Alkanes structural isomers

Draw the five alkane structural isomers for the molecular formula CeHu. 

Isomers are substances having the same molecular formula and molecular weight, but differing in physical and chemical properties. Since branched and straight-chain alkanes with the same molecular formula can exist as distinct structures having different geometrical arrangement of the atoms, they are termed structural isomers. One example is C H,j (butane) which has two isomers ... 

Isomers are distinctly different compounds, with different properties, that have the same molecular formula. In Section 22.1, we considered structural isomers of alkanes. You will recall that butane and 2-methylpropane have the same molecular formula, C4H10, but different structural formulas. In these, as in all structural isomers, the order in which the atoms are bonded to each other differs. 

Isomers are compounds that have the same molecular formulas but different structural formulas. Review the writing of the various structural isomers of alkanes. Make sure that each carbon atom has four bonds. 

This second branched molecule is called isobutane. Compounds sharing the same molecular formula but having different structures are called structural isomers. Normal butane and isobutane have different physical properties. The number of structural isomers for the alkanes is included in Table 15.1. It can be seen in this table that as the number of carbon atoms increases that the number of possible isomers also increases. The fact that numerous isomers exist for most organic compounds is another reason why there are so many organic compounds. 

If all alkanes had unbranched (straight-chain) structures, their nomenclature would be simple. Most alkanes have structural isomers, however, and we need a way of naming all the different isomers. For example, there are two isomers of formula C4H10. The unbranched isomer is simply called butane (or n-butane, meaning normal butane), and the branched isomer is called isobutane, meaning an isomer of butane. ... 

Draw the structural isomers for the alkane C6H14 and give the systematic name for each one. 

As we shall see, there are several different types of structural isomer. Isomers have to be named so that you can tell the difference between them. Consider the first member of the alkane series that shows structural isomerism, butane. 

As the number of carbons in a hydrocarbon increases, the number of possible structural isomers increases. For example, nine alkanes having the molecular formula C7H16 exist. C nH, has 316 319 structural isomers. 

Draw all of the structural isomers possible for the alkane with a molecular formula of CgHj4. Show only the carbon chains. 

Table 8.1. 1 Number of structural isomers for alkanes of increasing carbon number ...

Unbranched alkanes tend to have higher melting points, boiling points, and heats of vaporization than their branched structural isomers. 

In the alkane series, as the number of carbon atoms increases, the number of structural isomers increases rapidly. For example, butane, C4H10, has two isomers decane, C10H22, has 75 isomers and the alkane C30H62 has over 400 million, or 4 X 10, possible isomers Obviously, most of these isomers do not exist in nature nor have they been synthesized. Nevertheless, the numbers help to explain why carbon is found in so many more compounds than any other element. 

The following example deals with the number of structural isomers of an alkane. 

We can draw no other structure for an alkane having the molecular formula C5H12. Thus pentane has three structural isomers, in which the numbers of carbon and hydrogen atoms remain unchanged despite the differences in structure. 

How many structural isomers are there in the alkane C6H14 ... 

Two or more compounds with the same molecular formula but different properties are called isomers. Isomers with different arrangements of bonded atoms are constitutional (or structural) isomers alkanes with the same number of C atoms but different skeletons are examples. The smallest alkane to exhibit constitutional isomerism has four C atoms two different compounds have the formula C4H10, as shown in Table 15.3 on the next page. The unbranched one is butane (common name, /t-butane n- stands for normal, or having a straight chain), and the other is 2-methylpropane (common name, i obutane). Similarly, three compounds... 

Butane and all larger alkanes exhibit stmctural isomerism. Structural isomerism occurs when two molecules have the same atoms but different bonds. That is, the molecules have the same formulas but different arrangements of the atoms. For example, butane can exist as a straight-chain molecule (normal butane, or u-butane) or with a branched-chain stmcture (called isobutane), as shown in Figure 20.4. Because of their different stmctures, these structural isomers have different properties. 

Which alkanes cannot have structural isomers Why ... 

What are structural isomers What is the smallest alkane that has a structural isomer Draw structures to illustrate the isomers. 

Ans. The structural formula need not be used for this equation since the reaction involves complete dissection of the alkane. The molecular formula is sufficient and the same equation can be used for the combustion of any of the structural isomers of CgHig. The unbalanced equation is... 

In structural Isomerism, first met in the discussion of alkanes and which exists between but-l-ene, but-2-ene and 2-methylpropene, the compounds have their atoms bonded to different groups of atoms. For example, consider the underlined carbon atoms in the structural isomers of butene (C4H8) ... 

The number of possible structural isomers increases rapidly with the number of carbon atoms in the alkane. There are 18 isomers with the molecular formula CgHig, for example, and 75 with the molecular formula CiqH22-... 

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