Substituents s. a. Position shift

Substituents s. a. Position shift —, angular, stereospecific introduction 14, 754 Substitution (s. a. Addition, substituting. Replacement)... 

The position of the BII maximum, in flavones, is affected by the introduction of additional substituent(s) at position(s) 6 and/or 8 which, in general, produce a bathochromic shift placing this maximum above 270 nm (Voirin, 1983). This is the case of xanthomicrol (5,4-dihydroxy-6,7,8-trimethoxyflavone) (Figure 7.4). 

Polypyrrole can also be synthesized with substituents on the nitrogen. However, these substitutions can dramatically alter the properties of the films and have deleterious effects on their conductivities. For example, although poly- V-methylpyrrole has an appearance and level of doping similar to those of polypyrrole, the conductivity is diminished to 10 S cm" [4]. PoIy-A -methylpyrrole has an oxidation potential of 0.45 V (versus SCE), a positive shift of 0.65 V compared with polypyrrole. In general, N-substituted polypyrroles are more difficult to oxidize and correspondingly less air sensitive than the parent polymer [119]. Substituted pyrroles with ethyl, propyl, or butyl groups attached to the nitrogen can also... 

The of 33 shows a bathochromic shift, compared to that of the corresponding spironaphthopyran [ max 531, 558(s) nm in toluene].78 The substituent effect in 2, 5, 6 - and 5-position of 33 on the absorption band of the colored form has been examined.72,77,7s The donor substituent group in 6 -position, such as piperidino group, gives a hypsochromic shift by 35 nm, but 5 -carbomethoxy substitution results in a bathochromic shift by 20 nm. This may be due to interaction between oxygen atom of the phenolate and methoxy group. 

Referring first of all to the reactions over 0.2% platinum/alumina (Table V) the major features of the product distributions may be explained by a simple reaction via an adsorbed C5 cyclic intermediate. For instance, if reaction had proceeded entirely by this path, 2-methylpentane-2-13C would have yielded 3-methylpentane labeled 100% in the 3-position (instead of 73.4%) and would have yielded n-hexane labeled 100% in the 2-position (instead of 90.2%). Similarly, 3-methylpentane-2-I3C would have yielded a 2-methylpentane labeled 50% in the methyl substituent (instead of 42.6%), and would have yielded n-hexane labeled 50% in the 1- and 3-positions (instead of 43.8 and 49% respectively). The other expectations are very easily assessed in a similar manner. On the whole, the data of Table V lead to the conclusion that some 80% or so of the reacting hydrocarbon reacts via a simple one step process via an adsorbed C5 cyclic intermediate. The departures from the distribution expected for this simple process are accounted for by the occurrence of bond shift processes. It is necessary to propose that more than one process (adsorbed C6 cyclic intermediate or bond shift) may occur within a single overall residence period on the catalyst Gault s analysis leads to the need for a maximum of three. The number of possible combinations is large, but limitations are imposed by the nature of the observed product distributions. If we designate a bond shift process by B, and passage via an adsorbed Cs cyclic intermediate by C, the required reaction paths are... 

Among the earliest research on the transmission of substituent effects was the pioneering work of Lauterbur (58) and of Spiesecke and Schneider (59). For a wide series of substituted methanes and ethanes they found an approximate correlation of >3C chemical shifts with the electronegativity (E) of the substituents (X). So they concluded that inductive effects through o-bonds play an important role in determining the chemical shifts of a- and -positioned carbon atoms, and that this effect reflects the substituent s electron-withdrawing or -releasing ability. 

The fiavonoidal moiety of ficine was deduced from its UV spectrum, which was very similar to chrysin (37), and the bathochromic shift indicated a saturated alkyl substituent on ring A. Treatment with Gibb s reagent to detect the presence of a proton para to a phenolic OH (17) gave a positive result for 5 but not 4. Although no molecular ion could be seen in the mass spectrum, the peaks obtained were equivalent to the sum of the individual spectra of chrysin (37) and... 

Substituents on the phenyl groups of 3,3-diphenyl-3//-naphtho[2,l-6]pyran can have substantial effects on color, intensity, and fade. Electron-donating groups in the para position(s) result in a bathochromic shift in the visible spectrum, a lower equilibrium intensity, and a somewhat more rapid fade (Table 3.1). An additional... 

---