OCHM – Organic Synthesis Question Information Q-Bank MCAT Sim Non-Sim Subject Organic Chemistry Foundation OCHM – Organic Synthesis Validity 5 years Author(s) Reyes, V. M. Reviewer(s) 0000000 Editor(s) 0000000 Passage Information Passage ID Media ID(s) Passage Stem In the early 1830’s, when organic chemistry was still in its infancy, the early organic chemists usually performed only separation, purification and identification of pre-existing organic compounds or mixtures thereof, such as plant and animals extracts commonly referred to as “natural products.” The conceptual norm then was called “Vitalism,” which postulated that organic substances can only be produced by living organisms by the actions of some “vital force”, while inorganic compounds were synthesized from non-living matter, which was presumed to lack such vital force. More than 100 years later, organic chemistry became firmly established as a major branch of chemistry. In this modern day and age, perhaps the largest and most active area of organic chemistry is synthetic organic chemistry. Today the reason why many

a young chemists will choose to specialize in organic chemistry is to do ‘synthetic organic chemistry,’ that is, to be able to synthesize new organic compounds which have novel properties as drugs, materials for specialized applications (e.g., biomaterials), etc. In this passage we shall focus on the Grignard reaction, an important way to form new C-C bonds, and a prime example of a synthetic organic reaction. Before a Grignard reaction is carried out, the synthetic chemist must prepare what is called a Grignard reagent. A Grignard reagent is an organometallic compound of the form “R-Mg-X” where R is an alkyl or aromatic group (or aryl group, “Ar-Mg-X”), and X is a halide (except flouride). It is prepared by adding the alkyl (or aryl) halide to small trimmings of magnesium metal suspended in dry liquid ether (e.g., ethyl ether or THF) and heating the mixture: R-X R-Mg-X Mg in dry ether +heat The Grignard reagent can then be reacted with an aldehyde or a ketone in a weakly acidic solution to form a secondary or tertiary alcohol adduct, respectively (plus a precipitate of Mg(OH)X, to be removed in a subsequent step): O OH = H+ - R1-Mg-X + R2-C-R3 R2-C-R3 + Mg(OH)X ↓ - R1 R1, R2 and R3 are three alkyl groups which may or may not be identical to each other. For aldehydes, R2 or R3 is a hydrogen, and the resulting alcohol is a secondary one, while for ketones, it will be a tertiary alcohol, as shown above. For example, heating bromobenzene in THF with metallic Mg yields: Mg-Br Mg ∆ Then, adding acetone in a slightly acidic solution yields: OH H+ Mg-Br + Mg(OH)Br ↓ + acetone

Question Attributes #1 (QID: 000000) Passage References PMID/Page # Title of Publication or Book Type 000000000 R. Brewster & W. McEwen, Organic Chemistry textbook R. W. Griffin, Jr., Modern Organic Chemistry textbook 000000000 (N/A) en.wikipedia.com, youtube.com internet (N/A) Author’s own lecture notes Question Attributes #1 (QID: 000000) Topic Blueprint The Grignard Reaction Competency MCAT: BS-2: Application of Concepts & Principles To gain an understand of the Grignard reaction and be able to predict the product of the reaction given the reactants. Objective Media ID(s) 00000000 Question ID 00000000 Question Stem #1 Predict the molecular structure of the product of the following two-step reaction: ethyl iodide ethyl (Mg) iodide

isobutyraldehyde ethyl (Mg) iodide II Answer Choices #1 A) I B) C) III IV Correct: A) (Cont’d. on the next page.)

correspond to the carbonyl carbon of the reactant aldehyde. Explanation #1 The correct choice is B. Remember that the R or Ar (organic) group of the Grignard reagent attaches to the carbonyl carbon of the aldehyde, and the aldehyde’s carbonyl oxygen becomes oxidized to an OH group. This becomes more apparent if the C-C bond indicated in the above figure, which is actually molecule II, is rotated 180ᵒ. (Choice A) This choice is incorrect because the attachment of the OH group does not correspond to the carbonyl carbon of the reactant aldehyde. (Choice C) This choice is incorrect; this molecule has both an ether and an alcohol functional group, and the Grignard reaction does not produce an ether. (Choice D) This choice is incorrect for the same reason as choice A: the location of the OH group is incorrect.

to predict the product of the reaction given the reactants. Educational objective: To gain an understand of the Grignard reaction and be able to predict the product of the reaction given the reactants. References #1 PMID/Page # Title of Publication or Book 0000000 000000000 000000000 0000000 Verifications #1 Yes / No The question is at the Application or higher cognitive level. Yes / No The question is based on a realistic clinical scenario. Yes / No The question has at least one close distracter, and other options have educational value. Yes / No The question is appropriate to the entry level of nursing practice. Yes / No The explanation is short and concise, yet thorough. Yes / No The question has an appropriate table/flow chart/illustration.