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Related Concept Videos

Prochirality02:05

Prochirality

The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
Formation of Halohydrin from Alkenes02:41

Formation of Halohydrin from Alkenes

An alkene, such as propene, reacts with bromine in the presence of water to yield a halohydrin. Halohydrins contain a halogen and a hydroxyl group attached to adjacent carbons. When the halogen is bromine, it is called a bromohydrin, while a chlorohydrin has chlorine as the halogen.
Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration02:34

Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration

The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons01:03

¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons

Protons in identical electronic environments within a molecule are chemically equivalent and have the same chemical shift. The replacement test is a useful tool to identify chemical equivalence and predict NMR spectra. A substituent replaces each of the protons being examined and the resulting molecules are compared. If the same molecule is obtained, the protons are equivalent or homotopic. Replacement of any hydrogens in ethane by chlorine yields chloroethane because all six protons are...
¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons00:58

¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons

Replacing each alpha-hydrogen in chloroethane by bromine (or a different functional group) yields a pair of enantiomers. Such protons are called prochiral or enantiotopic and are related by a mirror plane. Enantiotopic protons are chemically equivalent in an achiral environment. Because most proton NMR spectra are recorded using achiral solvents, enantiotopic hydrogens yield a single signal.
In chiral compounds such as 2-butanol, replacing the methylene hydrogens at C3 produces a pair of...

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Related Experiment Video

Updated: Jul 11, 2026

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
05:51

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method

Published on: July 19, 2019

Isomerization of beta-HCH in aqueous solution.

P G Deo, S B Hasan, S K Majumder

    Journal of Environmental Science and Health. Part. B, Pesticides, Food Contaminants, and Agricultural Wastes
    |January 1, 1980
    PubMed
    Summary

    This study investigated whether beta-HCH changes into other isomers when mixed with water. The researchers shook beta-HCH with distilled water and analyzed the mixture. They found alpha, beta, gamma, and delta isomers, indicating isomerization. The extract was tested for toxicity against insects and showed high toxicity. Pure beta-HCH in acetone was nontoxic. The findings suggest beta-HCH isomerizes in water, producing more toxic forms. The study supports the idea that environmental conditions influence pesticide behavior.

    Keywords:
    hexachlorocyclohexane isomersinsecticide toxicitybeta-HCH transformationenvironmental pesticide behavior

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    Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
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    Published on: February 7, 2022

    Area of Science:

    • Environmental toxicology
    • Pesticide chemistry
    • Insecticide efficacy research

    Background:

    Prior research has shown that hexachlorocyclohexane (HCH) isomers exhibit varying toxicity levels. It was already known that beta-HCH is considered relatively inert compared to other isomers. However, no prior work had resolved how beta-HCH behaves in aqueous environments. That uncertainty drove this investigation into whether beta-HCH undergoes isomerization in water. This gap motivated the study of transformation processes under controlled conditions. No prior work had resolved the toxicity implications of such isomerization. This gap motivated the study of transformation processes under controlled conditions. No prior work had resolved the toxicity implications of such isomerization.

    Purpose Of The Study:

    The aim of this study was to investigate whether beta-HCH isomerizes in aqueous solution. The specific problem addressed is the potential transformation of beta-HCH into other isomers with different toxicological properties. The motivation stems from the need to understand how environmental conditions affect pesticide behavior. This study sought to determine if isomerization occurs and if it alters toxicity. The researchers propose that beta-HCH may not be inert in water. This study sought to determine if isomerization occurs and if it alters toxicity. The researchers propose that beta-HCH may not be inert in water.

    Main Methods:

    The study involved shaking beta-HCH with distilled water at a controlled temperature of 25 +/- 1 degree Celsius. Different time intervals were tested to observe changes. After shaking, the mixture was filtered to separate the aqueous and organic phases. Ether extraction was performed on the filtrate to isolate the HCH isomers. Gas liquid chromatography was used to analyze the ether extract for isomer presence. The researchers propose that this method effectively identifies isomerization. The study also tested the toxicity of the extract against mosquito larvae, flour beetle larvae, and house-flies. Acetone solutions of pure beta-HCH were tested for comparison.

    Main Results:

    The ether extract revealed the presence of alpha, beta, gamma, and delta HCH isomers after shaking. This finding suggests isomerization of beta-HCH in aqueous solution. The presence of multiple isomers indicates a transformation process. The acetone solution of the extract showed high toxicity to tested insects. Pure beta-HCH in acetone was nontoxic to the same insects. This result supports the hypothesis that isomerization increases toxicity. The GLC analysis confirmed the presence of multiple isomers. The toxicity data corroborates the GLC findings.

    Conclusions:

    The authors suggest that beta-HCH isomerizes in aqueous solution, producing other isomers. This transformation may increase the compound's toxicity. The study supports the idea that beta-HCH is not inert in water. The presence of multiple isomers indicates a dynamic transformation process. The high toxicity of the extract supports the isomerization hypothesis. The nontoxicity of pure beta-HCH suggests that isomerization is necessary for toxicity. The study does not claim that isomerization is essential for toxicity. The findings suggest that environmental conditions influence pesticide behavior.

    The study suggests beta-HCH isomerizes into alpha, gamma, and delta forms in aqueous solution.

    Gas liquid chromatography detected alpha, beta, gamma, and delta HCH isomers in the ether extract.

    Acetone was used to dissolve the ether extract for toxicity tests against insects.

    Mosquito larvae, flour beetle larvae, and house-flies were tested for toxicity.

    The extract showed high toxicity, suggesting isomerization converts beta-HCH to more toxic forms.

    The authors suggest beta-HCH isomerizes in water, increasing its toxicity.