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相关概念视频

¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.1K
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.1K
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

1.0K
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
1.0K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.1K
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
1.1K
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

775
When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
775
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

1.1K
Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the...
1.1K
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.0K
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
2.0K

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Generation and Coherent Control of Pulsed Quantum Frequency Combs
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量子计算机上的超细合常量:性能,错误和未来前景.

Phillip W K Jensen1, Gustav Stausbøll Hedemark1, Karl Michael Ziems2,3

  • 1Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.

Journal of chemical theory and computation
|August 11, 2025
PubMed
概括
此摘要是机器生成的。

研究人员首次使用量子硬件计算了电子自旋共振同otropic高精度合常量 (HFCs). 这种量子方法,结合误差减轻,准确地确定了小分子的HFC,为量子化学应用铺平了道路.

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科学领域:

  • 量子计算是一种量子计算.
  • 计算化学是一种计算化学.
  • 量子物理学的量子物理学

背景情况:

  • 电子自旋共振 (ESR) 对于分子结构的确定至关重要.
  • 计算同位素高精度合常量 (HFCs) 是计算密集的.
  • 量子计算为分子模拟提供了一个潜在的新范式.

研究的目的:

  • 首次在量子硬件上实现和计算ESR同otropic HFC.
  • 为了验证量子方法使用小基和阴离子测试案例.
  • 评估量子计算中误差缓解策略的有效性.

主要方法:

  • 集成量子比特-ADAPT算法与不受限制的轨道优化.
  • 使用一个活跃空间框架进行分子性质计算.
  • 采用先进的错误减轻,抑制和后选择技术,包括基于ansatz的读数和门错误减轻.

主要成果:

  • 成功计算了基 (OH•),氧化 (NO•) 和三重基离子 (OH+) 的 HFC.
  • 量子硬件的结果与经典的不受限制的完全活性空间自相一致场 (U-CASSCF) 计算有很强的一致性.
  • 证明了多方法错误策略的必要性和有效性,以获得准确的量子结果.

结论:

  • 这项工作在将量子计算应用于化学上相关的分子性质方面取得了重大进展.
  • 开发的量子方法,加上强大的误差减轻,是可行的计算HFCs.
  • 突出了错误处理在噪音中等尺度量子 (NISQ) 设备上取得可靠结果的关键作用.