Method of fragmentation

The first mass spectrometric study of thiazoles was carried out by Clark et al. (115), who investigated the method of fragmentation of thiazole, and 4-methyl- and 2,4-dimethylthiazole. 

For other methods of fragmentation of an a,p-epoxy ketone derivatives, see Mac Alpine, G.A. Warkentin, J. Can. J. Chem., 1978, 56, 308, and references cited therein. 

Two further methods of fragment elimination seem to be generally applicable controlled pyrolysis and hard base induced disproportionation. The thermal Fe(CO)2 fragment removal from 15a which completes the reversible interconversion of 84 and 15a (61) has already been mentioned. Similarly the leaving group HRe(CO)s can be eliminated thermally from 92 yielding the stable unsaturated cluster H3Re3(CO) o 13 (175). 

The enumeration of Kekule structures for rectangle-shaped benzenoids is treated. Combinatorial formulas for K (the Kekule structure count) are derived by several methods. The oblate rectangles, Rj(m, n), with fixed values of m are treated most extensively and used to exemplify different procedures based on the method of fragmentation (chopping, summation), a fully computerized method (fitting of polynominal coefficients), application of the John-Sachs theorem, and the transfer-matrix method. For Rj(m, n) with fixed values of n the relevant recurrence relations are accounted for, and general explicit combinatorial K formulas are reported. Finally a class of multiple coronoids, the perforated oblate rectangles, is considered in order to exemplify a perfectly explicit combinatorial K formula, an expression for arbitraty values of the parameters m and n. 

Fig. 3. Example of stripping the method of fragmentation applied to a hexagon. The arrow indicates the bond which successively is assumed to be double and single...

Fig. 4. Example of chopping the method of fragmentation applied to a pentagon...

The most successful method of fragment condensation for the synthesis of polypeptides and proteins in solution phase is NCL, reported by Dawson for the first time in 1994 [7]. This was a significant contribution because NCL overcomes one of the main limitations of solid phase peptide synthesis (SPPS), namely the production of long peptide sequences (>50 amino acid residues) [1, 3, 29]. NCL may be used in both solution and solid phases solution phase NCL has been used for the synthesis of small peptides and cyclic peptides [30-32] whereas SPPS is more widely applied in polypeptide and protein synthesis. 

FTICR mass spectrometers have the highest flexibiUty of all mass spectrometers in terms of methods of fragmentation. In quadrupole-FTICR-MS instruments, the ions can be isolated, accumulated, and accelerated into collision cells for collision-... 

Fig. 4.8 Correlation between fractal dimension and fractal prefactor left global values (from fractal growth, Eq. (4.32)) and individual prefactors (from method of fragmentation) right comparison with Sorensen and Roberts (1997) and linear fit...

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