Rings mesityl

The classic disilene 1 is unusual in that it exists in at least three crystalline modifications orange and yellow unsolvated forms and a yellow toluene solvate (Fig. 2). The orange polymorph has a helical conformation in which all of the mesityl substituents are twisted in the same direction thus molecules of 1 in this form are chiral.51 The toluene solvate has an unusual conformation in which two mesityl rings cis to each other are nearly coplanar with the Si=Si bond, while the other two cis mesityl groups are nearly orthogonal.41 The structure of the yellow unsolvated form is not yet known. Because of the flat potential surface for the Si=Si... 

Fig. 2. Thermal ellipsoid diagrams for X-ray crystal structures of 1. Left, orange unsolvated form right, yellow toluene-containing crystals (1-C7H8). The toluene, not shown, occupies a position between the two mesityl rings which are nearly orthogonal to the Si=Si bond.4151...

The more sterically demanding phosphide KPH(mes ) crystallizes solvent-free, even from solutions containing THF, as the ladder polymer [K PH(mes ) ]x (25) (72). Coordination about each K atom is completed by multihapto interactions (approximately if ) between the cation and the mesityl ring of an adjacent phosphide ligand. A... 

The orthogonal pitching of the mesityl rings (Fig. 1.25) may inhibit formation of p-oxo dimers (likely to inhibit catalytic oxidations) which can be formed by flat porphyrin rings in their metal complexes, e.g. (TPP) ligands [583]. 

SCHEME 19. The singlet biradical 43 is formed in the reaction between the two parent benzophe-nones and (t-BuMgCl)2. The radical 44 is formed from the two 2,4,6-trimethylbenzophenones and (t-BuMgCl)2. A, B, C and D denote for the respective phenyl and mesityl rings... 

The preference for the formation of the major ( )-enolate indicates that the attack occurs preferentially from the side of the formally bulkier mesityl ring. Ab initio calculations allow one to rationalize this result. The ketene adopts a conformation with a planar Ph—C=C moiety while the mesityl is nearly perpendicular to this plane. Since the attack onto the C=0 group occurs in the plane of the C=C double bond, the coplanar Ph is effectively bulkier and the preferred attack is from the mesityl side. 

The aromatic complex can be a neutral t °-benzene derivative or an anionic ri -cyclopentadienyl ring. Substituents on these aromatic rings can greatly influence the effectiveness of these catalysts. For example, with benzene derivatives the unsubstituted benzene rings give lower ees and the use of hexamethylbenzene results in lower catalytic activities whilst the cumenyl or mesityl rings give optimum catalyst systems. The two types of chiral bifunctional hnkers that have been most practical are anionic ones based on monosulfonated diamines and amino alcohols. 

On the other hand, an intramolecular reversible rotation of the two mesityl rings in 2,2-dimesityl-l-(trimethylsilyl)ethenol (202) occurs to give 203 (equation 83)258. The free energy of activation for the rotation (AG ) leading to the enantiomerization is... 

The absorption is also affected by the molecular geometry and steric hindrance. For example, bimesityl, which has methyl groups in the ortho positions of the aromatic rings, has a spectrum very similar to that of the individual mesitylene rings and not to that of biphenyl. The reason for this behavior is inhibition of resonance between the mesityl ring systems due to their improper alignment. 

On the basis of the above-mentioned studies, trimesitylmethane (7) is expected to have a propeller geometry in the ground state, and to exist in two enantiomeric forms, differing only in their sense of twist (helicity). Consequently, each of the three equivalent mesityl rings has two diastereotopic ortho methyl substituents, in addition to the para methyl group. In the absence of rapid stereoisomerization, the 1H-nmr spectrum of 7 in an achiral solvent should display three methyl resonances of equal intensity. This expectation is in fact realized at 37 °C,... 

X-Ray analysis indicated a zigzag polymeric structure of MesINTs (Mes = 2,4,6-trimethylphenyl) 139 (Fig. 6). In contrast to PhINTs, the polymeric structure uses 1-0 secondary bonds (2.857A) [215]. An intermolecular secondary bonding of iodine(III) to the mesityl ring of a neighboring unit of MesINTs was also observed. The centroid-to-iodine distance is 3.46 A, and below the sum of the van der Waals radii for the groups (-3.66 A) [219]. 

MesNC)2Au+BF4 is similar, but with a smaller dihedral angle between the planes of the two mesityl rings (56.0°)107a. 

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