Passage Students perform a synthesis of a carboxylic acid derivative.They mix a 10.00-mL sample of hexanoic acid, 2.33 mL of ethanol, and 0.64 mL of concentrated sulfuric acid in a flask with a water condenser fitted to its neck. The mixture is boiled for one hour and then poured into water when the reaction is complete. The aqueous and organic layers are separated, and the organic layer is washed once with NaHCO 3 and twice with water. Solid Na 2 SO 4 is added to the organic layer to remove any water present. The organic layer and Na 2 SO 4 are separated by filtration. The filtrate is purified by fractional distillation to yield the carboxylic acid derivative, a colorless liquid. -Which carboxylic acid would need to be used to form Compound A (shown below) based on the reaction described in the passage?

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11ecba2d_12b2_443c_a3bf_fb5c79f668a4_MD0008_00 Esters are formed by an acid-catalyzed reaction known as a Fischer esterification, in which a carboxylic acid and an alcohol combine. The alkyl group bonded to the carbonyl carbon comes from the carboxylic acid, and the alkyl chain bonded to the ester oxygen atom comes from the alcohol. Carboxylic acids are named based on the longest continuous carbon chain containing the carboxylic acid functional group (known as the parent chain). The parent chain is numbered beginning with the carbonyl carbon of the carboxyl group. Substituents on the parent chain are named beginning with the parent chain carbon number it is bonded to, followed by the prefix denoting the number of carbons in the substituent. The substituents are listed in alphabetical order. The parent chain is named last, and for carboxylic acids, the suffix -e of the parent alkane is replaced with -oic acid. The parent chain of the carboxylic acid used to form Compound A has five carbons (prefix pent-). There are two substituents, an ethyl group on C-2 and a methyl group on C-3. Therefore, the carboxylic acid used is 2-ethyl-3-methylpentanoic acid. (Choice A) The name 2-sec-butylbutanoic acid incorrectly identifies the parent chain as a four-carbon chain with a sec-butyl substituent on C-2. (Choice C) The name 2,3-diethylbutanoic acid incorrectly identifies the parent chain as a four-carbon chain with two ethyl substituents, one on C-2 and one on C-3. (Choice D) The name 4-ethyl-3-methylpentanoic acid correctly identifies the five-carbon parent chain. However, the parent chain is incorrectly numbered, giving the carbonyl carbon the highest number instead of the lowest, which affects the numbering of the substituents as well. Educational objective: Carboxylic acids are named by identifying the parent chain (longest continuous carbon chain containing the carboxyl group) and numbering the carbons beginning with the carbonyl carbon. The substituents are named beginning with the parent chain carbon number it is bonded to and followed by the substituent prefix. The parent chain is named last, replacing the -e from the parent alkane with -oic acid.

Passage Students Perform a Synthesis of a Carboxylic Acid Derivative.They Mix