14C_w08_e02_key - Chemistry 14C Winter 2008 Midterm Exam 2...

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Chemistry 14C Winter 2008 Midterm Exam 2 Solutions Page 1 Statistics: High score, average and low score will be posted on the course web site after exam grading is complete. The exam is ready to be picked up when these numbers are posted. A note about exam keys: The answers presented here may be significantly longer than expected from a student taking the exam. An exam key serves not only to reveal what was expected, but to instruct you as well. To see the projected course grade cutoffs, consult the grading scale on the Chem 14C course web page. 1. C 10 H 12 O 2 and C 10 N 2 O. For C 10 H 12 S the intensity of M+2 ~ 4%. C 10 H 14 NO violates the nitrogen rule. For C 11 H 18 O M has m/z = 166. C 10 N 2 O is highly unlikely, but cannot be ruled out based only on the mass spectrum . 2. (a) 226 (M), 227 (M+1), and 228 (M+2). (b) 224 and 225. All ions with m/z < M are fragments of that M. (c) Cannot determine. The given data includes only m/z values, and not relative ion abundances. The base peak is the most abundant ion in the spectrum, not just among the molecular ions (M, M+1, and M+2). 3. C 12 H 23 N and C 12 H 7 NO. For C 13 H 11 N the calculated intensity of M+1 is not a good fit with the given data. No other formulas are consistent with the given data.
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