Writing Organic Structures

Write the resonance structure obtained by nnoving electrons as indicated by the curved arrows. Compare the stabilities of the two Lewis structures according to the guidelines in Table 1.6. Are the two Lewis structures equally stable, or is one more stable than the other Why  

Sample Solution (a) The curved arrow shows how we move an unshared electron pair assigned to oxygen so that it becomes shared by carbon and oxygen. This converts a single bond to a double bond and leads to a formal charge of +1 on oxygen. 

The Lewis structure on the right is more stable because it has one more covalent bond than the original structure. Carbon did not have an octet of electrons in the original structure, but the octet rule is satisfied for both carbon and oxygen in the new Lewis structure. 

It is good chemical practice to represent molecules by their most stable Lewis structure. However, the ability to write alternative resonance forms and to assess their relative contributions can provide insight into both molecular structure and chemical behavior. 

Organic chemists use a number of shortcuts to speed the writing of structural formulas. Sometimes we leave out unshared electron pairs, but only when we are sure of our ability to count electrons to know when they are present and when they are not. In condensed formulas we leave out some, many, or all of the covalent bonds and use subscripts to indicate the number of identical groups attached to a particular atom. These successive levels of simplification are illustrated for diethyl ether, written first as 

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In writing organic structures, we often use primes when we wish to specify that the alkyl groups might be different, for example, R, R, R". 

Write the structure of the major organic product formed in the... 

Write a structural formula for the principal organic product... 

Write the structure of the principal organic product obtained on nitration of each of the following... 

Table 1.4 in this section sets forth the procedure to be followed in writing Lewis structures for organic molecules. It begins with experimentally deter-mined infor-mation the molecular formula and the constitution (order in which the atoms are connected). 

Each of the following reactions has been described in the chemical literature and involves an organic starting material somewhat more complex than those we have encountered so far. Nevertheless, on the basis of the topics covered in this chapter, you should be able to write the structure of the principal organic product of each reaction. 

Write the structural formula for the product of (a) the reaction of glycerol (1,2,3-trihydroxypropane) with stearic acid, CH5(CH2)16COOH, to produce a saturated fat (b) the oxidation of 4-hydroxybenzyl alcohol by sodium dichromate in an acidic organic solvent. 

In this question consider organic molecule with no rings or carbon-to-carbon double or triple bonds, (a) Show that ethers can be isomers of alcohols but not of aldehydes, (ft) Show that aldehydes and ketones can be isomers of each other, but not of acids or alcohols, (c) Write the structural formula for an alcohol isomeric with diethyl ether. 

Every once in a while you may run into an organic chemistry problem in Section II, on writing equations. An example is Write an equation that describes burning methanol in air. You would need to know the chemical formula and structural formula of methanol in order to do this problem. Writing organic reactions is covered in more detail in the chapter entitled Writing and Predicting Chemical Reactions. ... 

In writing structural isomers as well as any organic compound, remember that carbon forms four bonds One of the most common mistakes that a chemistry student makes is writing an organic structure with a carbon atom having less or more than four bonds. 

Write the structures of the following organic halogen compounds. 

Problem 6.19 Write the structural formula and name of the principal organic compound formed in the following reactions ... 

Problem 8.39 Write a structural formula for organic compounds (A) through (N) ... 

Problem 16.60 Name and write the structures of the main organic products (a) H2C=XHCH2l heated with NaCN b) CHjCH CONH, heated with P,0, (c) p-iodobenzyl bromide reacted with CH,COOAg (d) nitration of benzamide. M... 

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