Line-bond structure

It is not practical to draw Lewis structures for all compounds, especially large ones. As an example, consider the structure of amoxicillin, one of the most commonly used antibiotics in the penicillin family  

Previously fatal infections have been rendered harmless by antibiotics such as the one above. Amoxicillin is not a large compound, yet drawing this compound is time consuming. To deal with this problem, organic chemists have developed an efficient drawing style that can be used to draw molecules very quickly. Bond-line structures not only simplify the drawing process but also are easier to read. The bond-line structure for amoxicillin is 

You may find it worthwhile to purchase or borrow a molecular model set. There are several different kinds of molecular model sets on the market, and most of them are comprised of plastic pieces that can be connected to generate models of small molecules. Any one of these model sets will help you to visualize the relationship between molecular structures and the drawings used to represent them. 

Most of the atoms are not drawn, but with practice, these drawings will become very user-friendly. Throughout the rest of this textbook, most compounds will be drawn in bond-line format, and therefore, it is absolutely critical to master this drawing technique. The following sections are designed to develop this mastery. 

Bond-hne structures are drawn in a zigzag format ( ), where each corner or endpoint 

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In Chapter 1, we introduced one of the best ways of drawing molecules, bond-line structures. They are fast to draw and easy to read, but they have one major deficiency they do not describe molecules perfectly. In fact, no drawing method can completely describe a molecule using only a single drawing. Here is the problem. 

Figure 4.10 AX4, AX3E, and AX2E2 molecules (a) tangent sphere models or domain models with spherical domains B is a bonding pair and E is a lone pair and (b) conventional bond line structures.

Before we can talk about drawing Newman projections, we need to first review one aspect of drawing bond-line structures that we did not cover in Chapter l. To show how groups are positioned in 3D space, we often use wedges and dashes ... 

Bond-Line Structures (Molecular Graphs) 284 Alkyl Groups 284... 

You should be able to draw chemical formulas that show all of the valence electrons in a molecule (Lewis structures), using lines for bonds and dots to show unshared electrons. You should be proficient in representing structures as dash structural formulas, condensed structural formulas, and bond-line structural formulas. In particular, the more quickly you become skilled at using and interpreting bondline formulas, the faster you will be able to process structural information in organic chemistry. You have also learned about resonance structures, the use of which wiU help us in understanding a variety of concepts in later chapters. 

PRACTICE PROBLEM 2.10 Write bond-line structural formulas for (a) two constitutionally isomeric primary alkyl... 

One way of naming ethers is to name the two alkyl groups attached to the oxygen atom in alphabetical order and add the word ether. If the two alkyl groups are the same, we use the prefix di-, for example, as in dimethyl ether. Write bond-line structural formulas for (a) diethyl ether, (b) ethyl propyl ether, and (c) ethyl isopropyl ether. What name would... 

Write condensed and bond-line structural formulas for all of the constitutional isomers PRACTICE PROBLEM 4.1 with the molecular formula CyH-ie. (There are a total of nine constitutional isomers.)... 

Write bond-line structures for the keto and enol forms of 3-pentanone. 

In order to compare the structures of the compounds being discussed, we will need a more efficient way to draw the structures of organic compounds. Lewis structures are only efficient for small molecules, such as those we considered in the previous chapter. The goal of this chapter is to master the skills necessary to use and interpret the drawing method most often utilized by organic chemists and biochemists. These drawings, called bond-line structures, are fast to draw and easy to read, and they focus our attention on the reactive centers in a compound. In the second half of this chapter, we will see that bond-line structures are inadequate in some circumstances, and we will explore the technique that chemists employ to deal with the inadequacy of bond-line structures. 

Hydrogen atoms bonded to carbon are also not shown in bond-line structures, because it is assumed that each carbon atom will possess enough hydrogen atoms so as to achieve a total of four bonds. For example, the highlighted carbon atom below appears to have only two bonds ... 

It is certainly important to be able to read bond-line structures fluently, but it is equally important to be able to draw them proficiently. When drawing bond-line structures, the following rules should be observed ... 

Draw a bond-line structure for the following compound ... 

Drawing a bond-line structure requires just a few conceptual steps. First, delete all hydrogen atoms except for those connected to heteroatoms ... 

In Section 1.4 we saw that a formal charge is associated with any atom that does not exhibit the appropriate number of valence electrons. Formal charges are extremely important, and they must be shown in bond-Hne structures. A missing formal charge renders a bond-line structure incorrect and therefore useless. Accordingly, let s quickly practice identifying formal charges in bond-line structures. 

Formal charges must always be drawn and can never be omitted, unlike lone pairs, which may be omitted from a bond-line structure. 

Therefore, a bond-line structure will only be clear if it contains either all of the lone pairs or all of the formal charges. Since there are typically many more lone pairs than formal charges in any one particular structure, chemists have adopted the convention of always drawing formal charges, which allows us to leave out the lone pairs. 

Bond-line structures with wedges and dashes to indicate three dimensionality. 

The approach that chemists use to deal with the inadequacy of bond-line structures is called resonance. According to this approach, we draw more than one bond-fine structure and then mentally meld them together ... 

The violation in each example above is clear, but with bond-line structures, it can be more difficult to see the violation because the hydrogen atoms are not drawn (and, very often, neither are the lone pairs). Care must be taken to see the hydrogen atoms even when they are not drawn ... 

Earlier in this chapter, we said that it is not necessary to draw lone pairs, because they are implied by bond-line structures. In the example above, the lone pairs are shown for clarity. This raises an obvious question. Look at the first curved arrow above the tail is drawn on a lone pair. If the lone pairs had not been drawn, how would the curved arrow be drawn In situations like this, organic chemists will sometimes draw the curved arrow coming from the negative charge ... 

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