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Electrophiles02:28

Electrophiles

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This lesson explains the definition, classification, and characteristic features of an electrophile that are key features of nucleophilic substitution reactions. An analysis of their charge and orbital picture helps understand their reactivity for seeking electrons. Electrophiles can be classified into positive and neutral species. Other classes include free radicals and polar functional groups.
While a positive electrophile, like a proton, reacts due to its vacant, low-energy 1s orbital, the...
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Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence shell, and an anion (a negative ion) forms when a neutral atom gains one or more electrons in its valence shell. Compounds composed of ions are called ionic compounds (or salts), and their constituent ions are held together by ionic bonds: electrostatic forces of attraction between oppositely charged cations and anions. 
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Inductive Effects on Chemical Shift: Overview01:27

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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...
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Mass Spectrometry: Alkyl Halide Fragmentation01:22

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Chlorine isotopes exist as 35Cl and 37Cl in a 3:1 ratio, while bromine isotopes exist as 79Br and 81Br in a 1:1 ratio. The mass spectrum of alkyl halides typically produces two distinct molecular ion peaks, the molecular ion peak, [M], and the molecular ion plus two, [M + 2] peak. The relative heights of these two peaks are proportional to the isotopic abundance ratios of the halide. For example, 2‐chloropropane and 1‐bromopropane display two peaks with relative peak heights in a 3:1 and...
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9.8K
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
9.8K
Carbocations02:10

Carbocations

13.2K
Carbocations are one of the reaction intermediates formed during several nucleophilic substitutions or elimination reactions. A carbocation is an electron-deficient species with the central carbon atom having six electrons and three bonded atoms. The central carbon in a carbocation is sp2 hybridized with trigonal planar geometry. It has an empty p orbital perpendicular to the plane of the structure that can accept electrons. Thus, carbocations act as strong electrophiles and may react with any...
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Spatial Separation of Molecular Conformers and Clusters
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Protonated and Cationic Helium Clusters.

Linnea Lundberg1, Peter Bartl1, Christian Leidlmair1

  • 1Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria.

Molecules (Basel, Switzerland)
|March 4, 2020
PubMed
Summary
This summary is machine-generated.

Protonated helium clusters show distinct structural differences compared to pure helium clusters. Unlike heavier rare gases, neither cluster type displays icosahedral symmetries, revealing unique helium cluster behavior.

Keywords:
helium clustershelium dropletsmass spectrometrynoble gasesprotonation

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Area of Science:

  • Atomic and Molecular Physics
  • Quantum Chemistry
  • Condensed Matter Physics

Background:

  • Protonated rare gas clusters exhibit unique structural properties compared to their neutral counterparts.
  • Previous studies on heavier protonated rare gas clusters have indicated structural variations.
  • Helium clusters, especially when protonated, present a unique system due to helium's quantum nature.

Purpose of the Study:

  • To investigate and compare the structural characteristics of protonated helium clusters with pristine helium clusters.
  • To identify "magic numbers" in both protonated and pristine helium clusters using high-resolution mass spectrometry.
  • To determine if helium clusters, unlike heavier rare gas clusters, exhibit icosahedral symmetries.

Main Methods:

  • High-resolution mass spectrometry was employed to analyze helium clusters.
  • Measurements were performed on both protonated and pristine helium clusters containing up to 50 atoms.
  • Analysis focused on identifying characteristic "magic numbers" indicative of stable cluster structures.

Main Results:

  • Significant differences in magic numbers were observed between protonated and pristine helium clusters.
  • Neither protonated nor pristine helium clusters showed evidence of icosahedral symmetries.
  • The observed structures deviate from patterns seen in heavier rare gas clusters.

Conclusions:

  • Protonated helium clusters possess distinct structural properties compared to pure helium clusters.
  • Helium clusters do not adopt icosahedral structures, even when protonated, differentiating them from heavier systems.
  • These findings contribute to understanding the unique behavior of light quantum clusters.