Ring influence

As already mentioned, the macrocyclic ring can be further enhanced if the propylene moiety is substituted by a butylene group. Visible spectral data of a series of related compounds [Cu(L BF2)D]X 132 and the structural study of the derivative with D = H2O show that the seven-membered chelate ring influences the structure and other properties like electronic absorption of the copper(II) complex [193]. 

The size of the chelate ring influences the 9Be resonance frequencies, as has been noted previously The smaller the ring, the more... 

Both the degree and position of chlorine substitution on the biphenyl rings influence the physical-chemical and toxicological behavior of the individual PCB constituents (15). When PCBs are released into the environment, the original isomer distribution pattern of any PCB formulation may be altered as a result of specific interactions with the environment (14. 22. 23). 

Substituents already bonded to an aromatic ring influence both the rate of electrophilic substitution and the position of any further substitution. The effect of a particular substituent can be predicted by a consideration of the relative stability of the first-formed arenium cation, formation of which constitutes the rate-lintiting step. In general, substituents that are electron releasing activate the ring to further substitution - they help to stabilize the arenium ion. Substituents that are electron withdrawing destabilize the arenium ion, therefore, are deactivating and hinder further substitution. 

However, because the rhodium complexes of tetraphosphine ligand 4 behave differently than the rhodium complex of Josiphos ligand 3 for both substrates, we postulate that either a) different rhodium complexes are being formed (different binding modes as discussed above, see Fig. 2) by 3 and 4, or b) the substituents on the second cyclopentadiene (cp) ring influence the catalytically active site in the rhodium complexes of 4. 

Polarographic reductions of (21) are easier than those of ketones (138) and (139). The size of the bridging ring influences both the absorption of the ketone on the dropping mercury electrode (139 > 138) and the reduction potential (70MI52200). 

Frau J, Donoso J, Munoz F, Garcia Blanco F. Semiempirical and ab initio calculations on the alkaline hydrolysis of the P-lactam ring. Influence of the solvent. J Mol Struct THEOCHEM 1997 390 247-254. 

Metallocenes (Fig. 2) are sandwich structures, typically incorporating a transition metal such as titanium, zirconium, or hafnium in the center. The metal atom is linked to two aromatic rings with five carbon atoms and to two other groups—often chlorine or alkyl. The rings play a key role in the polymerization activity (23-27). Electrons associated with the rings influence the metal, modifying its propensity to attack carbon-carbon double bonds of the olefins. The activities of these metallocenes combined by aluminum alkyls, however, are too low to be of commercial interest. Activation with methylaluminoxane, however, causes them to become 10-100 times more active than Ziegler-Natta catalysts. 

Aromatic compounds undergo many reactions, but relatively few reactions that affect the bonds to the aromatic ring itself. Most of these reactions are unique to aromatic compounds. A large part of this chapter is devoted to electrophilic aromatic substitution, the most important mechanism involved in the reactions of aromatic compounds. Many reactions of benzene and its derivatives are explained by minor variations of electrophilic aromatic substitution. We will study several of these reactions and then consider how substituents on the ring influence its reactivity toward electrophilic aromatic substitution and the regiochemistry seen in the products. We will also study other reactions of aromatic compounds, including nucleophilic aromatic substitution, addition reactions, reactions of side chains, and special reactions of phenols. 

Azide derivatives of azines also equilibrate to give polyaza bicyclic heterocycles <2010T2863>. In the tetrazolo[l,5- ]pyridine-2-azidopyridine equilibrium 311 312, substituents on the pyridine ring influence the position of the equilibrium <1997MRC237>. For another example, see Scheme 16 in Section 2.2.5.3. 

Substituents in the 3- and 4-positions of the phenyl ring influence the acidity of benzoic acids in accordance with their ability to donate or withdraw electron density from the carboxyl function. Electron-donating substituents decrease the acidity through their +I and +M effects this effect is quite small, as can be seen from the data in Table 5.1. 

Choose two examples to show how different groups on the benzene ring influence the position of a second group... 

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