Louis Plack Hammett (April 7, 1894 – February 9, 1987) was an American

physical chemist Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical me ...

. He is known for the

Hammett equation The Hammett equation in organic chemistry describes a linear free-energy relationship relating reaction rates and equilibrium constants for many reactions involving benzoic acid derivatives with meta- and para-substituents to each other with jus ...

, which relates

reaction rate The reaction rate or rate of reaction is the speed at which a chemical reaction takes place, defined as proportional to the increase in the concentration of a product per unit time and to the decrease in the concentration of a reactant per unit ...

s to

equilibrium constant The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency ...

s for certain classes of organic reactions involving substituted

aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

compounds. He is also known for his research into

superacids In chemistry, a superacid (according to the classical definition) is an acid with an acidity greater than that of 100% pure sulfuric acid (), which has a Hammett acidity function (''H''0) of −12. According to the modern definition, a superacid ...

and his development of a scheme for comparing their acidities based on what is now known as the

Hammett acidity function The Hammett acidity function (''H''0) is a measure of acidity that is used for very concentrated solutions of strong acids, including superacids. It was proposed by the physical organic chemist Louis Plack Hammett and is the best-known acidity fu ...

. The Curtin–Hammett principle bears his name. The awards he obtained included the

Priestley Medal The Priestley Medal is the highest honor conferred by the American Chemical Society (ACS) and is awarded for distinguished service in the field of chemistry. Established in 1922, the award is named after Joseph Priestley, the discoverer of oxygen ...

in 1961,the

Willard Gibbs Award The Willard Gibbs Award, presented by thChicago Sectionof the American Chemical Society, was established in 1910 by William A. Converse (1862–1940), a former Chairman and Secretary of the Chicago Section of the society and named for Professor Jo ...

in 1961, the

National Medal of Science The National Medal of Science is an honor bestowed by the President of the United States to individuals in science and engineering who have made important contributions to the advancement of knowledge in the fields of behavioral and social scienc ...

in 1967, and in 1975 the

Barnard Medal for Meritorious Service to Science The Barnard Medal for Meritorious Service to Science was established in 1889 by the will of Columbia University president Frederick A. P. Barnard, and has been awarded by Columbia University, based on recommendations by the National Academy of Sc ...

. Hammett grew up in

Portland, Maine Portland is the largest city in the U.S. state of Maine and the seat of Cumberland County. Portland's population was 68,408 in April 2020. The Greater Portland metropolitan area is home to over half a million people, the 104th-largest metropol ...

, and studied in Harvard and Switzerland. He earned his Ph.D. at

Columbia University Columbia University (also known as Columbia, and officially as Columbia University in the City of New York) is a private research university in New York City. Established in 1754 as King's College on the grounds of Trinity Church in Manhatt ...

. He authored an influential textbook on

physical organic chemistry Physical organic chemistry, a term coined by Louis Hammett in 1940, refers to a discipline of organic chemistry that focuses on the relationship between chemical structures and reactivity, in particular, applying experimental tools of physical ch ...

,Hammett, Louis P. (1940) ''Physical Organic Chemistry'' New York: McGraw Hill. and is credited with coining the term.

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Further reading