For each problem, draw a structure or structures consistent with all of the information provided up to that point. In other words, your answer to (a) should be consistent with the information given in (a), your answer to (b) should be consistent with the information given in (a) and (b), your answer to (c) should be consistent with the information given in (a), (b), and (c), etc. Assume that the unknowns may consist of C, H, N, O, Cl, or Br. For best results, try to think of all the different possibilities at each stage of the question before moving on to the next piece of information.
When you are given the mass spectral data, the first step is to determine some likely formulas. Be sure to calculate the degrees of unsaturation in your compound. Then draw several structures consistent with the molecular weight, the M+1 and M+2 peaks, and the number of degrees of unsaturation. Then you'll be well on your way.
Problem 5 may be found to be particularly difficult.
(b) The only IR absorbances in the interpretable region (1500-4000 cm–1) are at 2900 and 1715 cm–1.
(c) The 13C NMR spectrum shows six resonances at δ 200 (s), 55 (d), 30 (t), 26 (t), 24 (t), and 20 (t).
(d) In the 1H NMR spectrum, there is a resonance at δ 3.8 which integrates to 1H and whose multiplicity is dddd.
(e) Can this compound be optically active?
(a) The compound has an M+ ion at 158 amu. There is no M+2 peak.
(b) The intensity of the M+1 peak is 9.9% of the M+ peak.
(c) The only IR absorbances in the interpretable region are at 2850 and 1740 cm–1.
(d) The spin-coupled 13C NMR spectrum shows seven resonances at δ 168 (s), 70 (t), 35 (d), 30 (d), 25 (t), 10 (q), and 8 (q) ppm. [How can this information be consistent with the information given in (b)?]
(e) The structure of the compound has been narrowed down to two possibilities. Now predict the 1H NMR spectrum of the compound you drew for (d). Label each H atom Ha, Hb, etc., giving equivalent H's identical letters. Then predict the approximate chemical shift, multiplicity, and integration of each resonance that you would see in the 1H NMR spectrum. If you can see the two possibilities, how might you distinguish them by 1H NMR?
(f) Can this compound be optically active?
(a) The compound has an M+ ion at 85 amu. There is no M+2 peak.
(b) The only IR absorbances in the interpretable region are at 3340 and 2900 cm–1.
(c) The 13C NMR spectrum shows three resonances at δ 40, 30, and 25.
(d) The 1H NMR shows three resonances at δ 2.7 (m, 4H), 1.5 (m, 6H), and a broad peak at ca. 5.0 (1H) that changes its position with concentration and temperature.
(a) The compound shows M+ at 122 amu. There is no M+2 peak.
(b) There are absorbances in the IR spectrum at 3500, 3050, and 2900 cm–1.
(c) The compound is optically active.
(d) The 1H NMR spectrum shows four resonances at δ 7.2 (m, 5H), 4.8 (q, 7.0 Hz, 1H), 1.3 (d, 7.0 Hz, 3H), and a broad peak at 1.6 ppm (1H) that changes its position with concentration and temperature.
(a) The compound has an M+ ion at 168 amu. There is no M+2 peak.
(b) The only IR absorbances in the interpretable region are at 3050 and 2900 cm–1.
(c) The spin-coupled 13C NMR spectrum shows only four resonances at δ 120 (d), 35 (d), 25 (t), and 8 (q) ppm.
(d) Predict the 1H NMR spectrum of the compound you drew for (c). Label each H atom Ha, Hb, etc., giving equivalent H's identical letters. Then predict the approximate chemical shift, multiplicity, and integration of each resonance that you would see in the 1H NMR spectrum.
(e) This compound can be converted into a more stable diastereomer. The diastereomer has very similar IR, 13C NMR, and 1H NMR spectra.
(a) The compound has an M+ ion at 102 amu. There is no M+2 peak.
(b) The only IR absorbances in the interpretable region are at 3500 and 2900 cm–1.
(c) The 13C NMR spectrum shows three resonances at δ 70 (d), 35 (t), and 30 (t).
(d) The 1H NMR spectrum shows four resonances at δ 4.0 (dd, 1H), 1.5 (m, 2H), 1.3 (m, 1H), and a fourth broad resonance that varies with concentration and temperature (1H).
(e) The compound is optically active.
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