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Related Concept Videos

¹H NMR: Interpreting Distorted and Overlapping Signals01:02

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

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993
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...
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Spin–Spin Coupling: One-Bond Coupling01:17

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956
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,...
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IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations01:08

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Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single...
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Thermal Sigmatropic Reactions: Overview01:16

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Sigmatropic rearrangements are a class of pericyclic reactions in which a σ bond migrates from one part of a π system to another. These are intramolecular rearrangements where the total number of σ and π bonds remain unchanged.
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All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics
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Reverse Intersystem Crossing Dynamics in Vibronically Modulated Inverted Singlet-Triplet Gap System: A Wigner Phase

Pijush Karak1, Pradipta Manna1, Ambar Banerjee2

  • 1Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata 700009, West Bengal, India.

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|July 19, 2024
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Summary
This summary is machine-generated.

The inverted singlet-triplet gap (INVEST) and reverse intersystem crossing (rISC) rate depend on molecular geometry. Nuclear motion, specifically puckering, is crucial for observing INVEST and its temperature-dependent rISC dynamics.

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Area of Science:

  • Photochemistry
  • Quantum Chemistry
  • Molecular Dynamics

Background:

  • Recent observations show an inverted singlet-triplet gap (INVEST) and slow changes in reverse intersystem crossing (rISC) rates with temperature.
  • Understanding the origins of these phenomena is crucial for controlling photophysical processes.

Purpose of the Study:

  • To investigate the origin of the inverted singlet-triplet gap (INVEST).
  • To explore the reasons behind the slow temperature dependence of the reverse intersystem crossing (rISC) rate.
  • To elucidate the role of nuclear degrees of freedom in these processes.

Main Methods:

  • Utilized Wigner phase space studies.
  • Analyzed equilibrium and non-equilibrium geometries.
  • Investigated variations in exchange interaction and double excitations.

Main Results:

  • The inverted singlet-triplet gap (INVEST) is present at equilibrium geometry.
  • Deviations from equilibrium, within the harmonic region, lead to non-INVEST behavior due to changes in exchange interaction and double excitations.
  • Nuclear degrees of freedom, particularly geometric puckering, significantly influence INVEST and rISC dynamics.

Conclusions:

  • The inverted singlet-triplet gap (INVEST) is not solely determined by equilibrium geometry.
  • Nuclear motion and molecular geometry play a critical role in the observed INVEST and temperature-dependent rISC rates.
  • Geometric puckering is identified as a key factor governing INVEST and associated rISC dynamics.