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Usually, Inductive effects are compared using the electronegativities and distances. However, this only works in compounds with similar structures. For example, we can predict the following orders of acidity:

$$ \ce{2-fluoropropanoic acid} \underset{K_\mathrm{a}}{\gt} \ce{3-fluoropropanoic acid}\\ \ce{3-fluoropropanoic acid} \underset{K_\mathrm{a}}{\gt} \ce{3-chloropropanoic acid}\\ $$

However, besides these (very valid) qualitative reasonings, I want to know if there is a quantitative way to measure inductive effect. I am aware that the concept of group electronegativities also exists, and that is not what I am referring to.

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    $\begingroup$ chemistry.stackexchange.com/questions/63273; chemistry.stackexchange.com/questions/12309 $\endgroup$
    – andselisk ♦
    May 9 at 9:09
  • $\begingroup$ Maybe the Hammett equation? You can distinguish resonance effects from other effects by comparing substitutions on aromatic vs saturated systems. $\endgroup$
    – Karsten ♦
    May 10 at 9:34
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    $\begingroup$ @Karsten the Hammett equation is quite general and does quantitatively describe combined inductive, mesomeric, and other effects upon substitution of benzene/benzoic-acid derivatives but does not quantitatively describe inductive effect alone. $\endgroup$
    – ananta
    May 10 at 19:29
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    $\begingroup$ If you use a parent molecule that is not aromatic, you can't have a mesomeric effect. So studying the distinct effect of substituents with different parent molecules does differentiate between mesomeric and inductive effects, e.g. this paper $\endgroup$
    – Karsten ♦
    May 10 at 19:58
  • $\begingroup$ Not an organic chemist myself, can this effects not be accounted for using quantum chemical methods and NBO analysis of the wavefunction? $\endgroup$
    – PAEP
    Jun 9 at 12:17

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Since Inductive Effect is a permanent effect involving generation of dipoles within molecules, there could be a way to measure it quantitatively. According to Wikipedia, relative inductive effects can be measured, it is unclear on how exactly could it be done.

However, it does mention that inductive effects can be calculated through something called the Hammett equation that makes relationship between reaction rates and equilibrium constants with respect to substituent (the one due to which inductive effect generates).

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  • $\begingroup$ The Hammett equation is quite general and does provide a quantitative description of (combined inductive, mesomeric, and other) substituent effects, but it only works for benzene/benzoic-acid derivatives. $\endgroup$
    – ananta
    May 10 at 4:13

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