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相关概念视频

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations01:08

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations

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 stretching vibration...
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
IR Spectroscopy: Molecular Vibration Overview01:24

IR Spectroscopy: Molecular Vibration Overview

When Infrared (IR) radiation passes through a covalently bonded molecule, the bonds transition from lower to higher vibrational levels. The fundamental vibrational motions that result in infrared absorption can be classified as stretching or bending vibrations.
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
IR Spectrometers01:25

IR Spectrometers

There are two main infrared (IR) spectrophotometers: dispersive IR spectrometers and Fourier transform infrared (FTIR) spectrometers. In a dispersive IR spectrometer, a beam of infrared radiation produced by a hot wire is divided into two parallel equal-intensity beams using mirrors. One beam passes through the sample, while another is a reference beam. The beams then move through the monochromator, which separates the radiations into a continuous spectrum of different frequencies. The...
IR Frequency Region: Fingerprint Region01:03

IR Frequency Region: Fingerprint Region

IR spectra are divided into two main regions: the diagnostic region and the fingerprint region. The diagnostic region of the spectrum lies above 1500 cm−1. The absorptions resulting from single-bond vibrations of the N–H, C–H, and O–H stretch at higher wavenumbers and appear on the left side of the spectrum. The stretching absorptions of the C≡C and C≡N occur between 2100–2300 cm−1. In contrast, those arising from stretching absorptions of the C=O, C=N, and C=C occur between 1600–1850 cm−1.
The...
IR Spectrum Peak Intensity: Dipole Moment01:20

IR Spectrum Peak Intensity: Dipole Moment

The dipole moment of a bond is the product of the partial charge on either atom and the distance between them. Dipole moments influence the efficiency of IR absorption and the peak intensity. When a bond with a dipole moment is placed in an electric field, the direction of the field determines if the bond is compressed or stretched. Electromagnetic radiation consists of an electric field component that rapidly reverses direction. It follows that polar bonds are alternately stretched and...

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Diffuse Reflectance Infrared Spectroscopic Identification of Dispersant/Particle Bonding Mechanisms in Functional Inks
10:31

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用IR多光子解离光谱检测气态-NO的pi复合结构.

Barbara Chiavarino1, Maria Elisa Crestoni, Simonetta Fornarini

  • 1Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Università di Roma La Sapienza, I-00185 Roma, Italy.

Journal of the American Chemical Society
|September 21, 2006
PubMed
概括

气相红外多光子解离 (IRMPD) 光谱学区分了[C(6) H(6) NO](+) 离子的两个异构体. 这种技术成功地区分了-NO ((+) pi复合物和质子化,这对于理解芳化反应至关重要.

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科学领域:

  • 物理化学 物理化学
  • 频谱学是一种光谱学.
  • 化学电离化 化学电离化

背景情况:

  • 芳香化反应涉及关键中间体,如[C(6) H(6) NO](+) 离子.
  • 区分这些中间体的异构形式对于理解反应机制至关重要.
  • 像碰撞诱导解离这样的先前方法在同位素歧视方面存在局限性.

研究的目的:

  • 在两个异构体形式中产生和分析气相[C(6) H(6) NO](+) 离子.
  • 为了利用红外多光子解离 (IRMPD) 光谱学进行结构阐明.
  • 为了将IRMPD光谱与计算的IR吸收光谱进行比较,以确定异构体.

主要方法:

  • 使用与离子陷 (FT-ICR和Paul离子陷) 合的自由电子激光 (FEL) 来产生[C(6) H(6) NO]+) 离子.
  • 通过IR多光子解离 (IRMPD) 光谱学分析800-2200厘米的离子.
  • 实验IRMPD光谱与密度函数理论 (DFT) 计算的IR吸收光谱的比较.

主要成果:

  • 产生和分析了两个不同的异构形式的[C(6) H(6) NO](+).
  • IRMPD光谱检测发现一个同位素为[,NO](+) pi-复合体,其特征是1963厘米的突出波段(-1).
  • 第二个异构体是通过化的电子喷射电离形成的,被确定为质子化,这是计算上最稳定的异构体.

结论:

  • IRMPD光谱是一种强大的技术,用于区分异构体[C(6) H(6) NO](+) 物种.
  • [,NO](+) pi复合体代表和NO(+) 之间的一种非共价离子离子添加物.
  • 这项研究为芳化反应的中间体提供了关键的结构见解.