Reactivity numbers phenanthrene

In cases where the oxirane ring is unsymmetrically substituted, the product structure can be predicted on the basis of attack at the most electrophilic center. This center has the lowest Dewar reactivity number (A/,) as predicted by MO calculations. The following example is illustrative. Benzo[c]phenanthrene 5,6-oxide (31) could give rise to two different zwit-terions (237 and 238). The former has a Dewar reactivity number 1.79 and the... 

There are principally two different approaches of correlating experimental rate data of electrophilic substitution with reactivity indices (1) Correlating the index with the rate data of a given reaction, e.g. bromination. For example, a satisfying correlation of Dewar reactivity numbers with the log of rate constants of the bromination of benzene, naphthalene (1- and 2-position), biphenyl (4-position), phenanthrene (9-position), and anthracene (9-position) has been observed [55]. In correlations of this type the reactivity index corresponds to the reactivity constant in the Hammett equation while the slope of the linear correlation corresponds to the reaction constant (see also Sect. 3) (2) correlating the index with experimental a values. 

To cast some light on the relative importance of steric effects on the positional reactivities of benzenoid hydrocarbons, correlations of experimental a values of phenanthrene (4), tetrahelicene (5), pentahelicene (<5), and hexahelicene (7) with purely topological reactivity indices (Huckel cation localization energy, Dewar reactivity number and Herndon structure count ratio) have been studied [59],... 

A nice example is provided by 10,9-borazarophenanthrene (V). The reactivity numbers for the isoconjugate AH, phenanthrene, are shown in (VI). The lowest numbers are in the 9,1- and 4-positions but the 4-position is sterically hindered. Experiment22 showed that the order of reactivity (nitration in acetic anhydride) for the various positions in phenanthrene was 9 > 1 > 3 4, 2. 

Nucleophilic Trapping of Radical Cations. To investigate some of the properties of Mh radical cations these intermediates have been generated in two one-electron oxidant systems. The first contains iodine as oxidant and pyridine as nucleophile and solvent (8-10), while the second contains Mn(0Ac) in acetic acid (10,11). Studies with a number of PAH indicate that the formation of pyridinium-PAH or acetoxy-PAH by one-electron oxidation with Mn(0Ac)3 or iodine, respectively, is related to the ionization potential (IP) of the PAH. For PAH with relatively high IP, such as phenanthrene, chrysene, 5-methyl chrysene and dibenz[a,h]anthracene, no reaction occurs with these two oxidant systems. Another important factor influencing the specific reactivity of PAH radical cations with nucleophiles is localization of the positive charge at one or a few carbon atoms in the radical cation. 

Phenanthrene (10.28, Fig. 10.10) is the positional isomer of anthracene, yet the differences in reactivity and metabolism between the two compounds are marked. Whereas epoxidation of anthracene in mammals occurs only at the 1,2-position (Fig. 10.9), phenanthrene is epoxidized at the 9,10- (major), 1,2- (minor), and 3,4-positions (trace). The reason for preferential oxygenation at the 9,10-position is due at least in part to its higher reactivity. This position within a phenanthrene-like topography, known as the K region, is found in a number of PAHs with four or more cycles. Phenanthrene is also representative of higher PAHs since it contains a so-called bay region (Fig. 

The relative performances of the two autoclaves were compared by the use of ratios. Three ratios were derived utilising (a) the unconverted phenanthrene, denoted by P (b) the amounts of the various hydro-derivatives of phenanthrene multiplied by the relative number of hydrogens added, eg % tetrahydrophenanthrene 4, denoted by HP (c) the total content of hydrocracked compounds, denoted by C. These ratios would indicate the reactivity of the autoclaves and their relative abilities towards hydrogenation and hydrocracking. 

Table 27. Reactivity Parameters of the Ring Atoms in Hexahelicene Nr (Dewar number), Fr (free valence number), pr (Mulliken overlap population) and Lr (localization energy), Rates of Protiodetritiation Relative to 9-T-Phenanthrene (kre[) and Corresponding Partial Rate Factors (f)...

As the number of fused rings increases, the delocalization energy per ring continues to decrease in absolute value, and compounds become more reactive, especially toward addition. The delocalization energies per ring for anthracene and phenanthrene are -117.2 and -126.8 kJ/mol, respectively. 

If reactions of the above type occur during extraction, one would expect that gradually less hydrogen exchange takes place as the extraction proceeds because the number of reactive groups decreases. This assumption was tested in the last experiment shown in Table V. The coal was heated for 6 hours at 340°C. with nontritiated phenanthrene prior to extraction with tritiated phenanthrene. When this pretreated coal was extracted, the tritium content of the product was only 15.6% as compared with 21.4%, in the nonpretreated product. This decreased tritium content supports the above assumption and agrees with the proposed reaction mechanism. 

The epoxides of several polycyclic aromatic hydrocarbons have been prepared by the use of a large excess of oxidant in a bipha-sic Oxone-ketone system under neutral conditions, as shown for the oxidation of phenanthrene (eq 11). However, the use of isolated dioxirane solutions is more efficient for the synthesis of reactive epoxides, since hydrolysis of the product is avoided. A number of unstable epoxides of various types have been produced in a similar manner, as discussed for Dimethyldioxirane and Methyl(trifluoromethyl)dioxirane. 

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