Both theoretical and experimental studies are reported for the gas-phase reactions of protonated hydroxylamine with acetic and propanoic acids which yield protonated glycine and alanine, GlyH(+) and AlaH(+), respectively. The key step for these reactions is an insertion of the amino group into a C-H bond. For the formation of AlaH(+), the reaction barrier for insertion into a C-beta-H bond is ca. 5 kcal center dot mol(-1) lower than that for the insertion into a C-alpha-H bond; the product beta-AlaH(+) is ca. 6 kcal mol(-1) lower in energy than alpha-AlaH(+). Thus, both kinetics and thermodynamics favor formation of the beta-form. The energetic preference for the beta-form is due to more efficient hydrogen bonding between the amino group and the carbonyl oxygen in the limiting transition structure and in the beta-AlaH(+) product. These theoretical results are in excellent accord with selected ion flow tube measurements of the gas-phase synthesis which show striking specificity for the beta-isomer according to multi-collision-induced dissociation of the AlaH(+) product ion. The results suggest that Gly and beta-Ala found in carbonaceous chondrite meteorites are products of interstellar chemistry.