Organic Chemistry II - Midterm 2008

Organic Chemistry II - Midterm 2008 - Midterm Answers CHM...

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Midterm Answers 1 of 11 CHM 2120 MIDTERM – ANSWERS October 26, 2008 9:00 – 11:00 am First Name: _____________________ Last Name: _____________________________ Student Number: ______________________ Section: A (MRN Aud): ___________ B (UCU Aud): ___________ Approximate total number of marks: 90 (subject to slight changes) Notes: - For questions in which mechanisms are not required, part marks might be given for incorrect answers with plausible mechanisms. - Re-marks requests might not be granted for midterms written in pencil. - There is an IR absorbance table and a 1 H NMR table on the last page.
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Midterm Answers 2 of 11 1. Name or draw the structure of the following molecules, as appropriate. (4 points) - 1 per error a. Br 1-bromo-3-ethylbenzene OR m-bromoethylbenzene b. 2,4,6-trinitrotoluene (TNT) O 2 N NO 2 NO 2 2. a. Explain why the following reaction will not work as shown. ( 2 points) b. Give the true product of the reaction. (1 point) Br NaNH 2 NH 2 NH 2 2 points for giving 2 of the 3 points below - There is a strong nucleophile and a secondary alpha carbon that bears a good LG. These are conditions for an S N 2 reaction (or E2) - An S N 1 reaction would give a mixture of stereoisomers NH 2 OR 1 3. What are the three criteria for aromaticity? (3 points) 1 point each Note: “ ring ” must be stated for full marks 1. ring is planar 2. all ring atoms are sp2-hybridized 3. 4n + 2 π electrons (n = 0, 1, 2. ..)
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Midterm Answers 3 of 11 4. a. Identify whether each of the following molecules is aromatic, anti-aromatic, or non-aromatic. b. Justify your response. i. ( 5 points) O 1 point for each point (total 3) + 1 point for justification of location of lone pairs 1. ring is planar 2. all ring atoms are sp 2 -hybridized (one lone pair on O is in a p-orbital, the other is in an sp 2 -hybridized orbital) 3. 6 π electrons (4 from π bonds, 2 from O lone pair) = 4n + 2, n = 1 Aromatic (1 point) ii. ( 6 points) 1 point for each point (total 3) + 1 point for justification of location of lone pair + 1 point for recognizing that the 4 π electrons fits the 4n rule.
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Organic Chemistry II - Midterm 2008 - Midterm Answers CHM...

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