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Related Concept Videos

Physical Properties of Alcohols and Phenols02:32

Physical Properties of Alcohols and Phenols

Alcohols are organic compounds in which a hydroxy group is attached to a saturated carbon. Phenols are a class of alcohols containing a hydroxy group attached to an aromatic ring. The physical properties of the alcohols and phenols are influenced by hydrogen bonding due to the oxygen–hydrogen dipole in the hydroxy functional group and dispersion forces between alkyl or aryl regions of alcohol and phenol molecules.
Alcohols possess a higher boiling point than aliphatic hydrocarbons of similar...
Acidity and Basicity of Alcohols and Phenols02:36

Acidity and Basicity of Alcohols and Phenols

Like water, alcohols are weak acids and bases. This is attributed to the polarization of the O–H bond making the hydrogen partially positive. Moreover, the electron pairs on the oxygen atom of alcohol make it both basic and nucleophilic. Protonation of an alcohol converts hydroxide, a poor leaving group, into water—a good one. The two acid–base equilibria corresponding to ethanol are depicted below.
Acidity of Carboxylic Acids01:21

Acidity of Carboxylic Acids

Carboxylic acids are the strongest organic acids. However, their acidic strength is much less than mineral acids like HCl. Carboxylic acids ionize in water and readily lose the hydroxyl proton to form a resonance-stabilized carboxylate ion.
Carboxylic Acids to Primary Alcohols: Hydride Reduction01:17

Carboxylic Acids to Primary Alcohols: Hydride Reduction

Carboxylic acids, upon reaction with strong reducing agents such as lithium aluminum hydride followed by hydrolysis, undergo reduction to form primary alcohols.
Oxidation of Phenols to Quinones01:17

Oxidation of Phenols to Quinones

In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...
Basicity of Aliphatic Amines01:21

Basicity of Aliphatic Amines

Amines can behave as Brønsted–Lowry bases by accepting a proton from the acid to form corresponding conjugate acids. Due to a lone pair of nonbonding electrons, aliphatic amines can also act as Lewis bases by forming a covalent bond with an electrophile.
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates higher...

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Related Experiment Video

Updated: Jun 25, 2026

Repeatable Stair-step Assay to Access the Allelopathic Potential of Weedy Rice (Oryza sativa ssp.)
09:00

Repeatable Stair-step Assay to Access the Allelopathic Potential of Weedy Rice (Oryza sativa ssp.)

Published on: January 28, 2020

Why phenolic acids are unlikely primary allelochemicals in rice.

Maria Olofsdotter1, Malou Rebulanan, Artemio Madrid

  • 1International Rice Research Institute, Makati Central Post Office, Makati City, Philippines.

Journal of Chemical Ecology
|March 1, 2002
PubMed
Summary

Rice allelopathy against weeds is known, but the specific chemicals are unidentified. Studies show rice cultivars and weeds do not have varying tolerance to phenolic acids, though rice is more tolerant than weeds. Release rates of phenolic acids are too low to be phytotoxic alone.

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Real-Time Detection of Reactive Oxygen Species Production in Immune Response in Rice with a Chemiluminescence Assay
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Repeatable Stair-step Assay to Access the Allelopathic Potential of Weedy Rice (Oryza sativa ssp.)
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Published on: November 25, 2022

Area of Science:

  • Agricultural Science
  • Plant Biology
  • Biochemistry

Background:

  • Allelopathy in rice (Oryza sativa, L.) shows potential for weed management, with ~3.5% of germplasm exhibiting allelopathic effects.
  • Phenolic acids are frequently cited as potential allelochemicals, but their role and concentration in rice ecosystems remain unclear.

Purpose of the Study:

  • To investigate the tolerance of rice cultivars and weed species to phenolic acids, specifically p-hydroxybenzoic acid.
  • To quantify the release rate of phenolic acids from rice plants and assess their potential phytotoxicity.

Main Methods:

  • Dose-response studies were conducted to compare the tolerance of different rice cultivars (traditional vs. improved, aerobic vs. anaerobic adapted) and Echinochloa weed species to p-hydroxybenzoic acid.
  • Phenolic acid release rates from rice plants were measured in solution culture over one month.

Main Results:

  • No significant differences in p-hydroxybenzoic acid tolerance were found between rice cultivars or between Echinochloa ecotypes.
  • All rice cultivars exhibited significantly higher tolerance to p-hydroxybenzoic acid than the tested weed species.
  • Measured phenolic acid release rates from rice plants were insufficient to reach phytotoxic concentrations alone.

Conclusions:

  • Phenolic acids alone are unlikely to be the primary cause of observed allelopathy in rice due to insufficient release concentrations.
  • Differential tolerance to phenolic acids does not explain the observed allelopathic effects in rice.
  • Phenolic acids may contribute to allelopathy as part of a complex chemical mixture.