Double doublet

The double doublet corresponds to Pfi, with splitting owing to phosphorus A (cis) (/(P-P) 25 Hz) and rhodium (/(Rh-P) 172 Hz). The fluxional behaviour is consistent with a rapidly rearranging (at room temperature) square planar structure rather than a tetrahedral one (Figure 2.11). 

Figure 5.34 Schematic representation of the coupling interactions of the H, and Hf, protons of Klibromobenzene. The H and protons are split into double doublets due to their couplings with //j and is split into a triplet by the two...

A diradical is an atom or molecule containing two impaired electrons. The properties of diradicals are for the most part like those of monoradicals. They are paramagnetic and show paramagnetic resonance absorption. Although they are very reactive chemically, this is not a reliable criterion for the diradical state. Spectroscopically the diradical will probably be a triplet state if a double bond structure coupling the two electrons is geometrically possible. But when the two electrons are fairly well isolated from each other the state is probably a double doublet, like two independent radicals. 

This molecule exists of isomers of the complex shown in Figure 11.7 that inter-convert rapidly, even at temperatures below 200 K, as shown by the off-diagonal peaks between the double doublets of one structure and the broad doublet of the other structure [23]. The isomeric structures are caused by the relative positions of the two ligands with respect to each other (i.e., parallel or anti-parallel orientation of the NMe2 groups). 

The H NMR spectram (CDClj, 500 MHz) of 12 showed two singlets (8 0.83 and 8 0.95), each integrating for three protons due to the C-18 and C-19 methyl protons. Three 3H doublets at 8 0.78 (J= 6.5 Hz), 8 0.79 (J= 6.5 Hz) and 8 0.85 (J = 7.0 Hz) were due to the secondary C-26, C-27 and C-21 methyl protons, respechvely. The C-3 methine proton resonated as a one-proton double doublet at 8 3.63 (JJ= 10.5 Hz and J2= 3.5 Hz) and its downfield chemical shift value was indicative of the presence of a geminal hydroxyl funchonality. A one-proton mulhplet at 8 5.21 was ascribed to the C-6 olefinic proton. The C-28 exocyclic methylene protons appeared as two broad singlets at 8 5.40 and 5.58. The C-NMR spectram (CDCl, 125 MHz) showed the resonance of all 28 carbon atoms. The combination of H and C-NMR data suggested that compound 12 has a sterol like structure as most of the H and C-NMR chemical shift values of 12 were similar to those of sterols reported in the literature [19, 20]. The H and C-NMR chemical shift values were assigned with the aid of COSY-45 , HSQC and HMBC spectral data. Compound 12 was found to have modest inhibitory activity against C. xerosis and S. aureus with minimal inhibitory concentration values of 82.35 and 146 pg/ml, respectively. 

NMR. The 300 MHz iR-spectrum of V-2 in D2O is shown in figure 5a. The three multiplets between 1.4 and 2.05 ppm, the two double doublets between 3.4 and 3.7 ppm, and the multiplet between 3.6 and 3.8 ppm comply well with a hydroxylysine substituent at a ring nitrogen (fig. 5b, table 2). No definite conclusion as to the total number of protons can be drawn from the spectrum, since impurities seem to be present, for example singlets at 2.2, 2.05 and 1.95 ppm. The compound V-2 was purified further by ion exchange- and adsorption chromatography and a 500 MHz ID iH- (fig. 6b) and a 2D TOCSY-spectrum (in D2O) were run. Also here, the main spin system present is the hydroxylysine residue (fig. 5b). 

The HREIMS of 2,7-dibromocarbazole (388) was identical to that of 3,6-dibromocarbazole (386). Differences were identified in the chemical shifts and splitting pattern of the H-NMR spectrum. Thus, a deshielded, two-proton doublet at 7.87 with ortho-coupling (/=8.3 Hz), assignable to the C-4 and C-5 protons, indicated the location of two bromine atoms at the C-2 and C-7 positions of the carbazole nucleus. This was also evident from the shielded ortho- and meto-coupled (/=8.3, 1.5 Hz) two-proton double doublet at S 7.36, assignable to the C-3 and C-6 protons. Further, a mutually meto-coupled (/= . 5 Hz) two-proton doublet at S 7.57, assignable to the C-1 and C-9 protons, supported the location of the two bromine atoms ortho to these carbons. Based on these spectral analyses and the HREIMS identical to that of... 

Substituted thiocoumarins have been thoroughly studied, and their infrared, NMR, and mass spectra critically examined. Their NMR spectra show a characteristic low-field singlet for the 4-proton and, with a strongly electron-withdrawing 3-substituent, H-5 is observed downfield from the complex aromatic multiplet, as a double doublet. 

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