Quantifying reactivity in substrates and electrophiles [closed]

What is "quantitative treatment of reactivity in substrates and electrophiles"? I read about it in Jerry March's Advanced Organic Chemistry textbook, but I'm finding it difficult to comprehend.

One large body of work aiming to quantify electrophilicity was accumulated by the Mayr group. Numerous reagents were tested against typical substrates, recording the kinetic rate constants allowed to attribute electrophilicity / nucleophilicity along the equation of

$$\log k (\pu{20 ^\circ{}C}) = s_N (N + E)$$

with
$E$ = electrophilicity parameter
$N$ = nucleophilicity parameter
$s_N$ = nucleophile-specific sensitivity parameter

Beside the selection of publication mentioned on the group page, work was invested to create a map, and a public database with currently "1075 nucleophiles and 276 electrophiles".

• So, testing various possible electrophiles on a given aromatic system, and quantifying the rates of reaction for each reaction is what you meant ? – Vishnu Haveri Jul 2 '17 at 13:41
• @VishnuHaveri Yes, I did mean as one way to quantify electrophilicity. An other, according to en.wikipedia.org/wiki/Electrophile, is the electrophilicity index $\omega$, as fraction of the square of electronegativity ($\chi^2$), and chemical hardness ($\eta{}$). This second approach leaves kinetics, and solvent dependency on nucleopilicity or electrophilicty of "the Mayr approach" out. – Buttonwood Jul 2 '17 at 13:55