Comparison of the Hydride-Donating Ability and Activity of Five- and Six-Membered Benzoheterocyclic Compounds in Acetonitrile

In this work, we compared the hydride-donating ability of five-membered benzoheterocyclic compounds (FMB) and six-membered benzoheterocyclic compounds (SMB), isomers of DMBI and DMIZ and of DMPZ and DMPX, using detailed thermodynamic driving forces [ΔG(o) (XH)], kinetic intrinsic barriers (ΔG(≠)(XH/X)), and thermo-kinetic parameters [ΔG(≠)° (XH)]. For DMBI and DMIZ, the values of ΔG(o) (XH), ΔG(≠)(XH/X), and ΔG(≠)° (XH) are 49.2 and 53.7 kcal/mol, 35.88 and 42.04 kcal/mol, and 42.54 and 47.87 kcal/mol, respectively. For DMPZ and DMPX, the values of ΔG(o) (XH), ΔG(≠)(XH/X), and ΔG(≠)° (XH) are 73.2 and 79.5 kcal/mol, 35.34 and 25.02 kcal/mol, and 54.27 and 52.26 kcal/mol, respectively. It is easy to see that the FMB isomers are thermodynamically dominant and that the SMB isomers are kinetically dominant. Moreover, according to the analysis of ΔG(≠)° (XH), compared to the SMB isomers, the FMB isomers have a stronger hydride-donating ability in actual chemical reactions.