The molecules consist of either straight chains of carbon atoms, connected one after the other, with the appropriate number of hydrogen atoms on each carbon, or as branched chains of carbon atoms having carbon substituents alkyl groups attached at various points along the chain.
Thus, the word "propane" indicates that there are three carbon atoms in the chain, all connected by single bonds. Thus, the name "2-methylpropane" indicated that there is a three-carbon longest chain, with a one-carbon branch on the second carbon; the name "2,3-dimethylbutane" indicates that there is a four-carbon longest chain, with two one-carbon substituents on carbons 2 and 3.
Some molecules of the same molecular formula can have their atoms arranged in a different order; we say that these molecules are structural isomers of each other. The simplest alkanes have only one way in which their atoms can be arranged, and have no structural isomers.
As the number of carbon atoms increases, the number of structural isomers increases rapidly see butane and isobutane below for examples. The carbon atoms in alkanes are sp 3 -hybridized, and have tetrahedral shapes, with the bonded atoms at angles of Free rotation is possible around the carbon-carbon single bonds in alkanes, making the carbon chains very flexible and "floppy" — particularly for the larger molecules.
Alkanes are nonpolar molecules, since they contain only nonpolar carbon-carbon and carbon-hydrogen bonds. They are therefore not soluble in water, and since they are generally less dense than water, they will float on water e. The only intermolecular forces acting between alkane molecules are very weak London forces also known as dispersion forces which result from the attractions between instantaneous dipoles formed as a result of random fluctuations of electrons in nonpolar molecules.
As the number of carbon atoms increases, the attractions due to these weak London forces increase, and the boiling point of the molecule increases. See Table 1 below. The lower-molecular mass alkanes 1 to 4 carbons are gases at room temperature, those having 5 to 20 carbons tend to be liquids with increasingly high boiling points, and those with more than 20 carbons are increasingly viscous liquids, and finally waxy solids at room temperature.
In the words of Stephen Wright, "It doesn't matter what temperature a room is, it's always room temperature. The low-molecular mass alkanes, from 1 to 4 carbons, are frequently used as cooking fuels; molecules of intermediate length carbons are found in gasoline and diesel fuels; longer carbon chains are found in motor oils, lubricants, emollients, greases, waxes, paraffin, and other applications.
Many of these compounds are isolated from petroleum, and may serve as the starting points for the synthesis of more complex molecules. Methane is an odorless, nontoxic, flammable gas, which has a boiling point of It is produced by the bacterial decomposition of organisms in the absence of oxygen, and is found in natural gas, marsh gas, bovine flatulence, etc.
It burns cleanly, and so is useful in cooking. Ethanethiol is added to natural gas to give it an unpleasant odor, thereby making gas leaks detectable. Both propane and butane are used as LPG fuels liquefied petroleum gas for outdoor cooking, either in camping stoves or outdoor gas barbecue grills.
Propane liquefies at Butane is a gas above In this form, it is used in cigarette lighters and lighter sticks. It is also possible to obtain a molecule with the formula C 4 H 10 by having a chain of three carbons with a one-carbon branch a methyl group attached to the middle carbon.
This molecule is given the common "trivial", i. Butane and isobutane are structural isomers of each other, having the same molecular formula, but with the atoms connected in a different order.
This slight difference is enough to give butane and 2-methylpropane different physical properties: for instance while butane boils at The lower boiling point is a result of the more compact structure of the 2-methylpropane isomer, which has less surface area than the straight-chain isomer, and thus fewer London forces between its molecules. Notice that as the number of carbons increases, the boiling point also increases; this is a result of the longer carbon chains having more London forces acting between them.
There are three structural isomers of C 5 H 12 :. Mixtures of structural isomers of hexane are commonly used as organic solvents.
There are five structural isomers of C 6 H 14 :. Using common or non-systematic names is not practical for molecules with a large number of carbon atoms, since it would be necessary to memorize unique names for each possible compound.
And as you can see in Table 1 below , the number of possible structural isomers increases drastically as more carbons are added! Systematic names, in which there is a one-to-one correspondence between the structure and the name, are a huge benefit to organic chemists.
There are 9 structural isomers of C 7 H Eight carbons is typical for the size of the hydrocarbons present in gasoline. There are 13 structural isomers of C 8 H 18 , one of which is isooctane see below. Branched alkanes tend to burn more smoothly than straight-chain alkanes when they are used in internal combustion engines.
Tetraethyllead, Pb CH 2 CH 3 4 , used to be widely used as an "anti-knocking" agent; this has been discontinued because of concerns about the release of lead into the atmosphere. Other compounds can be used as antiknocking agents, such as MTBE methyl tert -butyl ether — see the section on ethers for more information on this compound.
There are 35 structural isomers of C 9 H There are 75 structural isomers of C 10 H In diesel fuels, straight chains are preferable to branched chains because fuel is sprayed into the cylinder during the power stroke, and needs to ignite as it enters. Hexadecane is assigned a cetane number of , and the highly branched heptamethylnonane has a cetane number of 0. Cycloalkanes are alkanes in which the ends of the carbon chain are joined together, making a ring of carbon atoms which requires the loss of two hydrogen atoms compared to the straight-chain alkanes.
They have the general formula C n H 2n for molecules containing one ring. One Ring, of course, rules them all. Cycloalkanes are named in a similar fashion to straight-chain alkanes; the prefix cyclo- is added to the stem indicating the number of carbon atoms in the ring. Carbon groups that are attached to the ring are named as alkyl groups. Thus, the name "cyclobutane" indicates a ring of four carbon atoms, all linked by single bonds.
Free rotation is not possible around the carbon-carbon single bonds in rings, which leads to the introduction of stereoisomers — molecules having the same pattern of connectivity, but different arrangements of atoms in space.
This deviation from the ideal tetrahedral bond angles of Because free rotation is not possible around the single bonds in a cycloalkane, when two methyl groups are added to cyclopropane, there are two possible arrangements: both methyl groups can be pointing to the same side of the ring cis , or to opposite sides of the ring trans : Download 3D Download 3D These molecules are not structural isomers of each other, because the order in which the atoms are connected is the same, but the two methyl groups are pointing in different directions in space, making them stereoisomers of each other.
These types of stereoisomers are referred to as geometric isomers. As a molecule, it's not completely "square. The ring is able to "pucker" slightly to relieve some of the eclipsing interactions, and so all of the carbon atoms do not lie in the same plane. Cyclopentanes are a more stable than cyclopropanes and cyclobutanes, and are found in wide variety of naturally occurring molecules. Cyclohexane C 6 H 12 3D With cyclohexane, ring chemistry gets even more interesting and complicated.
However, cyclohexane can adopt one of two conformations which relieve this ring strain. In one of these conformations, the carbon atoms on either side of the ring bend slightly upwards; in this so-called "boat" conformation, the bond angles all Download 3D There are still a number of C—H eclipsing interactions, however, and this is not the lowest-energy conformation which is possible.
In the other possible conformation, one of the carbon atoms bends upwards, and the one on the opposite side bends downwards, producing the "chair" conformation; in this conformation, not only are the bond angles Cyclohexane rings are very stable, and are present in large numbers of naturally occurring molecules.
Download 3D This is drastically oversimplified, of course; the chair and boat conformation represent the extremes of a large number of possible intermediate conformations, and the energetics of the ring system change a great deal when substituents are added to the ring. Cycloheptane C 7 H 14 3D Download 3D There is a slight amount of strain energy in cycloheptane and larger cycloalkanes, since it is difficult for them to adopt bond angles of This molecule is often found on traffic signs:.
There are two geometric isomers of the molecule, the cis and trans form. Norbornane rings show up in a lot of interesting molecules, such as camphor. Adamantane 3D Download 3D Adamantane is a tricyclic molecule; the fused cyclohexane rings in this molecule are extremely rigid. Extending the structure of adamantane further into three dimensions results in the structure of diamonds.
Cole at the University of Chicago in Prismane 3D Download 3D Prismane is so named because it looks like a molecular prism duh. Methane also known as marsh or swamp gas is used for firing electrical generation stations, power automobiles etc. Methane is found in wetlands and oceans, atmosphere, human sources like burning fuel, raising livestock, fermentation of organic matter etc.
Butane can be obtained as a byproduct during extraction of crude oil and is a component of natural gas. Share this comparison:. If you read this far, you should follow us:. Diffen LLC, n. Comparison chart Differences — Similarities —. Chemical formula and Molecular structure of methane vs butane Butane is C 4 H 10 while methane has the chemical formula — CH 4.
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Korpl , B. Sage , W. Phase Equilibria in Hydrocarbon Systems. Adsorption, selectivity, and phase behavior in organic nanopores for shale gas and oil development.
Petroleum Research , 6 3 , Empirical correlations for second virial coefficients of nonpolar and polar fluids covering a wide temperature range. Fluid Phase Equilibria , , May , Eric W. Lemmon , Roland Span. Journal of Physical and Chemical Reference Data , 48 3 , Tarom , Md.
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