Anaerobic growth of the bacterium strain HxN1 with n‐hexane gives nearly equal amounts of (2R,1′R)‐ and (2S,1′R)‐(1‐methylpentyl)succinate, which are formed by the radical addition of the hydrocarbon to fumarate (see scheme). The highly selective attack on the pro‐S hydrogen atom at C2 of n‐hexane is associated with inversion of the configuration at C2 during binding to fumarate and exhibits isotopic