Compounds whose Chemistry is Incompletely Defined

When it comes to the heaviest of petroieum fractions, modern analytical methods are not able to isolate and characterize the molecules completely. In the absence of something better, the analyst separates the heavy fractions into different categories, which leads merely to definitions that are workable but are no longer in terms of exact structure. 

The portion that is soluble in normal heptane is given the term maltenes. 

According to the nature of the solvent employed, the yields and constitutions of the asphaltenes are different. In the United States, asphaltenes are obtained by precipitation from normal pentane. 

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