<P> This difference in energy between the two conformations, known as the torsion energy, is low compared to the thermal energy of an ethane molecule at ambient temperature . There is constant rotation about the C--C bond . The time taken for an ethane molecule to pass from one staggered conformation to the next, equivalent to the rotation of one CH group by 120 ° relative to the other, is of the order of 10 seconds . </P> <P> The case of higher alkanes is more complex but based on similar principles, with the antiperiplanar conformation always being the most favored around each carbon--carbon bond . For this reason, alkanes are usually shown in a zigzag arrangement in diagrams or in models . The actual structure will always differ somewhat from these idealized forms, as the differences in energy between the conformations are small compared to the thermal energy of the molecules: Alkane molecules have no fixed structural form, whatever the models may suggest . </P> <P> Virtually all organic compounds contain carbon--carbon, and carbon--hydrogen bonds, and so show some of the features of alkanes in their spectra . Alkanes are notable for having no other groups, and therefore for the absence of other characteristic spectroscopic features of a different functional group like--OH,--CHO,--COOH etc . </P> <P> The carbon--hydrogen stretching mode gives a strong absorption between 2850 and 2960 cm, while the carbon--carbon stretching mode absorbs between 800 and 1300 cm . The carbon--hydrogen bending modes depend on the nature of the group: methyl groups show bands at 1450 cm and 1375 cm, while methylene groups show bands at 1465 cm and 1450 cm . Carbon chains with more than four carbon atoms show a weak absorption at around 725 cm . </P>

Do long chain alkanes have higher boiling points