Octane molecular structure

Because of the existence of numerous isomers, hydrocarbon mixtures having a large number of carbon atoms can not be easily analyzed in detail. It is common practice either to group the constituents around key components that have large concentrations and whose properties are representative, or to use the concept of petroleum fractions. It is obvious that the grouping around a component or in a fraction can only be done if their chemical natures are similar. It should be kept in mind that the accuracy will be diminished when estimating certain properties particularly sensitive to molecular structure such as octane number or crystallization point. 

The naphthenes and aromatics both have cyclic (or ring-like) molecular structures and both possess high octane numbers. Napthenes are saturated and aromatics contain alternate double bonds on their ring. They are typically found in gasoline. The naphthenes also are an important part of kerosene. 

Increasing the octane number of a low-octane naphtha fraction is achieved by changing the molecular structure of the low octane number components. Many reactions are responsible for this change, such as the dehydrogenation of naphthenes and the dehydrocyclization of paraffins to aromatics. Catalytic reforming is considered the key process for obtaining benzene, toluene, and xylenes (BTX). These aromatics are important intermediates for the production of many chemicals. 

As shown above, CN and ON are important properties of diesel and gasoline fuels, respectively. Although a set of large databases are available, cetane and octane values of many individual compounds are still missing. Therefore, the prediction tools we have developed are very useful in correlating the molecular structures with properties of fuels. In this section, the predicted CN and ON values are implemented to construct the most effective catalytic strategies to optimize CN for diesel and ON for gasoline. 

One of the most fundamental elements of molecular structure is chain length. It serves to fix the hydrocarbon s position on its own subseries curve and thus becomes a factor in determining its physical constants. It also is a major factor in determining the hydrocarbon s rate of combustion and hence its octane number and critical compression ratio. 

There are 18 isomers of octane. Draw the molecular structure and name each. 

The foregoing discussion has shown, however, that the molecular structure of the parent alkane profoundly affects the distribution of the intermediate products of its cool-flame oxidation and clearly, there is a strong correlation between the distribution, the degree of branching of the carbon skeleton, the rate of formation of the hydroperoxyalkyl radicals and the Research Octane Number of the alkane. 

Gasoline is a complex mixture of hydrocarbons that bods below 200°C (390°F). The hydrocarbon constituents in this boiling range are those that have four to twelve carbon atoms in their molecular structure. Gasoline varies widely in composition, even those with the same octane number may be quite different. For example, low-boiling distillates with high aromatics content (above 20 percent) can be obtained from some crude oils. The variation in aromatics content as well as the variation in the content of normal paraffins, branched paraffins, cyclopentanes, and cyclohexanes all involve characteristics of any one individual crude oil and influence the octane number of the gasoline. 

Prediction of the NMR signals for derivatives of naphthalene was studied using statistical SCS values. F, H, and C NMR spectral data are reported for a variety of oxetane compounds containing fluorine on or near the ring. Effects of substituents on the spectra are analyzed and correlations of chemical shifts and coupling constants in terms of molecular structure are presented. A series of 2-aryl-2-hydroxy-1,1,3,3-tetramethyl-5,8-dioxaspir-o[3.4]octanes (1), 3-aryl-3-hydroxyl-2,2,4,4-tetramethylcyclobutanones (2), and... 

Broto, P., Moreau, G. and Vandycke, C. (1984b) Molecular structures perception, autocorrelation descriptor and SAR studies. System of atomic contributions for the calculation of the ra-octane/ water partition coefficients. Eur. J. Med. Chem., 19, 71-78. 

Fig. 4 (a) Normalized force curves of NC obtained in octane, (b) Comparison of a force curve of NC obtained in octane and the QM-FJC fitting curve, (c) Comparison of force curves of PAAm and NC obtained in octane, (d) Molecular structure of the dimer (cellobiose) used in QM calculations and the QM results. The arrows indicate the atoms defining the constrained distance. Figure reproduced with permission from [42]... 

Now, we will focus our attention to the molecular structure of C12E5 at the octane/water interface. In a molecular dynamics simulation, octane molecules were used to build an appropriate model for the oil phase (6). The computer simulation provides new insights into two-dimensional monolayers at the water/oil interface. By using the neutron reflection method, the structure of C12E5 on the water surface, with and without added dodecane, was recently investigated. It was found that the C12 chains change to an almost perpendicular orientation to the surface upon incorporation of dodecane into the C12E5 layer. 

The ethers and alcohols that are added to gasoline as oxygenates and octane boosters include methyl tertiary-butyl ether (MTBE), ethyl tertiary-butyl ether (ETBE), tertiary-amyl methyl ether (TAME), tertiary-amyl ethyl ether (TAEE), diisopropyl ether (DIPE), ethanol, methanol, isopropanol, and tertiary-butyl alcohol. Relevant properties of these compounds are listed in Table 1 and molecular structures are shown in Table 2. 

Materials 10. A Relationship of Molecular Structure and Vibrations to Decomposition Polynitro-3,3,7,7-tetrakis (trifluoromethyl)-2,4,6,8-tetraazabicyclo[3.3.0]octanes Journal of Physical Chemistry 90, 2679. 

Figure 6.9.1 Research octane numbers (ROMs) of hydrocarbons of different chain length and molecular structure (naphthenes cyclopentane, cyclohexane, methylcyclohexane, 1,3 dimethylcyclohexane, and 1,3,5-trimethylcyclohexane aromatics benzene, toluene, and m-xylene).

---