draw the Kekulé structure, condensed structure and shorthand structure of each of the first ten straight-chain alkanes. Surname each of the first ten straight-chain alkanes, given its molecule formula, Kekulé structure, condensed framework or shorthand structure. Explain the distinction in structure between a straight- and a branched-chain alkane, and also illustrate the difference using a perfect example. Define why the number of possible isomers because that a provided molecular formula boosts as the variety of carbon atom increases. Attract all the possible isomers that correspond come a given molecular formula the the form Cn H2n+2, where n is ≤ 7.

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Key Terms

Make details that you can define, and also use in context, the crucial terms below.

branched-chain alkane constitutional or structural isomer homologous series isomer saturation hydrocarbon straight-chain alkane (or regular alkane)
Study Notes

A series of link in which succeeding members differ from one another by a CH2 unit is called a homologous series. Thus, the collection CH4, C2H6, C3H8 . . . CnH2n+2, is an instance of a homologous series.

It is necessary that girlfriend commit to storage the surname of the very first 10 straight-chain alkanes (i.e., indigenous CH4 to C10H22). Friend will use these name repeatedly when you begin to learn how to have the organized names of a large variety of essential compounds. You require not remember the number of isomers possible for alkanes containing more than seven carbon atoms. Such info is easily accessible in reference publications when that is needed. When drawing isomers, be cautious not to deceive yourself into thinking the you have the right to draw an ext isomers 보다 you are an alleged to be able to. Remember that it is feasible to attract each isomer in several various ways and also you might inadvertently counting the exact same isomer more than once.

Alkanes room organic compounds that consist totally of single-bonded carbon and also hydrogen atoms and also lack any type of other practical groups. Alkanes are often called saturated hydrocarbons since they have actually the preferably possible number of hydrogens per carbon. In section 1.7, thealkane molecule, ethane, was shown to save a C-C sigma bond. By adding an ext C-C sigma bond bigger and more complexed alkanes deserve to be formed. Methane (CH4), ethane (C2H6), and also propane (C3H8) room the start of a series of compounds in which any two members in a sequence different by one carbon atom and two hydrogen atoms—namely, a CH2 unit. Any kind of family of compounds in which nearby members different from each various other by a definite element (here a CH2 group) is dubbed a homologous series. The members of together a series, called homologs, have properties that vary in a regular and also predictable manner.


Figure 25.3.1 : The Three simplest Alkanes

Methane (CH4), ethane (C2H6), and also propane (C3H8) space the beginning of a series of link in which any kind of two members in a sequence differ by one carbon atom and two hydrogen atoms—namely, a CH2 unit. Take into consideration the series in figure 25.3.3. The succession starts through C3H8, and also a CH2 unit is included in every step moving up the series. Any family of compounds in which adjacent members different from each various other by a definite factor (here a CH2 group) is referred to as a homologous series. The members of such a series, referred to as homologs, have actually properties that differ in a regular and also predictable manner.



Likewise the molecule formula: C5H12 has actually three feasible isomer. The compound at the far left is pentane due to the fact that it has actually all 5 carbon atoms in a consistent chain. The compound in the center is isopentane; favor isobutane, it has actually a one CH3 branch turn off the 2nd carbon atom that the consistent chain. The link at the far right, found after the various other two, was called neopentane (from the Greek neos, an interpretation “new”). Although every three have actually the very same molecular formula, castle have different properties, consisting of boiling points: pentane, 36.1°C; isopentane, 27.7°C; and neopentane, 9.5°C.


Of the structures present above, butane and also pentane are called normal alkanes or straight-chain alkanes, indicating the all contain a single continuous chain of carbon atoms and also can be stood for by a estimate formula whose carbon atoms room in a straight line. The other structures, isobutane, isopentane, and neopentane are called called branched-chain alkanes. Together the variety of carbons in one akane rises the variety of possible isomers also increases as presented in the table below.

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Table \(\PageIndex2\): number of isomers for hydrocarbons

Molecular FormulaNumber of structure Isomers
CH4 1
C2H6 1
C3H8 1
C4H10 2
C5H12 3
C6H14 5
C7H16 9
C8H18 18
C9H20 35
C10H22 75
C14H30 1858
C18H38 60,523
C30H62 4,111,846,763

Akanes deserve to be stood for in many different ways. The figure listed below shows several of the various ways straight-chain butane can be represented. Most regularly juniorg8.comists refer to butane through the condensed framework CH3CH2CH2CH3 or n-C4H10 wherein n denotes a normal right alkane.


Note that numerous of these structures only imply bonding connections and also do not suggest any certain geometry. The bottom two structures, described as "ball and stick" and also "space filling" do present 3D geometry because that butane. Since the four-carbon chain in butane might be bent in various means the teams can turn freely around the C–C bonds. However, this rotation does not change the identification of the compound. It is crucial to realize the bending a chain go not change the identification of the compound; all of the adhering to represent the very same compound, butane: