Jove
Visualize
Contact Us
JoVE
x logofacebook logolinkedin logoyoutube logo
ABOUT JoVE
OverviewLeadershipBlogJoVE Help Center
AUTHORS
Publishing ProcessEditorial BoardScope & PoliciesPeer ReviewFAQSubmit
LIBRARIANS
TestimonialsSubscriptionsAccessResourcesLibrary Advisory BoardFAQ
RESEARCH
JoVE JournalMethods CollectionsJoVE Encyclopedia of ExperimentsArchive
EDUCATION
JoVE CoreJoVE BusinessJoVE Science EducationJoVE Lab ManualFaculty Resource CenterFaculty Site
Terms & Conditions of Use
Privacy Policy
Policies

Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Pericyclic Reactions: Introduction01:17

Pericyclic Reactions: Introduction

Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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.
Phase II Conjugation Reactions: Overview01:14

Phase II Conjugation Reactions: Overview

Conjugation, a key component of phase II biotransformation reactions, is a vital process in drug detoxification. It involves transferring endogenous substances like glucuronic acid, sulfate, and glycine to drugs or their metabolites formed in phase I reactions. These conjugation reactions, often catalyzed by specific enzymes, transform potentially harmful metabolites into inactive, water-soluble forms easily excreted in urine or bile. By enhancing polarity and eliminating pharmacological...
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

You might also read

Related Articles

Articles linked to this work by shared authors, journal, and citation graph.

Sort by
Same author

Bond Resonance Energy Verification of σ-Aromaticity in Cycloalkanes.

The journal of physical chemistry. A·2020
Same author

Excited-State Intramolecular Proton Transfer and Global Aromaticity.

The journal of physical chemistry. A·2016
Same author

Aromatic Character of Irregular-Shaped Nanographenes.

The journal of physical chemistry. A·2016
Same author

Magnetic resonance energy and topological resonance energy.

Physical chemistry chemical physics : PCCP·2016
Same author

Kinetic Stability of Non-IPR Fullerene Molecular Ions.

The journal of physical chemistry. A·2015
Same author

Origin of kinetic instability of fullerenes that violate the isolated pentagon rule.

The journal of physical chemistry. A·2015

Related Experiment Video

Updated: Jul 5, 2026

Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
07:12

Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions

Published on: July 17, 2020

Macrocyclic conjugation pathways in porphyrins.

Jun-ichi Aihara1

  • 1Department of Chemistry, Faculty of Science, Shizuoka University, Oya, Shizuoka 422-8529, Japan.

The Journal of Physical Chemistry. A
|May 20, 2008
PubMed
Summary

Macrocyclic aromaticity in porphyrinoids is traced using bond resonance energy (BRE). A main conjugation pathway, identified by larger BREs, correlates with aromaticity, while smaller BREs indicate antiaromaticity pathways.

Area of Science:

  • Porphyrinoid chemistry
  • Theoretical organic chemistry
  • Computational chemistry

Background:

  • Macrocyclic aromaticity is a fundamental concept in porphyrinoid chemistry.
  • Bond resonance energy (BRE) quantifies stabilization from macrocyclic aromaticity.
  • Understanding conjugation pathways is crucial for porphyrinoid properties.

Purpose of the Study:

  • To develop a method for tracing main conjugation pathways in macrocyclic systems.
  • To investigate the relationship between bond resonance energy and macrocyclic aromaticity/antiaromaticity.
  • To correlate determined pathways with experimental chemical shift data.

Main Methods:

  • Calculation of bond resonance energy (BRE) for pi-bonds within porphyrinoid macrocycles.
  • Algorithmic identification of main conjugation pathways by selecting bonds with maximal BRE at network bifurcations.

More Related Videos

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

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
14:11

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

Published on: June 10, 2021

Related Experiment Videos

Last Updated: Jul 5, 2026

Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
07:12

Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions

Published on: July 17, 2020

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

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
14:11

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

Published on: June 10, 2021

  • Analysis of pi-electron delocalization and its impact on macrocyclic aromaticity.
  • Comparison of theoretical pathways with experimental proton chemical shifts.

    • Main Results:

    • A method to trace main conjugation pathways based on BRE at network bifurcations was established.
    • Macrocyclic aromaticity pathways are characterized by pi-bonds with large positive BREs.
    • Macrocyclic antiaromaticity pathways are identified by pi-bonds with smaller BREs.
    • The determined conjugation pathways align with observed proton chemical shifts in macrocycles.

    Conclusions:

    • Bond resonance energy is a reliable indicator for tracing macrocyclic conjugation pathways.
    • The developed method provides insights into the electronic structure and aromaticity of porphyrinoids.
    • This approach offers a theoretical framework consistent with experimental observations in porphyrinoid chemistry.