Conjugated structures

Fig. 9.3 Absorption spectra of panal in methanol (A), and in 18% acetonitrile/water (v/v) containing 20mM morpholine and acetic acid, pH 4.3 (B). The absorption peak in A is broad due to the partial enolization of the keto group forming a conjugated structure C=C-C=C-OH. In B, the C=0 group is completely converted into an enamine (C=C-C=C-NR2) by morpholine, giving a sharp absorption peak. From Shimomura, 1989, with permission from the American Society for Photobiology.

While the products of 2-furaldehyde polymerization by heat are branched polycondensates with highly conjugated structures (see Section Il-C), the photopolymerization of this furan derivative gives a linear polyaddition product 24>7S). 

The thiophene-2-sulfonyl radicals without substituents at position 3 exhibit rapid rotation about the C—S bond in the ESR time scale, while the 3-bromo-substituted ones demonstrate a marked conformational preference which has been interpreted in terms of a re-type conjugated structure similar to 3 (cf. entries 10 and 11 in Table 2)10. Calculations... 

The persistent radical anion II was obtained by chemical or electrochemical reduction of the parent neutral compound. The EPR spectrum of II is composed of a triplet of triplet (ap(2P)=3.50 mT and ap(2P)=0.89 mT) characteristic of a planar conjugated structure (Fig. 9) [87]. Amazingly, the dianion III was found to be paramagnetic exhibiting an EPR spectrum composed of a distorted dou-... 

The triplet state is usually the ground state for non-conjugated structures, but either species can be involved in reactions. The most common method for generating nitrene intermediates, analogous to formation of carbenes from diazo compounds, is by thermolysis or photolysis of azides.246... 

The solid-state polymerization of diacetylenes is an example of a lattice-controlled solid-state reaction. Polydiacetylenes are synthesized via a 1,4-addition reaction of monomer crystals of the form R-C=C-CeC-R. The polymer backbone has a planar, fully conjugated structure. The electronic structure is essentially one dimensional with a lowest-energy optical transition of typically 16 000 cm-l. The polydiacetylenes are unique among organic polymers in that they may be obtained as large-dimension single crystals. 

Anariba F, McCreery RL (2002) Electronic conductance behavior of carbon-based molecular junctions with conjugated structures. J Phys Chem B 106 10355-10362... 

A transition from ID- to 2D Jt-conjugated structures has important consequences for the n-electron structure.1131 Furthermore, it is challenging to investigate supramolecular architectures formed from disc-type structures. 

The molecule adopts a planar and completely conjugated structure which exhibits exceptional stability. The unit cell contains two centrosymmetric molecules. 

Most reactive metabolites produced by CYP metabolic activation are electrophilic in nature, which means that they can react easily with the nucleophiles present in the protein side chains. Several functional groups are recurrent structural features in M Bis. These groups have been reviewed by Fontana et al. [26] and can be summarized as follows terminal (co or co — 1) acetylenes, olefins, furans and thiophenes, epoxides, dichloro- and trichloroethylenes, secondary amines, benzodioxoles (methylenediox-yphenyl, MDP), conjugated structures, hydrazines, isothiocyanates, thioamides, dithiocarbamates and, in general, Michael acceptors (Scheme 11.1). 

Sulindac-Bovine-Serum-Albumin (BSA)] CONJUGATE STRUCTURES... 

Polydiacetylenes are obtained as single crystals by topochemical solid-state polymerization of the monomer single crystal. These compounds have received considerable attention because of their one-dimensionally -conjugated structure. Their unique --electron structures, and therefore superior third-order nonlinear optical properties, have been extensively investigated. 

Furanic black resins arising from furfural, furfuryl alcohol and furfurylidene acetone 3a are characterized by highly conjugated structures (6-8) their inhibiting power as radical scavengers was tested and turned out to be extremely nigh even in heterogeneous conditions, e.g. with the resin suspended in a monomer solution. 

For conjugated structures thermolytic reactions with loss of sulfur have been studied since 1980 and afford various types of cyclic and acyclic products (Section 4.11.5.1). Nucleophilic attack at ring carbon is very characteristic of 1,2,3-dithiazoles (Section 4.11.5.4). This type of reaction was especially prolific with Appel s salt, studied mostly by Appel, Rees and their co-workers. The preferential site of attack is C(5) but nucleophilic substitution may occur at C(4) when the C(5) site is blocked by poorly leaving substituents, see the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I) for examples of 1,2,3-dithiazoles <84CHEC-I(6)924> and 1,2,3-oxathiazoles <84CHEC-l(6)930>. Nucleophilic attack at ring sulfur in 1,2,3-dithiazoles occurs on S(2) (Section 4.11.5.5), see... 

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