A Hughes–Ingold symbol describes various details of the reaction mechanism and overall result of a

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

. For example, an S_N2 reaction is a

substitution reaction A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions ar ...

("S") by a

nucleophilic In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

process ("N") that is

bimolecular In chemistry, molecularity is the number of molecules that come together to react in an elementary (single-step) reactionAtkins, P.; de Paula, J. Physical Chemistry. Oxford University Press, 2014 and is equal to the sum of stoichiometric coeffici ...

("2" molecular entities involved) in its

rate-determining step In chemical kinetics, the overall rate of a reaction is often approximately determined by the slowest step, known as the rate-determining step (RDS or RD-step or r/d step) or rate-limiting step. For a given reaction mechanism, the prediction of the ...

. By contrast, an E2 reaction is an

elimination reaction An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one- or two-step mechanism. The one-step mechanism is known as the E2 reaction, and the two-step mechanism is known as the E1 r ...

, an S_E2 reaction involves electrophilic substitution, and an S_N1 reaction is unimolecular. The system is named for British chemists

Edward D. Hughes Edward David Hughes (June 18, 1906June 30, 1963) was a British organic chemist. He was a professor first at University College, Bangor and then at University College in London, eventually rising to the rank of dean at each. He was elected as a F ...

and

Christopher Kelk Ingold Sir Christopher Kelk Ingold (28 October 1893 – 8 December 1970) was a British chemist based in Leeds and London. His groundbreaking work in the 1920s and 1930s on reaction mechanisms and the electronic structure of organic compounds was resp ...

References

{{DEFAULTSORT:Hughes-Ingold symbol Chemical reactions Reaction mechanisms Chemical nomenclature