Aldehydes are organic compounds used as intermediates in metabolism and are also encountered in everyday life.  Common aldehydes include formaldehyde, which is used in the fixation of tissues, and cinnamaldehyde, which provides the flavor and smell of cinnamon (Figure 1).Figure 1  Common aldehydesThe aldol condensation shown in Figure 2 is an important carbon-carbon bond-forming reaction that has many applications in the synthesis of bioactive molecules.  It also takes place in some metabolic processes, such as the citric acid cycle and gluconeogenesis.  The aldol condensation begins with the aldol reaction, which can be acid- or base-catalyzed and requires nucleophilic addition to a carbonyl to provide the aldol product, which can be a β-hydroxy ketone or aldehyde.  The final step of the aldol condensation consists of an acid- or base-catalyzed dehydration of the aldol product to yield an α,β-unsaturated ketone or aldehyde.Figure 2  General aldol reaction and condensationThe reverse of an aldol reaction or condensation is known as a retro-aldol, which is important in metabolism, most notably in glycolysis.  This reaction breaks a carbon-carbon bond to form aldehydes and/or ketones.  In glycolysis, fructose 1,6-bisphosphate is broken down into an aldehyde and a ketone, glyceraldehyde 3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP), respectively (Figure 3).Figure 3  Retro-aldol in glycolysis Question 35Do aldehydes and ketones tend to have higher or lower boiling points than their corresponding alcohols?A.Higher, because they are at a higher oxidation stateB.Higher, because they have a dipole momentC.Lower, because they cannot form hydrogen bonds with each otherD.Lower, because they have increased intermolecular forces