Pentane formulas

Bond line formula of n pentane Bond line formula of n hexane... 

Three isomeric alkanes have the molecular formula C5H12 The unbranched isomer is as we have seen n pentane The isomer with a single methyl branch is called isopen tane The third isomer has a three carbon chain with two methyl branches It is called neopentane... 

Photochemical chlorination of pentane gave a mixture of three isomenc monochlorides The pnncipal monochlonde constituted 46% of the total and the remaining 54% was approximately a 1 1 mixture of the other two isomers Write structural formulas for the three monochlonde iso mers and specify which one was formed in greatest amount (Recall that a secondary hydrogen is abstracted three times faster by a chlonne atom than a pnmary hydrogen)... 

There are three isomeric pentanes, ie, saturated aHphatic hydrocarbons of molecular formula C H 2- They are commonly called / -pentane [109-66-0] isopentane [78-78-4] (2-methylbutane), and neopentane [463-82-1] (2,2-dimethylpropane). 

The next six alkanes are named pentane, hexane, heptane, octane, nonane, and decane. Their molecular formulas are CjHij, C5H14, CjHjg, C Hjg and... 

With the five-carbon alkane, pentane, there are three ways to draw the structural formula of this compound with five carbon atoms and twelve hydrogen atoms. The isomers of normal pentane are isopentane and neopentane. The structural formulas of these compounds are illustrated in Table 2, while typical properties are given in Table 1. 

Table 2. Illustrates the Structural Formulas for Isomers of Pentane.

Note that whereas n-, neo-, and isopentanes have the same molecular formula, C5H12, and are therefore isomers, cyclopentane has the formula C5H10, and so is not an isomer of the open-chained pentanes. 

Dispersion forces increase in strength with the number of electrons, because larger electron clouds are more polarizable than smaller electron clouds. For molecules with comparable numbers of electrons, the shape of the molecule makes an important secondary contribution to the magnitude of dispersion forces. For example. Figure 11-11 shows the shapes of pentane and 2,2-dimethylpropane. Both of these molecules have the formula C5 H12, with 72 total electrons. Notice that 2,2-dimethylpropane has a more compact structure than pentane. This compactness results in a less polarizable electron cloud and smaller dispersion forces. Accordingly, pentane has a boiling point of 36 °C, while 2,2-dimethylpropane boils at 10 °C. 

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. 

Similarly, three isomers of pentane, C5H12, exist. As the number of carbon atoms in a molecule increases, the number of possible isomers increases markedly. Theoretically, for the formula c2()h... 

Write structural formulas for the three isomers of pentane. 

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. 

This model is, in any case, unacceptable Examination of formula 70 shows that, according to what was previously stated regarding the n-pentane, in the G G conformation two carbon atoms approach to about 2.5 A and consequently this conformation has little probability of existence. The introduction of correlation between adjacent rotation angles entails the use of a mathematical formulation (the matrix multiplication method) which will not be discussed here the reader is referred to the texts cited and to the specialized literature for details. 

Problem 12 Show the 3 isomers of pentane as condensed structural formulas. 

Symmetry leads to more order, which in turn leads to a decrease in entropy. Consider the three isomers pentane, isopentane, and neopentane, with symmetry numbers a =2, 1 and 12, respectively (table 4.22). When placed in a two-dimensional lattice, neopentane can be represented as a cross, and there is only one configuration possible, W =. Isopentane can have W = 2, but the flexible pentane has nine configurations. The experimental entropies at 25 °C support the expectation that pentane should have a somewhat higher entropy than isopentane. The even more rigid neopentane may be expected to have a smaller entropy due to the lower flexibility however, the higher symmetry contributes to an additional large drop of entropy according to the formula A5 = -/ ln(a) = 20.7. 

Octane A hydrocarbon with the formula C8H18 having 18 different isomers. These isomers have typical boiling points between 210.2°F and 257°F (99°C and 125°C). The most important of these isomers is 2,2,4-trimethyl pentane or isooctane. It is a colorless liquid with a boiling point of 210.2°F (99°C) and is used as a standard for rating the antiknock properties of gasoline. 

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 ... 

Problem 2.17 The boiling points of n-pentane and its isomer neopeniane are 36.2 °C and 9.5 °C, respectively. Account for this difference. (See Problem 1.4 for the structural formulas.) ... 

Problem 6.13 Give the structural formulas for the alkenes formed on dehydrobromination of the following alkyl bromides and underline the principal product in each reaction (a) 1-bromobutane, (b) 2-bromobutane, (c) 3-bromopentane, (d) 2-bromo-2-methylpentane, (e) 3-bromo-2-methylpentane, (/) 3-bromo-2,3-dimethyl-pentane. ... 

Continuing in the alkane series (also called the paraffin series because the first solid hydrocarbon in the series is paraffin, or candle wax), the next compound is pentane. This name is derived from the Greek word penta, for five. As its name implies, it has five carbon atoms, and its molecular formula is C,H12. From pentane on, the Greek prefix for the numbers five, six, seven, eight, nine, ten, and so on are used to name the alkanes, the Greek prefix corresponding to the number of carbon atoms in the molecule. The first four members of the alkane series do not use the Greek... 

Figure 1. Illustrates the structural formulas for isomers of butane and pentane.

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