Franz Sondheimer FRS (17 May 1926 – 11 February 1981) was a British chemist.
Sondheimer was born in Stuttgart, Germany in 1926 and, following the rise of the Nazis, fled to the United Kingdom in 1937. He was a pupil at Highgate School and subsequently studied chemistry, receiving his degree from Imperial College London.
From 1949 to 1952, Sondheimer was a Research Fellow, Harvard University, where he obtained his Ph.D. under R. B. Woodward. In 1952 he was employed by Syntex SA, Mexico City, as Associate Director of Research. He held that position until 1956, at which time he moved to Israel where he became Head of the Organic Chemistry Department at the Weizmann Institute of Science, Rehovot, a position he held until 1964.
While with the Institute, from 1960 to 1964 he was the Rebecca and Israel Sieff Professor of Organic Chemistry. He also held the post of Vice-President, Research, of Syntex SA from 1961 to 1963.
After a stay in Israel of eight years, Sondheimer returned to Britain in 1964 and was there appointed as Royal Society Research Professor at the University of Cambridge and Fellow of Churchill College, Cambridge, both from 1964 to 1967. In May 1967 he was elected a Fellow of the Royal Society. His membership citation read: Professor Sondheimer is distinguished for his work on the total synthesis of a range of natural products, the partial synthesis of steroid hormones and analogues, and especially for his syntheses of the hitherto unknown class of conjugated unsaturated macrocyclic compounds which has led to some interesting theoretical conclusions. On these topics he has so far published 167 papers.