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The carbon-hydrogen bond — 2/3 of all bonds in hydrocarbons — has defied chemists’ attempts to open it up and add new chemical groups. A team has now cracked the strongest of C-H bonds, those on a molecule’s terminal carbon. The reaction catalyst is an iridium atom to break the bond and a methyl group to add a boron compound. Boron is easily exchanged for other groups, allowing additions to hydrocarbons and natural products.