1559T_ch10_175-19810/30/0518:09Pa9e192 ⊕ EQA 192.chapter 10 USING NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY TO DEDUCE STRUCTURE 43.The NMR of the p embles that of the tertiary trum C).but the thync,and the signas in the ecinm are ad mlarly Ho CHCH2CH2OH- CHCH-CH OHS CH. -CH-CH→ C-CH2-CH3 CH CHa Br -CH2-CH3 CH, that the entire spectum consists of first order signals:=0.92(triplet,CHa).1.36(sextet,C4 CH).1.42(quintet.C3 CH2).1.79 (quintet,C2 CH2).3.53 45. t and tran r.all of which a H BrH,一ic (b)No splitting. (c)H aret fro doublet of doublets.the doublet splitting with the (cis)H being larger than that to the (trans)H. 、只 b 43. The NMR of the product closely resembles that of the tertiary alcohol 2-methyl-2-butanol (Problem 40, spectrum C), but the signal for the OH group is missing, and the molecular formula has a Br instead of an OH. The product is 2-bromo-2-methylbutane, and the signals in the spectrum are assigned similarly. How does it form? Rearrangements! 44. At 60 MHz, only the CH2 next to Cl ( 3.5) is clearly resolved. The very distorted CH3 triplet is barely separated ( 0.9) from the other three CH2’s, which overlap from 1.02.0. At 500 MHz, the separation of signals in hertz is so much greater that the entire spectrum consists of nearly first-order signals: 0.92 (triplet, CH3), 1.36 (sextet, C4 CH2), 1.42 (quintet, C3 CH2), 1.79 (quintet, C2 CH2), 3.53 (triplet, Cl CH2). Notice how the multiplets appear so much narrower at 500 MHz. In reality, the coupling constants are unchanged. However, recall that, at 60 MHz, the distance between 0 and 4 is only 240 Hz, whereas, at 500 MHz, the same 4-ppm spectrum width corresponds to 2000 Hz! So the 6- to 8-Hz splittings appear to spread out over a much larger chemical-shift range at 60 MHz than they do at 500 MHz. 45. Neighboring nonequivalent hydrogens split one another. When a hydrogen is split by two or more hydrogens that are themselves not equivalent, the coupling constants of those splittings may be different in magnitude, as illustrated by the spectrum of 1,1,2-trichloropropane (Figures 10-25 and 26). (a) Ha—a triplet of triplets, from large splitting by the two cis neighbors (Hc) and smaller splitting by the two trans neighbors (Hb); Hb—a quartet, from geminal splitting to the Hc on the same carbon and trans splittings to Ha and the Hc one carbon over, all of which are approximately the same in magnitude; Hc—a doublet of triplets, the doublet splitting with the (cis) Ha being larger than the triplet splitting to the two Hb (one geminal and one trans). (b) No splitting. (c) Ha—a quartet, from geminal splitting to Hb and trans splittings to the two Hc; Hb—a doublet of triplets, the doublet geminal splitting with Ha being smaller than the triplet splitting to the two cis Hc; Hc—a doublet of doublets, the doublet splitting with the (cis) Hb being larger than that to the (trans) Ha. Br Br Ha Hc Hc Hb Hb Hb Hc Hc Br Ha vicinal (trans) vicinal (cis) geminal CHCH2CH2OH CH3 CH3 CHCH CH H 3 CH3 CH2 OH2  C CH H 3 CH3 CH CH3  C Br CH3 CH3 CH2 CH3 C CH3 CH3 CH2 CH3  192 • Chapter 10 USING NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY TO DEDUCE STRUCTURE 1559T_ch10_175-198 10/30/05 18:09 Page 192