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相关概念视频

Mass Spectrometry: Molecular Fragmentation Overview01:20

Mass Spectrometry: Molecular Fragmentation Overview

5.4K
The ionization of a molecule into a molecular ion inside the mass spectrometer causes instability in the molecule's structure due to the loss of an electron. This eventually leads to the fragmentation or breaking of some bonds in the molecule. The fragmentation occurs predominantly at specific bonds to yield relatively stable fragments.
One type of fragmentation pattern is the cleavage of a single bond in the molecular ion. The cleavage leads to a radical and a cation. The cleavage can occur at...
5.4K
Mass Spectrometry: Carboxylic Acid, Ester, and Amide Fragmentation01:01

Mass Spectrometry: Carboxylic Acid, Ester, and Amide Fragmentation

2.4K
The fragmentation patterns observed for compounds such as carboxylic acids, esters, and amides in the mass spectra include ⍺-cleavage and McLafferty rearrangement. Fragmentation by ⍺-cleavage preferentially occurs at the carbon-carbon bond at the ⍺-position next to the carboxylic group to generate a neutral radical and a cation. Long chain compounds with hydrogen at their γ-carbon undergo McLafferty rearrangement to give a radical cation and a neutral alkene.
For example, the...
2.4K
Mass Spectrometry: Alkene Fragmentation00:59

Mass Spectrometry: Alkene Fragmentation

3.5K
Alkenes lose one electron from the unsaturated π bond upon ionization and form stable molecular ions. Further fragmentation of alkenes occurs through three different reaction pathways. The most prominent fragmentation is the cleavage at the allylic position. The resultant allylic carbocation is resonance stabilized. In the mass spectra of terminal alkenes, this fragment appears at a mass-to-charge ratio of 41. In the internal alkenes, where there are two choices of allylic cleavage, the...
3.5K
Mass Spectrometry: Long-Chain Alkane Fragmentation01:18

Mass Spectrometry: Long-Chain Alkane Fragmentation

2.4K
The molecular ions of linear alkanes prefer to fragment at the carbon-carbon bond away from the end of the chain since the cleavage of an inner bond creates a stable carbocation and a stable radical. Consequently, the mass signals of linear alkanes feature intense peaks in the middle of the mass-to-charge ratio plot with weaker peaks on either end. The fragmentation of each carbon-carbon bond with the release of a methyl group in each splitting leads to prominent peaks in the mass spectra...
2.4K
Mass Spectrometry: Alcohol Fragmentation01:03

Mass Spectrometry: Alcohol Fragmentation

4.4K
Alcohols (R-OH) ionize to lose one non-bonded electron from the oxygen atom, forming molecular ions. Due to their tendency to fragment rapidly, the intensity of the molecular ion peak in the mass spectrum is weak or sometimes absent. The fragmentation patterns for alcohols occur in two ways, i.e. ⍺-cleavage and dehydration. During ⍺-cleavage, the bond at the ⍺-position adjacent to the hydroxyl group cleaves to give a resonance-stabilized cation and a radical. However, intramolecular...
4.4K
Tandem Mass Spectrometry01:21

Tandem Mass Spectrometry

2.3K
Tandem mass spectrometry is a technique that uses multiple mass analyzers in series to obtain a higher selectivity and reduce chemical noise during analyte detection. Instruments with multiple analyzers separated by an interaction cell enable secondary fragmentation and selected study of the fragment ions.Secondary fragmentations occur in the interaction cell and can be induced by various factors. Fragmentation induced by collision with inert gases, such as N2, Ar, He, etc., is called...
2.3K

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Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
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密度矩阵嵌入理论的自动分子碎片化.

Satoshi Imamura1, Naoki Iijima1, Akihiko Kasagi1

  • 1Computing Laboratory, Fujitsu Limited, 1-1, Kamikodanaka 4-chome, Nakahara-ku, Kawasaki 211-8588, Japan.

The journal of physical chemistry. A
|September 24, 2025
PubMed
概括
此摘要是机器生成的。

我们开发了一种基于图的自动分子碎片化 (GAF) 技术,用于密度矩阵嵌入理论 (DMET). GAF-DMET提供了准确和高效的量子化学计算,性能优于基于原子的启动嵌入 (ABE).

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Analysis of Complex Molecules and Their Reactions on Surfaces by Means of Cluster-Induced Desorption/Ionization Mass Spectrometry
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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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科学领域:

  • 量子化学 是一个量子化学.
  • 计算化学计算化学
  • 材料科学 材料科学 材料科学

背景情况:

  • 对大分子的高精度量子化学计算在计算上昂贵.
  • 量子嵌入方法如密度矩阵嵌入理论 (DMET) 和引导嵌入 (BE) 降低了计算成本.
  • 由于DMET的准确性和成本取决于手动分子碎片化,这限制了其实际应用.

研究的目的:

  • 开发基于图的自动分子碎片化 (GAF) 技术,以更轻松地应用DMET.
  • 与基于原子的BE (ABE) 相比,评估GAF-DMET的准确性和计算效率.
  • 为了证明GAF-DMET适用于化学结合能和反应计算的适用性.

主要方法:

  • 以图形形式表示分子结构,并具有原子间相互作用边缘重量.
  • 解决图形分区问题以确定最佳的分子碎片化.
  • 开发跨不同基准集和自动碎片数调整的原子间相互作用的指标.
  • 对14个小分子的GAF-DMET和ABE性能进行比较,包括结合能量和SN2反应计算.

主要成果:

  • GAF成功地确定了精确的分子碎片化模式.
  • GAF-DMET的精度与ABE的精度相当或更高,墙壁时钟时间缩短.
  • 与ABE相比,GAF-DMET在结合能量的计算和SN2反应模拟中表现出卓越的准确性.

结论:

  • GAF为DMET提供了一个自动化和有效的碎片化策略.
  • 在计算上,GAF-DMET为现有的嵌入方法提供了一个高效和准确的替代方案.
  • 拟议的GAF技术增强了DMET对复杂化学系统和反应的适用性.