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Related Concept Videos

Mass Spectrum01:23

Mass Spectrum

A mass spectrum is the graphical representation of the relative abundance of the charged fragments in an analyte plotted against their mass-to-charge ratio (m/z). The plot's x-axis represents the ratio of the mass of the charged fragment to the number of charges it carries. The y axis of the plot represents the relative abundance of each charged species. The relative abundance is calculated from the signal intensity of each charged species recorded at the detector. The most intense signal (the...
Inductive Effects on Chemical Shift: Overview01:27

Inductive Effects on Chemical Shift: Overview

The protons in unsubstituted alkanes are strongly shielded with chemical shifts below 1.8 ppm. Methine, methylene, and methyl protons appear at approximately 1.7, 1.2 and 0.7 ppm, while the proton signal from methane appears at 0.23 ppm. An electronegative substituent, such as chlorine, withdraws the electron density from the protons, increasing their chemical shift. Progressive substitution of the hydrogens in methane by chlorine shifts the proton signals increasingly downfield, to 3.05 ppm in...
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

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 have a...
IR Frequency Region: X–H Stretching01:24

IR Frequency Region: X–H Stretching

In IR spectroscopy, signals produced by the X−H bonds (such as C−H, O−H, or N−H) can be observed in the frequency range of  2700–4000 cm–1. The C−H stretching vibration forms sharp bands in the region 2850–3000 cm–1. The presence of the O−H stretching vibration leads to the forming of an absorption band in the frequency range 3650–3200 cm−1. At the same time, N−H stretching can be confirmed by absorption bands in the 3500–3100 cm−1 range. Even though both O−H and N−H bonds vibrate at a similar...
NMR Spectroscopy: Chemical Shift Overview01:15

NMR Spectroscopy: Chemical Shift Overview

The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...
Mass Spectrometry: Long-Chain Alkane Fragmentation01:18

Mass Spectrometry: Long-Chain Alkane Fragmentation

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...

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Related Experiment Video

Updated: Jun 13, 2026

Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer
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Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer

Published on: July 26, 2024

Methane line parameters for the 2.3-microm region.

L R Brown, L S Rothman

    Applied Optics
    |April 17, 2010
    PubMed
    Summary

    Researchers compiled new methane line parameters in the 4136-4666 cm(-1) region. This dataset combines experimental measurements with known quantum assignments for improved accuracy in spectroscopic analysis.

    Area of Science:

    • Spectroscopy
    • Molecular Physics
    • Atmospheric Chemistry

    Background:

    • Accurate methane line parameters are crucial for interpreting atmospheric spectra.
    • Existing datasets may have limitations in specific spectral regions.

    Purpose of the Study:

    • To create a comprehensive dataset of methane line parameters.
    • To improve the accuracy of spectroscopic measurements in the 4136-4666 cm(-1) region.

    Main Methods:

    • Experimental measurement of methane absorption positions and intensities.
    • Combination with literature-derived quantum assignments.
    • Computerized analysis of spectral data.

    Main Results:

    • A new compilation of methane line parameters.

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    Multimodal Nonlinear Hyperspectral Chemical Imaging Using Line-Scanning Vibrational Sum-Frequency Generation Microscopy
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    Multimodal Nonlinear Hyperspectral Chemical Imaging Using Line-Scanning Vibrational Sum-Frequency Generation Microscopy

    Published on: December 1, 2023

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    Last Updated: Jun 13, 2026

    Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer
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    Published on: July 26, 2024

    Visualizing Methane-Cycling Microbial Dynamics in Coastal Wetlands
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    Visualizing Methane-Cycling Microbial Dynamics in Coastal Wetlands

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    Multimodal Nonlinear Hyperspectral Chemical Imaging Using Line-Scanning Vibrational Sum-Frequency Generation Microscopy
    08:49

    Multimodal Nonlinear Hyperspectral Chemical Imaging Using Line-Scanning Vibrational Sum-Frequency Generation Microscopy

    Published on: December 1, 2023

  • High accuracy achieved: +/-0.0005 cm(-1) for positions and 2% for intensities.
  • Data validated for single unblended absorptions.

    • Conclusions:

    • The new dataset provides a valuable resource for methane spectroscopy.
    • Enhanced accuracy facilitates more precise atmospheric and molecular studies.
    • This work contributes to the refinement of spectroscopic databases.