Trans geometry

This interpretation is supported by literature studies on copper(II) complexes containing two -amino-acid ligands. For N-unsubstituted -amino-acid ligands, deductions as to position of the cis -trans geometrical equilibrium in solution are difficult as illustrated by the fact that for some -amino acids solid complexes have been isolated of both the ds and trans geometry. In contrast it seems as if copper(II) complexes containing two N-alkylated -amino-acid ligands crystallise exclusively in the trans form ". ... 

Where is the trans stereochemistry of the overall reduction decided Which is the first intermediate that shows a preference for a trans geometry Is this preference maintained for all successive intermediates ... 

Gratifyingly, when compound 24 is refluxed in a solution of toluene at 110°C, it undergoes quantitative [4+2] cycloaddition to polycyclic system 25. The indicated stereochemistry of 25 was anticipated on the basis of the trans,trans geometry of the phenyl-diene system in precursor 24 and the presumed preference for an exo transition state geometry. These assumptions were vindicated by the eventual conversion of 25 to endiandric acids A (1) and B (2). 

The complex reacts with CO reversibly via a series of redox reactions. Rh(TMPP)2+ forms adducts with bulky isocyanides RNC (R = Bu , Pr ), retaining the +2 state but changing to a trans-geometry (Figure 2.34) with monodentate phosphines (and uncoordinated ethers) (R = Bu , Mefr = 2.04 B gj. = 2.45, g = 1.96). 

The properties of excited states are not easy to measure because of their generally short lifetimes and low concentrations, but enough work has been done for us to know that they often differ from the ground state in geometry, dipole moment, and acid or base strength. For example, acetylene, which is linear in the ground state, has a trans geometry... 

The complex [imH][IrCl4(im)2], imH = imidazole, is prepared by the reaction of either H2IrClg or IrCl3 with imidazole and HC1.118 X-ray diffraction confirmed the trans geometry around the Ir center and showed that the im ligands are nearly perpendicular to one another (84°). The complex is stable in aqueous solution pH = 7.4, as confirmed by H NMR studies. 

The trans-geometry (confirmed by X-ray) keeps the bulky PPh3 groups as far apart as possible (Figure 2.22). 

Rigid diphosphines have been used to enforce trans-geometries thus with the phenanthrene-derived diphosphine (Figure 3.49, R = Et) the complexes PdLCl and PtLCl2 have closely similar geometries (Pd—P 2.307 A, Pd—Cl 2.306 A, P-Pd-P 177.4° Pt-P 2.293 A, Pt-Cl 2.304A, P-Pt-P 177.1°)... 

The benzo-derivative BDTA exhibits particularly unusual behaviour. Pass-more showed that in samples prepared by sublimation in vacuo it formed a diamagnetic dimer (but not a 71-stack) with a trans-geometry and close... 

To support the various spectroscopic methods for structure determination of dienes and polyenes we will mention some typical chemical reactions yielding derivatives that aid in the location of the double bonds, assign the cis or trans geometry and indicate whether these double bonds are conjugated. It is not our intention to review the chemical versatility of dienes and polyenes but rather to show some cases where the variation helps in the analysis. 

The conversion of the monofunctional adducts into bifunctional lesions depends drastically on the structure of the Pt drug. Obviously, Pt compounds exhibiting trans geometry form different bisadducts than cisplatin and hence, a different spectrum of antitumor activity is expected. Mechanistically, the formation and possible isomerization of bisadducts are not well understood. The assumption that hydrolysis of the second leaving group controls the formation of bisadduct may be an oversimplification. Studies with model compounds as well as with oligonucleotides have indicated that a certain nucleobase may be a powerful nucleophile toward Pt(II) if spatially in a correct position. Unfortunately, our knowledge on these interactions is at present very limited. 

Problem What is the critical weighting i/>dip of the alternative dipolar amide resonance structure in (5.102) that would reverse the preference for pseudo-c/s over pseudo-trans geometry at Cal What are the corresponding bond lengths Rco and Rcn at this critical resonance weighting ... 

The structure of [Fe(salten)(4-methyl-pyridine)]BPh4 has been determined at 293 K [194]. The Fe(III) ion is in a pseudo-octahedral environment in which the basal plane is formed by two salicylideneiminate entities (average Fe-0= 1.885 A, Fe-N= 1.987 A) oriented in trans geometry. The two axial positions are occupied by the secondary amine nitrogen atom of the di(3-aminopropyl) moiety of the ligand (Fe-N=2.035(7) A) and the nitrogen... 

We first consider the union of the ethylenic fragments A and B in a cis and trans geometry. The interaction diagrams for these unions are shown in Fig. 3. We distinguish two types of interactions ... 

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