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Related Concept Videos

Halogens03:01

Halogens

23.9K
Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. Astatine is a highly unstable radioactive element, so currently, most of its properties are unknown due to its short half-life. Tennessine is a synthetic element also predicted to be in this group. 
23.9K
ortho–para-Directing Deactivators: Halogens01:24

ortho–para-Directing Deactivators: Halogens

7.0K
Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
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Alkyl Halides02:45

Alkyl Halides

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Structural Properties
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...
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Halogenation of Alkenes02:46

Halogenation of Alkenes

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Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
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Mass Spectrometry: Alkyl Halide Fragmentation01:22

Mass Spectrometry: Alkyl Halide Fragmentation

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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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Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene01:14

Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene

3.9K
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.
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Related Experiment Video

Updated: Mar 12, 2026

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

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UV excitations of halons.

Ljiljana Stojanović1, Abdulrahman O Alyoubi2, Saadullah G Aziz2

  • 1Aix Marseille Univ, CNRS, ICR, Marseille, France.

The Journal of Chemical Physics
|November 17, 2016
PubMed
Summary

This study benchmarks UV excitation calculations for Halons-9 molecules. Density functional theory methods show limitations in accurately predicting higher excited states, especially those with valence-Rydberg mixing.

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Area of Science:

  • Computational Chemistry
  • Theoretical Chemistry
  • Quantum Chemistry

Background:

  • Accurate computation of ultraviolet (UV) excitation energies is crucial for understanding molecular properties.
  • Halon molecules are important in atmospheric chemistry, necessitating precise theoretical studies.
  • Evaluating computational methods for excited states is essential for reliable predictions.

Purpose of the Study:

  • To assess the performance of Density Functional Theory based Multi-Reference Configuration Interaction (DFT/MRCI) and Time-Dependent Density Functional Theory with CAM-B3LYP functional (TD-CAM-B3LYP) methods.
  • To benchmark these methods against Coupled-Cluster with Singles and Doubles (CCSD) for UV excitations of nine gaseous halon molecules (Halons-9).
  • To evaluate the accuracy for both localized and delocalized excited states up to ionization limits.

Main Methods:

  • The study employed DFT/MRCI and TD-CAM-B3LYP computational methods.
  • Excited states and ionization potentials were calculated for the Halons-9 molecular set.
  • Results were benchmarked against high-level Equation of Motion Coupled-Cluster with Singles and Doubles (EOM-CCSD) calculations.

Main Results:

  • TD-CAM-B3LYP significantly underestimated excitation energies for higher mixed valence-Rydberg and Rydberg states (MADs of 1.06 and 0.76 eV, respectively).
  • DFT/MRCI provided a better, though still imperfect, description of higher excited states (MADs of 0.66 and 0.47 eV for mixed valence-Rydberg and Rydberg states).
  • Both methods showed good agreement with EOM-CCSD for oscillator strengths of most singlet states, with larger deviations for high-lying multiconfigurational states.

Conclusions:

  • Neither TD-CAM-B3LYP nor DFT/MRCI fully satisfies the accuracy requirements for describing complex excited states, particularly those with valence-Rydberg mixing.
  • DFT/MRCI offers improved accuracy over TD-CAM-B3LYP for higher excited states in Halons-9.
  • Further development of computational methods is needed for precise prediction of UV excitations in such systems.