Jr-bonds

From this sort of data it can be concluded that the cobalt(III) ion in this complex is a soft, or class b, Lewis acid. It has been suggested previously that the cobalt(III) ion in vitamin B12 was also a class b acid (138). The kinetic order, which presumably corresponds closely to the order of thermodynamic stability, suggests that for at least some ligands jr-bonding may be important. In this connection it is noteworthy that methylcobaloxime forms a complex with CO (139). 

E. Stretched cr-bond , Twisted jr-bond and Carbene Minima... 

Step 1. Norbornadiene C7H8 of symmetry C2V contains 8 CH single, 8 CC single and 2 jr-bonds, occupied by 36 electrons. (We disregard the inner carbon ls-orbitals). Accordingly, a SCF treatment yields 18 bonding canonical molecular orbitals (CMOs) irreducible representation Ai, 2 to A2, 4 to B and 5 to 82- We collect these 18 CMOs in a column vector... 

The use of UV-VIS spectra to analyse dienes and polyenes was historically the first method of choice. The spectra of isolated non-conjugated polyenes is actually the superposition of the spectrum of each one of the double bonds. For each double bond the spectrum depends on the various substituents and also on its location in the molecule. It also depends on the stereochemistry, since conjugated double bonds have either E or Z configuration around each jr-bond but also a cisoid and transoid conformer3 around the single bond marked as s-cis and s-trans4. 

FIGURE 2. Planar jr-bonded (Xpi) group. Superscripts L and S designate the larger and smaller, respectively of the Z groups attached to the central M atom. The bond order of the MZL and/or the MZS bonds is not less than 1.5. The MG bond is collinear with the group axis... 

These Xpjr groups represent an especially difficult problem because their delocalized electrical effect depends on the steric effect when they are bonded to planar jr-bonded skeletal groups, Gp7r. An approach to the problem has been developed45,46. The electrical effect parameters are a function of the dihedral angle formed by Xp3r and Gpn. The relationship generally used has the form ... 

An attempt62 to prepare a jr-bonded product using pentaphenylcyclopentadienyl yielded instead the sigma-bonded, bulky ligand product Ph5C.5GcC.l3 with normal values for GeC = 197.5 pm and GeCl = 213.1 pm. 

Two types of bonds may be formed when orbitals overlap. These are named sigma (o) and pi (jr) bonds. 

Synthetic applications of carbon radical additions to allenes cover aspects of polymerization, selective 1 1 adduct formation and homolytic substitutions. If heated in the presence of, e.g., di-tert-butyl peroxide (DTBP), homopolymerization of phenylal-lene is observed to provide products with an average molecular weight of 2000 (not shown) [58]. IR and 1H NMR spectroscopic analyses of such macromolecules point to the preferential carbon radical addition to CY and hence selective polymerization across the 2,3-double bond of the cumulene. Since one of the olefinic jr-bonds from the monomer is retained, the polymer consists of styrene-like subunits and may be... 

Transfer of an electron from a a- or jr-bond leads to a radical cation (Eq. la), oxidation with a preceding (Eq. lb) or a succeeding deprotonation generates a radical, and oxidation of the radical forms a cation (Eq. Ic). The radical cations can react according to Scheme 1 [1, 2]. 

Ab initio calculations at the HF/6-31G level have been used to explore energy changes, structural variation, and electron density shifts during jr-face selective addition of substituted acetylide ions to cyclohexanone and cyclohexanethione. Charge polarization of the jr-bond on approach of the nucleophile is such that the carbonyl carbon becomes considerably electron deficient for most of the reaction path (and may... 

Ethylene (ethene, C2H4) is planar, with bond angles of about 120°, and it contains one jr bond. 

This is undoubtedly true, but is part of the process of refining the model as we need to explain new observations. We make models to describe nature nature merely adopts a minimum energy situation. We gain confidence in the approach by using similar rationale to account for the second of the observations above, that ethylene is planar, with bond angles of about 120°, and contains one jr bond. 

C-N jr bonds, leaving a lone pair of electrons on nitrogen in an sp atomic orbital (Figure 2.23). The cyanide/nitrile system is linear, just like an alkyne. 

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