Jump to content
mundane

inductive effect

Recommended Posts

so the decreasing order of -I effect is NO2>CN>F>COOH>Cl>Br..... In chloro acetic acid, chlorine pulls the electrons towards itself rather than COOH, why? isn't COOH more strong than Cl? please help me out! 

IMG_20200726_202641.jpg

Share this post


Link to post
Share on other sites

 

2 hours ago, mundane said:

so the decreasing order of -I effect is NO2>CN>F>COOH>Cl>Br..... In chloro acetic acid, chlorine pulls the electrons towards itself rather than COOH, why? isn't COOH more strong than Cl? please help me out! 

IMG_20200726_202641.jpg

 

 

Look carefully at the structure.

The carbon of the CH2 group has two competing electronegative groups attached, the chlorine and the carbonyl.

The chlorine 'pulls' electrons towards itself a bit , increasing the resisiting effect of the CH2 carbon,  thus reducing the electron pulling effect of the carbonyl , and vice versa.

This makes it easier for the carbonyl carbon to pull an electron from the attached hydrogen, releasing a proton to solution.

This makes the chlorinated acid a bit stronger than the non chlorinated acid.

 

That is the the basis of the inductive effect. An electron attraction is passed 'down the line' in the structure with effects on groups not directly connected.

 

Share this post


Link to post
Share on other sites

great explanation yet I failed to understand as to why COOH being the strongest couldn't overcome the inductive effect of Cl. please clarify! 

Share this post


Link to post
Share on other sites
17 hours ago, mundane said:

great explanation yet I failed to understand as to why COOH being the strongest couldn't overcome the inductive effect of Cl. please clarify! 

It's not a question of 'overcoming' , that implies all or nothing ie full transfer of an electron.

The inductive effect refers to only partial transfer.

Looking at you  attachment, is see that the explanation is interms of electric dipole moments.

I find that many Chemists are a bit hazy about dipole moments and have other ways to look at it.

The other point about dipole moments is that they are vectors, which means you must add them vectorially, taking account of direction usually in 3D.

So planar, linear, skeletal representations are often inadequate.

So here is an alternative by considering charge redistribution or delocalisation within a molecule.
(You can have the dipole version if you want it)
I don't know if you have come across the curly arrow convention?

It is a good idea to first understand what happens with a plain hydrocarbon carboxylic acid (acetic acid).

#4 on my list shows a list of Ka the acidity equilibrium constant for acetic acid in a number of solvents, water being the most common.
#1 shows the equilibrium reaction (with water).

The acid anion formed is resonance stabilised as shown which leads to a stable anion and is the reason carboxyl groups are more acidic than phenols which in turn are more acidic than alcohols.

Effectively the two oxygens share half the negative charge as shown in #2.

I we now substitute an electron withdrawing species such as chlorine at #3
This pulls charge back from the methyl carbon,
Which in turn pulls charge back from the 'carboxyl' carbon
Delocalising the negative charge over the whole molecule.

induct1.thumb.jpg.fdd769f6f56be6a423d287ad090337cd.jpg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.