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As a rule of thumb, the boiling point rises 20–30 °C for each carbon added to the chain; this rule applies to other homologous series. [18] A straight-chain alkane will have a boiling point higher than a branched-chain alkane due to the greater surface area in contact, and thus greater van der Waals forces, between adjacent molecules.
Higher alkanes are naturally present in crude oil and can be obtained via fractional distillation.Saturated fatty acids decarboxylate to higher alkanes. Long olefins can be hydrogenated to yield higher alkanes. n-alkanes can be isolated via the formation of urea clathrates.They can also be synthesized through Kolbe electrolysis or other coupling reactions like the Wurtz reaction.
Cycloalkanes have higher boiling points, melting points, and densities than alkanes. This is due to stronger London forces because the ring shape allows for a larger area of contact. Even-numbered cycloalkanes tend to have higher melting points than odd-numbered cycloalkanes.
The following is a list of straight-chain alkanes, the total number of isomers of each (including branched chains), and their common names, sorted by number of carbon atoms. [ 1 ] [ 2 ] Number of C atoms
Normal boiling points of straight chain alkanes. Within that series, many physical properties such as boiling point gradually change with increasing mass. For example, ethane (C 2 H 6), has a higher boiling point than methane (CH 4).
The melting and boiling points of chloro-, bromo-, and iodoalkanes are higher than the analogous alkanes, scaling with the atomic weight and number of halides. This effect is due to the increased strength of the intermolecular forces —from London dispersion to dipole-dipole interaction because of the increased polarizability.
A given pure compound has only one normal boiling point, if any, and a compound's normal boiling point and melting point can serve as characteristic physical properties for that compound, listed in reference books. The higher a compound's normal boiling point, the less volatile that compound is overall, and conversely, the lower a compound's ...
The boiling points of the pentane isomers range from about 9 to 36 °C. As is the case for other alkanes, the more thickly branched isomers tend to have lower boiling points. The same tends to be true for the melting points of alkane isomers, and that of isopentane is 30 °C lower than that of n-pentane.