Electronegativity, influence

The electronegative influence of the thiadiazole system greatly increases the acidity of substituents (Table 2). The effect is further enhanced in the 1-monoxide and 1,1 -dioxide analogues. The ionization constants of 4- and 5-hydroxy-2,l,3-benzothiadiazoles were determined in water <70AC(R)80l>. 

Electronegativity influences the basic strength of the compound. If we compare the fluoride ion, hydroxide ion, amide ion and the methyl carbanion, then the order of basicity is as shown in the following figure ... 

Compound (13.154) has electronegative influences on both the axial and equatorial positions, and as a result is less stable than (13.153), and exists in equilibrium with a pyramidal form [34]. 

An unexpected feature of a sulphur analogue of the azepines, 4,5-dihydro-thiepin 1,1-dioxide (55), is the shortness of the C(ip )-C(sp) bonds (average 1.311 A). It is postulated that this effect may arise from the electronegative influence of the group. 

The polarizing influence of an electronegative atom decreases with the number of inteiwening rr-bonds. This is called the inductive effect and is indicated in Figure 3-6b by a progression of 6 symbols, (t is generally accepted that the inductive effect is attenuated by a factor of 2-3 by each intervening bond. The inductive ctlcct is not... 

Sulfates —0—SO2—0— Primary alkyl salts Secondary alkyl salts 1415-1380 (s) 1200-1185 (s) 1315-1220 (s) 1140-1075 (m) 1270-1210 (vs) 1075-1050 (s) Electronegative substituents increase frequencies. Strongly influenced by metal ion Doublet both bands strongly influenced by metal ion... 

Substitution of fluorine for hydrogen in an organic compound has a profound influence on the compound s chemical and physical properties. Several factors that are characteristic of fluorine and that underHe the observed effects are the large electronegativity of fluorine, its small size, the low degree of polarizabiHty of the carbon—fluorine bond and the weak intermolecular forces. These effects are illustrated by the comparisons of properties of fluorocarbons to chlorocarbons and hydrocarbons in Tables 1 and 2. 

Elemental boron has a diverse and complex chemistry, primarily influenced by three circumstances. Eirst, boron has a high ionization energy, 8.296 eV, 23.98 eV, and 37.75 eV for first, second, and third ionization potentials, respectively. Second, boron has a small size. Third, the electronegativities of boron (2.0), carbon (2.5), and hydrogen (2.1) are all very similar resulting in extensive and unusual covalent chemistry. 

Substituent effects (electronegativity, configuration) influence these coupling constants in four-, five- and seven-membered ring systems, sometimes reversing the cis-tmns relationship so that other NMR methods of structure elucidation, e.g. NOE difference spectra (see Section 2.3.5), are needed to provide conclusive results. However, the coupling constants of vicinal protons in cyclohexane and its heterocyclic analogues (pyranoses, piperidines) and also in alkenes (Table 2.10) are particularly informative. 

Many properties have an influence on nucleophilicity. Those considered to be most significant are (1) the solvation energy of the nucleophile (2) the strength of the bond being formed to carbon (3) the size of the nucleophile (4) flie electronegativity of the attacking atom and (5) the polarizability of the attacking atom. Let us consider how each of these factors affects nucleophilicity ... 

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