Midterm exam - 1 C HM 21 20 In C l ass T est N ov emb er 1...

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CHM 2120 In Class Test November 13, 2009 TIME: 75 min. TONY DURST SEAT NUMBER PLEASE PASTE TICKET HERE NAME:[FAMILY]__________________________ NAME [FIRST] __________________________ STUDENT NUMBER:_____________________ THE FOLLOWING PARTIAL PERIODIC TABLE MAY BE OF USE Li _ B C N O F Na Mg Al Si P S Cl K Se Br I TOTAL POINTS: Approx. 50-55. SUBJECT TO SMALL CHANGES. KEEP TRACK OF TIME! Question 1. 5 points Name the following structures using either the IUPAC system or an acceptable trivial nomenclature OR Draw a clear unambiguous structure. O H 3 C CH 3 a) H 3 C O H b) c) NH 2 Cl Cl d) e) 3-keto-4-methylhexanal. meta-trifluoromethybenzoic acid. Markingl. I gave 0.5 pts if the answer was close but not quite correct Acceptable names and structures were: 2,2-diemthylcyclohexanone (E)- 2-butenal 2,5-dichloroaniline CF 3 CO 2 H H 3 C O O CH 3 1
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MARK OBTAINED MAXIMUM MARK 62 Comments: The median mark is 71-72%.Approximately 1out of 6 students obtained a mark of >90%. It suggests that to prepare the final with a largere number of demanding questions while still making it relatively straight froward fo pass or obtain a reasonably good mark. The last question was worth 3 points, 2 of which can be considered bonus. Question 2. 2X2 = 4 points. Which of the two compounds shown is the stronger acid? Use structures and a few phrases to make your case. OH NO 2 or OH O a) O(-) NO 2 + H(+) O(-) O + H(+) The EWG nitro group helps stabilize the negative charge. The electron donating group destabilized the charge. Thus this is the weaker acid N H CH 3 (+) (+) or N CH 3 H b) N CH 3 N CH 3 + H(+) + H(+) loss of a proton generates an aromatic rings , thus gain of resoance enery. This is more favourable than the right had case. no resonce eneryy in either species Question 3. 2 points Which of the following pair is more basic? Explain briefly, again ideally using structures. O (-) or O(-) CH 3 CH 3 The negative charge on the oxygen is localized , that on the right can be delocalized. A localized charge is less favourable than one that is delocalized. Thus the alkoxide is more basic. 2
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Question 4. 3 points Draw additional IMPORTANT resonance structures, where applicable, for each of the following. Underline the most important resonance contributor. COMMENT: THE MARKING WAS CHANGED. MAX 5 POINTS FOR THE QUESTION : 2 For a) and 1 or 2 points for either b) or c). Underlining was important. I was disappointed with the answers for the most part. I would estimate that less than 20% of the class earned 5 points. Most of you still do not know, or follow the rules for drawing resonance structures. If you cannot do this or and use resonance structures in your rationalizations, then this course will never really make any sense. O
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This note was uploaded on 01/10/2012 for the course CHM CHM 2120 taught by Professor Alysonflynn during the Spring '11 term at Carleton CA.

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Midterm exam - 1 C HM 21 20 In C l ass T est N ov emb er 1...

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