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Pentane is an organic compound with the formula C 5 H 12 —that is, an alkane with five carbon atoms. The term may refer to any of three structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, pentane means exclusively the n-pentane isomer, in which case pentanes refers to a mixture of them; the other two are called isopentane (methylbutane) and neopentane ...
However, the chain of carbon atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of carbon atoms. For example, for acyclic alkanes: [3] C 1: methane only; C 2: ethane only; C 3: propane only; C 4: 2 isomers: butane and isobutane; C 5: 3 isomers: pentane, isopentane, and neopentane
2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula (CH 3) 3 CCH 2 CH(CH 3) 2.It is one of several isomers of octane (C 8 H 18).This particular isomer is the standard 100 point on the octane rating scale (the zero point is n-heptane).
Isopentane is a major component (sometimes 30% or more) of natural gasoline, an analog of common petroleum-derived gasoline that is condensed from natural gas. [4] Its share in commercial car fuel is highly variable: 19–45% in 1990s Sweden, [ 13 ] 4–31% in 1990s US [ 14 ] and 3.6–11% in the US in 2011. [ 15 ]
Therefore, neopentane is a gas at room temperature and atmospheric pressure, while the other two isomers are (barely) liquids. The melting point of neopentane (−16.6 °C), on the other hand, is 140 degrees higher than that of isopentane (−159.9 °C) and 110 degrees higher than that of n -pentane (−129.8 °C).
In the Benson heat of formation group additivity dataset, cis isomers suffer a 1.10 kcal/mol stability penalty. Exceptions to this rule exist, such as 1,2-difluoroethylene, 1,2-difluorodiazene (FN=NF), and several other halogen- and oxygen-substituted ethylenes. In these cases, the cis isomer is more stable than the trans isomer. [10]
Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural (or constitutional) isomerism, in which bonds between the atoms differ; and stereoisomerism (or spatial isomerism), in which the bonds are the same but the relative positions of the atoms differ. Isomeric relationships form a ...
Enumerating or counting structural isomers in general is a difficult problem, since one must take into account several bond types (including delocalized ones), cyclic structures, and structures that cannot possibly be realized due to valence or geometric constraints, and non-separable tautomers.