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CHEM14C_s08_lec01_e02_key - Chemistry 14C Lecture 1 Spring...

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Chemistry 14C Lecture 1 Spring 2008 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. To see the projected course grade cutoffs, consult the grading scale on the Chemistry 14C course web page. 1. A mass spectrum is a plot of mass-to-charge ratio (m/z) on the x-axis versus relative abundance (%; or intensity) on the y-axis. This spectrum contains two types of peaks: molecular ions (which are useful to determine molecular formula) and fragment ions (which are not useful to determine molecular formula). 2. (a) Camphor (b) Camphor (c) Para-dichlorobenzene 3. Camphor ? No, because the IR spectrum lacks a C=O stretch in zone 4. Naphthalene ? No, because the IR spectrum indicates presence of sp 3 C–H in zone 2. 4. (a) Camphor Due to the C=O stretch (b) Camphor (c) Para-dichlorobenzene 1 H-NMR has just one signal due to molecular symmetry . (d) Camphor The only signals in the 1 H-NMR spectra of naphthalene and para-dichlorobenzene are benzene ring hydrogens, which are significantly deshielded (chemical shifts typically 6.5-8.0 ppm). None of the camphor protons experience this strong deshielding . 5. 1727.5 cm -1 The characteristic C=O stretching frequency range for a ketone is 1750-1705 cm -1 . 6. Nine hydrogens. Each hydrogen atom with a methyl group is equivalent to the other hydrogens in the methyl group, and camphor contains three methyl groups. All of the other hydrogen atoms are not equivalent to any other hydrogen atoms in the molecule .
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