Electronegativity hydrogen

Because most organic compounds we will encounter will contain hydrogen (electronegativity = 2.20) and carhon (2.55), and may also contain nitrogen (3.04) and/or oxygen (3.44), we can appreciate... 

Similar considerations apply to carbon bonded to noncarbon atoms in the main chain. The —Si—CH3 is not so polar as —SiHa, and so the dimethyl derivative is sufficiently stable to enable poly(dimethylsiloxanes), - Si(CH3)2—to be produced commercially. By contrast, Ti—C and A1—C bonds are sensitive to oxygen and hydrogen (electronegativity of... 

Electronegativity of UMO (unoccupied molecular orbital) state f< ELH (hydrogen) Electronegativity of UMO state for EM (oxygen)... 

The electronegativity system may be used. For example, in the chemisorption (with dissociation) of hydrogen on tungsten. 

The unequal distribution of charge produced when elements of different electronegativities combine causes a polarity of the covalent bond joining them and, unless this polarity is balanced by an equal and opposite polarity, the molecule will be a dipole and have a dipole moment (for example, a hydrogen halide). Carbon tetrachloride is one of a relatively few examples in which a strong polarity does not result in a molecular dipole. It has a tetrahedral configuration... 

Many of the reactions of halogens can be considered as either oxidation or displacement reactions the redox potentials (Table 11.2) give a clear indication of their relative oxidising power in aqueous solution. Fluorine, chlorine and bromine have the ability to displace hydrogen from hydrocarbons, but in addition each halogen is able to displace other elements which are less electronegative than itself. Thus fluorine can displace all the other halogens from both ionic and covalent compounds, for example... 

The correction term in Eq. (9) shows that the basic assumption of additivity of the fragmental constants obviously does not hold true here. Correction has to be appHed, e.g., for structural features such as resonance interactions, condensation in aromatics or even hydrogen atoms bound to electronegative groups. Astonishingly, the correction applied for each feature is always a multiple of the constant Cu, which is therefore often called the magic constant . For example, the correction for a resonance interaction is +2 Cj, or per triple bond it is -1 A detailed treatment of the Ef system approach is given by Mannhold and Rekker [5]. 

The direction of the dipole moment is toward the more electronegative atom In the listed examples hydrogen and carbon are the positive ends of the dipoles Carbon is the negative end of the dipole associated with the C—H bond... 

Electronegativity The effect of electronegativity on acidity is evident m the following senes involving bonds between hydrogen and the second row elements C N O and F... 

Oxygen is the most electronegative atom in ethanol hydrogen is the least electronegative... 

An easy way to keep track of the effect of the s character of carbon is to associ ate It with electronegativity As the s character of carbon increases so does that carbon s electronegativity (the electrons m the bond involving that orbital are closer to carbon) The hydrogens m C—H bonds behave as if they are attached to an increasingly more electronegative carbon m the series ethane ethylene acetylene... 

The effect of structure on acidity was introduced m Section 1 15 where we developed the generalization that electronegative substituents near an lomzable hydrogen increase Its acidity Substituent effects on the acidity of carboxylic acids have been extensively studied... 

Dipole-dipole interactions especially hydrogen bonding are present m amines but absent m alkanes But because nitrogen is less electronegative than oxygen an N—H bond IS less polar than an O—H bond and hydrogen bonding is weaker m amines than m alcohols... 

Hydrogen is less electronegative than carbon so the carbonyl carbon of —CH=0 is more shielded than the carbonyl carbon of a ketone... 

Hydrogen Bond Formation. This faciUtates adsorption if the mineral and the adsorbate have any of the highly electronegative elements S,0,N,F, and hydrogen. A weak (physical) bond is estabflshed between the sohd wall and the reagent through the alignment of the cited elements. 

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. 

Phenyllithium caimot be formed from fluoroben2ene. Instead, the electronegativity of fluorine makes the ortho hydrogen sufficiently acidic to permit reaction with / -butyUithium in tetrahydrofuran at —50°C to give 2-fluorophenyllithium [348-53-8]. An isomer, 4-fluoropheny11ithium [1493-23-8] was reported to be explosive in the soHd state (167). 

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