Bond-line structures drawing

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. 

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 ... 

Every pair of bonded atoms shares one or more pairs of electrons. Each bond line we draw in a Lewis structures represents two shared electrons. In every cr bond at least one pair of electrons is localized in the space between the atoms. The appropriate set of hybrid orbitals used to form the cr bonds between an atom and its neighbors is determined by the observed geometry of the molecule. The correlation between the set of hybrid orbitals and the geometry about an atom is given in Table 9.4. 

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. 

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. 

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... 

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 ... 

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. 

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 ... 

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 ... 

Bond-line structures are faster to draw and easier to interpret than other drawing styles. 

Draw bond-line structures for all constitutional isomers... 

Drawing and Interpreting Bond-Line Structures (Section 2.2) Identifying Lone Pairs (Section 2.5)... 

There are five constitutional isomers with molecular formula C6H14. Draw a bond-line structure for each isomer and identify the parent in each case. 

Draw bond-line structures using wedges and dashes for the following compounds ... 

LEARN the skill Draw a bond-line structure showing the tripeptide Phe-Val-Trp (assume that all three residues are L amino acids). 

Draw a bond-line structure of the peptide that corresponds with the following sequence of amino acid residues, and identify the N terminus and C terminus ... 

Methionine enkephalin is a pentapeptide that is produced by the body to control pain. From the sequence of its amino acid residues, draw a bond-line structure of methionine enkephalin. 

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