Neopentane structural formula

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. 

There is one more alkane with molecular formula C6H 2, called neopentane. Draw its structural formula. 

Problem 2.16 The boiling points of n-pentane and its isomer neopentane are 36.2 C and 9.5"C, respectively. Account for this difference (see Problem l.4 for the structural formulas.) -4... 

There is significant information encoded in structural formulas, however, the information is essentially qualitative. It is true that molecules described by different structures have different properties and that a ranking of expected properties may be predicted from the formulas of isomers however, the structural formula lacks a quantitative character. How numerically different are pentane, isopentane and neopentane The structural formula representation has usually been considered outside the realm of quantitative structure description, bounded by quantum mechanics and a count of atoms. 

So we can draw three (and only three) different structural formulas that correspond to the molecular formula C5H12, and in fact, we find that only three different chemical substances with this formula exist. They are commonly called -pentane (n for normal, with an unbranched carbon chain), isopentane, and neopentane. 

Isobutane, isopentane, and neopentane are common names or trivial names, meaning historical names arising from common usage. Common names cannot easily describe the larger, more complicated molecules having many isomers, however. The number of isomers for any molecular formula grows rapidly as the number of carbon atoms increases. For example, there are 5 structural isomers of hexane, 18 isomers of octane, and 75 isomers of decane We need a system of nomenclature that enables us to name complicated molecules without having to memorize hundreds of these historical common names. 

There are three alkanes with molecular formula C5H12. Pentane is the straight-chain alkane. Isopentane, as its name indicates, has an iso stmctural unit and five carbon atoms. The third isomer is called neopentane. The structural unit with a carbon surrounded by four other carbons is called neo. ... 

Butane and isobutane have the same molecular formula C4H10- The two compounds have their atoms connected in a different order and are, therefore, constitutional isomers (Section 1.3). Pentane, isopentane, and neopentane are also constitutional isomers. They, too, have the same molecular formula (C5H12) but have different structures. 

Effect of molecular shape. For a pair of nonpolar substances with the same molar mass, stronger attractions occur for a molecular shape that has more area over which the electrons can be distorted. For example, the two five-carbon alkanes, n-pentane and neopentane (2,2-dimethylpropane) are structural isomers— same molecular formula (C5H12) but different properties. n-Pentane is more cylindrical and neopentane more spherical (Figure 12.15). Thus, two -pentane molecules make more contact than do two neopentane molecules, so dispersion forces act at more points, and n-pentane has a higher boiling point. 

Recall from Section 3.2 that two or more compounds with the same molecnlar formula but different properties are called isomers. Those with different arrangements of bonded atoms are constitutional (or structural) isomers alkanes with the same number of C atoms but different skeletons are examples. The smallest alkane to exhibit constitutional isomerism has fonr C atoms two different compounds have the formula C4H10 (Table 15.3). The unbranched one is butane (common name, n-butane n- stands for normal, or having a straight chain), and the other is 2-methylpropane (common name, wobntane). Similarly, three compounds have the formula C5H12. The unbranched isomer is pentane (common name, n-pentane) the one with a methyl group at C-2 of a four-C chain is 2-methylbntane (common name, isopentane). The third isomer has two methyl branches on C-2 of a three-C chain, so its name is 2,2-dimethylpropane (common name, neopentane). 

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