Carbon spectroscopic properties

Annelation increases the complexity of the spectra just as it does in the carbocyclic series, and the spectra are not unlike those of the aromatic carbocycle obtained by formally replacing the heteroatom by two aromatic carbon atoms (—CH=CH—). Although quantitatively less marked, the same trend for the longest wavelength band to undergo a bathochromic shift in the heteroatom sequence O < NH < S < Se < Te is discernible in the spectra of the benzo[Z>] heterocycles (Table 17). As might perhaps have been anticipated, the effect of the fusion of a second benzenoid ring on to these heterocycles is to reduce further the differences in their spectroscopic properties (cf. Table 18). The absorption of the benzo[c]... 

The PFg" salts of [Ru(bpy)2(110)] and [Ru(110)3] and analogous complexes containing 4,4 -bis(substituted) ferrocenyl ligands (110 ), have been synthesized and characterized the tris(chelate) complexes are either poorly soluble or insoluble. Electropolymerization of [Ru(110 )3][PF6]2 produces an electrochromic film. The complex [Ru(bpy)2(lll)] undergoes electropolymerization on Pt and glassy carbon electrodes, although the related complex [Ru(bpy)2(112)] does not. Electrochemical and spectroscopic properties of the films indicate that they form by both head-to-tail and tail-to-tail monomer coupling. ... 

Aromaticity reveals itself in benzene both by the structural phenomena of equal carbon-carbon and equal carbon-hydrogen bond lengths and a characteristic pattern of reactivity. For five-membered heteroaromatics the bond length equivalence found in benzene is not attainable. This is clearly seen in the structure of thiophene (1) as shown the structure is derived from microwave data <6lJSP(7)58). Nevertheless, aromaticity indisputably influences the reactions undergone and the spectroscopic properties. 

So it would seem that the lone carbon atom in these molecules may adopt a number of geometries with a range of spatial requirements. It remains to be seen whether or not there is any correlation between the effective radius of the carbon atom and its chemical or spectroscopic properties. 

Deplancheine (82), from the stem bark of Alstonia deplanchei van Heurck et Miill.-Arg., is an indoloquinolizidine alkaloid of a novel type in which the three-carbon unit that is normally attached to C-15 is missing.620 The structure (82) was deduced from its spectroscopic properties, and has been confirmed by two independent syntheses (Scheme 10).62° 6 It is of some interest that racemic (82) had been prepared,62c and its configuration established, some six years before its isolation from natural sources. 

In this article the infrared spectroscopic evidence for interstellar PAHs will be reviewed. The spectroscopic properties of PAHs studied in salt pellets rather than amorphous carbons will be primarily used since a wealth of very detailed information is available (thanks to the sustained, dedicated effort of Cyvin and his coleagues over many years) and molecule-sized emitters can account for many details of the interstellar spectra. Infrared spectra of amorphous carbon particles and carbonaceous films, synthesized to study the connections with interstellar carbonaceous material, are just now becoming available. The work of Bussoletti and coworkers ([33] and references therein) and Sakata and colleagues ([34] and references therein) is particularly noteworthy in this regard. 

These results indicate that the properties of the redox polymers, such as redox potentials and spectroscopic properties, can be varied systematically and, more importantly, can be predicted from those observed for mononuclear model compounds. As an example of the transfer of photochemical properties from monomeric analogues to the corresponding polymers, the photochemical behavior of the redox polymer [Ru(bpy)2(PVP)sCl]Cl will be considered. This polymer contains one metal center for every five-monomer units. Photolysis of a thin layer of this material on a glassy carbon surface leads to a change in the redox potential of the material from about 650 to 850 mV (See Figure 4.17) [32]. The voltammetric process affected is associated with a metal-center-based Ru(ll/m) redox process. By analogy to the behavior observed for the mononuclear species [Ru(bpy)2(py)Cl]+ (py = pyridine),... 

Inspection of the density and the temperature dependence of the vibrational intensity B (see Eq. 6.2-3) provides further evidence of the weakness of intermolecular interactions in compressed carbon monoxide. Thus, the spectroscopic properties in the dense fluid phase are either quite similar to the corresponding gas phase values or are closely related to these values and may be derived from data of the gas phase spectrum. Fig. 6.2-6 shows the density dependence of the reduced vibrational intensity for the first and second overtones of CO. 

---