Isopentane 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. 

Problem 4.27 Write the structural formulas and give the IUPAC names for all monochloro derivatives of (a) isopentane, (CH3)2CHCH2CH3 (b) 2,2,4-trimethylpentane, (CH3)3CCH2CH(CH3)2. ... 

P oUem 7.2 Isopentane is allowed to undergo free-radical chlorination, and the reaction mixture is separated by careful fractional distillation, (a) How many frac tions of formula CsHnCl would you expect to collect (b) Draw structural formulas, stereochemical where pertinent, for the compounds making up each fraction. Specify each enantiomer as R or S. (c) Which if any, of the fractions, as collected, would show optical activity (d) Account in detail—just as was done in the preceding section— for the optical activity or inactivity of each fraction. 

The answer to the first question is that you cannot easily calculate the number of isomers. The data in Table 2.3 were determined by a mathematician who concluded that there was no simple expression from which to calculate the number of isomers. The best way to ensure that you have written all the isomers of a particular molecular formula is to work systematically, beginning with the unbranched chain and then shortening it while adding branches one by one. It is essential that you be able to recognize when two different-looking structural formulas are actually the same molecule written in different ways. The key point is the connectivity of the carbon chain. For example, the following group of structural formulas do not represent different compounds they are just a portion of the many ways we could write a structural formula for isopentane. Each one has a continuous chain of four carbons with a methyl branch located one carbon from the end of the chain. 

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. ... 

The three pentanes, which are known, can be prepared by methods which indicate that they have the structures represented by the formulas deduced above. These hydrocarbons are not appreciably affected by acids, bases, or oxidizing agents. They react with chlorine and bromine, and burn in the air. Normal pentane boils at 36.3° isopentane, or dimethyl-ethyl-methane at 27.9°, and tetramethyl-methane at 9.5°. It has been observed as the result of the study of a number of hydrocarbons that isomers have different boiling points, and, in general, the isomer with the longer chain has the higher boiling point. In normal pentane there is a chain of five carbon atoms, in isopentane a chain of four, and in tetramethyl-methane a chain of three. 

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. 

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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