Conjugation n-electrons

Ultraviolet visible (UV VIS) spectroscopy, which probes the electron distribution especially m molecules that have conjugated n electron systems Mass spectrometry (MS), which gives the molecular weight and formula both of the molecule itself and various structural units within it... 

This section deals mainly with nitrogen-containing, eight-membered heterocycles that are able to form a fully conjugated n-electron system, including both 8 n ( pyrrole type ) and iOn ( pyridine type ) systems, i.e. the free lone pair electrons of the heteroatom incorporated, or not incorporated, in conjugation. 

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]. 

The phthalocyanine [1-4] system is structurally derived from the aza-[18]-annulene series, a macrocyclic hetero system comprising 18 conjugated n-electrons. Two well known derivatives of this parent structure, which is commonly referred to as porphine, are the iron(III)complex of hemoglobin and the magnesium complex of chlorophyll. Both satisfy the Htickel and Sondheimer (4n + 2)- electron rule and thus form planar aromatic systems. 

Dissociation of the 7-OH generates an anion with an extended conjugated n electron system, which will favor absorption of long-wavelength light (Chapter 23) and a blue color. Notice that a large number of resonance structures can be drawn for both the anthocyanin and the dissociated forms. Formation of complexes of Mg2+ or other metal ions with the 4 -0 and adjacent OH groups may also stabilize blue colored forms.d... 

We restrict our attention in this chapter to the simple but widely used Hiickel MO (HMO) method for calculating orbitals for rc-electron and aromatic molecules [2], The HMO scheme assumes that a conjugated n-electron molecule consists of a network of sp2-hybridized carbon atoms lying in a plane and each participating atom i has a 2p electron in an atomic orbital, < ) , perpendicular to this plane. Linear combinations of these atomic orbitals (LCAO) result in the molecular n wavefunctions, q/j, each of which has a discrete energy, Ej. In terms of the parameters used in HMO computations,... 

Conjugated n Electron and Cumulative Systems of Heavier Group 14 Elements 24... 

A concept of conjugation of n electrons plays an important role in the chemistry of hydrocarbons. One can easily hit upon butadienes (C=C-C=C) as typical conjugated n electron systems, and their unique properties are well known. Similarly, allenes (C=C=C) are also well studied in the chemistry of hydrocarbon systems. Since it is now concluded that the doubly bonded compounds between heavier group 14 elements can be isolated when they are well kinetically stabilized, a new and exciting challenge should be the synthesis and stabilization of the heavier congeners of another class of important low-coordinated... 

Macrocycles 9.24-9.27 contain fully conjugated n-electron frameworks, but are formally non-aromatic. Nevertheless, they each exhibit a rather strong absorption band in the visible spectrum (e.g., >.max for 9.26 = 384.5 nm, e = 87 100 M cm ). Moreover, these molecules adopt a highly planar conforma-... 

In an intriguing comparison of the uptakes of heptanoic and benzoic acids by a mesoporous carbon adsorbent, Morgun and Khabalov [763] make an inconsequential reference to the study of Mattson [6], and when they should cite the work of Coughlin and coworkers, for the statement that there is additional interaction between the n electrons of the benzoic ring and the conjugated n electron system of the carbon adsorbent, they fail to do so. 

In addition to the CD exciton chirality method, we have recently reported that the theoretical calculation of the CD spectra by the jt-electron SCF-CI-dipole velocity MO method8-l4 has become an important tool for determination of the absolute configuration of a variety of twisted and conjugated n-electron systems. In fact, we have recently determined the absolute stereochemistry of (8aS)-(+)-l,8a-dihydro-3,8-dimethylazulene 10, a labile biosynthetic intermediate for 1,4-dimethylazulene 11 isolated from a liverwort, by application of the MO method to the theoretical calculation of the CD spectra of the twisted tetraene system (8a/ )-12.15 In that case, we have also succeeded in the experimental verification of the absolute configuration theoretically determined, by comparison of the CD spectra of the natural product with those of synthetic chiral model compounds (8a5)-(+)-... 

Molecular size and formula Functional groups present Carbon-hydrogen framework Nature of conjugated n electron system... 

Cyclohexadienes and 1,3,5-Hexatrienes. Not only the standard El mass spectra but also the CID spectra of the isomeric cyclohexadienes are indistiguishable, as shown by McLaf-ferty and coworkers. Owing to the conjugated n electron system, the 1,3-isomer has a significantly lower ionization energy than the 1,4-isomCT (AIE = 13 kcalmol" ) but fragmentation to, e.g., ions, whose structure has been a matter of debate in sev-... 

Other Specific Properties of Conjugated n-Electron-Systems 5... 

Tetraethynylethenes, Fully Cross-Conjugated n-Electron Chromophores, and Other Perethynylated Molecules... 

In 1910 Green and Woodhead first reported an aniline polymer that exhibited a marked increase in electrical conductivity when treated with acetic acid [5]. At that time, however, the phenomenon was not explained in terms of electronic conductivity due to conjugated n-electron systems, and it was then forgotten. 

In choosing a solvent, consideration must be given not only to its possible effects upon the absorbing system. Quite generally, polar solvents tend to obhterate spectral fine structure arising from vibrational effects. In addition, the positions of absorption maxima are influenced by nature of the solvent, n it and n n transitions show electronic spectra with conjugated n electrons in the UV region at about 300-350 nm (B band) and in the visible portion at 500-600 nm. 

Polymeric phthalocyanines such as 31 exhibit good thermal stability under inert gas up to -500 °C and under oxidative conditions up to -350 °C [59]. One way to enhance the electrical conductivity is by enlarging the conjugated n-electron system in the two-dimensional plane of the polymeric phthalocyanines. Compressed powders of polymer 31 exhibit intrinsic conductivities in the order of 10 -10 S cm [55,56,100,101]. The conductivity increases to 10 -10 S cm for thin films of 31 prepared by the reaction of a Cu-film with tetracyanobenzene as described before [89]. 

The first principle of ordering is the number of conjugated n-electrons of unsubstituted basic radicals Str-electrons allyl, propargyl... 

Radicals with 5 conjugated n-electrons 43.1 Pentadienyl radicals... 

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