Electron attracting property

Because of the electron-attracting properties of the ring nitrogen atoms, methyl groups undergo aldol-like condensations. For example, 3- and 4-methylpyridazine react with chloral to give 3- or 4-(2-hydroxy-3,3,3-trichloropropyl)pyridazine, and 4-methylpyridazine reacts with anisaldehyde to yield 4-(p-methoxystyryl)pyridazine. 

On the other hand, the electron-attracting properties (—I and —M) of the 2-thienyl groups should also facilitate prototropic reactions, where the rate-determining step is the removal of a proton from the a-carbon and which thus is facilitated by electron-attracting sub-... 

The acidic strength of various quinoxaline derivatives is also listed in Table II. -Methyl groups have an acid-weakening effect and quinoxalin-2-one (2-hydroxyquinoxaline) is, as expected, a weaker acid than quinoxaline-2-thione (2-mercaptoquinoxaline), The marked enhancement of the acidic strength of 5-hydroxyquinoxaline 1-methiodide compared to 5-hydroxyquinoxaline itself, is due to the electron-attracting property of the positively charged nitrogen, ... 

Thus, SCI and SCN have different electron-attraction properties. That conclusion was not predictable a priori. Until recently, the extent of polarization in the SCI group has been considered to be comparable to that in the SCN group, according to the S8+-X8 scheme. For instance, Kharash et al. (1953), have pointed out that nitroaryl thiocyanates as well as nitroaryl sulfenyl chlorides, when dissolved in concentrated sulfuric acid, are converted into the same nitroaryl sulfenium ions, 02NArS+. However, the preceding findings indicate otherwise. 

The fact that the nitro group is a meta-orienting one can be explained by the induction effect, caused by its electron attracting properties (I) ... 

The rate of the dehydration of the irreducible dihydroxylamine to the nitroso compound depends on the electron-attracting properties of the aryl group thus the aryldihy-droxylamine can be detected experimentally when Ar is an electron attracting group as protonated pyridyl or /7-nitrophenyl [103]. The electron-attracting group helps to stabilize the hydrated form just as in the case of hydrated aldehydes. 

Electron attracting properties of nitrate esters and charge-transfer complexes... 

ELECTRON ATTRACTING PROPERTIES OF NITRATE ESTERS AND CHARGE-TRANSFER COMPLEXES... 

The kinetics of the rotation about the C—N bond in hindered systems have been studied by Mannschreck and Klle. AG values evaluated from the H-NMR methyl signals (see Table 8) indicate that the rate of rotation in enamines 31-35 depends upon the electron-attracting properties of the substituents. In 36 and 37 the benzo ring reduces the rotational barriers by 9.7-12.5 kj mol as compared to 38 and 39. A formyl group raises the free energies of activation by 13.3-17.9 kJ mol , as can be seen in the table by comparing 36 to 37,38 to 39 and 39 to 40. If one of the N-methyl groups is replaced by another substituent, rotational isomers are possible. It will be difficult to separate such isomers in systems like 40 or 41, since the AG values for the isomerization are expected to be only 84.4 or 89.9 kJ mol ... 

X 10 , and 10 x 10 , respectively, indicating the electron-attracting property of the nitro group. 2-Hydroxyquinazoline is hydrated to the extent of about 25% in the neutral species. ... 

The electronic effects of the halogens are ascribed to their inductive electron attracting properties. These latter are... 

Substituents such as carbonyl and cyano are electron-withdrawing and activate the dienophile toward cycloaddition. The electron-attracting properties of these groups arise from bond dipoles, which place a partial positive charge on the carbonyl or cyano carbon (see Section 1.5). Acrolein has one electron-withdrawing group attached to its dienophilic double bond. Diethyl fumarate and maleic anhydride, the most reactive and synthetically useful dienophiles you will encounter in this section, both have two. 

In Figure 2, the logarithmic chain transfer constant is plotted against Hammett s a constant (3). The chain transfer constant increases as the electron attracting property of the substituents increases. Although the experimental data are very limited, almost linear relationship is observed, and the p value of +1.4 is obtained from the slope. 

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