CHAPTER ELEVEN Arenes and Aromaticity FIGURE 11.2 Heats of hydro An imaginary molecule. 3-cyclohexadiene, a hyp cyclohexatriene thetical 1, 3, 5-cyclohexatriene and benzene. All heats of hy drogenation are in kilojoules per mole. 3×120 2H,+ 231 A real We reach a similar conclusion when comparing benzene with the open-chain con- jugated triene(Z)-1, 3, 5-hexatriene. Here we compare two real molecules, both conju gated trienes, but one is cyclic and the other is not. The heat of hydrogenation of(z)- 1, 3, 5-hexatriene is 337 kJ/mol (80.5 kcal/mol), a value which is 129 kJ/mol (30.7 kcal/mol) greater than that of benzene H H H +3H2—>CH3CH2)4CH3△H=-337kJ H (-80.5kca) (2)-1, 3, 5-Hexatriene Hydrogen The precise value of the resonance energy of benzene depends, as comparisons with 1, 3, 5-cyclohexatriene and(Z)-1, 3, 5-hexatriene illustrate, on the compound chosen as the reference. What is important is that the resonance energy of benzene is quite large, six to ten times that of a conjugated triene. It is this very large increment of resonance energy that places benzene and related compounds in a separate category that we cal aromatic PROBLEM 11.2 The heats of hydrogenation of cycloheptene and 1, 3, 5-cyclo- heptatriene are 110 kJ/mol (26. 3 kcal/mol) and 305 kJ/mol (73.0 kcal/mol), respec tively. In both cases cycloheptane is the product What is the resonance energy of 1, 3,5-cycloheptatriene? How does it compare with the resonance energy of ben Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteWe reach a similar conclusion when comparing benzene with the open-chain con￾jugated triene (Z)-1,3,5-hexatriene. Here we compare two real molecules, both conju￾gated trienes, but one is cyclic and the other is not. The heat of hydrogenation of (Z)- 1,3,5-hexatriene is 337 kJ/mol (80.5 kcal/mol), a value which is 129 kJ/mol (30.7 kcal/mol) greater than that of benzene. The precise value of the resonance energy of benzene depends, as comparisons with 1,3,5-cyclohexatriene and (Z)-1,3,5-hexatriene illustrate, on the compound chosen as the reference. What is important is that the resonance energy of benzene is quite large, six to ten times that of a conjugated triene. It is this very large increment of resonance energy that places benzene and related compounds in a separate category that we call aromatic. PROBLEM 11.2 The heats of hydrogenation of cycloheptene and 1,3,5-cyclo￾heptatriene are 110 kJ/mol (26.3 kcal/mol) and 305 kJ/mol (73.0 kcal/mol), respec￾tively. In both cases cycloheptane is the product. What is the resonance energy of 1,3,5-cycloheptatriene? How does it compare with the resonance energy of ben￾zene? H°  337 kJ (80.5 kcal) H H H H H H H H (Z)-1,3,5-Hexatriene 3H2 Hydrogen CH3(CH2)4CH3 Hexane 404 CHAPTER ELEVEN Arenes and Aromaticity Energy 2H2 H2 120 231 208 152 3H2 A real molecule, benzene An imaginary molecule, cyclohexatriene 3  120  360 3H2 FIGURE 11.2 Heats of hydro￾genation of cyclohexene, 1,3-cyclohexadiene, a hypo￾thetical 1,3,5-cyclohexatriene, and benzene. All heats of hy￾drogenation are in kilojoules per mole. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website