The Hierarchy of Models in Chemistry

Chemists make sense of the world with the aid of a variety of models, which may be pictorial, verbal, or mathematical. We develop criteria for useful models and describe in general terms several prevalent models widely used in chemistry. These include the structural formula ; classical and staitistical thermodynamics; and a variety of bonding models. Finally, we describe the possibilities and potential advantages of encoding the chemist\u27s essentially non - numerical conceptual models of bonding as computer programs according to the methods of Artificial Intelligence research

The Hierarchy of Models in Chemistry

Chemists make sense of the world with the aid of a variety of models, which may be pictorial, verbal, or mathematical. We develop criteria for useful models and describe in general terms several prevalent models widely used in chemistry. These include the structural formula ; classical and staitistical thermodynamics; and a variety of bonding models. Finally, we describe the possibilities and potential advantages of encoding the chemist\u27s essentially non - numerical conceptual models of bonding as computer programs according to the methods of Artificial Intelligence research

Production of Carbamic Acid Dimer from Ammonia-Carbon Dioxide Ices: Matching Observed and Computed IR Spectra

The production of complex molecules in ammonia–carbon dioxide ices is presumed to pass through species of formula H3N:CO2 with further addition of ammonia and carbon dioxide. One possible landmark, carbamic acid, H2NCOOH, has been implicated among the products of warming and irradiation of such ices. Experimental study of the IR spectra of residues has suggested the presence of related species, including weakly bound 1:1 and 2:1 complexes of ammonia with carbon dioxide, zwitterionic carbamic acid, ammonium carbamate, and the dimer of carbamic acid. We computed the energetics and vibrational spectra of these species as well as the complex between ammonia and carbamic acid for gas and condensed phases. By means of a new spectrum-matching scoring between computed and observed vibrational spectra, we infer species that are most probably present. The leading candidates are ammonium carbamate, the carbamic acid–ammonia complex, and the carbamic acid dimer

CH Activation by a Heavy Metal Cation: Production of H2 from the Reaction of Acetylene with C4H4-Os(+) in Gas phase

While first-row transition metal cations, notably Fe(+), catalyze the gas-phase conversion of acetylene to benzene, a distinct path is chosen in systems with Os, Ir, and Rh cations. Rather than losing the metal cation M(+) from the benzene–M(+) complex, as is observed for the Fe(+) system, the heavy metal ions activate CH bonds. The landmark system C4H4-Os(+) reacts with acetylene to produce C6H4-Os(+) and dihydrogen. Following our work on isomers of the form C2nH2n-Fe(+), we show by DFT modeling that the CH bonds of the metalla-7-cycle structure, C6H6-Os(+), are activated and define the gas-phase reaction path by which H2 is produced. The landmark structures on the network of reaction paths can be used as a basis for the discussion of reactions in which a single Os atom on an inert surface can assist reactions of hydrocarbons