Applications to Other Types of Systems

Exercise 21-2 Calculate the heat of formation of 1,3-butadiene in the gas phase at 

25° from the bond energies in Table 4-3 and the knowledge that AH° for C(s)------  

C4H6(g). The experimental value of the heat of formation is 26.3 kcal. Calculate the stabilization energy of 1,3-butadiene. 

Many important molecules have alternating single and double bonds (are conjugated), but have atoms that are more (or less) electron-attracting than carbon. An example is propenal (acrolein), 18  

With such molecules we need to take into account the fact that the it electrons will be attracted to oxygen from carbon, because oxygen is more elecvronega-tive than carbon. With the VB method we can do this by considering ionic electron-pairing schemes, 18c and 18d, along with the dienelike structures, 

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In 1980, Sindorf and Maciel " published the first high-resolution example of the use of X CP for surface-selective X detection in a demonstration of H- Si CP in silica gel. Since that time, Si CP has remained the most popular application of this strategy, although there has been significant success with applications to other types of systems. Figure 34.2 shows typical Si spectra of silica gel and related samples obtained by CP-MAS and direct polarization (DP) MAS (based on Si spin-lattice relaxation, not CP). 

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