7i-Electrons

The most important classes of functionalized [60]fullerene derivatives, e.g. methanofullerenes [341, pyrrolidinofullerenes [35], Diels-Alder adducts [34i] and aziridinofullerene [36], all give rise to a cancellation of the fivefold degeneration of their HOMO and tlireefold degeneration of their LUMO levels (figure Cl.2.5). This stems in a first order approximation from a perturbation of the fullerene s 7i-electron system in combination with a partial loss of the delocalization. 

For 7i-electron systems Hiickel made the following approximations ... 

The 7i-electron wave functions in the Hiickel method are given by... 

Fig. 10.4. Total 7i-electron density for some substituted benzenes. [From STO-3G calculations as reported by W. J. Hehre, L. Radom, and J. A. Pople, J. Am. Chem. Soc. 94 1496 (1972).]...

Flexible six- and eight-7t-electron systems would impose an entropic barrier to concerted 10-7i-electron concerted reactions. Most of the examples, as in the cases above, involve cyclic systems in which the two termini of the conjugated system are held close together. 

This chapter describes some of the recent results on the low-temperature synthesis of crystalline graphite and CNTs, referring to various characteristics relating to the 7i-electron materials, which have been found in the Yoshimura 7i-Electron Materials Project [11] of the ERATO program in Japanese... 

With ten 7i-electrons delocalized over seven atoms, trithiadiazepine is electron rich and should undergo electrophilic substitution, which indeed it does. Nitronium tetrafluoroborate at — 10 C or copper(II) nitrate gives the mononitro derivative 5, which can be converted into the dinitro compound 6 by the action of an excess of nitronium tetrafluoroborate at 10 C.388... 

Nuclear Magnetic Resonance Spectra. The CNMR spectra of quinoxaline and a dozen 5-substituted quinoxalines have been determined for comparison with those of corresponding naphthalene derivatives. Aspects of the H, and NMR spectra of quinoxaline and related heterocycles have been correlated with the 7i-electron densities of the system." In contrast with the... 

Dendrimer chemistry has taught us that these molecules create a nano-sized closed space that, presumably, is the origin of the specific physical properties of this class of materials. As the next stage of dendrimer chemistry, a macromolecule capable of creating such a space inside its molecule is proposed. To create the nano-sized space, porphyrin is considered to be the best candidate for the component molecules, because it has versatile properties associated with its expanded 7i-electron system and the incorporated metal. The resultant multi-detectable properties of porphyrin, that is, a number of its properties are detectable by many physical methods, may reveal the function of the nanometer-sized space. 

The absorption bands for both quinoid and dipolar structures have been calculated by the PPP method.2,12 The calculations for a more simplified model of the colored form of some spirobenzopyrans using the normal parameters are shown in Table 2.12 In this case, the spiro carbon in the indoline moiety is ignored in the 7i-electron system, and the quinoid structure is assumed. 

Using the data from Table 1 and plotting 1/A vs 1/[TBSM], the value of Kc for the formation of the TBSM. .. MA complex was determined (involving 7i-electrons of double bonds due to the shift of anhydride protons) ... 

The 7i electron density in the triple bond of ethyne is cylindrically symmetric. 

The 7i electrons of the initial alkene can then be used to form a bond with a proton at the terminal carbon, forming a secondary or tertiary carbocation. 

The scientific interest in porphyrin ligands (Fig. 5) derives in part from their ability to accommodate a large series of different elements, often in various oxidation states. On the other hand porphyrins are planar molecules with a delocalized 18 7i-electron system and a diatropic ring current [25], which makes them interesting for the design of new materials with applications in photochemistry [25-27]. 

The solid state structure of 33 reveals a dimeric molecule with an eight-membered B2C2N2O2 heterocyclic ring in a chair conformation. The N—B and B—O bond lengths of 1.585(2) and 1.541(2) A, respectively, as well as the C—N and C—O bond lengths of 1.294(3) and 1.285(3) A, respectively, indicate delocalization of the 7i-electron density in the acylamino moiety [65]. 

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