Aromaticity values

The a2-alkyl value is included in the a-alkyl value. The phenolic value is included in the aromatic value. 

Sulfur. Thiophene and benzo[ >] thiophene are both aromatic heterocycles, as discussed earlier in this review. Isothiazole is a planar molecule with an aromaticity comparable with those of thiazole and pyrazole, and higher than those of isoxazole and oxazole,122 140 as evaluated on the basis of Bird s aromaticity index A, based upon the statistical degree of uniformity of the bond orders of the ring periphery. Theoretical calculations and experimental data in connection with the aromaticity of isothiazole have been reviewed.141 Thiazole is also viewed as an aromatic molecule, similar to thiophene. It lacks an experimental aromaticity value, but the heat of formation together with bond lengths and angles have been calculated by various computational meth-... 

Many, but not all, endothermic compounds have been involved in violent decompositions, reactions or explosions, and in general, compounds with significantly positive values of standard heat of formation may be considered suspect on stability grounds. Notable exceptions are benzene and toluene (AH°f +82.2, 50.0 kJ/mol 1.04, 0.54 kJ/g, respectively), where there is the resonance stabilising effect of aromaticity. Values of thermodynamic constants for elements and compounds are tabulated conveniently [1], but it should be noted that endothermicity may change to exothermicity with increase in temperature [2], There is a more extended account of the implications of endothermic compounds and energy release in the context of fire and explosion hazards [3], Many examples of endothermic compounds will be found in the groups ... 

These values are summarized in Figure 2 and compared with our results on the soluble fractions from depolymerization. Van Krevelen (9) reported aromatic hydrogen values ranging from 23 to 54% for coals containing 76 to 89% carbon. Aromatic hydrogen content varies directly with rank. Brown (i) obtained values of 19-42% for a series of vitrains and showed a similar relationship with rank displaced toward lower aromatic values. Ladner and Stacey (5) analyzed two additional coals using the procedure developed by Brown, and the results fit Brown s correlation. 

The differences between the known aromaticity values and those calculated from the least squares equation are given in Table I. The mean value of the deviations, 2.3% absolute, indicates the accuracy of the method, although in reality it only tests the fit of the calculated equation. The deviations were surprising in that they were smaller than anticipated. 

The first five parameters were obtained directly from intensity measurements on the proton and C13 spectra. The largest error is in the C13 measurement, although its magnitude is only about 4%. The aromaticity value and the limits placed on sigma and on the H/C ratio for the hypothetical unsubstituted aromatic nucleus are in reasonable agreement with the known values. It should be pointed out that three of the six components of the blend were not used in the original calibration curve. 

Crude Petroleum. This method, in principle, should be applicable to all carbonaceous materials regardless of origin. Preliminary C13 measurements made on a sample of Ponca City crude oil (original petroleum of Project 6, American Petroleum Institute) yielded an aromaticity value of 0.15. 

Figure 7 shows the effect on ethylene production cost from naphtha cracking with BTX aromatics value increases as a parameter. (The basis we have used for determining the effect of aromatics price increases is given in Table XII). Figure 7 indicates that a 5 /gal increase in BTX... 

With imported naphtha at, say 1.1 /lb and aromatics at current values, ethylene cost is 1.94 /lb. However, with finished aromatics valued at 5 /gal over the current base values, production cost drops to 1.59 /lb. The breakeven curves for naphtha vs. ethane, propane, and n-butane are given in Figures 8, 9, and 10. These assume premium byproducts, with aromatics valued above current levels, but do not include the effect of increased propylene and butylene valuations that would further accentuate the picture. With 1.1 /lb naphtha and aromatics at 5 /gal above current prices, the breakeven prices for ethane, propane, and n-butane are 0.33, 0.7, and 0.83 /lb, respectively. Such prices are... 

Under the assumptions of naphtha price and aromatics value stated above, naphtha pyrolysis clearly would be superior to light hydrocarbon pyrolysis at their current feed prices. A similar analysis can probably be made also for gas oil. Thus, if the possible developments discussed above do materialize, the heavier feeds could probably dominate almost all new U.S. ethylene plant construction in the future. 

Among the rr4,/.5- analogues of 17-21, only 22-24 (Scheme 18) are of practical importance, since it is hard to accommodate the increasing number of positively charged o l5-P atoms in the four-membered ring. The aromaticity% values [128], discussed by Mucsi and Csizmadia [127], are -8%, +46%, and -46% for 22, 23, and 24, respectively. All these values indicate significantly less destabilization than... 

The close aromaticity values for AAphosphinine, pyridine, and benzene according to spectral, structural, theoretical, and energetic criteria are discussed in detail in Nyulaszi s review [214],... 

Aromaticity values (f ) for all solubilization fractions were essentially identical ( 0.52) f values were higher (0.60) for the hydrogenation product (HVL-P)... 

In the case of benzenoid aromatics, values range between 10 and 10 , provided that tetraalkylammonium salts have been used as supporting electrolytes [8b]. In solvents of low dielectricity constant, additional effects are observed, showing influences of the supporting electrolyte concentration and of the nature of the cations [6]. In the tetra-alkylamonium series the strongest (contact) ion pairs are formed by Et N, and Kq is largest for that cation [8b,52]. 

Thus, values for the index between 0 and 15 indicate a predominance of paraffinic hydrocarbons in the fraction values from 15 to 50 indicate a predominance of either naphthenes or mixtures of paraffins, naphthenes, and aromatics values above 50 indicate a predominant aromatic character. Although the correlation index yields useful information, it is in fact limited to distillable materials and, when many petroleum samples are to be compared, the analysis of results may be cumbersome. 

Figure 18. Relation between specific gravity and reciprocal molecular weight for hydrocarbons of various molecular types. Aromaticity value is calculated by the percentage of total carbon atoms in the molecule which are within the benzene ring. ( J), Benzene (Q), cycloparaffins (A), n-alkyl benzenes (O),...

Thus, concepts of coal structure must also satisfy any of the relevant data from the variety of chemical manipulations of coal that have been described in a previous section and add positive knowledge about the nature of coal. In addition, a consensus of the aromaticity values reported would be that there appears to be a definite increase with rank. The values reported range from 40% to 50% for low-rank lignite and subbituminous coals to nearly 100% for anthracites. 

Fig. 8.3 Local aromaticity values for catafiisenes according to Polansky and Derflinger...

When going from 2C to SLR chemical hardness analytical forms of any of Koopmans orders, on the horizontal axis through the Tables 4.3. 5, one systematically record an increasing of the average chemical hardness/aromaticity values from 2C to 6T schemes of computations while going again down towards SLR scheme of Table 4.1. 

An aroma is a chemical substance sensed by the taste and/or the smell defined by parameters such as its volatility, its polarity, and its aromatic value. The aromas must be protected throughout the retail chain until its use. The conservation of these aromatic contents is mainly based on the packaging (Risch 2000). 

Trigonal dianion metal clusters, X X=Bq, Mg, Cu exhibit bond stretch isomerism . While one of the isomers is Ti-aromatic, the other isomer is a-aromatic. However their mono- and disodium complexes (Fig. 17) do not exhibit any bond stretch isomerism. Associated frontier molecular orbitals (Fig. 28) and the Z component of the induced magnetic field (Fig. 29) also dictate the same. The aromaticity values suggest their aromatic behavior in most cases. 

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