We report results of a crossed molecular beam study on the reactions K + i-C3H7I --> KI + i-C3H7 (R1) and K + t-C4H9I --> KI + t-C4H9 (R2) performed at an elevated collision energy of 1.55 eV for both nonoriented and oriented reagent molecules. Orientation was achieved by using the brute force technique. The most important results are the following: (i) The flux of scattered products of R2 consists of a dominant fast and a minor slow component; the two reaction channels occur with a branching ratio of 100:2. In R1 the fast component only has been observed. (ii) In the center-of-mass frame the dominant component is preferentially scattered into the backward hemisphere with a propensity for sideways and backward scattering while the minor one is sharply forward scattered and travels on the average with the spectator stripping velocity. (iii) The parallel and perpendicular differential steric effects in both R1 and the dominant channel of R2 are very substantial and amount to a size close to the theoretical upper boundary. The parallel steric effect in the minor channel of R2 is rather weak, and the sign is likely to be opposite to the one of the dominant channel. (iv) From the differential steric effects we have deduced the moments J(10) and J(11) of an expansion of the orientation-dependent double-differential cross section in a series of real spherical harmonics. (v) Shape and magnitude of the moments are consistent with a tight vector correlation between the directions of the main product flux and the molecular principal a-axis. (vi) The steric opacity functions for R1 and the dominant channel of R2 indicate that attacks of the K atoms to the I end of the reagent molecules are favorable for the formation of the fast products. The favored end for the production of the minor component of R2 is Likely to be the alkyl group. (vii) The emergence of the minor slow component in R2 has been qualitatively rationalized on the basis of the harpooning mechanism and electronic structure arguments. The model identifies the slow products as KI and electronically excited t-C4H9.