Various conformers of 1-C(4)Hgl(+.), 2-C(4)Hgl(+.), and i-C(4)Hgl(+.) were prepared selectively by mass-analyzed threshold ionization with coherent vacuum ultraviolet radiation. Conformer-selective photodissociation of these ions was studied in the 560-730 nm spectral region, which corresponds to excitation to the first excited electronic state. Rapid dissociation was observed as manifested by noticeable laser polarization dependence of the product signals. In particular, photodissociation of i-C(4)Hgl(+.), was found to be conformer specific, occurring without interconversion between conformers. The product's asymptote energies estimated from the experimental data were compared with the reaction enthalpies at 0 K to get information on the structures and states of products. It was found that a simple S(N)2-type mechanism deduced from the previous study of 1-C3H7I+. was compatible with the present observations. Validity of the widely adopted postulate in stereochemistry that different conformations can be gateways to different reactions has been demonstrated in the gas phase.