Stationary points on the potential energy surfaces describing the reactions between Al and H2O, NH3, HCl, and Cl-2 respectively, have been optimized at the ab initio MP2 and QCISD levels as well as by density functional theory (DFT) using the B3LYP functional and the 6-31G(d,p) basis set. Reaction energies were computed using the MP2 and B3LYP methods and the QCISD and CCSD(T) methods in conjunction with the 6-311+G(2df,p) and 6-31G(d,p) bases, respectively. Isotropic hyperfine coupling constants (hfcc＇s) of Al, N, Cl, and H were computed using the MP2, B3LYP, and QCISD methods in conjunction with the 6-311+G(2df,p) basis, and at the PWP86/IGLO-III level for isotropic and anisotropic coupling constants. For HAlCl and AlCl2, the theoretical study predicts positive isotropic Cl hyperfine coupling constants at variance with the previously reported experimental values. A revised analysis of the experimental ESR spectra led to new assignments of the Cl hyperfine coupling tensors, in agreement with the computed results.