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Related Concept Videos

Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation01:27

Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation

Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, β-ketoesters, or β-diketones) and α,β-unsaturated carbonyl acceptors. Named after Sir Robert Robinson, who discovered it, this reaction yields a six-membered ring with three new C–C bonds (two σ bonds and one π bond).
Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
Disubstituted Cyclohexanes: cis-trans Isomerism02:37

Disubstituted Cyclohexanes: cis-trans Isomerism

Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers.
Stability of Substituted Cyclohexanes02:30

Stability of Substituted Cyclohexanes

This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...

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Related Experiment Video

Updated: May 16, 2026

Constructing Cyclic Peptides Using an On-Tether Sulfonium Center
07:11

Constructing Cyclic Peptides Using an On-Tether Sulfonium Center

Published on: September 28, 2022

[Cyclopeptides from Rubia schumanniana].

Bin Kuang1, Jun-ting Fan, Si-meng Zhao

  • 1Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China. kuangb2@126.com

Zhongguo Zhong Yao Za Zhi = Zhongguo Zhongyao Zazhi = China Journal of Chinese Materia Medica
|December 15, 2012
PubMed
Summary
This summary is machine-generated.

Researchers isolated nine cyclopeptides from Rubia schumanniana tubers for the first time. This study details the separation and structural identification of these novel compounds.

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Area of Science:

  • Natural Product Chemistry
  • Phytochemistry

Context:

  • Rubia schumanniana, a plant species, is known for its potential bioactive compounds.
  • Cyclopeptides represent a class of natural products with diverse biological activities.

Purpose:

  • To isolate and elucidate the structures of cyclopeptides from the tubers of Rubia schumanniana.
  • To contribute to the understanding of the chemical constituents of this plant species.

Summary:

  • The 70% methanol extract of Rubia schumanniana tubers underwent extensive purification using silica gel, RP-18, Sephedax LH-20, and High-Performance Liquid Chromatography (HPLC).
  • Nine cyclopeptides, including RA-II, RA-V, RA-VIII, rubiyunnanin C, RA-X, RY-II, RA-I, RA-XIII, and RA-XIII-OMe, were successfully separated and identified through spectral analysis.
  • This marks the first reported isolation of these nine cyclopeptides from R. schumanniana.

Impact:

  • Provides a comprehensive chemical profile of Rubia schumanniana tubers.
  • Identified compounds may serve as leads for future pharmacological investigations.
  • Expands the known diversity of cyclopeptides in the plant kingdom.