| 查看: 595 | 回复: 0 | ||
[求助]
求助翻译啊 ，关于核磁共振分析的 ，急用！！
|
|
The 13C NMR spectra indicated that glucose was in the forms of a-pyranose (2) and b-pyranose (1; Scheme 1) in [BMIM]Cl at room temperature in the absence of GeCl4 (Figure 9 a). However, when 1 equivalent of GeCl4 was added into the mixture, a new peak at d=76.4 ppm appeared (Figure 9b). The ability of heavier main-group elements to accommodate more than eight electrons in their valence shells, thus forming so-called hypervalent or hypercoordinate compounds, is well established.[ 20] The cations of Group 14 elements can be stabilized thermodynamically by introduction of auxiliary NR2 or OR groups, the lone electron pairs of which could, in principle, be capable of bonding to the empty p orbital of the Group 14 element.[ 21] Therefore, we speculated that GeIV interacted with the two O atoms of 1,2-dihydroxy group of a-glucose to form a stable intermediate 3 (Scheme 1). When the 13C NMR spectrum was recorded at 508C, the relative intensity of the peak at d= 76.4 ppm decreased, and two new peaks at d=152.1 and 103.6 ppm appeared. The intensity of the signal at d= 152.1 ppm increased when the reaction was held at higher temperatures (Figure 9d ande) and also increased over time (data not shown). Therefore, this signal was assigned to the 13C-labeled carbon of HMF at the 2-position. Assignment of the signal at d=103.6 ppm was more tricky. Because this signal was found only at 508C, it should be associated to a relatively stable intermediate with a short lifetime along the reaction pathway to HMF. In other words, at higher temperature, the turnover of this intermediate was greatly accelerated. Therefore, we suppose it was from fructose,[22] which indicated that the intermediate fructose was formed through glucose isomerization. Moreover, the signal at d=76.4 ppm was missing at 808C, indicating that the conversion of 3 was fast. As proposed by zhao et al., fructose was formed from glucose through an enediol intermediate catalyzed by GeCl4. [10] Fructose then lost one water molecular to form the fructofuranosyl oxocarbenium ion.[18] Due to the basicity and nucleophilicity of the halide ion (X), the oxocarbenium ion lost HX to form the enolic species through the nucleophile or the base pathway, followed by loss of two water molecules to form HMF. Our results also suggested that increasing the reaction temperature would enhance the interaction of glucose and GeCl4, and thus promote a ring-opening step of the intermediate 3 to form the straight-chain intermediate 4 through hydrogen transfer, which could be enolated to form 5, followed by the release of GeCl4 to give fructose (Scheme 1). At 80 8C, three new signals at d=56.1, 110.9 and 124.3 ppm appeared, which were attributed to C6, C4 and C3, respectively, of HMF. A new peak at d=80.1 ppm was also observed at 80 8C and 100 8C, which was attributed to a byproduct formed during the reaction. |
回复此楼» 猜你喜欢
271材料工程求调剂
已经有5人回复
-
281求调剂（0805）
已经有16人回复
-
304求调剂
已经有6人回复
-
材料工程专硕调剂
已经有6人回复
-
一志愿天大材料与化工（085600）总分338
已经有4人回复
-
085700资源与环境308求调剂
已经有3人回复
-
求材料调剂
已经有8人回复
-
294求调剂材料与化工专硕
已经有5人回复
-
一志愿华中科技大学，080502，354分求调剂
已经有4人回复
-
一志愿吉林大学材料学硕321求调剂
已经有6人回复
找到一些相关的精华帖子，希望有用哦~
求助usp中的翻译
已经有7人回复
- 新人第一次发帖，求大神帮我分析一下这个核磁的问题！感激不尽！
已经有20人回复
- 氢谱核磁与样品浓度关系
已经有7人回复
- 核磁氢谱的分析
已经有5人回复
- 核磁共振 氢谱和碳谱
已经有4人回复
- 请问哪里可以做固体核磁？
已经有6人回复
- 求助英语句子结构分析和翻译
已经有7人回复
- 求英语翻译啊！！！有急用啊！！拜托拜托～
已经有3人回复
- 英文文献中的一句话，求助翻译，句子结构分析！
已经有7人回复
- 求微普解析化合物结构
已经有3人回复
- 药物分析方面资料翻译求助
已经有2人回复
- 高金币跪求英语翻译成西班牙语，恳求懂西班牙语的帮忙，文章急用啊！！
已经有14人回复
- NTSYS软件做聚类分析图时，能把图片编辑成像MEGA软件做出的效果吗？
已经有9人回复
- 核磁碳谱峰值不明显的原因及解决方法
已经有6人回复
- 【求助】一种有机气体，两种无机气体能否用一个色谱柱分开？急用，望各位前辈指教
已经有9人回复
- 【求助】13C-NMR中，55ppm的季碳是什么呀？
已经有7人回复
- 【求助】求高手翻译，急用，合适者奖励100金币，多谢了
已经有5人回复
- 【求助】请问“色谱柱老化”翻译成英文怎么说啊?
已经有3人回复
- 【求助】请教：质谱，翻译问题？
已经有4人回复
- 【求助】请教几个模糊物元分析方法专业词汇的翻译【求助完毕】
已经有6人回复
点击这里搜索更多相关资源科研从小木虫开始，人人为我，我为人人
