Bonds preference

Photoelectron spectroscopy shows that the carbon-tin bond prefers that orientation in which it lies parallel to the pir orbitals of the double bond, to permit carbon-metal hyperconjugation (146). 

Scheme 37 Electron-donating geminal a bonds prefer the Z-position in products via cyclic transition states...

A review11 with 123 references is given on amino acid bonding preferences in complexes of platinum and palladium. The preferences for a particular donor atom for Pd11 depends primarily on relative thermodynamic stabilities of the complexes formed. Sizes of potential chelate rings often play a crucial role in determining donor atom preferences. 

Zimmerman suggests that this bonding preference is consistent with approximate triplet energies of his isoconjugate models for bridge formation ... 

Key Words Binding affinity, H-bonding, Preferred sites, NMR pulse sequence... 

R. K. Castellano, J. Rebek, Jr, Formation of Discrete, Functional Assemblies and Informational Polymers through the Hydrogen-Bonding Preferences of Calixa-rene Aryl and Sulfonyl Tetraureas , J. Am. Chern. Soc 1998,120, 3657-3663. 

Molecular ions of phenylalkanes are comparatively stable due to the good charge stabilizing properties of the aromatic ring and thus, they normally give rise to intense peaks. Those molecular ions, possessing a benzylic bond preferably show... 

Much evidence supports the conclusion that the elimination of the group HX from alkyl halides by bases is a trans elimination reaction. This means that the atoms H and X leave from the opposite site of the incipient double bond. It is mostly explained by assuming that the electrons which are left by the leaving proton and which will form the double bond prefer to attack the leaving group X from the rear (50). The transition state for the elimination, if it is concerted, is most stable if H, X, and the carbon atoms 1 and 2 lie on one plane, which in most molecules is best realized in the trans position (51). ... 

Sharpless et al. recently introduced the term click chemistry for the use of simple (but selective), high-yielding reactions forming mostly carbon-heteroatom bonds, preferably in aqueous medium, using only easily available compounds [72]. The authors urge the synthetic community to concentrate on the development of new properties rather than new compounds. 

This enzyme [EC 3.4.21.39], also referred to as mast cell protease I and skeletal muscle (SK) protease, is an endopeptidase that has been isolated from mast cell granules. It belongs to the peptidase family SI and catalyzes the hydrolysis of peptide bonds, preferring Phe-Xaa > Tyr-Xaa > Trp-Xaa > Leu-Xaa. 

A cocrystallisation study of the hydrogen bond preferences of 2-amino-pyrimidine 9 by Etter and Adsmond provided further evidence of the utility... 

The conformational equilibrium of 1,3-dithiane 1-oxide (the sulfoxide) was studied by low-temperature H and NMR spectroscopy <1999RJC5> at —80 to —90°C the two chair conformers could be detected (the one with the equatorial S —> O bond preferred by ca. 90%). Besides discussing the influence of the sulfoxide conformation on both NMR spectra, the enthalpy and entropy differences AH° = 0.55 0.1 kcal mol AS° = 1.88 e.u.) between the two conformers were detected in CDCl3 CS2= 1 2. 

The basic principle underlying VSEPR theory is that valence electron pairs, whether they re lone pairs or they occur within bonds, prefer to be as far from one another as possible. There s no sense in crowding negative charges any more than necessary. 

The term bond direction arises from the fact that certain covalent bonds prefer to lie in particular directions with respect to the bonded atoms. For example, the bonds from carbon point from the center to the vertices of a regular tetrahedron. 

Table II Hydrogen Bonding Preferences Symmetric vs. Asymmetric...

The fact that -hybridized C-C bonds prefer the honeycomb bond angles of 120° contributes to the exceptional stability of benzene and graphite. HuckeFs rule stipulates that aromaticity is associated with a cyclic conjugated system of 4n + 2... 

The fluoro substituent would be sterically similar to thymine, but would have a different hydrogen bonding preference due to the lone pairs on fluorine. So, for a rapidly reproducing cell (such as a virus or a tumor), FUdR would disrupt transcription and cause mutations in expression and function. 

There are further properties of ligands beyond their HSAB characteristics that determine their bonding preferences to metal ions. The simplest lig-... 

Today, it is known that Cram was wrong about this preferred conformation (he assumed that the bulkiest Ca carbon bond was oriented anti to the C=0 double bond actually this Ca carbon bond prefers a syn-orientation). If Cram had known this conformation at that time, he would certainly not have based his explanation of Cram selectivity upon a reaction with the most stable conformer of the aldehyde. This is because, in order to establish the experimentally found product geometry, the nucleophile would have been required to approach the C=0 double bond of the truly favored conformer from the sterically more hindered side. However, even at that time this error could have been avoided (see below). 

---