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Related Concept Videos

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...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
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...
Mass Spectrometry: Branched Alkane Fragmentation01:29

Mass Spectrometry: Branched Alkane Fragmentation

This lesson delves into the mass spectrometry of branched alkane fragmentation. Branched alkanes possess secondary or tertiary carbon atoms, which generate relatively stable carbocations if the cleavage occurs at the branching point. The high stability of carbocations drives the instant fragmentation of branched alkanes. Accordingly, the branched alkane's molecular ion peak is very weak or invisible in the mass spectra, especially in comparison to a linear alkane.
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...

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Related Experiment Video

Updated: Jul 15, 2026

Methane Hydrate Crystallization on Sessile Water Droplets
08:46

Methane Hydrate Crystallization on Sessile Water Droplets

Published on: May 26, 2021

NMR study of methane + ethane structure I hydrate decomposition.

Steven F Dec1, Kristen E Bowler, Laura L Stadterman

  • 1Center for Hydrate Research, Department of Chemical Engineering, Colorado School of Mines, Golden, CO 80401, USA.

The Journal of Physical Chemistry. A
|April 27, 2007
PubMed
Summary

Methane and ethane hydrate decomposition rates were studied. Ethane-filled large cages decomposed faster due to a model of methane molecule distribution within structure I cages.

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On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes
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Area of Science:

  • * Materials Science
  • * Chemical Engineering
  • * Physical Chemistry

Background:

  • * Methane and ethane form structure I hydrates, crystalline solids trapping gas molecules.
  • * Understanding hydrate decomposition is crucial for energy storage and geological processes.

Purpose of the Study:

  • * To investigate the decomposition kinetics of methane + ethane structure I hydrates.
  • * To elucidate the role of ethane in the decomposition rate of large hydrate cages.

Main Methods:

  • * Utilized 13C magic-angle spinning (MAS) Nuclear Magnetic Resonance (NMR) spectroscopy.
  • * Studied decomposition as a function of hydrate composition and temperature.

Main Results:

  • * Observed a higher decomposition rate in large structure I cages initially containing ethane.
  • * Developed a model where unit cells with zero methane molecules are least stable and decompose faster.
  • * This distribution explains the accelerated decomposition of ethane-rich large cages.

Conclusions:

  • * The distribution of methane molecules within structure I cages significantly impacts decomposition rates.
  • * Ethane presence in large cages enhances their decomposition due to a higher proportion of less stable, methane-deficient unit cells.