Straight-chain pentane

Pentane is a colorless, flammable liquid (the first liquid member of the alkanes) that is lighter than water. It has a pleasant odor that can be detected at 900 ppm, and a moderate odor intensity is observed at 5000 ppm. It occurs as two other isomers, including isopentane [(CH3)2CHCH2CH3] and neopentane [C(CH3)4]. Isopentane (2-methylbutane) apparently has physical and physiological characteristics similar to straight-chain pentane. Neopentane (2,2-dimethylpropane) is similar to butane in physical and physiological characteristics. In air, one part per million of C5 pentane is equivalent to 3 mgm. ... 

In addition to aromatics with benzene ring structures, modern refinery processes tend to increase the number of hydrocarbons with simpler types of carbon ring structures. Typical chemicals include cyclopentane, where the straight-chain pentane has been wrapped into a five-carbon ring. Other transformations of aliphatic hydrocarbons include cylcohexane and cyclopentane. These ring compounds are usually called naphthenes. 

Butane (C Hj ) and the other alkanes above it can exhibit constitutional isomerism. If the alkane is unbranched and has a straight chain, it is called -alkane. For example, the straight chain pentane is called n-Pentane. 

In this case the longest continuous chain has five carbon atoms the compound is named as a derivative of pentane The key word here is continuous It does not matter whether the carbon skeleton is drawn m an extended straight chain form or m one with many bends and turns All that matters is the number of carbons linked together m an uninterrupted sequence... 

Compounds like butane and pentane, whose carbons are all connected in a row, are called straight-chain alkanes, or normal alkanes. Compounds like 2-methylpropane (isobutane), 2-methylbutane, and 2,2-dimethylpropane, whose carbon chains branch, are called branched-chain alkanes. The difference between the two is that you can draw a line connecting all the carbons of a straight-chain alkane without retracing your path or lifting your pencil from... 

Straight-chain alkanes are named according to the number of carbon atoms they contain, as shown in Table 3.3. With the exception of the first four compounds—methane, ethane, propane, and butane—whose names have historical roots, the alkanes are named based on Greek numbers. The suffix -one is added to the end of each name to indicate that the molecule identified is an alkane. Thus, pentane is the five-carbon alkane, hexeme is the six-carbon alkane, and so on. We ll soon see that these alkane names form the basis for naming all other organic compounds, so at least the first ten should be memorized. 

Another interesting effect seen in alkanes is that increased branching lowers an alkane s boiling point. Thus, pentane has no branches and boils at 36.1 3C, isopentane (2-methylbutane) has one branch and boils at 27.85 °C, and neopentane (2,2-dimethylpropane) has two branches and boils at 9.5 °C. Similarly, octane boils at 125.7 °C, whereas isooctane (2,2,4-trimethylpentane) boils at 99.3 °C. Branched-chain alkanes are lower-boiling because they are more nearly spherical than straight-chain alkanes, have smaller surface areas, and consequently have smaller dispersion forces. 

Isomerization (Figure 4.15) converts n-butane, n-pentane and n-hexane into then-respective isoparaffins of substantially higher octane number. The straight-chain... 

Alkanes are straight-chained or even branch-chained hydrocarbon molecules made up of methyl groups having the formula CnH2n+2i such as butane, isobutane, and pentane. 

There are three forms of pentane the straight-chain normal pentane (a = 2), the branched isopentane (a = 1), and the doubly branched neopentane (a = 12) in the shape of a tetrahedron. Figure 4.37 shows that normal pentane has the highest density and boiling point, which can be attributed to the superior packing efficiency of linear molecules isopentane, in comparison, has lower density and lower melting and boiling points. Neopentane does not follow the usual rules it has the lowest... 

Isomerization A refinery process used to produce branched compounds from straight-chain molecules. Butane, pentane, and hexane are isomerized to branched, higher-octane compounds through isomerization. Isomerization reactions are catalyzed through the use of aluminum chloride and other metal catalysts. 

You can refer to the same molecule in a number of different ways. For example, you can refer to pentane by its name (ahem. .. pentane)] by its molecular formula, CjHj2 or by the complete structure in Figure 6-2. Clearly, these names include different levels of structural detail. A condensed structural formula is another naming method, one that straddles the divide between a molecular formula and a complete structure. For pentane, the condensed structural formula is CH3CH2CH2CH2CH3. This kind of formula assumes that you understand how straight-chain alkanes are put together. Here s the lowdown ... 

Ipatieff and coworkers observed first that A1C13 catalyzes the destructive alkylation of aromatics with branched alkanes.179 For example, rm-butylbenzene (35%), p-di-rm-butylbenzene (25%), and considerable isobutane are the main products when benzene is reacted at 20-50°C with 2,2,4-trimethylpentane. Toluene and biphenyl are alkylated at 100°C in a similar way.180 Straight-chain alkanes required more severe reaction conditions. n-Pentane reacted at 175°C to yield 8% propylbenzene, 25% ethylbenzene, and 20% toluene.181 Phosphoric acid afforded similar products at higher temperature (450°C).182 Pentasil zeolites and dealumi-nated pentasils have been found to promote alkylation of benzene with C2—C4 alkanes to form toluene and xylenes.183,184... 

When every carbon atom in a hydrocarbon except the two terminal ones is bonded to only two other carbon atoms, the molecule is called a straight-chain hydrocarbon. (Do not take this name literally, for, as the w-pentane structures in Figure 12.1 show, this is a straight-chain hydrocarbon despite the zigzag nature of the drawings representing it.) When at least one carbon atom in a hydrocarbon is bonded to either three or four carbon atoms, the molecule is a branched hydrocarbon. Both wo-pentane and /w-pentane are branched hydrocarbons. 

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. 

The 2-bromopentane used in this preparation was prepared by the action of hydrobromic acid on secondary amyl alcohol (methyl M-propyl carbinol) obtained from Stanco Distributors, Inc. Other commercial straight chain amyl alcohols when converted to the bromides gave a pentane boiling at 33-3 50, showing that a considerable quantity of iso-pentane was present. 

Inject 0.1 n 1 samples of each of the following straight chain aliphatic ketones butan-2-one, pentan-3-one, pentan-2-one and heptan-3-one. After each injection clean the syringe by filling it with acetone and expelling the latter several times and finally evaporating the residual acetone as before. 

A geometrically accurate picture of a "straight" chain [32] of pentane modules would have the pentagons oriented in an alternating up and down pattern. 

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