name of straight chain hydrocarbon
Answers
For a given number of carbon atoms, an unbranched alkane has a higher boiling point than any of its branched-chain isomers. This effect is evident upon comparing the boiling points (bp) of selected C8H18 isomers. An unbranched alkane has a more extended shape, thereby increasing the number of intermolecular attractive forces that must be broken in order to go from the liquid state to the gaseous state. On the other hand, the relatively compact ellipsoidal shape of 2,2,3,3-tetramethylbutane permits it to pack into a crystal lattice more effectively than octane and so raises its melting point (mp).
Hydrocarbon. Structural formula for unbranced alkanes, octane, 2-methylheptane, 2,2,3,3-tetramethylbutane.
In general, solid alkanes do not often have high melting points. Unbranched alkanes tend toward a maximum in that the melting point of CH3(CH2)98CH3 (115 °C [239 °F]) is not much different from that of CH3(CH2)148CH3 (123 °C [253 °F]).
The viscosity of liquid alkanes increases with the number of carbons. Increased intermolecular attractive forces, as well as an increase in the extent to which nearby molecules become entangled when they have an extended shape, cause unbranched alkanes to be more viscous than their branched-chain isomers.
The densities of liquid hydrocarbons are all less than that of water, which is quite polar and possesses strong intermolecular attractive forces. All hydrocarbons are insoluble in water and, being less dense than water, float on its surface. Hydrocarbons are, however, usually soluble in one another as well as in organic solvents such as diethyl ether (CH3CH2OCH2CH3).
Sources and occurrence
The most abundant sources of alkanes are natural gas and petroleum deposits, formed over a period of millions of years by the decay of organic matter in the absence of oxygen. Natural gas contains 60–80 percent methane, 5–9 percent ethane, 3–18 percent propane, and 2–14 percent higher hydrocarbons. Petroleum is a complex liquid mixture of hundreds of substances—including 150 or more hydrocarbons, approximately half of which are saturated.
Approximately two billion tons of methane are produced annually by the bacteria that live in termites and in the digestive systems of plant-eating animals. Smaller quantities of alkanes also can be found in a variety of natural materials. The so-called aggregation pheromone whereby Blaberus craniifer cockroaches attract others of the same species is a 1:1 mixture of the volatile but relatively high-boiling liquid alkanes undecane, CH3(CH2)9CH3, and tetradecane, CH3(CH2)12CH3. Hentriacontane, CH3(CH2)29CH3, is a solid alkane present to the extent of 8–9 percent in beeswax, where its stability and impermeability to water contribute to the role it plays as a structural component.
With the exception of the alkanes that are readily available from petroleum, alkanes are synthesized in the laboratory and in industry by the hydrogenation of alkenes
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