Conformational analysis of p-X-anilino dioxaphosphinanes. Substituent effects on 31P and 15N NMR signals and on negative hyperconjugation (n–σ*)

Measurement and Applications of Long‐Range Heteronuclear Scalar Couplings: Recent Experimental and Theoretical Developments

“…It is also found that the average difference of coupling constants obtained by these two methods is 0.512. For a series of methyl aldopyranosides (12)(13)(14)(15)(16)(17)(18)(19)(20) as given in Scheme 5, Table 5 shows good agreement between experimental 3 J CH values and those predicted through Equation (3) using the torsional angles obtained by X-ray spectroscopy. [112] …”

“…2I z S z ) by the 1 H 908 pulse applied along the y axis (I is proton and S is carbon). The first gradient which acts as a z-purge does not affect this term and eliminates coherences that are not oriented along the z axis or those arising from protons attached to 12 C. [37,49,50] It is followed by an X-filter, which is a combination of two 908 pulses with phases (x, x) and (x, Àx), respectively. [24] The first scan with (x, x) phases of both 908 pulses collectively acts as a 1808 pulse and inverts only the magnetization of 1 H attached to 13 C (I y À2I z S z ), where I y is the transverse magnetization of a proton not attached to 13 C, whereas in the subsequent scan (x, Àx) phases of both 908 pulses collectively execute a 08 pulse (I y + 2I z S z ).…”

“…[61] For instance, the E configuration around the exocyclic C=C bond in enaminone (9 in Scheme 2) was established on the basis of 3 J CH between the methylidene proton (H2') and the carbonyl carbon atoms [O-C(1) and O-C(3)], measured from the anti-phase splitting of cross peaks in the HMBC spectrum. It is also well known that the magnitudes of the coupling constant ( 3 J CH ) between nuclei with cis configuration around the C=C double bond are smaller (2-6 Hz) than those of trans-oriented nuclei (8)(9)(10)(11)(12). [62,64] The magnitudes of couplings 3 J C(1)ÀH(2') = 7 Hz (trans) and 3 J C(3)ÀH(2') = 5 Hz (cis) confirms the E configuration around the exocyclic C=C double bond.…”

Applications of nuclear shielding

“…Theoretical Kohn-Sham DFT calculations support the participation of the cited stereoelectronic interactions not only to understand the conformational behaviour of these systems but also to give an explanation of the observed substituent-induced chemical shift (SCS) on 31 P and 15 N NMR signals. 395 For B-DNA, the strong linear correlation observed by NMR between the 31 P chemical shifts (d P ) and three recurrent internucleotide distances demonstrates the tight coupling between phosphate motions and helicoidal parameters. It allows to translate d P into distance restraints directly exploitable in structural refinement.…”

“…331 Wild-type phospholamban (WT-PLB) is a pentameric transmembrane protein that regulates the cardiac cycle (contraction and relaxation). From a physiological prospective, unphosphorylated WT-PLB inhibits sarcoplasmic reticulum ATPase activity, whereas its phosphorylated form relieves the inhibition in a mechanism that is not completely understood.…”