Roald Hoffmann Nobel laureate co-developer of Woodward-Hoffmann rule

Roald Hoffmann – co-developer of Woodward–Hoffmann rule

Woodward–Hoffmann rules are formulated to explain the striking stereospecificity of electrocyclic reactions.
Article On Roald Hoffmann

Biography & contributions

Roald Hoffmann the organic chemist, was born on July 18,1937. Hoffmann was the Nobel laureate at the time of 1981 for the work quantum mechanics.

Hoffmann applied the theories of quantum mechanics from the filed of physics to explain chemical reactions and chemical compounds.He investigated both organic and inorganic substances. Hoffmann was introduced the principle called isolobal principle. Hoffmann in the years of 1955 and 1956 studied the chemistry of cement and hydrocarbons.

Hoffmann along with other Nobel laureate Woodward used quantum mechanics to develop rules that would enable scientists to predict whether a particular compbinations of chemicals will reult in a reaction. He also worked on inorganic molecules and organometallics and published number of bookes like A chemist's view of bonding in Extended structures and Chemistry imagined:reflections of science.

Hoffmann got awards and honors like Pure chemistry award in the year of 1969 from the American chemical society, the Arthur C.Cope Award in the year of 1973, the Linus pauling award in the year of 1974, the Nichols medal in the year of 1981,Priestly medal in the year of 1990.

Woodward–Hoffmann rule

The two eminent scientists woodward and roald hoffmann together proposed rule called woodward-hoffmann rule. Woodward-hoffmann applied to electrocyclic reactions, cycloaddition reactions, cheletropic reactions,sigmatropic reactions and group transfer reactions.

This rule first formulated to explain the stereospecificity of electrocyclic reactions and thermolysis of the substituted cyclobutene trans-1,2,3,4-tetramethylcyclobutene and the (E,E)-3,4-dimethyl-2,4-hexadiene.

Woodward-hoffmann rule explains following concepts in organic chemistryIn an open-chain system containing 4n-electrons, the orbital symmetry of the highest occupied molecule orbital is such that a bonding interaction between the termini must involve overlap between orbital envelopes on opposite faces of the system and this can only be achieved in a conrotatory process.

In open systems containing 4n + 2 electrons, terminal bonding interaction within ground-state molecules requires overlap of orbital envelopes on the same face of the system, attainable only by disrotatory displacements.In a photochemical reaction an electron in the HOMO of the reactant is promoted to an excited state leading to a reversal of terminal symmetry relationships and reversal of stereospecificity.

Isolobal Principle


Rober hoffmann also deduced the principle isolobal principle or isolbal analogy.Isolobal principle is a strategy used in organometallic chemistry to relate the structure of organic and inorganic molecular fragments in order to predict bonding properties of organometallic compounds. According to Hoffmann if the number, symmetry properties, approximate energy and shape of the frontier orbitals and the number of electrons in them are similar then they are in isolobal condition.

Isolobal compounds are analogues to isoelectronic compounds that share the same number of valence electrons and structure.The isolobal analogy can also be used with isoelectronic fragments having the same coordination number, which allows charged species to be considered.

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