# Comparison between groups with -I effects

So I have a few questions in my book that require me to compare between two different groups on the basis of their -I effects. I have a few questions on this that have been bugging me for quite a while. I am preparing for an exam, and please not we will not be given any energy data or charts so we wont be able to reference them while giving the exam, so all I can do I understand.

1. What happens if I have to compare between a compound that has a single group with a stronger -I effect (like $$\ce{NO2}$$) and a compound that has more than one group with a comparatively weaker -I effect (like $$\ce{Cl}$$)? In which case is the -I effect stronger, and how to understand that?

2. What is the actual order of -I effect? Wikipedia and my books sometimes are conflicting in their orders. For example, Wikipedia states it as:

$$\ce{–NH3+} > \ce{–NO2} > \ce{–SO2R} > \ce{–CN} > \ce{–SO3H} > \ce{–CHO} > \ce{–CO} > \ce{–COOH} > \ce{–COCl} > \ce{-CONH2} >\ce{-F} > \ce{–Cl} > \ce{–Br} > \ce{–I} > \ce{–OR} > \ce{-OH} > \ce{-NR2} > \ce{–NH2} > \ce{–C6H5} > \ce{–CH=CH2} > \ce{–H}$$

One of my books states this as:

$$\ce{-NMe3+}>\ce{-NH3+}>\ce{-NO2}>\ce{-CN}>\ce{-F}>\ce{-Cl}>\ce{-Br}>\ce{-I}>\ce{-OAr}>\ce{-COOR}>\ce{-OR}>\ce{-OH}>\ce{-C6H5}>\ce{-CH=CH2}>\ce{-H}$$

And another states this as:

$$\ce{-NF3+}>\ce{-NH3+}>\ce{-CF3}>\ce{-NO2}>\ce{-CN}>\ce{-SOO-OH}>\ce{-COOH}>\ce{-COCl}>\ce{-COH}>\ce{-COR}>\ce{-F}>\ce{-Cl}>\ce{-Br}>\ce{-I}>\ce{-OH}>\ce{-OC6H5}>\ce{-OR}>\ce{-NH2}>\ce{-CH=CH2}>\ce{-C6H5}>\ce{-H}$$

Clearly some do not contain some compounds while in some cases the orders are a tiny bit switched up. Which one should I use? I know that some of this is really close comparisons but a definitive order if possible would reall help me out. Thanks.

• Basically, the inductive effect is determined quantitatively by Heemat's equation. I haven't study it yet. I also have the same doubt. My teacher told me that those groups which have conflicting orders between them have approximately same result from Heemat's equation. I think in examination, examiner ask about only general groups for which order is correctly determined. I myself had never encountered any inductive effect question for which the order of groups was conflicting. Same answer for the first part.
– Manu
Apr 21 '20 at 15:40
• @Manu I have encountered such questions. I wouldn't have asked this question if I hadn't. Apr 21 '20 at 15:42
• Oh sorry. But I think studying Heemat's equation will help.
– Manu
Apr 21 '20 at 15:45
• @Manu Thanks, that's a lead atleast. :) Apr 21 '20 at 15:46