Benzene-iodine complex atoms

Figure 7.14 Formation and dissociation of the excited benzene-iodine charge-transfer complex. Top Transient of free iodine atoms following the excitation of the Bz-l2 complex to its charge-transfer state. (The full line is a single exponential convoluted with the response time of the detector system.) Bottom The four panels (a), (b), (c) and (d) illustrates a possible series of structural changes see text...

The dipole moment varies according to the solvent it is ca 5.14 x 10 ° Cm (ca 1.55 D) when pure and ca 6.0 x 10 ° Cm (ca 1.8 D) in a nonpolar solvent, such as benzene or cyclohexane (14,15). In solvents to which it can hydrogen bond, the dipole moment may be much higher. The dipole is directed toward the ring from a positive nitrogen atom, whereas the saturated nonaromatic analogue pyrroHdine [123-75-1] has a dipole moment of 5.24 X 10 ° C-m (1.57 D) and is oppositely directed. Pyrrole and its alkyl derivatives are TT-electron rich and form colored charge-transfer complexes with acceptor molecules, eg, iodine and tetracyanoethylene (16). 

Other bimolecular reactions of complex systems, such as those of benzene and iodine and acid-base reactions, have also been studied. Currently, we are examining the inelastic and reactive collision of halogen atoms with polyatomics (e.g., CH3I). Other groups at the National Institutes of Science and Technology and at the University of Southern California have studied a new class of reactions O + CH4 — [CH3OH] — CH3 + OH and H + ON2 — HO + N2 or HN + NO. 

Introduction of cyclophane unit, as an integral part of the crown ether, instilled unique properties. Stoddart and co-workers prepared the oxa-thiacrown ether incorporating a rigid horseshoe-shaped aromatic moiety 108 in two steps from hydro-quinone and an excess of l,4-bis(bromomethyl)benzene < 1997JCD1496>. Yields of the first intermediate and 108 were 40% and 61%, respectively. The Cul complex with 108 was a 2 1 (Cu+/108) complex, as a one-dimensional infinite array of cubane-like units consisting of four Cu, four iodine, and four sulfur atoms from four different macrocycles (Scheme 15). 

In the presence of a small excess of iodide, Pd gives Pdt which is sparingly soluble in acidic media. When shaken with benzene or DIPE, PdE passes into the organic phase it has been the basis for a sensitive indirect determination method. The suspension of Pdh in the organic solvent is stripped by dilute ammonia. The aqueous solution is acidified, then the iodide is oxidized by bromine to IO3. This iodate reacts with added T to liberate iodine, which is determined as its coloured complex with starch (see Section 25.2.1). One Pd atom in PdE is equivalent to twelve atoms of iodine. 

Benzene formed from photolysis of the 1 1 complex is a cage-escape product from 3(Jul-CHO+ /Ph ). Benzene formed from the photolysis of the 2 1 complex is an in-cage product from 3((Jul-CHO)2 /Ph ). The formation of 2 1 complexes of amino-substituted ketones and iodonium salts has been suggested to account for the high photosensitivity of polymeric Mannich bases with iodonium salts [102]. Formation of 2 1 donor iodonium cation complexes has been rationalized by consideration of the crystal structures of diphenyliodonium halides, which crystallize as dimers with square planar iodine atoms with two bridging halide counterions [102,108]. 

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