Pair coupling

Paarling, n. conjugated substance (jOld Chem.) copula (Biol.) allelomorph. Paarung, /. pairing, coupling, conjugation, paarweise, adv. in pairs, in couples. 

A convenient method of carrying out such a galvanic test in the laboratory has been described by Wesley in which the vertical circular-path machine is used. Each assembly includes two pairs of dissimilar metals—one pair coupled galvanically while the other pair is left uncoupled in order to determine the normal corrosion rates under the same environmental conditions. The type of motion provided (specimens moving in a vertical circular path) enables electrical connections to be made without mercury cup or commutator and the leads can be connected to a calibrated resistance for current measurements attached to the specimen carrier. 

Instead, the conformational characteristics are explained by the stringent requirement of the ionic interaction between the carboxylate/imidazolium ion pair coupled with the attempt of the former group to maintain as many H-bonds as possible (e.g. four H-bonds, cf. Ref. 75c). Such an attempt is obviously supported by the intramolecular H-bond in 1 Im 2 H20. The geometry of the corresponding moieties indicates the presence of strongly interacting ionic species (Fig. 42). 

Table 1 Time-averaged base-pair couplings (in cm and their variance a...

Complete NMR spectral assignments have been made for the trans,cis and transjrans spiroepoxides derived by epoxidation of (Z)-3-arylidenethioflavanones, their 1-oxides and 1,1-dioxides (Table 7). As a consequence of the similarity of the chemical shifts of the signals in the 13C NMR spectra of the isomer pairs, coupling constants data for 37n-2,c-8a (37hc 7.0-7.6 Hz sulfide Vhc 6.2-6.5 Hz sulfoxide Vhc 2.0-3.4 Hz sulfone) and NOESY experiments were used extensively together with ab initio MO calculations to elucidate the conformation of the various isomers <2001MRC251, 2003MRC193>. 

Compound B has no symmetry element in the planar conformation. C-5 is a chiral center, and the protons of each CH2 group are diastereotopic pairs. Each proton of the pair has its own chemical shift. The H-4 proton adjacent to the chiral center is distinctly separated, but the H-3 protons are not, at 300 MHz. Each proton of a diastereotopic pair couples geminally with the other and independently (different coupling constants) with the vicinal protons to give complex multiplets. 

Inhibitory Effects of Added Salts on Ion-Pair Coupling... 

The actual reactions of the diradicals and radical pairs formed by triplet state hydrogen abstraction are those expected of radical pairs coupling (cyclization) ... 

Whereas the spectral behavior of solvent-separated ion pairs and free ions is very similar, the UV/Vis spectra of contact and solvent-separated ion pairs are usually different from each other, as has been shown with sodium fluorenide [141, 164]. Due to the penetration of solvent molecules between the ion-pair couples, the direct influence of the metal cation on the r-electron system of the carbanion is lost. With increasing dissociation, the absorption maximum of sodium fluorenide in tetrahydrofuran solution is shifted bathochromically in the direction of the absorption maximum of the free... 

---