显示出独特的交叉峰，但酚类 C-OH 通过羟基-质子选择可以明确观察到。虽然亚甲基连接的呋喃环相当常见，但先前分配给呋喃 Cα-Cα 键的信号显示来自丰富、稳定的邻苯二酚，其 HO-C=C-OH 结构在羟基-质子选择后通过 2D13C-13C NMR 证明。低温和高温水炭的定量 13C NMR 波谱已与代表性结构模型的化学位移模拟相匹配。由酮和烷基接头连接的混合酚和呋喃环提供了与实验光谱的良好拟合，而以大簇熔合环为主且酚或烷基连接酮较少的文献模型则没有。