Woodward–Hoffmann rules

Summary

The Woodward–Hoffmann rules (or the pericyclic selection rules), devised by Robert Burns Woodward and Roald Hoffmann, are a set of rules used to rationalize or predict certain aspects of the stereochemistry and activation energy of pericyclic reactions, an important class of reactions in organic chemistry. The rules are best understood in terms of the concept of the conservation of orbital symmetry using orbital correlation diagrams (see Section 3 below). The Woodward–Hoffmann rules are a consequence of the changes in electronic structure that occur during a pericyclic reaction and are predicated on the phasing of the interacting molecular orbitals. They are applicable to all classes of pericyclic reactions (and their microscopic reverse 'retro' processes), including (1) electrocyclizations, (2) cycloadditions, (3) sigmatropic reactions, (4) group transfer reactions, (5) ene reactions, (6) cheletropic reactions, and (7) dyotropic reactions. The Woodward–Hoffmann rules exemplify the pow

Official source

https://en.wikipedia.org/wiki/Woodward%E2%80%93Hoffmann_rules

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related publications (6)

Related publications

Related people

Related units

Related concepts (19)

Related concepts

Related courses (6)

Related courses

Related lectures (10)

Related lectures

Direct Observation of Aggregation-Induced Emission Mechanism

Han Han, Kun-Han Lin, Antonio Prlj

The mechanism of aggregation-induced emission, which overcomes the common aggregation-caused quenching problem in organic optoelectronics, is revealed by monitoring the real time structural evolution and dynamics of electronic excited state with frequency and polarization resolved ultrafast UV/IR spectroscopy and theoretical calculations. The formation of Woodward-Hoffmann cyclic intermediates upon ultraviolet excitation is observed in dilute solutions of tetraphenylethylene and its derivatives but not in their respective solid. The ultrafast cyclization provides an efficient nonradiative relaxation pathway through crossing a conical intersection. Without such a reaction mechanism, the electronic excitation is preserved in the molecular solids and the molecule fluoresces efficiently, aided by the very slow intermolecular charge and energy transfers due to the well separated molecular packing arrangement. The mechanisms can be general for tuning the properties of chromophores in different phases for various important applications.

WILEY-V C H VERLAG GMBH2020

Understanding how crystalline materials are assembled is important for the rational design of metal-organic frameworks (MOFs). Controlling their formation can allow researchers to streamline the synthesis of new materials as well as control their properties for targeted applications. In the first chapter of this thesis we report the construction of two 3-dimensional TbIII based MOFs (SION-1 and SION-2). Here, SION-2 acts as a metastable MOF and intermediate phase that partially dissolves and transforms into the thermodynamically stable MOF, SION-1. This chemical transformation occurs in a DMF/water solvent mixture, and is triggered when additional energy is provided to the reaction. In situ studies reveal the partial dissolution of the metastable phase after which the MOF components are reassembled into the thermodynamically stable phase. The marked difference in thermal and chemical stability between the kinetically and thermodynamically controlled phases is contrasted by their identical chemical building unit composition. Following the understanding of this transformation, an isostructural family of SION-1 and SION-2 had been constructed using lanthanide metal salts, where LnIII-SION-1 is comprised of Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu and LnIII-SION-2 is formed using Ce, Nd, Eu, Gd, Tb and Yb. The electronic properties of lanthanide based MOFs have not been extensively studied due to the general cognizance that LnIII ions behave as isolated free ions as their 4f orbitals do not contribute to bonding. Here, we systematically studied the electronic properties (UV-vis) of LnIII-SION-1 and LnIII-SION-2 and show that the higher the intensity of this absorption band in LnIII-SION-1 is due to the better overlap between Ln(5d) and ligand(pi*) orbitals and reveals that the lowest unoccupied crystalline orbitals are dispersed over an energy range and can be considered as a conduction band. We validated this observation by the non-linear I-V curves collected on CeIII- and YbIII-SION-1, both of which display dielectric properties. In the second chapter of this thesis, we rationally design a novel biologically derived MOF featuring unobstructed Watson-Crick faces of Ade pointing towards the MOF cavities. We show, through a combined experimental and computational approach, that Thy molecules diffuse through the pores of the MOF and become base-paired with Ade. The Ade-Thy pair binding at 40-45% loading reveals that Thy molecules are packed within the channels in a way that fulfill both the Woodward-Hoffmann and Schmidt rules, and upon UV irradiation, Thy molecules dimerize into ThyThy. This study highlights the utility of MOFs as nanoreactors for the synthesis of molecules that are otherwise difficult. Concluding this thesis, a biologically derived multimodal sensor MOF is synthesized and a formed into a device. The MOF, SION-9, is comprised of Ade and a porphyrin based ligand, and has tuneable conductive properties ranged from 2.69-4.20 x 10-8 - 7.43-7.34 x 10-6 S/cm. SION-9 is sensitive to both pressure and temperature simultaneously, and demonstrated both fast response times (< 60 ms) and a long shelf life (> 6 months).

EPFL2019

Nucleobase pairing and photodimerization in a biologically derived metal-organic framework nanoreactor

Samantha Lynn Anderson, Peter George Boyd, David Lyndon Emsley, Andrzej Gladysiak, Dominik Józef Kubicki, Ngoc Tú Nguyên, Berend Smit, Kyriakos Stylianou

Biologically derived metal-organic frameworks (bio-MOFs) are of great importance as they can be used as models for bio-mimicking and in catalysis, allowing us to gain insights into how large biological molecules function. Through rational design, here we report the synthesis of a novel bio-MOF featuring unobstructed Watson-Crick faces of adenine (Ade) pointing towards the MOF cavities. We show, through a combined experimental and computational approach, that thymine (Thy) molecules diffuse through the pores of the MOF and become base-paired with Ade. The Ade-Thy pair binding at 40-45% loading reveals that Thy molecules are packed within the channels in a way that fulfill both the Woodward-Hoffmann and Schmidt rules, and upon UV irradiation, Thy molecules dimerize into ThyThy. This study highlights the utility of accessible functional groups within the pores of MOFs, and their ability to 'lock' molecules in specific positions that can be subsequently dimerized upon light irradiation, extending the use of MOFs as nanoreactors for the synthesis of molecules that are otherwise challenging to isolate.

2019

EPFL2019