Graphitized carbon energy values

K). T is the measurement temperature and Tq is the "degeneracy temperature," equal to kEo, where k is the Boltzmann constant. According to a two-dimensional electron gas model for graphitic carbons (see ref. 2a), is the energy "shift" from the Fermi level (Ep), to the top of the valence band. Small values of To ( <344 K) and consequently of Eq signify a more perfect graphite... 

In this model, it has been assumed that the incident ions cause a preferential displacement of the graphitic carbon and increase the possibility of sp diamond-like bond formation in the optimal ion energy range. This assumption is based on the values of the displacement threshold of graphite and diamond as 30 eV and 80 eV respectively. Robertson observed that the values are actually much closer to each other, namely, in the range of 25-42 eV for graphite and in the range of 37-45 eV for diamond. 

Table 5.1 Molecular interaction energy values for saccharides on graphitized carbon calculated using the MM2 program. MIPS, MIVW, MIHB and MIES represent the molecular interaction energy value of the final (optimized) structure, the van der Waals energy, the hydrogen-bonding energy, and the electrostatic energy (kcal mol ), respectively. tR represents the retention time. Reproduced by permission of Elsevier, ref. 24.

The hydrogen-bonding energy seemed to contribute to the retention on the graphitized carbon (Hypercarb ) column, but not to the retention on another carbon BioTechnologyResearch (BTR ) column. Therefore, only alkyl-group-substituted compounds were selected and their log k values were correlated with MI values. The correlation coefficient was 0.718 for log A ref- The log A ref values of benzene, toluene, o- grlene, m- ylene,p- g lene, o-te/t-butylphenol, 4-ethylphenol,... 

The molecular interaction energy values of alkenes were smaller than for their related alkanes. This result supports the idea that the hydrophobic interaction due to the van der Waals energy is the predominant molecular interaction in reversed-phase liquid chromatography. No dipole-dipole or 71-71 interactions influenced the direct interaction. The lack of dipole-dipole or 71-71 interactions can be studied from chromatographic behavior on a graphitized carbon phase. 

The precision of the correlation between the log k and molecular interaction energy values vras high, as long as the analyte structure was simple and flat, as demonstrated in Section 6.9.2. Specifically, such analyses are most successful when studying retention mechanisms on graphitized carbon phases (Section 6.3). This is because the most effective system for such analyses is a homogeneous and flexible model phase where the docking process may not cause errors. 

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