Fragmentation additivity

Chou, J.T., Jurs, PC. (1979) Computation of partition coefficients from molecular structures by a fragment addition method. In Physical Chemical Properties of Drugs. Medical Research Series, Vol. 10, Yalkowsky, S.H., Sindula, A.A., Valvani, S.C., Editors, Marcel Dekker, New York. pp. 163-199. 

Radical chemistry has seen tremendous progress in the past two decades and can now be considered as an eminent sub discipline in synthetic organic chemistry [1-6]. Diastereoselective radical chemistry is well established and many examples of enantioselective radical reactions have appeared in the recent literature. For reviews on diastereoselective radical chemistry see [7-11] for reviews on enantioselective radical chemistry see [12-16] and for reviews on conjugate additions, see [17,18]. This review will detail different ways to introduce asymmetry during a radical reaction. These transformations can be broadly classified into atom transfer reactions, reductive alkylations, fragmentations, addition and trapping experiments, and electron transfer reactions. 

Augite, Mossbauer spectrum of, 6 474 Au(PRj) fragment, addition to homonuclear gold cluster compounds, 39 329-332 Auranofin, 36 21 cytotoxicity, 36 22, 34 Auro-bis(thiosulfate), 36 18-19 Aurosomes, gold in, 36 21-22 Aurothioglucose, 36 18-19 Aurothiomalate, 36 18-21... 

Au(PRj) fragment addition, 39 329-332 coreduction, 39 332-333 gold atom addition, 39 332 miscellaneous reactions, 39 333-334 performed gold cluster compound reactions, 39 333... 

Feldman239,240 and Oshima and Utimoto241 have introduced a very sophisticated sequence of reactions that effects a radical annulation starting from a vinylcyclopropane. Scheme 59 provides two examples and a likely mechanism for this sequence, which involves fragmentation, addition and cyclization. The... 

The fragments Fe(CO) (n= 2 or 3) and NiCp seem to be most easily attached to or removed from clusters since they appear in so many uncontrolled cluster syntheses. In a designed fashion Fe(CO)2 units can be added to 84 and removed from the product ISa in good yields (61). The interrelation of the two cluster types is obvious from their framework shapes. Similarly, cluster growth by Fe(CO)3 fragment addition occurs in the sequence 85 - 86 - 87 (162). In both cases polynuclear iron carbonyls are the source of the Fe(CO) fragments. 

Atkinson (1987) developed very reliable fragment additivity SARs for estimating kHO(air) from molecular structure using more than 400 compounds in the database (Chapter 14 describes procedures for using these SARs). SARs for HO are based on the premise that rate constants for each of the several different classes of reactions of HO with organic compounds — abstraction of H- atom (kH), addition to double, triple or aromatic bonds (kE), and reaction with S or N atoms (kA) — can be estimated separately and then summed to give the total molecular rate constant, kHO ... 

The fragment additive 7t values can therefore serve to estimate the solubility of solvents (and solutes in general) in water, with a standard error of - 30%, see Figure 4.6. 

Thus, precursors of (RPCP)Ir and Rh(PR3)2Cl gave excellent catalysts, in contrast with the converse pair, (RPCP)Rh and Ir(PR3)2Cl. Calculations (DFT) by Krogh-Jespersen[21] indicated that this surprising relationship was related to the respective M-H bond strengths of the fragments. Addition of H-H to the model... 

The fuzzy electron density fragment additivity rules (23) - (27) are exact at any given ab initio LCAO level, hence the reconstruction of the calculated electronic density p(r) of the given molecule from the corresponding fuzzy fragment electron densities pk(r) is also exact. 

The exact additivity of the fragment density matrices Pk and the fuzzy fragment densities pk(r) defined according to Mezey s scheme (eqs. (23)-(27)) motivates the terminology additive, fuzzy electron density fragmentation method. The fuzzy electron density fragment additivity rule is exact at the given ab initio LCAO level. 

Rule 4. Each biphenyl fragment additionally increases the ef-values of its two hexagons. 

It may be concluded that, in spite of the complicated mass-spectrometric behavior of sulfated oligosaccharides, the method has been successfully used many times for characterization of fragmentation products of red algal galactans, especially of enzymolysis fragments (additional examples will be given below). 

Metal fragment addition with nido to closo cluster change ... 

Most of the commercial molecular modeling systems also provide some property calculations, which range from simply calculating the polar surface area of a structure to a full range of topological and physicochemical descriptors. These may be based on fragment additivity, like most of the programs mentioned above, or they may involve correlations with quantum mechanical or even molecular dynamics-based calculations. 

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