Complex multiplets

The a-plienylcinnamonitrile (Note 4) present in the distillation flask can be recovered. The residue is broken up with 75 ml. of methanol, the mixture stirred and cooled, and the product recovered by filtration. Recrystallization from methanol gives 17-20 g. of crystalline material, m.p. 86-88°. The proton magnetic resonance spectrum (chloroform-d) shows complex multiplets at 5 7.20-8.00. 

These new derivatives were isolated in good yields (60-94%) as high boiling liquids and were fully characterized by NMR spectroscopy (1H, 13C, and 11B) and elemental analysis. The proton NMR of the starting material 1 shows a well-resolved multiplet and quintet for the trimethylene bridge. Upon monosubstitution, however, three complex multiplets are observed, indicative of the unsymmetrical structures of these derivatives. Also, the nonequivalence of the N-C carbon atoms is clearly apparent in the 13C NMR spectra of 2-4. 

Figure 38 shows three fluorine-19 spectra a potassium fluoride in D20 b trifluoroacetic acid and c p-fluorophenol in CDC13 (with expansion). Line-widths are small 1.9 Hz in spectrum a, 1.3 Hz in spectrum b. The computer printout in c shows that what is apparently one single line is in fact a multiplet, and the expansion shows a complex multiplet due to coupling of the fluorine nucleus with the two protons ortho and the two protons meta to it. 

The combination of cross polarization (basically a pulse sequence) and MAS is sufficient to drastically reduce the linewidths of spin-Vi nuclei. Liquid-state proton NMR spectra, as we have seen, are characterized by extremely narrow lines and complex multiplets due to spin-spin coupling in addition, the normal chemical shift range is only around 10 ppm. 

In Problem 42 we have included the results of several homodecoupling experiments (Section 1.1.1), which simplify multiplets and allow ready determination of coupling constants in otherwise complex multiplets. 

Because of long-range F—F coupling constants that contribute to the second-order nature of the system, the fluorine signals of 2,3,5,6-tetrafluoroaryl groups generally consist of complex multiplets. The chemical shifts of a few examples of such systems are given in Scheme 6.33. 

The complex multiplet centred at 5.04 ppm results from the overlap of the methine and -OH protons (i.e., they are accidentally equivalent ) whilst the equally complex methyl signal is centred at 1.48 ppm. Because of this overlap, their lines are indistinguishable and so the -OH is said to be virtually coupled to the methyl group. Virtual coupling is another potential consequence of non-first order behaviour. 

If all the pentane is removed before pyrolysis, the bicyclo [2.1.0]pentane shows no impurities on vapor phase chromatography with a 20% Dow 710 on 50/60 U Anaprep column. Analysis by n.m.r. also revealed the absence of any traces of cyclo-pentene in the spectrum consisting of three complex multiplets at 0.3-0.8, 1.1-1.7, and 1.9-2.4 p.p.m. (downfield from internal tetramethylsilane reference). 

Pentacarbonyl(diphenylmethylene)tungsten(0) is a moderately air-stable soild that is readily soluble in most organic solvents. The resulting solutions are air and light sensitive and decomposed thermally at about 50°. The infrared spectrum of a heptane solution shows bands in the metal carbonyl region at 2070 (m), 1971 (s), and 1963 (s) cm"1, characteristic of a group VI pentacar-bonyl species. The proton NMR spectrum in CS2 or acetone-d6 shows a complex multiplet at 5 7.2 relative to internal tetramethylsilane. 

Dichloropropane, CljCH CHjCH, a triplet (H" ), a complex multiplet more downfield (H ). and a triplet still more downfield (H°). 

The HNMR spectrum, recorded in a chloroform- solution, shows the two nonequivalent methylene groups of the propionate as multiplets at <51.38 and <5 2.97 ppm, respectively, and a singlet at <5 3.7 ppm corresponding to a methyl group bound to oxygen. The ethyl groups of the two nonequivalent triethylphosphines appear as complex multiplets centered at <5(C 2) 1.75 ppm and <5(Ch3) 1.10 ppm. 

The H spectra of both compounds show all facets of spectral appearance, well resolved spectral regions as well as regions with heavy signal overlap and simple first order multiplets as well as complex multiplet structures caused by strong coupling effects. 

By addition of one equivalent of base to solutions of 7-(2-hydroxyethoxy)-4-nitrobenzofurazan and 7-(2-hydroxyethoxy)-4-nitrobenzofuroxan in either water or a dipolar aprotic solvent, the spiro adducts 169 and 170 are completely formed212 and can be characterized by their UV-visible and H-NMR spectra. They display substantial upfield chemical shifts relative to the ring signals for the starting substrate and a complex multiplet centered at 8 4.16 for the nonequivalent dioxolane methylene protons. Isolation of the adducts as the potassium salts from acetonitrile solution was accomplished by removal of the solvent. 

Parameters are taken from computer simulations of the observed complex multiplets. 

The spectrum of pyran-2-one (17) consists of two complex multiplets of equal intensity centred at 8 6.4 (H-3 and H-5) and 7.6 (H-4 and H-6). Despite the complexity, PMR is described as a reliable technique for establishing the position of substituents, since their... 

Chroman-3-one (62) shows singlets for 2-CH2 (8 4.32) and 4-CH2 (3.51). The H-5 signal is no longer separated from the other aromatic protons and a complex multiplet is observed (70JHC197, 81JHC1123). 

Recorded in C6D6 relative to TMS. c Recorded in hexane. d Complex multiplet. 

As can be seen from Fig 2, the isolated H-4 signal at r 0.11 in the monohydrate cation has moved strikingly upfield to r 3.40, indicating that this proton has taken on a more aliphatic character because the 3=4 bond has become saturated. That this was truly the cation of 3,4-dihydro-4-hydroxypteridine was confirmed by measuring a set of C-methylpteridines. In this monohydrate, the complex multiplet signal presented by the H(2), H(6), and H(7) atoms had moved slightly upfield with no loss of coherence. When this solution of the monocation was... 

---