Jt-electron conjugation

Related compounds, cyclo[2.2.3]azine and l,2,3,4-dibenzocyclo[2.2.3]azine, also give ion-radicals with peripheral Jt-electron conjugate systems (Gerson et al. 1973, Matsumoto et al. 1996). 

Fig. 2.3 Various Jt-electron conjugated systems constructed on the [60]fuIlerene skeleton. (a) C60Br6. (b, c, d) Open-cage fullerenes with a 14-, 13- and 18-membered orifice,...

The spherical Jt-electron conjugated system of [60]fullerene contains the [lOjcyclo-phenacene system, which may be unraveled by removal of the top and bottom two [5]radialene structures (20jt electrons) at both poles of [60]fullerene. The approach shown in Fig. 2.4 constitutes double application of the method that removes one radialene moiety out of conjugation to leave a 50jt-electron bowl-shaped conju-... 

N. Hayashi, A. Matsuda, E. Chikamatsu, K. Mori and H. Hignchi, Synthesis and properties of unsynunetricaUy extended Jt-electronic conjugation system of octaethylporphyrin(Ni)-dihexybithiophene-octaethylporphyrin(Pd) connected with diacetylene linkage. Tetrahedron Lett., 44, 7155—7158 (2003). 

In type 1 metallopolymers (see Figs. 3.7 and 3.8), the metal center is connected to the Jt-electron conjugated polymer backbone by a long enough, typically sam-rated, non-conducting organic chain, that makes the two conductive systems act independent of each other, in respect to the intra-molecular conduction. 

Ogawa T, Usuki N, Ono N (1998) A new synthesis of jt-electron conjugated phosphonates and phosphonic bis(diethylamides) and their SHG activities. J Chem Soc Perkin Trans 1 2953-2958... 

Sigmatropic rearrangement (Section 24.13) Migration of a cr bond from one end of a conjugated jt electron system to the other. The Claisen rearrangement is an example. 

In general compounds with heteroatoms (N, O, S and P) are more amenable to fluorescence reactions" than pure hydrocarbons. Under the influence of the catalytic sorbents substances rich in Jt-electrons are formed, that conjugate to rigid reaction products that are fluorescent when appropriately excited. The formation of fluorescent derivatives is frequently encouraged by gassing with nitrogen or carbon dioxide. 

Numerous colorless organic compounds with extended jt-electron systems can be converted to colored cations or anions with polymethyne chromophore by protonation or deprotonation. The intense coloration of the corresponding salts is usually attributable to the fact that the lone pairs of electrons of the heteroatoms participate in the mesomerism of the conjugated n-electron systems [4]. 

Fernando and Senadeera [40] used different natural pigments incorporating anthocyanins that were extracted from various tropical flowers. The extract was acidified to p H < 1, assuming a deeper coloration, and was used for the preparation of the photovoltaic apparatus. The generation at pH <1 of the oxonium ion allows the wide conjugation of the Jt-electron density throughout the aglycone portion of the... 

The film composed of compounds with highly conjugated Jt-electron systems showed larger pyroelectricity. 

Glowka et al. studied two tetrahydro[l,2,4]triazolo[4,3- ]pyrimidine derivatives 66a and 66b by X-ray diffraction <1994JCX375>. In the solid state, both molecules had the same conformation and were found to be packed in similar manner. The triazole rings proved to be planar, and the conjugation of the Jt-electrons with the lone pair of the N-8 atom was assumed to be the reason of the sofa conformation of the saturated six-membered ring. 

A basic property of all conducting polymers is the conjugation of the chain-linked electroactive monomeric units, that is, the monomers interact via a jt-electron system. In this respect, they are fundamentally different from redox polymers. Although redox polymers also contain electroactive groups, the polymer backbone is not conjugated and the interaction between the isolated redox counters is weak. Consequently, redox polymers are nonconductors [17]. They will not be discussed in this context. 

Carbon and nitrogen are the most common elements from the first row of the periodic table to form aromatic compounds, characterized by cyclic electron delocalization. The bonding of these elements in the conjugated systems shows a large variety. Carbon can be a divalent (carbene), sp carbon with one jT-electron, but also sp carbon can be part of hyperconjugate aromatic systems, provided that it is properly substituted. The pyrrole- and pyridine-type nitrogens also allow the formation of cyclic electron delocalization in a large variety of aromatic systems. 

The electron-donating effect originates from the lone pair electrons on oxygen, with overlap into the Jt electron system. This electron donation will stabilize the non-ionized acid via electron delocalization, but would destabilize the conjugate base by creating a double charge in the carboxylate system. The net result is lower acidity. 

Their isolation by flash chromatography on silica gel was comparatively easy. The CD spectra of related pairs of diastereomers whose addition pattern represent pairs of enantiomers, reveal pronounced Cotton effects and mirror image behavior. It is the chiral arrangement of the conjugated Jt-electron system within the fullerene core that predominantly determines the chiroptical properties. Adducts with a C2-... 

Aromaticity was found to be a general property of many (but not all) cyclic, conjugated jt systems. Moreover, it was found diat aromaticity in molecules can be predicted by Huckel s rule. The structural requirements implicit in Huckel s rule are that there be An + 2 (n is an integer) n electrons in a cyclic, conjugated n system. Obviously benzene, which has six jt electrons (An + 2, n = 1) in a conjugated it system, is aromatic. However, Huckel s rule predicts that molecules such as cyclodecapentaene An + 2 = 10 (n = 2) and [18]-annulene An + 2 = 18 (n = A) should be aromatic, have equal bond lengths, and be planar—and they are. 

Following the standard system of nomenclature, the names of porphyrinoids consist of three parts (i) a number in the square bracket corresponds to the number of jt-electrons in the shortest conjugation pathway (ii) a core name representing the number of pyrroles or other heterocycles in the overall system and (iii) numbers in round brackets specify the number of bridging C-atoms between each pyrrole subunit, starting with the largest. 

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