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14C_s11_lec02_e02_key

# 14C_s11_lec02_e02_key - Chemistry 14C Lecture 2 Spring 2011...

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Chemistry 14C Lecture 2 Spring 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) (12 x 14) + (8 x 1) + (4 x 16) = 240 (b) (14 x 1.107%) + (8 x 0.015%) + (4 x 0.037%) = 15.8% (c) (4 x 0.204%) = 1% 2. Base peak : The tallest peak, due to the most abundant ion, in the mass spectrum. The base peak is not necessarily a molecular ion or a fragment. 3. Yes. m/z = 162 for M agrees with C 10 H 14 N 2 . The observed intensity for M+1 (11.88%) is within experimental error for the calculated M+1 intensity (12.01%). Nicotine has no oxygen, sulfur, chlorine, or bromine so a very small M+2 intensity is consistent . 4. 5. 3375 cm -1 , 1598 cm -1 , and 1495 cm -1 . Despite the complexity of its structure, the 4000–1500 cm -1 region of the cellulose acetate IR spectrum is simple: peaks ~2950 cm -1 for sp 3 C-H and ~ 1740 cm -1 for the C=O. Other peaks are probably impurities . 6. All are possible impurities. DHAQ is definitely present, but the given impurity peaks do not rule out any of the other impurity choices from also being present . 7. The 13 C-NMR spectrum of nicotine has ten signals, five of which are doublets. None of the carbons are equivalent, and five are bonded to a single hydrogen atom . 8. [ 81 Br– 81 Br] +. This radical cation causes the M+4 peak . 9. (a) The 1 H-NMR spectrum of α - D -glucopyranose has six signals from hydrogen atoms bonded to carbon. The molecule has seven hydrogens bonded to carbon. Of these, only the methylene hydrogens are equivalent to other hydrogens (i.e., themselves) in the molecule.

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14C_s11_lec02_e02_key - Chemistry 14C Lecture 2 Spring 2011...

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