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24 Organic and Biological Chemistry Solutions to Exercises 24.42 -5157 kJ -(-6286) kJ +1129kJ 5(-285.8) kJ Compare this with the heat of hydrogenation of ethylene: + H₂(g) -> C₂H₆(g); = -84.7 - (52.3) = -137 kJ. This value applies to just one double bond. For five double bonds, we would expect about -685 kJ. The fact that hydrogenation of napthalene yields only -300 kJ indicates that the overall energy of the napthalene molecule is lower than expected for five isolated double bonds and that there must be some special stability associated with the aromatic system in this molecule. Functional Groups and Chirality (sections 24.4 and 24.5) 24.43 Analyze/Plan. Match the structural features of various functional groups shown in Table 24.6 to the molecular structures in this exercise. Solve. (a) -OH, alcohol (b) -NH- amine; alkene (c) ether (d) ketone; -C=C-, alkene (e) CH (-CHO), aldehyde (f) -C=C-(-CC-), alkyne; -COOH, carboxylic acid 24.44 (a) ester (b) halocarbon; -OH, alcohol (aromatic alcohols are phenols) (c) amide (d) alkane (e) alkene; CH aldehyde (f) C ketone 24.45 Analyze/Plan. Given the name of a molecule, write the structural formula of an isomer molecular formula of the given molecule, draw the structural formula of a molecule with the same formula that contains the specified functional group. Solve. 732