Trans effect coupling constants

A seminal paper [155] examined platinum-phosphorus NMR coupling constants in a series of cis- and trans-platinum(II and IV) complexes. The trans-influence had hitherto been explained in terms of d7r-p7r bonding, in other words, such a mechanism dominated with trans-effect... 

For the ds-l-chloro-2-fluoroethylene, an a-deuterium isotope effect (one D) of 0.6 ppm is observed, along with a trans-P-deuterium isotope effect of 0.4 ppm. Looking at the /rau.v-l -chloro-2-fluoroethylcnc system, the a-deuterium isotope effect is 0.5 ppm and the c/s-P-isotope effect is 0.2 ppm. For the 1-chloro-l-fluoroethylene system, trans-P-isotope effect is 0.5 ppm, with the ds-(3-isotope effect being 0.4 ppm. From these results, it appears that trans-deuterium substitution transmits its isotope effect better than ds-deuterium substitution, the same trend as is observed in transmission of coupling constants. 

The relative stereochemistry of hyperaspine 93 was determined by 2-D NMR spectroscopic and mass spectrometry (MS) methods. It has a m-fused bicyclic conformation 93a <2001TL4621>. The trans-fused one is disfavored by an axial pentyl group at C-8 and by a destabilizing dipole-dipole interaction between the N- and O-atoms, which does not exist in the alternative //.(-conformation. The geminal coupling constant of C( 1 )H2 in 93 (11.0 Hz), and that of its 6-hydroxy derivative (11.2 Hz), indicates that they exist preferentially in / //-conformations, whereas their 6-epimers adopt trans-conformations (9.3 and 8.4 Hz, respectively) <2005EJ01378>. Nuclear Overhauser enhancement spectroscopy (NOESY) studies also confirmed the stereochemistry of 93 by the marked nuclear Overhauser effect (NOE) correlation between H-3 and H-4a <20030L5063>. 

Table 3 presents the values of the force constants corresponding to the C skeleton vibrations of s-trans-1,3-butadiene obtained at several levels of calculation. The computed values are very sensitive to the inclusion of electron correlation. Stretching C=C and C—C force constants decrease when electron correlation is taken into account. This effect is generally larger for basis sets without polarization functions than for those with polarization functions23. On the contrary, the values of the C=C/C—C and C=C/C=C coupling constants do not vary much upon increasing the level of calculation of electron correlation. 

Compounds in which the carbons are sp3 hybridized display the same confused situation. Erickson 78> reports that the trans vicinal H—H coupling constant of c//-dibromosuccinic anhydride (which is reasonably rigid) varies from 2.5 Hz in CHC13 to 6.0 Hz in acetone and dioxane. The same paper reports that the meso dibromosuccinic anhydride and the two corresponding dichloro compounds do not display any solvent dependence of their coupling constants. (Erickson also reports that lJc.H of the dl- dibromide decreases from 172 Hz in chloroform to 166 Hz in acetone and 165 Hz in dioxane exactly the opposite behavior from that observed for any other 1JC H coupling ever studied). It is at least possible that these data result from chemical degradation of the solute rather than from true solvent effects as discussed here. 

A. Ground-state properties a) Bond lengths b) Force constants c) Spin coupling constants d) Optical spectra e) Magnetic moments f) etc. Ground state tram effect Structural trans effect trans influence Static trans effect... 

The structures of the di- and trimeric profisetinidins from Pithecellobium dulce (Guamii-chil) were rigorously corroborated via synthesis.The synthetic approach was additionally motivated by the precariousness of unequivocally differentiating between 2,3-cis-3,4-trans-and 2,3-c7.s-3,4-c7.s-confugurations of the chain-extension units on the basis of H NMR coupling constants.Furthermore, the powerful nuclear Overhauser effect (NOE) method for differentiating between 2,4-cis- and 2,4-tra i -substitution is less useful at the di- and trimeric levels due to the adverse effects of dynamic rotational isomerism about the interflavanyl bond(s) on NMR spectra at ambient temperatures. 

On the basis of the nuclear Overhauser effect, the cis arrangement of the methoxyl group on C-2 and in the side chain was established. The trans relationship of H-4 and H-5 was deduced from their coupling constant (/4>5 3.7 Hz). The post-hydroxylation mixture was shown to contain two other isomers of 317, as well as some of 318. The compounds were reported unsuitable for further transformation involving hydrolytic cleavage, as they polymerized readily in acidic media.205 This difficulty has been overcome in the following synthesis of racemic streptose tetramethyl acetal. 

This effect is also shown by comparison of the coupling constants in the perhydropyrido[l,2-c]pyrimidines 35 and 36,65 trans-fused dibenzo-[a,/]quinolizidine (29) (J6ai,6eq — 12.7 Hz),51 and quinolizidine (Jgem — 11.3 Hz).66 The similar coupling constants of the C-l and C-3 methylenes in the... 

It is possible to distinguish a 4,5-trans-disubstituted oxazolidinone or imidazolidinone from its 4,5-ds-analogue by using H NMR analysis. Indeed, both H4 and H5 protons resonate systematically at lower field for the ds-isomer than for the trans-isomer, and higher /4i5 coupling constants are observed for the ds-oxazolidinones (Table 8). In addition, nuclear Overhauser effect (NOE) enhancement experiments confirm the cis or trans relationship of the H4 and H5 protons. 

A study of the coupling constants between the hydrogen atoms at C-2 and C-3 in trans- 2-methoxy-4-methyl-3,4-dihydro-2//-pyran established that the conformer in which the alkoxy group is axial (187) predominates in the equilibrium mixture. However, the cis isomer exists preferentially as (188) despite the anomeric effect, since there is no 1,3-diaxial interaction between the 2-methoxy and 4-methyl groups (72BSF1077,78JOC667). 

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