SP23 CHEM 226-ONLY_Exp9_Pechmann_POSTLAB_001

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Harvard University *

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226

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Chemistry

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Dec 6, 2023

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© jth.v.001 Post-Lab Assignment CAREFULLY READ EVERYTHING IN THIS COLUMN: This is the Postlab Assignment for Exp 9. Your entire assignment must be produced and submitted electronically. Do not scan or hand write anything, unless explicitly directed to do so. Hand drawn images or written words or structures will not receive credit. Proper drawing of chemical structures (including bond angles, bond length, etc.) will be closely evaluated. All chemical structures must be generated by you, using ChemDraw, or they will not be graded. To be clear, if you copy/pasted from another source, including a peer, it is deemed plagiarism. See the last page of Pre-Organic Chemistry II Laboratory Proficiency document for more information about ChemDraw. This is normally very expensive software, but it is free to NYU students! Ambiguous answers will be counted as incorrect, so please provide concise but explicit answers. Clarity, details, and proper use of terminology matter. Explanations for questions are typically valued as much or more than the simple answer. Also, all “non-wrong” explanations are not considered equal . Your assignment must be submitted to NYU Brightspace (for authenticity evaluation) under the Assignments tab as a complete electronic file (no hand-writing/drawing), AND as a hard copy to your section instructor. All sections may submit your hard copy and electronic copy of the assignment by the start of your Exp #10a laboratory session. Failure to submit both forms of your report/postlab assignment at the start of your lab session will result in a 25% penalty. Failure to submit both forms of your report/postlab assignment within 24 hours of the due date/time will result in a score of zero. ************************************************************************** All report/postlab assignments must be completed INDEPENDENTLY . If you fail to comply with this rule on part of your assignment, then your entire assignment will be scored as a zero . Further, all of your coursework to date will be subjected for thorough review for originality. ************************************************************************** Be sure to put (1) your name, (2) section number, (3) section instructor’s name, and (4) the due date at the top of your postlab assignment. A 2 point deduction will be assessed for each missing item . ************************************************************************** Do NOT include the following questions in the document you submit, ONLY include your answers in the document you submit. A 10 point deduction will be assessed if the text from the postlab document is included in the document that you submit. ************************************************************************** This experiment involves a very nice multi-step mechanism. It was tempting to ask you to draw it for this assignment using ChemDraw (what a masterpiece that would be!), but we will forgo this formal requirement. Still, we strongly suggest that you write out the full mechanism several times for your own benefit of learning, and appreciating, these transformations. 1) What is one advantage to using Amberlyst 15 as an acid source, as opposed to using sulfuric acid? (There are many possible answers. Do not consider cost here) Justify your answer in 2 sentences or less. 2) Why was bubbling in the reaction flask an important observation in this week’s experiment (i.e. what does it indicate at the molecular level about the reaction)? Give your best explanation in 4 sentences or less. 3) In many cases when we heat a reaction flask such that boiling is observed, we would add a reflux condenser. Why would it potentially be a disadvantage to use a reflux condenser in this reaction set-up? Give your best explanation in 4 sentences or less. 4) See the example TLC plate from this experiment (pg 2 of this document) as viewed under short and long wavelength UV light (a rather nice experiment outcome). Take a moment to marvel at the effectiveness of this recrystallization. Then, based on these images , answer the following questions. i) Why is the percent yield expected to be less than 100%. Give two reasons. Justify each claim in two sentences or less (for each reason ). ii) We have talked several times about how a TLC plate works, and why spots are observed. Resorcinol and the product are observed differently in the two images (i.e. resorcinol is not observed in one of the images). Consider the respective absorption profiles. Give your best explanation for the observed difference between resorcinol and the product in 4 sentences or less. 5) See the separate document called Questions 5-6 Postlab Data. Determine a structure that is consistent with all of the data on the page labeled “Question 5”. Include the structure as your answer in your assignment document (you should not include the entire data page in the submitted assignment). 6) Same instructions as the previous question, but interpret the data on the page labeled “Question 6”

© jth.v.001 Lanes from left to right: Lane 1 (SM): resorcinol Lane 2 (P): purified product Lane 3 (F): filtrate after recrystallization Lane 4 (C): crude from before recrystallization Lane 5 (Px2): purified product spotted twice Short Wave Long Wave

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