Lewis basic electrostatic potentials

Draw a Lewis strueture for each molecule that shows the location of all nonbonding electrons. Examine electrostatic potential maps for both imidazole and pyrazole. Predict which is the more basic nitrogen in each molecule. What kind of orbital contains this nitrogen s nonbonding electrons What kind of orbital contains the other nitrogen s nonbonding electrons ... 

Indirect methods depend on the establishment of family-dependent (site-dependent) relationships of the log KiS with quantum chemical descriptors of basicity (e.g. electrostatic potentials), Hammett substituent constants or IR frequency shifts of Lewis acids [132,142-145]. 

Lewis [5] was the first to describe acids and bases in terms of their electron accepting and electron donating properties. Mulliken [6] further refined the understanding of the acid base interactions for which he was awarded the Nobel Prize for Chemistry. His quantum mechanical approach introduced the concept of two contributions, an electrostatic and a covalent, to the total acid-base interaction. Pearson [7] introduced the concept of hard and soft acids and bases, the HSAB principle, based on the relative contributions from the covalent (soft) interaction and the electrostatic (hard) interaction. In his mathematical treatment he defined the absolute hardness of any acid or base in terms of its ionisation potential and electron affinity. Pearson s is probably the most robust approach, but the approaches in most common use are those developed by Gutmann [8] and Drago [9], who separately developed equations and methods to quantify the acid or basic strength of compounds, from which their heats of interaction could be calculated. 

Several individuals have worked to quantify these trends, making scales of Lewis acidity and basicity. Gutmann has created a series of donor numbers (DN) and acceptor numbers (AN) for various solvents, while Drago and Wayland have assigned parameters E and C, which measure electrostatic interactions and covalent bonding potential, respectively. Lastly, Pearson treats each Lewis acid and base with two parameters, relating what is called the strength of the acid/base and the softness/hardness of the acid/base. In fact, the HSAB trend discussed above is primarily a concept developed by Pearson. 

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