The reactions of the ions HnC3N+ (n = 0-4) and HnC3O+ (n = 0-3) with several molecules have recently been studied in a SIFT apparatus at 300 +/- 5 K. Here we compare the reactivities of these ions and the ions C4Hn+ (n = 0-4) (which have been studied independently by other groups) with the neutrals H-2, CO, C2H2, and HCN. Several authors have previously commented that linear hydrocarbon ions containing two or more hydrogen atoms are much less reactive than ions with zero or one hydrogen; our results suggest that this trend applies to ions functionalized by-the heteroatoms nitrogen and oxygen as well as by hydrogen. These observations support and extend an existing model in which ions possessing "bare" terminal carbon atoms are particularly reactive.