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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
Directing and Steric Effects in Disubstituted Benzene Derivatives01:18

Directing and Steric Effects in Disubstituted Benzene Derivatives

When disubstituted benzenes undergo electrophilic substitution, the product distribution depends on the directing effect of both substituents. When the directing effects of both substituents reinforce each other, a single product is obtained. For example, bromination of p-nitrotoluene occurs ortho to the methyl group and meta to the nitro group, which is the same position, resulting in a single product. However, if the directing effects of the two groups oppose each other, the more strongly...
Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry01:29

Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry

Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
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.
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry01:28

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.
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.

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Related Experiment Video

Updated: Jun 4, 2026

A Customizable Approach for the Enzymatic Production and Purification of Diterpenoid Natural Products
07:59

A Customizable Approach for the Enzymatic Production and Purification of Diterpenoid Natural Products

Published on: October 4, 2019

Electrostatic effects on (di)terpene synthase product outcome.

Ke Zhou1, Reuben J Peters

  • 1Department of Biochemistry, Biophysics, & Molecular Biology, Iowa State University, Ames, IA 50011, USA.

Chemical Communications (Cambridge, England)
|February 10, 2011
PubMed
Summary

Terpene synthases use electrostatic effects, not just steric templates, to control complex reactions. A single residue change can alter product complexity by influencing carbocation stability and interaction with the pyrophosphate co-product.

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Last Updated: Jun 4, 2026

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Light-driven Enzymatic Decarboxylation
09:58

Light-driven Enzymatic Decarboxylation

Published on: May 22, 2016

Area of Science:

  • Biochemistry
  • Enzymology
  • Organic Chemistry

Background:

  • Terpene synthases (TPS) are enzymes that catalyze the formation of complex cyclic molecules from acyclic precursors.
  • Traditionally, TPS reactions were thought to be controlled primarily by steric effects, with the enzyme acting as a template.
  • Emerging evidence suggests electrostatic interactions also play a significant role in modulating TPS activity and product outcome.

Purpose of the Study:

  • To investigate the role of electrostatic effects in terpene synthase catalysis.
  • To understand how enzyme active site residues influence carbocation intermediates and their interactions with the pyrophosphate co-product.
  • To elucidate the mechanistic basis for how single residue changes can drastically alter reaction pathways and product complexity.

Main Methods:

  • Site-directed mutagenesis of key residues in terpene synthases.
  • Analysis of reaction products using mass spectrometry and NMR.
  • Crystallographic studies of enzyme-intermediate complexes.
  • Computational modeling of reaction mechanisms and electrostatic interactions.

Main Results:

  • A single amino acid substitution (hydroxyl to aliphatic) was sufficient to "short-circuit" complex cyclization reactions, leading to simpler products.
  • The converse mutation (aliphatic to hydroxyl) increased reaction complexity.
  • Hydroxyl residues stabilize carbocation intermediates via dipole interactions, preventing further migration.
  • Lack of hydroxyl stabilization promotes carbocation migration towards the pyrophosphate co-product, increasing reaction complexity.
  • Synergy between pyrophosphate and aza-analogs is greater for late-stage carbocations, consistent with observed mechanisms.

Conclusions:

  • Electrostatic effects, particularly hydroxyl dipole stabilization of carbocations, are crucial for controlling terpene synthase reaction pathways.
  • Enzymes actively counteract the templating effects of the pyrophosphate co-product through electrostatic interactions.
  • Fine-tuning active site electrostatics offers a mechanism to precisely control the complexity and outcome of terpene biosynthesis.