Isomers Same Formula, Different Structure

In addition to linking together in straight chains to form the n-alkanes, carbon atoms can form branched structures called branched alkanes. The simplest branched alkane is called isobutane and has the structure  

Isobutane and butane are isomers, molecules with the same molecular formula but different structures. Because of their different structures, they have different properties indeed, they are different compounds. Isomerism is common in organic compounds. We have seen that butane has two isomers. Pentane (C5H12) has three isomers, hexane (QH14) has five, and decane (C10H22) has seventy-five  

To start, always draw the carbon backbone. The first isomer is the straight-chain isomer, C—C—C—C—C—C. Then, determine the carbon backbone structure of the other isomers by arranging the carbon atoms in four other unique ways. 

To finish, fill in all the hydrogen atoms so that each carbon has four bonds. 

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Isomers — different structural arrangements with the same chemical formula (e.g., n-butane and t-butane). 

Within each analogous series of hydrocarbons there exist isomers of the compounds within that series. An isomer is defined as a compound with the same molecular formula as another compound but with a different structural formula. In other words, if there is a different way in which the carbon atoms can align themselves in the molecule, a different compound with different properties will exist. 

The substitution of one hydroxyl radical for a hydrogen atom in propane produces propyl alcohol, or propanol, which has several uses. Its molecular formula is C3H7OH. Propyl alcohol has a flash point of 77°F and, like all the alcohols, bums with a pale blue flame. More commonly known is the isomer of propyl alcohol, isopropyl alcohol. Since it is an isomer, it has the same molecular formula as propyl alcohol but a different structural formula. Isopropyl alcohol has a flash point of 53 F. Its ignition temperamre is 850°F, while propyl alcohol s ignition temperature is 700 F, another effect of the different stmcture. Isopropyl alcohol, or 2-propanol (its proper name) is used in the manufacture of many different chemicals, but is best known as rubbing alcohol. 

Compounds like the two C4M [() molecules and the three C3I I 12 molecules, which have the same formula but different structures, are called isomers, from the Greek isos + meros, meaning "made of the same parts." Isomers are compounds that have the same numbers and kinds of atoms but differ in the way the atoms are arranged. Compounds like butane and isobutane, whose atoms are connected differently, are called constitutional isomers. We ll see shortly that other kinds of isomers are also possible, even among compounds whose atoms are connected in the same order. As Table 3.2 shows, the number of possible alkane isomers increases dramatically as the number of carbon atoms increases. 

Alkanes are a class of saturated hydrocarbons with the general formula C H2n. -2- They contain no functional groups, are relatively inert, and can be either straight-chain (normal) or branched. Alkanes are named by a series of IUPAC rules of nomenclature. Compounds that have the same chemical formula but different structures are called isomers. More specifically, compounds such as butane and isobutane, which differ in their connections between atoms, are called constitutional isomers. 

As noted on several previous occasions, isomers are compounds that have the same chemical formula but different structures. We ve seen several kinds of isomers in the past few chapters, and it s a good idea at this point to see how they relate to one another (f igure 9.14). 

Isomers (Sections 3.2,9.9) Compounds that have the same molecular formula but different structures. 

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. 

We have now found all possible structural formulas for the ethanol molecule. The oxygen atom is either directly bonded to one carbon atom or to two carbon atoms. Once a choice between these two possibilities is made, the structure of the rest of the molecule can be determined from the molecular formula and the bonding rules. The two possible structures are shown in Figure 18-2. Such compounds with the same molecular formula but different structural formulas are called structural isomers. The existence of the two compounds I and 2 was known long before their structures were clarified. Hence the existence of these isomers perplexed chemists for decades. Now we recognize the crucial impor-... 

Structural isomers are molecules that have the same formula but in which the atoms are connected in a different order. Two isomers of disulfur difluoride, S2F2, are known. In each the two S atoms are bonded to each other. In one isomer each of the S atoms is bonded to an F atom. In the other isomer, both F atoms are attached to one of the S atoms, (a) In each isomer the S—S bond length is approximately 190 pm. Are the S—S bonds in these isomers single bonds or do they have some double bond character (b) Draw two resonance structures for each isomer, (c) Determine for each isomer which structure is favored by formal charge considerations. Are your conclusions consistent with the S—S bond lengths in the compounds ... 

Although they are built from the same numbers and kinds of atoms, structural isomers have different chemical formulas, because the formulas show how the atoms are grouped in or outside the coordination sphere. Stereoisomers, on the other hand, have the same formulas, because their atoms have the same partners in the coordination spheres only the spatial arrangement of the ligands differs. There are two types of stereoisomerism, geometrical and optical. 

Molecules (b) and (c) are identical. The atoms of molecule (e) are joined together in the same arrangement as that of (b) and (c), but the structure looks different because it has been rotated 180° and twisted so (b), (c), and (e) are the same. There are therefore only three distinct isomers with formula C5H12 (a), (b), and (d). 

Structural isomers have identical molecular formulas, but their atoms are linked to different neighbors. Geometrical isomers have the same molecular and structural formulas but different arrangements in space. Molecules with four different groups attached to a single carbon atom are chiral they are optical isomers. 

Two or more substances that have the same molecular formula but different structures and properties are called isomers. Two main types of isomers exist. Structural isomers are ones in which the atoms are bonded in different orders. In stereoisomers, all the bonds in the molecule are the same, but the spatial arrangements are different. 

While Lavoisier had established a rational system for naming elements and compounds, Frankland developed the system that we use today for writing chemical formulas and for depicting the bonds between the atoms in molecules. As Frankland synthesized more and more isomers, compounds with the same formulas but different molecular structures, he found traditional formulas confusing they showed the types and numbers of elements but provided no clue as to how the atoms were arranged inside the molecule. To remedy the problem, Frankland depicted the atoms in functional groups and drew lines between them to indicate the bonds between the elements. 

The molecules of two organic compounds are sometimes composed of the same type and number of atoms, but arranged in different ways. The molecular formula of each one of such compounds, which are known as isomers (for example, isoleucine and alloisoleucine, shown in Fig. 73), is therefore identical to that of the other only the structural formulas of the two isomers show the differences between their molecules (see Textbox 63). 

The ability of a carbon atom to link to more than two other carbon atoms makes it possible for two or more compounds to have the same molecular formula but different structures. Sets of compounds related in this way are called isomers of each other. For example, there are two different compounds having the molecular formula C4HI0. Their structural formulas are as follows ... 

Thus the isomers in these cases have the same molecular and structural formulae but slightly different physical and chemical properties. So in general it can be said that all olefinic compounds having the formula... 

Compounds that have the same molecular formulas, but different structural formulas, are isomers. When dealing with hydrocarbons, this amounts to a different arrangement of the carbon atoms. Isomers such as these are structural isomers. 

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. 

Draw and name three aromatic isomers with the molecular formula C10H14. [Isomers are compounds that have the same molecular formula, but different structures. See the Concepts and Skills Review for a review of structural isomers.)... 

The molecular formulas just shown for 10 alkane hydrocarbon molecules represent the proportions of carbon to hydrogen in each molecule. These formulas do not reveal much about their structures, but rather indicate the proportions of each element in their molecules. Each molecule may have several different structures while still having the same formula. Molecules with different structures but the same formulas are called isomers. For example, n-butane is formed in a straight chain, but in an isomer of butane, the CH branches off in the middle of the straight chain. Another example is ethane, whose isomeric structure can be depicted as H,C H,C-CH,. The name for the normal structure sometimes uses n in front of the name. 

Isomers are compounds with the same molecular formula but different structural formulas. Some organic and biochemical compounds may exist in different isomeric forms, and these different isomers have different properties. The two most common types of isomers in organic systems are cis-trans isomers and isomerism due to the presence of a chiral Ccirbon. 

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. 

Structural Isomer compounds that have the same formula but have different atomic arrangement... 

Another important concept from organic chemistry that has an impact on polymer structure is that of isomerism. Recall that structural isomers are molecules that have the same chemical formula, but different molecular architectures. For example, there are two different types of propyl alcohols, both with the same formula, depending on where the —OH functional group is placed on the carbon backbone (see Figure 1.53). Another type of isomerism results in stereoisomers, in which the functional groups are... 

Organic compounds show a widespread occurrence of isomers, which are compounds having the same molecular formula but different structural formulas, and therefore possessing different properties. This phenomenon of isomerism is exemplified by isobutane and -butane [Fig. l-l(a) and (b)]. The number of isomers increases as the number of atoms in the organic molecule increases. 

Compounds with the same molecular formula but different structures are called isomers. For example, 1-butene and 2-butene have the same molecular formula, C4H8, but structurally they are different because of the different positions of the double bond. There are two types of isomer constitutional isomers and stereoisomers. 

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