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14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:10 AM Page 296 & 296 — Nuclear Magnetic Resonance Spectroscopy + Part Three: Spin-Spin Coupling E Rg dede sã gãii 1 SESESI Pai dit I (c) | nr [OR O) | hi H | AH | | £/ Ia || 14 q NO 1 | ] dot Il! it) nt Hd Mi, UA uv pd A o A Vo (a) (9) OR FIGURE 5.67 Expansions of the ring proton resonances from the 300-MHz "H NMR spectrum of 2-picoline (2-methylpyridine). The methyl resonance is not shown. PROBLEMS *1. Determine the coupling constants for the following compounds from their NMR spectra shown in this chapter. Draw tree diagrams for each of the protons. (a) Vinyl acetate (Fig. 5.45). (b) Crotonic acid (Fig. 5.48). (c) 2-Nitrophenol (Fig. 5.64). (d) 3-Nitrobenzoic acid (Fig. 5.65). (e) Furfuryl alcohol (Fig. 5.66). () 2-Picoline (2-methylpyridine) (Fig. 5.67). 14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:10 AM Page 297 & Problems 297 *2. Estimate the expected splitting (J in Hertz) for the lettered protons in the following compounds; ie. give Jp, Jucs Jhes and so on. You may want to refer to the tables in Appendix 5. (0) H al (db) H, ci (OD Ho H (e) jo! (o (go H CH; (db) cH; H H, CH; “sx al Cr H, H, cl X a H (o) (o) à) H, ci H, >= cl OCH; H, H, *3. Determine the coupling constants for methyl vinyl sulfone. Draw tree diagrams for each of the three protons shown in the expansions, using Figures 5.50-5.53 as examples. Assign the pro- tons to the structure shown using the letters a, b, c, and d. Hertz values are shown above each of the peaks in the expansions. o, CH. H Ns ' As Se=c7 o a / N H H d e b e ço Lo o | a | Lo du nm Ao (ppm) grid Gaê (ppm) (ppm) l | [| | | E Pol . | | l | j 14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:10 AM Page 300 & 300 — Nuclear Magnetic Resonance Spectroscopy + Part Three: Spin-Spin Coupling *5, The proton NMR spectrum shown in this problem is of trans-2-pentenal. Expansions are shown for each of the five unique types of protons in this compound. Determine the coupling constants. Draw tree diagrams for each of the protons shown in the expansions and label them with the appropriate coupling constants. Also determine which of the coupling constants are 3J and which are *J. Assign the protons to the structure using the letters a, b, c, d, and e. Hertz values are shown above each of the peaks in the expansions. a 3H | ? I H — NV Demo ;—CH; H 14782 05. Ch5 p233-328.pp3.qxd 2/6/08 8:10 AM Page 302 O 302 — Nuclear Magnetic Resonance Spectroscopy + Part Three: Spin-Spin Coupling *6. In which of the following two compounds are you likely to see allylic (“J) coupling? 7. The reaction of dimethyl malonate with acetaldehyde (ethanal) under basic conditions yields a compound with formula C,HioO4. The proton NMR is shown here. The normal carbon-13 and the DEPT experimental results are tabulated: Normal Carbon DEPT-135 DEPT-90 16 ppm No peak s22 No peak s23 No peak 129 No peak No peak 146 Positive Positive 164 No peak No peak 166 No peak No peak Determine the structure and assign the peaks in the proton NMR spectrum to the structure. dana aass aaa doublet 3 20 1 14782 05 Ch5 p233-328.pp3.qxd 2/7/08 7:41 PM Page 303 O Problems 303 8. Diethyl malonate can be monoalkylated and dialkylated with bromoethane. The proton NMR spectra are provided for each of these alkylated products. Interpret each spectrum and assign an appropriate structure to each spectrum. triplet quartet ri T Er triplet triplet rd o] FC tmiplel ia i . RE FERE k a E 5 5 4 3 2 1 õ 9. The proton NMR spectral information shown in this problem is for a compound with formula CroHyçOs. A disubstituted aromatic ring is present in this compound. Expansions are shown for each of the unique protons. Determine the J values and draw the structure of this compound. The doublets at 6.45 and 7.78 ppm provide an important piece of information. Likewise, the broad peak at about 12.3 ppm provides information on one of the functional groups present in this compound. Assign each of the peaks in the spectrum. + Ge — lreoca som. = 14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:10 AM Page 305 & Problems 305 — usem — um — ms Drs 11. The proton NMR spectral information shown in this problem is for a compound with formula Ci HgNO,. An expansion is shown for the region between 8.3 and 7.2 ppm. No other peaks appear in the spectrum. Analyze this region to determine the structure of this compound. Strong bands ap- pear at 1352 and 1522 cm in the infrared spectrum. Draw the structure of this compound. 44 did PESAPUAPUAPEHAMPAPATAM M545050500404514052000108535001040518037451+05550040401280554555853/8049451/0825404500258 (ppm) —6— 14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:11 AM Page 306 & 306 — Nuclear Magnetic Resonance Spectroscopy + Part Three: Spin-Spin Coupling 12. The proton NMR spectral information shown in this problem is for a compound with formula CH NO. Expansions of the protons appearing in the range 9.8 and 3.0 ppm are shown. No other peaks appear in the full spectrum. The usual aromatic and aliphatic C—H stretching bands appear in the infrared spectrum. In addition to the usual C—H bands, two weak bands also appear at 2720 and 2842 cm”. A strong band appears at 1661 cm”! in the infrared spectrum. Draw the structure of this compound. (ppm) (ppm) (ppm) 13. The fragrant natural product anethole (C,9H,20) is obtained from anise by steam distillation. The proton NMR spectrum of the purified material follows. Expansions of each of the peaks are also shown, except for the singlet at 3.75 ppm. Deduce the structure of anethole, including stereochemistry, and interpret the spectrum. a00 MHz ' LT 14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:11 AM Page 308 & 308 Nuclear Magnetic Resonance Spectroscopy + Part Three: Spin-Spin Coupling *14. Determine the structure of the following aromatic compound with formula CsH;BrO: 300 MHz: + : o 75 MHz *15. The following spectrum of a compound with formula CsH,9O shows interesting patterns at about 2.4 and 9.8 ppm. Expansions of these two seis of peaks are shown. Expansions of the other pat- terns (not shown) in the spectrum show the following patterns: 0.92 ppm (triplet), 1.45 ppm (sextet), and 1.61 ppm (quintet). Draw a structure of the compound. Draw tree diagrams of the peaks at 2.4 and 9.8 ppm, including coupling constants. i 7 E SFA 8300 MHz pi. o dticidio pi + 14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:11 AM Page 309 & 1.9-Hz spacings ) 9.8 ppm Problems 309 74Hz n ' 2.4 ppm *16. The proton NMR spectral information shown in this problem is for a compound with formula CioH1205. A broad peak appearing at 12.5 ppm is not shown in the proton NMR reproduced here. The normal carbon-13 spectral results, including DEPT-135 and DEPT-90 results, are tabulated: Normal Carbon DEPT-135 DEPT-90 15 ppm 40 63 ns 125 130 158 179 Positive Negative Negative Positive No peak Positive No peak No peak No peak No peak No peak Positive No peak Positive No peak No peak 14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:11 AM Page 311 & Problems 311 Draw the structure of this compound and assign each of the protons in your structure. The cou- pling constants should help you to do this (see Appendix 5). CEP IS JM [6 6 SS RAS a 35 SD ES AD NS a as TO ão (ppm) as zs RE Rê MI 1 RO RAS RO RSS RSO RAS RO CRIS RO RSS RD MIS RO is amo (ppm) 14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:11 AM Page 312 & 312 Nuclear Magnetic Resonance Spectroscopy + Part Three: Spin-Spin Coupling nam E magra OS Side 210748 210648 t E | AO ão os 2 abs asa (ppm) 18. The proton NMR spectral information shown in this problem is for a compound with formula CsHy4O. Expansions are shown for all the protons. The normal carbon-13 spectral results, including DEPT-135 and DEPT-90 results, are tabulated: Normal Carbon DEPT-135 DEPT-90 14 ppm 22 278 28.0 32 104 no 141 157 Positive Negative Negative Negative Negative Positive Positive Positive No peak No peak No peak No peak No peak No peak Positive Positive Positive No peak Draw the structure of this compound and assign each of the protons in your structure. The cou- pling constants should help you to do this (see Appendix 5). 14782. 05 Ch5 p233-328.pp3.qxd 2/6/08 8:11 AM Page 314 & 314 — Nuclear Magnetic Resonance Spectroscopy + Part Three: Spin-Spin Coupling (ppm) 19. The proton NMR spectral information shown in this problem is for a compound with formula CioH1205. One proton, not shown, is a broad peak that appears at about 12.8 ppm. Expansions are shown for the protons absorbing in the region from 3.5 to 1.0 ppm. The monosubstituted benzene ring is shown at about 7.2 ppm but is not expanded because it is uninteresting. The normal carbon-13 spectral results, including DEPT-135 and DEPT-90 results, are tabulated: Normal Carbon — DEPT-135 — DEPT-90 22 ppm Positive No peak 36 Positive Positive 43 Negative No peak 1264 Positive Positive 1266 Positive Positive 128 Positive Positive 145 No peak No peak 179 No peak No peak Draw the structure of this compound and assign each of the protons in your structure. Explain why the interesting pattern is obtained between 2.50 and 2.75 ppm. Draw tree diagrams as part of your answer. —6— i | ro ) | MM h h to so as do as (ppm) secgas ss 4Es2Es 58 RRá sia SE RRRRER Se LATA LT ] (ppm) 
