Chapter 4 - Instructor Supplemental Solutions to Problems...

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Instructor Supplemental Solutions to Problems © 2010 Roberts and Company Publishers Chapter 4 Introduction to Alkenes. Structure and Reactivity Solutions to In-Text Problems 4.1 (b) 3-Hexene can exist as both cis and trans isomers; both carbons of the double bond (carbons 3 and 4) are stereocenters. (d) 2-Methyl-2-pentene cannot exist as cis, trans isomers because two of the groups at one carbon of the double bond are the same (the methyl groups). This molecule contains no stereocenters. 4.2 (b) (d) Some chemists were educated in nomenclature to understand that if the position of a substituent is unambiguous it need not be cited by number. Thus, compound (b) could be called methylpropene, because the methyl substituent must be on carbon-2. That is, if it is on carbon- 1, the compound would not be named as a propene; it would be named as a butene. None of the formal “rule books” on nomenclature support this idea. Hence, we number all substituents. The 1993 nomenclature recommendations of the IUPAC went a step further and recommended numbering not only substituents, but also all double bonds, whether ambiguous or not; furthermore, the number is always cited before the suffix “ene.” Thus, compound (b) in the 1993 system is called 2-methylprop-1-ene. (The 1993 recommendations are discussed in the sidebar on text p. 134.) A positive aspect of this recommendation is that it creates consistency in the way that all alkene names are constructed. However, this recommendation has not yet been generally accepted, and for that reason it has not been used in this text. 4.3 (b) 3-Heptene 4.4 (b) ( Z )-3-Isopropyl-2-hexene 4.5 (b)
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INSTRUCTOR SUPPLEMENTAL SOLUTIONS TO PROBLEMS • CHAPTER 4 2 4.6 (b) (d) 4.7 (b) Use Eq. 4.7 on text p. 139 to obtain U = 3. 4.8 (b) The prefix “cyclo” as well as the suffix “ane” indicates that the compound has one ring; consequently, U = 1. 4.10 (a) This cannot be a correct formula, because a compound containing only C, H, and an odd number of nitrogens must have an odd number of hydrogens. Another way to tell whether a formula is reasonable is to calculate its unsaturation number using Eq. 4.7 on text p. 139. A formula that gives a negative or fractional unsaturation number is not possible. (b) This could be the formula of an organic compound. (c) This could not be the formula of an organic compound, because the maximum number of hydrogens possible in a compound containing 10 carbons, 3 nitrogens, and any number of oxygens is 25. (d) This could be the formula of an organic compound. 4.11 (b) In propene, the H 3 C—C bond dipole adds vectorially to the smaller H—C bond dipole; the resultant is smaller than the H 3 C—C bond dipole itself, as the following diagram shows. In 2-methylpropene, the resultant of the two H 3 C—C bond dipoles is about equal in magnitude to one H 3 C—C bond dipole. (This can be shown analytically if we assume 120° bond angles.) 2-Methylpropene has a somewhat greater dipole moment. (In the following vector analysis, the H—C bond dipoles of the CH
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Chapter 4 - Instructor Supplemental Solutions to Problems...

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