More Spectroscopy Problems

1. If you needed to distinguish each of the compounds in the following pairs ( A & B) from each other, which spectroscopic method (infrared or 1H nmr would be best (most certain)? Assume that you do not have a reference sample of either compound for direct comparison.
Compound A
Compound B
IR
NMR





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2. Match the infrared spectrum characteristics given below with a compound from the following group:


(A) 1-butyne (H-C=CCH2CH3 ) (B) 1-methoxypropane (CH3-O-CH2CH2 CH3) (C) ethyl vinyl ketone (CH3CH2COCH=CH2) (D) 3-pentanone (CH3CH2COCH2CH3) (E) octane (CH3(CH2)6CH3) (F) butyric acid (CH3(CH2)2CO2H) (G) 2-propanol ( (CH3)2CHOH ) (H) acryonitrile (CH2=CH-C=N)


(i) Strong absorption band at 1715 cm-1; no absorption >3000 cm-1

(ii) Sharp absorption bands at 3300 cm-1 and 2120 cm-1

(iii) Absorption bands at 3050 cm-1, 1690 cm-1 and 1630 cm-1

(iv) A broad strong absorption at 3350 cm-1, no absorption from 1650 to 1760 cm-1

(v) Broad strong absorption from 2600 to 3400 cm-1and a strong band at 1710 cm-1
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3. Three C3H6O isomers have the spectroscopic properties given below. Select the most likely structure for each from the compounds in the following group:


(i) One 1H nmr peak; infrared absorption at 2900 and 1715 cm-1

(ii) Three 13C nmr peaks (two at d>100 ppm); infrared absorption at 3100, 2900, 1650 & 1100 cm-1

(iii) Three 13C nmr peaks (one ca. d200 ppm); Three 1H nmr peaks (one near d9.0 ppm)

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4. What splitting pattern in the 1H nmr spectrum would you expect for the designated hydrogen atom(s) in the compounds shown below? Select your answer from the listed choices.






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5. Which of the following compounds would not be expected to show spin-spin splitting in their 1H NMR spectra? (Check the appropriate box).
Compound
Splitting
No Splitting
Compound
Splitting
No Splitting
(CH3)3C-O-CH3
(CH3)2CH-O-CH3

Br-CH2CH2-Br
Br-CH2CH2CH2-Br


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Select answers to the following problems from the structural formulas (A through S) at the end of the page.
6. A C5H12O2 compound has strong infrared absorption at 3300 to 3400 cm-1 The 1H NMR spectrum has three singlets at d 0.9 , d 3.45 and d3.2 ppm; relative areas 3:2:1. The 13C NMR spectrum shows three signals all at higher field than 100 ppm. Suggest a structure for this compound. (type the letter ONLY)
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7. A C4H8O2 compound has a strong infrared absorption at 1150 cm-1, but no absorption at 3300 to 3400 cm-1. It's 1H NMR spectrum shows a singlet at d 3.55 ppm. The 13C NMR spectrum shows one signal at d 66.5 ppm. Suggest a structure for this compound. (type the letter ONLY)
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8. A C9H12O compound has strong infrared absorption at 3300 to 3400 cm-1. The 13C NMR spectrum of this compound has six discrete signals. It's 1H NMR spectrum has three sets of lines: singlets at d1.1 (6H), 1.9 (1H) and 7.3 (5H) ppm. Suggest a structure for this compound. (type the letter ONLY)
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9. A C10H14 compound. The 1H NMR spectrum has two singlets at d 2.45 and 7.0 ppm (ratio = 6:1). The 13C NMR spectrum shows three signals at d132.9, 130.5 and 18.9 ppm. Suggest a structure for this compound. (type the letter ONLY)
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10. A C8H4N2 compound shows a sharp infrared absorption at 2230 cm-1. It's 1H NMR spectrum has a singlet at d 7.6 ppm. The 13C NMR spectrum shows three signals at d132, 119 and 117 ppm. Suggest a structure for this compound. (type the letter ONLY)
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11. A C14H22 compound. The 1 H NMR spectrum has two singlets at d 1.1 and 7.25 ppm (ratio = 9:2). The 13C NMR spectrum shows four signals at d 147, 125, 39.3 and 30.8 ppm. Suggest a structure for this compound. (type the letter ONLY)
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12. A C9H12O3 compound has strong infrared absorption near 1100 cm-1. Its 1H NMR spectrum has sharp singlet peaks at d 3.6 and 6.6 ppm (intensity ratio 3:1). Its 13C NMR spectrum shows three lines at d 165, 115 and 55 ppm. Suggest a structure for this compound. (type the letter ONLY)
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13. A C9H18O compound has a strong infrared absorption at 1710 cm-1. Its 1H NMR spectrum has a single sharp peak (a singlet) at d 1.2 ppm. Its 13C NMR spectrum shows three lines at d210, 45 and 25 ppm. Suggest a structure for this compound. (type the letter ONLY)
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14. A C9H10O compound has a strong infrared absorption at 1720 cm-1. Its 1H NMR spectrum has signals at d 2.8 (mult., 4H), 7.3 (s, 5H) and 9.8 (t, 1H) ppm. Its 13C NMR spectrum shows seven lines at d200, 138, 129, 128, 125, 35 and 30 ppm. Suggest a structure for this compound. (type the letter ONLY)
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15. A C5H10O2 compound shows a strong infrared absorption at 1100 cm-1, but no absorption at 3300 to 3400 cm-1. Its 1H NMR spectrum has sharp singlet peaks at d1.3 and 4.0ppm (intensity ratio 3:2). Its 13C NMR spectrum shows three lines at d 98, 68 and 20 ppm. Suggest a structure for this compound. (type the letter ONLY)
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16. A C9H10O2 compound has strong infrared absorption at 1690 and 1100 cm-1 . Its 1H NMR spectrum has sharp singlet peaks at d 2.8 and 3.8 ppm (3H each) and two doublets at d 6.9 and 7.8 ppm (2H each). Its 13C NMR spectrum shows seven lines Suggest a structure for this compound. (type the letter ONLY)
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17. A C9H10O2 compound has strong infrared absorption at 1695 cm-1. The 1H NMR spectrum has five sets of lines: a triplet at d1.3(3H), a quartet at d>4.1(2H), a doublet at d7.0(2H), a doublet at d7.8(2H) and a singlet at d9.8(1H) ppm. Suggest a structure for this compound. (type the letter ONLY)
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18. A C4H8O3 compound has strong infrared absorption at 2500 to 3300 cm-1 and 1710 cm-1 . The 1H NMR spectrum has four signals: a doublet at d1.2(3H), a quartet at d4.5(1H), a singlet at d3.6(3H) and a singlet at 12.5 ppm. The 13C NMR spectrum has four signals at d177, 70, 54 and18 ppm. Suggest a structure for this compound. (type the letter ONLY)
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19. A C9H9N compound shows infrared absorption at 2250 cm-1. It's 1H NMR spectrum has three signals: singlets at d 2.4 (3H), 3.8 (2H) and 7.2 (4H) ppm. The 13C NMR spectrum has seven signals, five at fields lower than d 100 ppm and two at higher fields. Suggest a structure for this compound. (type the letter ONLY)
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20. A C4H11N compound shows two infrared absorption bands at 3200 to 3400 cm-1 and a strong band at 2900 cm-1. It's 1H NMR spectrum shows two singlets at d 1.0 (9H) and 1.3 (2H) ppm. The 13C NMR spectrum has two signals, both at fields higher than 100 ppm. Suggest a structure for this compound. (type the letter ONLY)
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21. A C5H11N compound shows infrared absorption at 3300 cm-1. It's 1H NMR spectrum has three signals: singlets at d1.0 (6H), 1.4 (1H) and 2.7 (4H) ppm. The 13C NMR spectrum has three signals, all at fields higher than d100 ppm. Suggest a structure for this compound. (type the letter ONLY)
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