Kenneth Sanborn Pitzer (January 6, 1914 – December 26, 1997) was an American physical and theoretical chemist, educator, and university president.

[3] He was described as "one of the most influential physical chemists of his era" whose work "spanned almost all of the important fields of physical chemistry: thermodynamics, statistical mechanics, molecular structure, quantum mechanics, spectroscopy, chemical bonding, relativistic chemical effects, properties of concentrated aqueous salt solutions, kinetics, and conformational analysis.

Pitzer was director of research for the U.S. Atomic Energy Commission from 1949 to 1951 and a member of the National Academy of Sciences.

There is in fact a barrier to internal rotation, an important discovery upsetting the conventional wisdom and affecting the thermodynamic properties of hydrocarbons.

His son, Russell M. Pitzer is also a notable chemist who is currently retired from the faculty at Ohio State University.