Butane alkane isomers

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. 

The inclusion of reactions to represent the low-temperature chemistry in a detailed model for n-butane oxidation at high pressures, that is appropriate to temperatures down to about 600 K began in 1986 [225]. At the present time, models which include around 500 species and more than 2000 reversible reactions to represent alkane isomers up to heptane, are in use [219] and still larger schemes are under development [220]. Progress in the validation and application of these models, and kinetic representations for propane and propene oxidation, are discussed in the next subsection. Modelling of the low-temperature combustion of ethene has also been undertaken more recently [20]. 

Methane is the only alkane of molecular formula CH4 ethane the only one that is C2H6 and propane the only one that is C3Hj Beginning with C4H10 however constitutional isomers (Section 1 8) are possible two alkanes have this particular molecular formula In one called n butane, four carbons are joined m a continuous chain The nmn butane stands for normal and means that the carbon chain is unbranched The second isomer has a branched carbon chain and is called isobutane... 

Butanes are naturally occurring alkane hydrocarbons that are produced primarily in association with natural gas processing and certain refinery operations such as catalytic cracking and catalytic reforming. The term butanes includes the two stmctural isomers, / -butane [106-97-8] CH2CH2CH2CH2, and isobutane [79-28-9], (CH2)2CHCH2 (2-methylpropane). 

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 ... 

Constitutional isomerism is not limited to alkanes—it occurs widely throughout organic chemistry. Constitutional isomers may have different carbon skeletons (as in isobutane and butane), different functional groups (as in ethanol and dimethyl ether), or different locations of a functional group along the chain (as in isopropylamine and propylamine). Regardless of the reason for the isomerism, constitutional isomers are always different compounds with different properties, but with the same formula. 

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. 

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. 

An alkane with all the carbons in a row is called butane, and the form with one carbon in the middle is known as isobutane. The iso is short for isomer, which means a molecule that has the same atoms arranged in a different way. 

Butanes are chosen as the simplest models for the normal and branched isomers. Both branched and normal isomers contain a C-C bond (2 ) interacting with the terminal C-H bonds (2 and 2 ) (Scheme 26a). The cyclic -aj-a2 -a3 a2- interaction (Scheme 26b) occurs in the polarization of the middle C-C a-bond by the interactions with the antiperiplanar C-H a-bonds. The orbital phase is continuous in the branched isomer and discontinuous in the normal isomer (cf Scheme 4). The branched isomer is more stable. The basic rule of the branching effects on the stability of alkanes is ... 

Methane, CH4, has one carbon atom. The next two members of the alkane family are ethane, C2H6, and propane, C3H8. Molecules of these compounds contain chains of two carbon atoms and three carbon atoms, respectively. Alkanes with more than three carbon atoms have more than one isomer. There are two structural formulas for butane, C4H10, and three structural formulas for pentane, C5H12. 

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. 

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. 

Butane (C4H10) can exist in two different isomeric forms, e.g. n-butane and isobutane (2-methylpropane). Open chain alkanes have free rotation about their C—C bonds, hut cycloalkanes cannot undergo free rotation, so substituted cycloalkanes can give rise to cis and trans isomers (see Section 3.2.2). 

Alkanes appear to react with platinum(IV) in an identical manner to benzene (34, 84) chloromethane and chloroethane can be detected as the reaction products from methane and ethane, respectively. When propane, butane, or hexane is the reactant, the terminal chloro isomers predominate over the internal isomers. This was interpreted to mean that primary C—H bonds are the most reactive (34), but a more detailed study has shown that this conclusion does not necessarily follow from the experimental results (84). When cyclohexane is the reactant, dehydrogenation (or chlorination and then dehydrohalogenation) occurs to give benzene as one of the reaction products (29, 34, 84). 

There is free rotation around carbon-carbon single bonds. Therefore, alkane chains are quite flexible and can adopt a large number of conformations. For example, two conformations of butane are shown in Figure 11.5. The first structure converts into the second by rotation around the C2-C3 bond. These two structures are not isomers of each other because it is not possible to separate them. 

Alkanes having a particular molecular formula can exist as different constitutional isomers. For example, the alkane having the molecular formula C4H10can exist as two constitutional isomers-the straight chain alkane (butane) or the branched alkane (2-methylpropane Following fig.). These are different compounds with different physical and chemical properties. 

For example, butane has a boiling point of -0.5°C, while 2-methylpropane s boiling point is -11.7°C. Only hydrocarbon chains with at least four carbon atoms are capable of forming a branch. Because there must be a way to distinguish isomers, the nomenclature must take these into account. The following are general rules for naming branched-chain alkanes ... 

In addition to the locations of the double bonds, another difference of alkenes is the molecule s inability to rotate at the double bond. With alkanes, when substituent groups attach to a carbon, the molecule can rotate around the C-C bonds in response to electron-electron repulsions. Because the double bond in the alkene is composed of both sigma and pi bonds, the molecule can t rotate around the double bond (see Chapter 6). What this means for alkenes is that the molecule can have different structural orientations around the double bond. These different orientations allow a new kind of isomerism, known as geometrical isomerism. When the non-hydrogen parts of the molecule are on the same side of the molecule, the term cis- is placed in front of the name. When the non-hydrogen parts are placed on opposite sides of the molecule, the term trans- is placed in front of the name. In the previous section, you saw that the alkane butane has only two isomers. Because of geometrical isomerism, butene has four isomers, shown in Figure 19.12. 

Although we have derived the CnH2n+2 formula using the unbranched n-alkanes, it applies to branched alkanes as well. Any isomer of one of these n-alkanes has the same molecular formula. Just as butane and pentane follow the C H2 +2 rule, their branched isomers isobutane, isopentane, and neopentane also follow the rule. 

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. ... 

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