An asymmetrically distorted structure of the n-pentane radical cation (trans-trans) has been located in B3LYP/6311G(d,p) calculations, and it has a C-s symmetric geometry with one of the two central C-C bonds elongated. The B3LYP and Cl calculations indicate that the C-s structure is lower in energy than the C-2v (B-2(2)) structure. The calculated isotropic proton hyperfine coupling constants for the C-s and C-2v (B-2(2)) structures are in fairly good agreement with the experimental couplings observed in an SF6 matrix and in an C6F14 matrix, respectively.