Molecular electronegativity

Regardless of preference, we are faced with three definitions of the term ionic character, in terms of electronegativity, molecular orbitals, or valence bond wave functions. Any paper on the nature of the H bond must be evaluated in the light of what the writer meant when he wrote that paper. 

R. D. Brown and M. I. Heffernan, Trans. Faraday Soc., 54, 757 (1958). Study of Formaldehyde by a Self-Consistent Electronegativity Molecular Orbital Method. 

Dissociative Electron Attachment to Molecules as a Major Mechanism of Negative Ion Formation in Electronegative Molecular Gases... 

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... 

To become familar with the algorithm for charge calculation by partial equalization of orbital electronegativity (PEOE) and by a modified Hiickel Molecular Orbital method... 

The presence of the q B term with its implied distance dependency means that the charges depend upon the molecular geometry. Thus, should the conformation of a molecule change the atomic charges will also change. Just three parameters are required for each atom in the system (the electronegativity, the idempotential and the covalent radius). 

Because carbon is sp hybridized m chlorobenzene it is more electronegative than the sp hybridized carbon of chlorocyclohexane Consequently the withdrawal of electron density away from carbon by chlorine is less pronounced m aryl halides than m alkyl halides and the molecular dipole moment is smaller... 

Oxygen usually exhibits a valence of —2 in combination with other chemical elements to form compounds such as oxides. Most elements combine with oxygen, which is highly electronegative, in more than one ratio because of the variety of valences exhibited by the other element, or because of the existence of compHcated molecular stmctures. An extended discussion of oxides is available in the Hterature (13). 

The stabihty of these products varies (38). When R is methyl, the compound decomposes below room temperature, but when R is phenyl it is stable up to 40—45°C. Increasing the molecular weight of the alkyl group and introducing an electronegative group on the phenyl increases the stabihty. The aUphatic mixed anhydrosulfide can be decomposed by two different routes (53) ... 

Another useful generalization is the principle of maximum hardness. This states that molecular arrangements that maximize hardness are preferred. Electronegativity and hardness detennine the extent of electron transfer between two molecular fragments in a reaction. This can be approximated numerically by the expression... 

Molecular iodine is not a very powerful halogenating agent. Only very reactive aromatics such as anilines or phenolate anions are reactive toward iodine. Iodine monochloride can be used as an iodinating agent. The greater electronegativity of the... 

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