14C_w11_e02_key

14C_w11_e02_key - Chemistry 14C Winter 2011 Exam 2...

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Chemistry 14C Winter 2011 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. (a) Formula is C 14 H 30 N 2 O 4 , so M has m/z = (12 x 14) + (1 x 30) + (2 x 14) + (4 x 16) = 290. (b) (1.107% x 14) + (0.015% x 30) + (0.366% x 2) + (0.037% x 4) = 16.828% 17% (c) Four oxygen atoms gives an M+2 relative abundance of about 0.8% 1%. (d) Fragment, impurity, and base peak. 2. H H O Might be present. Aldehyde C–H at ~ 2700 cm -1 . CH 3 CH 2 OH Might be present. Alcohol O–H at ~3500 cm -1 and sp 3 C–H < 3000 cm -1 . H O O H Might be present. Aldehyde C–H at ~ 2700 cm -1 and sp 3 C–H < 3000 cm -1 . OH Might be present. Phenol O–H at ~3500 cm -1 , aryl C–H > 3000 cm -1 , and benzene ring ~1600 cm -1 and ~ 1500 cm -1 . 3. The peak at ~ 2200 cm -1 leads us to conclude than an alkyne or nitrile may also be present. 4. (a) Ignoring splitting, the 1 H-NMR spectrum includes four signals. (b) The 1 H-NMR spectrum has two singlets and two triplets. (c) When the smallest integral = 1, the total number of 1 H-NMR signals with integral = 1 is three . (d) Ignoring splitting, the 13 C-NMR spectrum includes five signals. (e) The 13 C-NMR spectrum has one singlet and three triplets. 5. Seven DBE. Two rings and five pi bonds. The identity of X is irrelevant; the DBEs can be determined just from looking at the structure . 6. In infrared spectroscopy, photon absorption causes changes in bond vibration , whereas in NMR spectroscopy photon absorption causes nuclear spin flip .
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This note was uploaded on 09/06/2011 for the course CHEM 140A taught by Professor Whiteshell during the Fall '04 term at UCSD.

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14C_w11_e02_key - Chemistry 14C Winter 2011 Exam 2...

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