Calculations for the properties and reactions of the NH, PH, and AsH counterparts of dimethyl ether and acetone.

The properties and reactions of compounds in which the O of dimethyl ether or acetone has been replaced by NH, PH, or AsH have been studied computationally using CBS-QB3, CBS-APNO, G4, and W1BD. The properties include the bond dissociation energies and ionization potentials, and the reactions include those with with protons, methyl cations, and lithium cations. The effect on keto-enol equilibria also was examined. In all cases there was good agreement with the available experimental data. The agreement between these methods suggests that the least computationally costly model (CBS-QB3) should be of general use in studying organic compounds. The double-bond dissociation enthalpies of CH2═XHn were linearly related to those of the corresponding CH3-XHn+1 single bonds with a slope of 2.5. With the exception of C-C, the order corresponded to the electronegativity of X, suggesting that the differences are largely determined by internal Coulombic interactions. The differences in the electronegativities of the heteroatoms are largely responsible for the differences in the properties and reactions. Oxygen has a significantly higher electronegativity than the others, and as a result, the oxygen-substituted compounds are often different than the others.