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Related Concept Videos

Alkyl Halides02:45

Alkyl Halides

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...
Halogenation of Alkenes02:46

Halogenation of Alkenes

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.
Halogens03:01

Halogens

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.
Types of Toxins01:36

Types of Toxins

Humans continually engage with an environment rich in potentially harmful chemicals. These are introduced to our bodies through inhalation, ingestion, or skin contact. These chemicals exist in various forms, such as air and environmental pollutants, agricultural chemicals, organic solvents, and heavy metals.
Air pollutants, primarily gases, pose significant threats to respiratory health, leading to conditions like hypoxia, lung cancer, and in extreme cases, death.
Environmental pollutants like...
Electrophilic Addition to Alkynes: Halogenation02:38

Electrophilic Addition to Alkynes: Halogenation

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.
Radical Substitution: Halogenation of Alkanes and Alkyl Substituents01:27

Radical Substitution: Halogenation of Alkanes and Alkyl Substituents

In the presence of heat or light, alkanes react with molecular halogens to form alkyl halides by a substitution reaction called radical halogenation. This reaction has three steps: initiation, propagation, and termination, as seen in the radical chlorination of methane to produce methyl chloride.
In the initiation step of the reaction, the chlorine molecule undergoes homolytic cleavage in the presence of light or heat, forming two highly reactive chlorine radicals. Propagation occurs in two...

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Related Experiment Video

Updated: May 30, 2026

High Content Screening Analysis to Evaluate the Toxicological Effects of Harmful and Potentially Harmful Constituents (HPHC)
11:38

High Content Screening Analysis to Evaluate the Toxicological Effects of Harmful and Potentially Harmful Constituents (HPHC)

Published on: May 10, 2016

Structure-toxicity relationships for selected halogenated aliphatic chemicals.

K S Akers1, G D Sinks, T W Schultz

  • 1Department of Pathology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814-4799, USA.

Environmental Toxicology and Pharmacology
|July 26, 2011
PubMed
Summary

Quantitative structure-activity relationships (QSARs) were developed for halogenated alkanes, alkanols, and alkanitriles using toxicity data. Hydrophobicity and electrophilicity were key factors, revealing distinct toxicity mechanisms for different chemical classes.

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In Silico Modeling Method for Computational Aquatic Toxicology of Endocrine Disruptors: A Software-Based Approach Using QSAR Toolbox
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In Silico Modeling Method for Computational Aquatic Toxicology of Endocrine Disruptors: A Software-Based Approach Using QSAR Toolbox

Published on: August 28, 2019

Area of Science:

  • Environmental toxicology
  • Computational chemistry
  • Quantitative structure-activity relationships (QSARs)

Background:

  • Assessing the ecotoxicity of halogenated organic compounds is crucial for environmental risk assessment.
  • Understanding the relationship between chemical structure and biological activity (toxicity) can predict the environmental impact of chemicals.
  • Previous studies have explored QSARs for various chemical classes, but comprehensive models for mixed halogenated compounds are needed.

Purpose of the Study:

  • To experimentally determine the toxicity of 39 halogen-substituted alkanes, alkanols, and alkanitriles to the ciliate Tetrahymena pyriformis.
  • To develop quantitative structure-activity relationships (QSARs) correlating toxicity with physicochemical properties like hydrophobicity (logK(ow)) and electrophilicity (E(lumo)).
  • To investigate the mechanisms of toxicity for different classes of halogenated compounds.

Main Methods:

  • Experimental determination of toxicity (log(IGC(50)(-1))) for 39 halogenated compounds.
  • Calculation of hydrophobic (logK(ow)) and electrophilic (E(lumo)) parameters.
  • Development of QSAR models using regression analysis, including surface-response modeling for combined chemical classes.

Main Results:

  • Hydrophobicity-dependent QSARs were established for haloalkanes and haloalcohols, with haloalkane toxicity aligning with baseline toxicity (narcosis).
  • Haloalcohols exhibited toxicity exceeding baseline, suggesting additional mechanisms beyond narcosis.
  • A QSAR model for halonitriles was dependent on electrophilicity, not hydrophobicity, indicating distinct reactivity.
  • A comprehensive surface-response model incorporating hydrophobicity and electrophilicity was developed for all three chemical classes, highlighting mixed toxicity mechanisms for haloalcohols and halonitriles.

Conclusions:

  • The toxicity of halogenated compounds to Tetrahymena pyriformis varies significantly based on their chemical structure and functional groups.
  • Haloalkanes primarily exhibit baseline toxicity, while haloalcohols and halonitriles display toxicity influenced by specific chemical reactivity (electrophilicity) beyond narcosis.
  • The findings suggest that haloalcohols and halonitriles exert toxicity through multiple and/or mixed mechanisms of action, involving electrophilic or nucleophilic interactions.