CHAPTER FIVE Structure and Preparation of Alkenes: Elimination Reactions Br"Higher Lower Lower Lower Z configuration E configuration Higher ranked substituents(CI and Br) Higher ranked substituents(CI and Br) are on opposite sides of double bond he substituent groups on the double bonds of most alkenes are, of course, more com- ped by R. 5. Cahn and Sir plicated than in this example. The rules for ranking substituents, especially alkyl groups, are described in Table 5.1 and Vladimir Prelog (Switzer and)in the context of a dif- ferent aspect of organic PROBLEM 5.6 Determine the configuration of each of the following alkene stereochemistry,they will ap.Z or E as appropriate hapter 7 a)H2C、 CH2OH (c)H3c CH2CH2OH (b)H3C CH2 CH2F CH2CH2 CH2 CH3 CH3 CH2 SAMPLE SOLUTION (a)One of the doubly bonded carbons bears a meth group and a hydrogen. According to the rules of Table 5.1, methyl outranks hydro- gen. The other carbon atom of the double bond bears a methyl and a-CH2OH group. The -CH2OH group is of higher priority than methyl s HaO CH2OH+ Higher CO, H, H Lower(H)、H CH3← s Lower C(H,H, H) Higher ranked substituents are on the same side of the double bond; the config uration is Z a table on the inside back cover(right page)lists some of the more frequently encountered atoms and groups in order of increasing precedence. You should not attempt to memorize this table, but should be able to derive the relative placement of one group versus another 5.5 PHYSICAL PROPERTIES OF ALKENES Alkenes resemble alkanes in most of their physical properties. The lower molecular weight alkenes through CAHs are gases at room temperature and atmospheric pressur The dipole moments of most alkenes are quite small. Among the Isomers I-butene, cis-2-butene, and 2-methylpropene have dipole moments in the 0.3-0.5 D range; trans-2-butene has no dipole moment. Nevertheless, we can learn some things about alkenes by looking at the effect of substituents on dipole moments. Experimental measurements of dipole moments give size, but not direction. We mally deduce the overall direction by examining the directions of individual bond Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteThe substituent groups on the double bonds of most alkenes are, of course, more com￾plicated than in this example. The rules for ranking substituents, especially alkyl groups, are described in Table 5.1. PROBLEM 5.6 Determine the configuration of each of the following alkenes as Z or E as appropriate: (a) (c) (b) (d) SAMPLE SOLUTION (a) One of the doubly bonded carbons bears a methyl group and a hydrogen. According to the rules of Table 5.1, methyl outranks hydro￾gen. The other carbon atom of the double bond bears a methyl and a ±CH2OH group. The ±CH2OH group is of higher priority than methyl. Higher ranked substituents are on the same side of the double bond; the config￾uration is Z. A table on the inside back cover (right page) lists some of the more frequently encountered atoms and groups in order of increasing precedence. You should not attempt to memorize this table, but should be able to derive the relative placement of one group versus another. 5.5 PHYSICAL PROPERTIES OF ALKENES Alkenes resemble alkanes in most of their physical properties. The lower molecular weight alkenes through C4H8 are gases at room temperature and atmospheric pressure. The dipole moments of most alkenes are quite small. Among the C4H8 isomers, 1-butene, cis-2-butene, and 2-methylpropene have dipole moments in the 0.3–0.5 D range; trans-2-butene has no dipole moment. Nevertheless, we can learn some things about alkenes by looking at the effect of substituents on dipole moments. Experimental measurements of dipole moments give size, but not direction. We normally deduce the overall direction by examining the directions of individual bond Higher Lower Higher Lower ±C(O,H,H) ±C(H,H,H) (C) (H) H3C H CH2OH CH3 C C CH3CH2 H CH3 C C H3C H CH2CH2F CH2CH2CH2CH3 C C H3C H CH2CH2OH C(CH3)3 C C H3C H CH2OH CH3 C C Cl Br F Higher Lower Higher Lower C H C Z configuration Higher ranked substituents (Cl and Br) are on same side of double bond Cl F Br Higher Lower Lower Higher C H C E configuration Higher ranked substituents (Cl and Br) are on opposite sides of double bond 174 CHAPTER FIVE Structure and Preparation of Alkenes: Elimination Reactions The priority rules were devel￾oped by R. S. Cahn and Sir Christopher Ingold (England) and Vladimir Prelog (Switzer￾land) in the context of a dif￾ferent aspect of organic stereochemistry; they will ap￾pear again in Chapter 7. The physical properties of se￾lected alkenes are collected in Appendix 1. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website