For years, chemists were unable to explain how the bonds were being rearranged.

The key, Mr. Chauvin figured out in 1971, is a metal-carbon catalyst. The catalyst pairs with a molecular fragment, like two dancers with all four hands clasped together. Letting go of one pair of hands, they reach for a second pair of molecular pieces to form a ring of four. The ring then breaks apart, with the catalyst carrying away a new molecular piece and leaving its original partner behind. That rearranges the carbon bonds.

The others who shared the Nobel — Robert H. Grubbs of the California Institute of Technology and Richard R. Schrock of the Massachusetts Institute of Technology — took Mr. Chauvin’s findings, developed new catalysts and showed how the paradigm could be applied to a wide range of organic compounds.

The phone call from Stockholm in October 2005 took Mr. Chauvin by surprise.

“For me, it was unexpected, because my contribution is not very important in my opinion,” he said that day. “My research opened the way, but the main part of the research has been made by Schrock and Grubbs.”

He was born to French parents — his father was an electrical engineer — on Oct. 10, 1930, in Menin, Belgium, near the border with France, and grew up with four brothers and sisters amid the upheaval of World War II. “The war taught me to eat what there was,” Mr. Chauvin wrote in his Nobel Prize biography. “I am still not a fussy eater, although I do enjoy good food.”

He confessed that he was not a brilliant student, even in chemistry. “I chose chemistry rather by chance,” he wrote, “because I firmly believed (and still do) that you can become passionately involved in your work, whatever it is.”