1559r.ch03.38-5410/22/052:59Page42 EQA 42.Chapter 3 REACTIONS OF ALKANES analkane in which all hydrogens are chemically indistinguishable(methane.ethane.opent)bec ause they mined by the number of different types of hydrogens present and whether the desired product derives from substitution of a more reactive or a less reactive hydrogen in the molecule. ter example.there are one an carbon.a less CH: CHa-CH-CH3 Br2-CH3-C-CH3 Major product CH3-CH-CHs F2-F-CH2-CH-CHs Major product 3-10.Combustion and Relative Stability In order to obtain thermodynamic information experimentally.several methods may be used.The measure on.h the a ot a re sure of the energy content of the compound relative to that of the product molecules.COand HO.Such data ⊕ ve ent structure Solutions to Problems 13.This revious chapter.For shorthand purposes.we (a)CH:CH2CH2CHs (b)CH;CHzCH2CH2CHs 2 1 2° d”一HCH-” e CH2-CH2 14.(a Table2-4) CH.CH.CH.CH Primary (ess stable Remember:Identify radicals as 1 2.or 3 by the radical carbon.None of the other carbons matter.Two hyperconiugation pictures may be drawn for 1-methylpropyl radical.one with two42 • Chapter 3 REACTIONS OF ALKANES an alkane in which all hydrogens are chemically indistinguishable (methane, ethane, neopentane), because they can produce only one monohalogenation product. In the case of most alkanes, synthetic utility will be deter￾mined by the number of different types of hydrogens present and whether the desired product derives from substitution of a more reactive or a less reactive hydrogen in the molecule. In isobutane, for example, there are one 3° and nine 1° hydrogens. If we desire to halogenate at the 3° cen￾ter, the natural selectivity of bromine makes it the obvious halogen to choose. If we desire to halogenate a 1° carbon, a less selective, more reactive halogen would allow us to take best advantage of the statistical factor of nine possible 1° hydrogens available to be replaced in each molecule. Thus, 3-10. Combustion and Relative Stability In order to obtain thermodynamic information experimentally, several methods may be used. The measure￾ment of equilibrium constants gives energy differences between species. Directly measuring the heat of a re￾action accomplishes the same thing. When the reaction is combustion of a hydrocarbon, the result is a mea￾sure of the energy content of the compound relative to that of the product molecules, CO2 and H2O. Such data allow comparisons to be made between related compounds, which in turn reveal factors influencing the rela￾tive stabilities of different structures. Solutions to Problems 13. This problem is really a reminder of material from the previous chapter. For shorthand purposes, we use the symbols 1° primary, 2° secondary, and 3° tertiary. (a) (b) (c) (d) 14. (a) Remember: Identify radicals as 1°, 2°, or 3° by the radical carbon. None of the other carbons matter. Two hyperconjugation pictures may be drawn for 1-methylpropyl radical, one with two 1-Methylpropyl (sec-butyl; see Table 2-4) Secondary (2), more stable CH3CH2CHCH3 Butyl radical Primary (1), less stable CH3CH2CH2CH2 CH3 1 2 2 3 CH2 CH2 CH2 CH2 H C As you will see in Chapter 4, most “ring” compounds can be treated just like molecules without rings. CH3 1 1 2 3 CH3CH2CH2CH2CH3 1 2 1 CH3CH2CH2CH3 1 2 1 CH3 CH CH3
Br2 CH3 CH3 C CH3 Major product CH3 Br CH3 CH CH3
F2 F CH3 CH2 CH CH3 Major product CH3 1559T_ch03_38-54 10/22/05 2:59 Page 42