Passage
Ethanol is an important source of energy that is frequently used as a supplement to gasoline. It can be obtained from renewable resources such as the cellulose found in plant matter. When subjected to a process called gasification, the plant mass is converted to a mixture called syngas, composed predominantly of carbon monoxide and molecular hydrogen. Syngas can be passed over a rhodium catalyst to generate ethanol and other products. After using this method, a group of researchers analyzed the resulting products by gas chromatography using helium as a carrier gas. The results are shown in Figure 1.
Figure 1 Gas chromatograph of syngas catalysis productsMass spectrometry revealed that the process yielded similar amounts of ethanol, acetic acid, and acetaldehyde, with trace amounts of ethane. In addition, the ethanol peak was found to be contaminated with ethyl acetate. Another group of researchers in the same laboratory had recently produced Compound 1 as a by-product in a separate reaction. They combined Compound 1 with purified ethyl acetate to form megestrol acetate, a drug used in the treatment of certain cancers. This reaction also produced ethanol, as shown in Scheme 1.
Scheme 1
Adapted from Lopez L, Velasco J, Montes V, Marinas A, Cabrera S, Boutonnet M, Järås S. Catalysts 2015.
- What atom indicated would be most readily deprotonated if Compound 2 reacts with NaOH?

Question

Passage
Ethanol is an important source of energy that is frequently used as a supplement to gasoline. It can be obtained from renewable resources such as the cellulose found in plant matter. When subjected to a process called gasification, the plant mass is converted to a mixture called syngas, composed predominantly of carbon monoxide and molecular hydrogen. Syngas can be passed over a rhodium catalyst to generate ethanol and other products. After using this method, a group of researchers analyzed the resulting products by gas chromatography using helium as a carrier gas. The results are shown in Figure 1.

Figure 1 Gas chromatograph of syngas catalysis productsMass spectrometry revealed that the process yielded similar amounts of ethanol, acetic acid, and acetaldehyde, with trace amounts of ethane. In addition, the ethanol peak was found to be contaminated with ethyl acetate. Another group of researchers in the same laboratory had recently produced Compound 1 as a by-product in a separate reaction. They combined Compound 1 with purified ethyl acetate to form megestrol acetate, a drug used in the treatment of certain cancers. This reaction also produced ethanol, as shown in Scheme 1.

Scheme 1
Adapted from Lopez L, Velasco J, Montes V, Marinas A, Cabrera S, Boutonnet M, Järås S. Catalysts 2015.
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What atom indicated would be most readily deprotonated if Compound 2 reacts with NaOH?

Quizplus · Accepted Answer

11ecba2d_126e_365c_a3bf_a3d7df5719b8_MD0008_00 For a compound in solution, as the pH is increased, the most acidic functional group of the compound will be deprotonated first. The acidity of a functional group is determined largely by the electronegativity of the proton-donating atom and by the ability to stabilize the negative charge in the corresponding conjugate base through charge distribution (atom size) or delocalization (resonance). Negative charge is stabilized better on more electronegative atoms, and negative charge that can participate in resonance will be stabilized further by being delocalized across more than one atom. Sites that better stabilize a negative charge are more likely to be deprotonated (more acidic). Atoms I-IV in Compound 2 are oxygen (alcohol), sp² carbon (alkene), sp³ carbon (alkane), and methyl ketone (α-H), respectively. Upon deprotonation, the negatively charged atom in the conjugate base of these functional groups is oxygen for alcohols and carbon for the others. Because oxygen is more electronegative than carbon, a negative charge on oxygen in the conjugate base of the alcohol is more stabilized than the charge on the carbon atoms in the three other functional groups. Therefore, the alcohol oxygen atom has the most acidic proton and will be deprotonated when reacted with NaOH. (Choices B and C) Alkene protons (sp² C-H) are more acidic than alkane protons (sp³ C-H), but both are less acidic than an alcohol proton because the conjugate bases of alkenes and alkanes are less stable, with the negative charge concentrated on a less electronegative carbon atom. (Choice D) Ketones are less acidic than alcohols but more acidic than hydrocarbons. The negative charge in the conjugate base of a ketone is delocalized by resonance across the α-carbon and carbonyl oxygen atoms, which helps stabilize the charge. Educational objective: Acidity of a functional group is determined by the stability of the conjugate base it forms. Factors such as the size and electronegativity of the proton-donating atom as well as the ability to stabilize the negatively charged atom in the conjugate base by charge distribution or resonance contribute to acidity.

Passage Ethanol Is an Important Source of Energy That Is Frequently