Calculation from fragment contributions examples

Direct ES-MS characterization of a combinatorial library has been performed on the example of modified xanthene derivatives [30]. To circumvent the analysis of 104 to 10s possible compounds, small representative sublibraries rather than the whole library were synthesized and investigated [31].The results obtained were then extrapolated to the synthesis of the target library. A xanthene library was also used for ES-FT-ICR-MS investigation [32], A more recent contribution deals with the calculation of elemental compositions from FTICR mass spectra. FIowever,the mass accuracy required increases exponentially with the mass of the analyte [33], Therefore, elemental compositions are calculated from the exact measurement of fragment ions performing MS"-experiments [34],... 

Mass fractions are obtained from the concentrations of the different fragments (Eqs (3.148) (3.151) and Eqs (3.166) (3.171)). In particular, fragments y and 8f are considered devoid of mass. This means that the contribution of the initiator mass is neglected and the mass of Af is distributed among the (f/2) functional groups, with individual masses equal to (2/f)Mf, attached to a skeleton devoid of mass. For example, using Eq. (3.169), we can calculate the mass fraction of fragment 8f as... 

There are many other examples in the literature of how semiempirical calculations have contributed to recent progress in fullerene chemistry (often in combination with other quantum chemical calculations). The cases discussed above should be sufficient to illustrate typical conclusions from such studies which provide not only specific numerical results, but also new qualitative insights, for example, with regard to the correlation between curvature and stability, the relative importance of strain and tt conjugation, the connection between structure and reactivity, or the mechanism for fullerene annealing and fragmentation. 

For example, it is intuitively obvious that the two principal ai components of the reaction coordinate for fragmentation to H2 and CO are s-CH stretch and HCH bend, whereas CO stretch contributes very little. However, all that the analysis based on Figs. 10.5 and 10.6 can state firmly is that the out-of-plane bend (61) can be omitted from the reaction coodinate for the molecular fragmentation (Pathway I) but must be included with the other five in calculation... 

---