Passage
Aldehydes are organic compounds encountered in everyday life and used as intermediates in metabolism. 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
-Do aldehydes and ketones tend to have higher or lower boiling points than their corresponding alcohols?

Question

Passage
Aldehydes are organic compounds encountered in everyday life and used as intermediates in metabolism. 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
-Do aldehydes and ketones tend to have higher or lower boiling points than their corresponding alcohols?

Quizplus · Accepted Answer

11ecba2d_125e_3087_a3bf_c59659dec7c0_MD0008_00 The boiling point of a substance depends on the strength of the intermolecular forces holding molecules together. Stronger intermolecular forces require more energy to break and therefore contribute to higher boiling points. The electronegative oxygen in the hydroxyl (-OH) group of alcohols pulls electron density away from hydrogen, creating a dipole in which oxygen has a partial negative charge and hydrogen has a partial positive charge. Because opposite charges attract, the dipole provides an increase in intermolecular forces and therefore an increase in boiling point relative to alkanes. In addition, the hydroxyl group can act as both a hydrogen bond donor and hydrogen bond acceptor, allowing alcohols to form hydrogen bonds with themselves and further increasing intermolecular forces. Ketones and aldehydes contain carbonyls, in which the electronegative oxygen has a partial negative charge and the carbon has a partial positive charge. Like alcohols, ketones and aldehydes have dipoles and therefore have stronger intermolecular interactions than alkanes. Unlike alcohols, aldehydes and ketones have hydrogen bond acceptors but not donors, so they cannot form hydrogen bonds with themselves. Therefore, they have lower boiling points than their corresponding alcohols. (Choices A and B) An increased oxidation state and a dipole moment cause the boiling point of ketones and aldehydes to increase with respect to their analogous alkanes but not sufficiently enough to exceed the boiling point of their corresponding alcohols, which can form hydrogen bonds. (Choice D) Ketones and aldehydes have increased intermolecular forces relative to alkanes but not alcohols. Furthermore, the increased forces contribute to raising the boiling point, not lowering it. Educational objective: Ketones and aldehydes contain carbonyls, which create dipoles and increased intermolecular forces. Because the oxygen of the carbonyl can accept but not donate hydrogen bonds, ketones and aldehydes cannot form hydrogen bonds with themselves. Alcohols have dipoles and can form hydrogen bonds with themselves, resulting in a higher boiling point than ketones and aldehydes.

Passage Aldehydes Are Organic Compounds Encountered in Everyday Life and Used