Isomers of pentane

Table 2. Illustrates the Structural Formulas for Isomers of Pentane.

Following this system, the IUPAC names of the isomers of pentane are... 

Construct three different isomers of pentane, C5H12. 

Similarly, three isomers of pentane, C5H12, exist. As the number of carbon atoms in a molecule increases, the number of possible isomers increases markedly. Theoretically, for the formula c2()h... 

Write structural formulas for the three isomers of pentane. 

Constitutional isomerism becomes more complex as the size of the hydrocarbon molecule is increased. For example, there are three constitutional isomers of pentane, C5H12. The number of constimtional isomers increases quite rapidly with an increasing number of carbon atoms. Thus, there are five constimtional isomers of hexane, CeH, nine isomers of heptane, C7H16, 75 isomers of decane, C10H22, and 366,319 isomers of eicosane, C20H42. You can begin to understand why it is possible to make so many different molecules based on carbon. 

Problem 12 Show the 3 isomers of pentane as condensed structural formulas. 

The number of isomers of paraffin is very large see table 5.1. We see that the iso-paraffins are not as well investigated as the normal paraffins. We have the boiling points of all three isomers of pentane, but not the 75 isomers of deeane. It is inevitable that we have to resort to estimations. 

An example is the method proposed by Kier and Hall, which usually considers only the C atoms and excludes the H atoms from consideration. Take the four isomers of pentane below, which are connected very differently. Each molecule can be described by a connection number 5 for each of the carbon atoms, 1 for a primary carbon, 2 for a secondary carbon, etc. 

Problem 4.12 Name by the lUPAC system the isomers of pentane derived in Problem 4.2. ... 

First, one has to identify and name the groups attached to the chain, and number the chain so that the substituent gets the lowest possible number. For example, one of the isomers of pentane is 2-methylbutane, where the parent chain is a four-carbon butane chain, and is numbered starting from the end nearer the substituent group (methyl group). Therefore, the methyl group is indicated as being attached to carbon atom number 2. 

The continuous chain hydrocarbons are known as normal hydrocarbons, and the prefix n- is usually attached to the name. The branched-chain hydrocarbons may have the prefix iso- attached to the name. Usually the prefix iso- is reserved for substances with two methyl groups attached to carbon atoms at the end of an otherwise straight chain. In a straight chain, each carbon atom is connected to no more than two other carbon atoms. The prefix neo- denotes three methyl groups on a carbon atom at the end of a chain. For example, the isomers of pentane are illustrated below. 

CH, j CH3CCH3 2,2-Dimethylpropane - T J —7I° This isomer of pentane has a more compact spherical shape, which allows it to pack better into the crystal lattice, resulting in a significantly higher melting point. 

In the previous section, we mentioned that different molecules, isomers, can have the same molecular formula but have a different structure. We saw that butane, C4H10, has two isomers—butane (also known as n-butane) and 2-methylpropane. As molecules get longer, more and more isomers become possible. In the first sample, we will consider the number of isomers of pentane. 

Sample Determine the number of isomers of pentane, and draw each isomer s structure. 

There are three constitutional isomers of pentane (C5H12), whose common names are n-pentane, isopentane, and neopentane. The number of isomers increases rapidly as the number of carbon atoms increases. 

Draw out the structure of another isomer of pentane CH3CH2CH(CH3)CH3 and give it its systematic name based on the longest carbon chain (see Figure 2.21). 

Practice Problem 20.1 5 Name and draw condensed formulas for the three ketones that are isomers of pentanal. ... 

Nomenclature. The question arises as to how the various isomers of a hydrocarbon can be named and distinguished. When the number of poffiible isomers is small this offers no problem. The two isomers of butane are named normal butane and isobutane. The three isomers of pentane are known as normal pentane, isopentane, and neopentane. 

Dimethylpropane (neo-pentane) is unique amongst the isomers of pentane since it contains no secondary or tertiary C—H bonds. This unusual structure of the dimethylpropyl radical has been exploited in the study of... 

Is cyclopentane an isomer of pentane Explain your answer. 

How many isomers of pentane did you build How many isomers of hexane ... 

These are two distinctly different compounds, with different chemical and physical properties for example, they have different boiling points. Similarly, three isomers of pentane, C5HJ2 exist, and so on. 

Solved Problem 14.4 Write the structural formulas for the three isomers of pentane. ... 

Structure and properties are closely related, as you can see by examining the isomers of pentane. Although all three compounds have the formula C5H12, differences in the amount of branching affect their properties. Note the differences in the shapes of the molecules. 

Despite their identical molecular formulas, isomers have different properties. The boiling and melting points of 2-methylpropane and butane are different, as are their densities and solubilities in water. In addition, their chemical reactivity is different. Figure 18.3 shows some property differences in the isomers of pentane. 

There are three isomers of pentane, five of hexane, and more than 4 billion isomers of the alkane with the formula C30H62. 

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