Fluorenyl rings

In the study of 8, one problem remains. In species like 3 and 5, the ring systems are not planar, thus the two ring systems can t interact through resonance. If the substituent R is to affect the antiaromaticity of the fluorenyl ring system, how is the effect transmitted to the ring system ... 

The transient zwitterion (15), obtained from the /(-hydroxy acid precursor by laser flash photolysis, has been characterized 46 it reacts with nucleophiles more slowly than does the 9-fluorenyl cation itself. The parent acid was also characterized.46 Evidence has been presented that (16) undergoes substantial El elimination via a primary carbocation.47 An analysis of solvolysis results for (17) is indicative of extensive charge delocalization throughout the fluorenyl ring at the transition state apparently... 

Later, Klemm and co-workers [86,87] achieved partial resolution of aromatic compounds by low-pressure chromatography on silica gel impregnated with TAPA. The separation was attributed to n-n complexation between TAPA and the enantiomers. Mikes et al. [88] used a column packed with an (i )-(-)-TAPA aminopropyl-bonded silica support to accomplish the full resolution of helicenes. The authors extended their study to other homologues of TAPA (Figure 22-19). These compounds were coated on silica gel or ion-paired to an aminopropyl-bonded phase, and they were used in the HPLC separation of helicenes. To describe the selective interactions that occur between the stationary phase and the helicenes, the authors assumed that the 2,4,5,7-tetranitro-9-fluorenylidene moieties of the selector are laying down on the silica surface, while the X groups point away from the surface and above the plane of the fluorenyl ring. 

Table XIII. Fluorenyl Ring Atom Charges as Estimated by the Method of Ref. 87 and CNDO II Calculation (83)...

We can carry this further and ask given a positive point charge in the position noted above for one potassium atom, where is the next minimum in the electrostatic potential—that is, where will the second potassium atom be most likely to coordinate The lowest potential energy minimum calculated for a fluorenyl group with one interacting K atom is on the opposite side of the fluorenyl ring and vertically above the plane just to the inside of the Cu—Ci2 bond of the five-membered... 

Determined on radical fully deuterated in the fluorenyl rings. McLachlan calculations of spin densities. ... 

Third, to the extent that the catalyst system preferentially utilizes the more stereoselective site for monomer insertion, enhancement of the stereoselectivity at that site will lead to higher isotacticity. Thus, efforts to increase the size of the fluorenyl ring have led to enhanced isoselectivity, presumably because a substituted benzo moiety is more repulsive in the transition state than the benzo group itself. Catalysts derived from fert-butylated fluorenes such as f-16 ([mmmm] = 95.7%, = 153 °C)... 

FIGURE 7.17 Stereonormal insertion transition state for 5 MA09, showing attractive van der Waals interaction between the propylene monomer and the substituted fluorenyl ring (dashed line). Counterion is not shown... 

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