Electron attracting substitutents

For R=N02, such conjugation increases the stability of I and decreases that of the nitrene intermediate, II hence >-N02 and other electron-attracting substitutents should lower the energy of 1 and increase that of II, resulting in a higher energy of activation for the reaction such is actually the case (Table 19), and the opposite... 

Anionic polymerization is induced by sodium or alkali or alkaline earth hydroxides which form lactam anions in situ. The lactam anion attacks the coinitiator, which can be, for example, a lactam derivative with an electron attracting substitutent on the N atom. This coinitiator can also be formed in situ for example, by addition of acetic anhydride or a ketene. The ring opens and an A -substituted lactam is formed. This lactam reacts very rapidly with a lactam molecule by proton exchange. A new propagation step follows this... 

This basic reactivity pattern is not greatiy affected by the presence of a 1- or 2- substituent, although electron-attracting substituents do diminish the reactivity. The pattern for substitution in 3-substituted indoles can be compHcated by the fact that the electrophile may preferentially attack the 3-position, even when it is already substituted. When this is the case, migration of either the new or the original substituent to C-2 may occur. 

Bicyclo[3.3.1]nonan-9-one is another ketone that exhibits interesting stereoselectivity. Reduction by hydride donors is preferentially syn to electron-attracting substituents at C-5 (X = EWG in the structure shown below) and anti to electron-releasing substituents (X = ERG below). These effects are observed even for differentially substituted phenyl... 

These effects are attributed to differences in the c-donor character of the C—C bonds as a result of substitution. Electron-attracting groups diminish the donor capacity and promote syn addition. An alternative explanation invokes a direct electrostatic effect arising from the C-X bond dipole. 

It should be noted that not all electron-attracting groups enhance reactivity. The sulfonyl and trifluoro groups, which cannot participate in diis type of n conjugation, retard the rate of substitution at an adjacent caibon. ... 

The rates of both formation and hydrolysis of dimethyl acetals of -substituted benzaldehydes are substituent-dependent. Do you expect to increase or decrease with increasing electron-attracting capacity of the pam substituent Do you expect the Ahydroi to increase or decrease with the electron-attracting power of the substituent How do you expect K, the equilibrium constant for acetal formation, to vary with the nature of the substituent ... 

The 1,3-dipolar cycloadditions offluonnatedallenes provide a rich and varied chemistry Allenes, such as 1,1-difluoroallene and fluoroallene, that have fluorine substitution on only one of their two cumulated double bonds are very reactive toward 1,3-dipoles Such activation derives from the electron attracting inductive and hyperconjugative effects of the allylic fluorine substituent(s) that give nse to a considerable lowering of the energy of the LUMO of the C(2)-C(3) n bond [27]... 

Melles and Backer " found, from a study of the oxidation of substituted thiophenes with perbenzoic or peracetic acid, that sulfones could be obtained from polysubstituted methyl- and phenyl-thiophenes and that the presence of electron-attracting groups, such as nitro, hindered the oxidation. Oxidation of thiophene - led to a product which was formed through a Diels-Alder reaction between the intermediate thiophene sulfoxide (211) and thiophene sulfone (212) and for which two alternative structures, (213) or (214), were suggested. Similar sesquioxides were also obtained from 2- and 3-methylthiophene and 3-phenylthiophene. The structures were not proved. Bailey and Cummins synthesized thiophene-1,1-dioxide... 

There is a difference of opinion about the net effect of resonance between the leaving group and an electron-attracting heterocycle, carbocycle, or substituent- This conjugation (101, 102) has been regarded as a deactivating influence on nucleophilic substitution since the C— Le bond is lower in polarity and higher in... 

Substituted quinoxalines afford mono-A -oxides, presumably the 1-oxides, and are resistant to further oxidation, though 5-methoxyquinoxaline is exceptional in forming a 1,4-dioxide. In the case of 6-substituted quinoxalines, as the substituent becomes more electron attracting, the yields of 1,4-dioxide decrease but more of the corresponding 2,3-dioxo compound (41) is formed. ... 

Since it is clear that the presence of an unshared pair of electrons on the sulfur of the sulfoxide group leads to no special instability in the case of the known thiirene oxides (i.e., 18a, 28a,b and the first alkyl-substituted thiirene oxide 30 recently synthesized60), the reduced antiaromatic properties of the thiirene oxides relative to that of thiirenes have been manifested experimentally. As far as the possibility of electron-attracting conjugative stabilization involving the sulfur atom in thiirene oxides is concerned, the experimental evidence accumulated so far is not decisive. Thus, the chemical shift of the vinylic carbon of... 

Pathway A shows the most common reaction where the nucleophilic substitution reaction occurs at the electron-deficient carbon atom due to the strong electron-attracting character of the sulfonyl group. Nucleophilic displacements at the allylic position (SN2 reaction) are shown in pathway B. Pathway C is the formation of a-sulfonyl carbanion by nucleophilic attack on the carbon atom p to the sulfone moiety. There are relatively few reports on substitution reactions where nucleophiles attack the sulfone functionality and displace a carbanion as illustrated in pathway D3. 

Substituted phenylacetic acids form Kolbe dimers when the phenyl substituents are hydrogen or are electron attracting (Table 2, Nos. 20-23) they yield methyl ethers (non-Kolbe products), when the substituents are electron donating (see also chap. 8). Benzoic acid does not decarboxylate to diphenyl. Here the aromatic nucleus is rather oxidized to a radical cation, that undergoes aromatic substitution with the solvent [145]. 

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