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相关概念视频

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

918
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
918
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

1.6K
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...
1.6K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

1.0K
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...
1.0K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

1.9K
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
1.9K
Structure of Benzene: Molecular Orbital Model01:18

Structure of Benzene: Molecular Orbital Model

8.6K
According to the molecular orbital (MO) model, benzene has a planar structure with a regular hexagon of six sp2 hybridized carbons. As shown in Figure 1, each carbon is bonded to three other atoms with C–C–C and H–C–C bond angles of 120°. The C–H bond length is 109 pm, and the C–C bond length is 139 pm which is midway between the single bond length of sp3 hybridized carbons (154 pm) and sp2 hybridized carbons (133 pm).
8.6K
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

1.2K
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
1.2K

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A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
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在多环拓中,最佳的纠分布是多环拓.

B C Ciobanu1, T A Calafeteanu1, A B Popa1

  • 1Computer Science and Engineering Department, National University of Science and Technology POLITEHNICA Bucharest, Bucharest, 60042, Romania.

Scientific reports
|May 12, 2025
PubMed
概括

这项研究优化了量子互联网的多环量子网络中的纠分布. 开发了算法,以高效地管理网络资源,尽量减少请求执行时间,提高网络性能.

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科学领域:

  • 量子通信网络是一个量子通信网络.
  • 网络拓优化网络拓优化
  • 量子信息科学是一种量子信息科学.

背景情况:

  • 纠分布是量子互联网的关键.
  • 多环拓提供了可扩展性,但增加了路由复杂性.
  • 有效的纠分布对于网络性能至关重要.

研究的目的:

  • 解决多环量子网络拓中最佳纠分布的问题.
  • 分析两个不同的多环网络配置:单层路由和多层路由.
  • 开发用于优化时间和资源的算法,用于纠补给请求.

主要方法:

  • 对两个多环网络配置 (单层与多层路由) 的分析.
  • 开发算法以确定纠分布的最佳时间和资源配置.
  • 计算机模拟以评估拟议算法的性能.

主要成果:

  • 与单层路由相比,多层路由为服务请求提供了最小的节省时间的好处.
  • 多层路由可能会减少非阻断纠分布所需的资源数量.
  • 算法为多环网络中的时间和资源分配提供最佳解决方案.

结论:

  • 量子网络中多层路由的复杂性在请求服务时间方面提供了有限的优势.
  • 在多环量子网络中,可以通过允许层切换来提高资源效率.
  • 提出的算法为优化复杂网络拓中的纠分布提供了有效的解决方案.