Inductive Effect (help)

[A.J.]

Hi, Can you help me with this?

 

What is inductive effect? How does it works?

 

These are my explanations:

".Inductive Effect."

 

Using the example: CF3OH

 

The lewis structure would be: (ignore the dots)

 

...F

...|

F-C-O-H

...|

...F

 

The Fluorine is more electronegative than C so it pulls the electron density towards itself. The inductive effect affects all parts in the chain. In this case, Carbon is more affected by the effect. Carbon will be electron deficient (so then it is more electronegative than its original Electronegativity). To compensate with this deficiency, this carbon pulls the electron density of the next part of the chain, which is O. As an effect, Oxygen pulls electron density from Hydrogen. This chain reaction is the inductive effect. The consequence of this effect is that the O-H bond weakens (can also be explained: the effect decreased O's EN). The O pulls the electrons in the O-H bond for itself causing a polarized bond. This is why this molecule is acidic, that it reacts readily. In acidic reaction, the the molecule will be broken and leaves an ion and the H+.

 

Oxygen taking the electron pair from the Hydrogen so that Oxygen will have the partial negative charge and Hydrogen will have the partial positive charge since Oxygen is more electronegative than Hydrogen. By calculating the electronegative difference between Oxygen and Hydrogen we would consider their bond as a covalent bond:

delta EN/(EN of A+ EN of B) = (3.5-2.1)/(3.5+2.1) = 0.25 <--closer to 0 so it's covalent bond.

 

On the other hand, if we are to include O-H in the CF3OH, then we have

to include the inductive effect. The inductive effect includes the weakening of individual parts of the chain as electron density is pulled away from them by the most Electronegative (fluorine, in this case).

F takes from C which takes from O which takes from H. O initially has an increase in electron density when it takes electrons from H but it decreased when C takes the electron density from it. C was electron deficient and this is the reason why it took the electron density from O.

 

Is my explanation correct? Pls. add more information if necessary.

 

Some follow-up questions for clarification:

(1) Did the inductive effect really decreased O's electronegativity? How?

(2) Did the O-H bond weakened? (so that it becomes acidic?) How?

 

Thank you very much for your help! I appreciate it! Very Happy

[woelen]

O initially has an increase in electron density when it takes electrons from H but it decreased when C takes the electron density from it. C was electron deficient and this is the reason why it took the electron density from O.

Reasoning in this way is very cumbersome. Your initial reasoning makes things easier. Compare an R-O-H bond without any electron withdrawing properties of the R-O bond with the situation where R is strongly electron-withdrawing. So, your initial reasoning without the latter sentence makes perfect sense to me. The three F's withdraw electrons from C, which in turn withdraws electrons from O, making the O-H bond weaker. H(+) can more easily be split off than in e.g. CH3OH.

 

Question (1): I would not say that the electronegativity of O itself is descreased (or increased). An element has a certain electronegativity, and that is a property of an element. I would say that the group F3C-O- is more electronegative at its O- terminal than a comparable group H3C-O- .

Question (2): Yes it weakened and makes the compound more acidic. You explained yourself.

[A.J.]

Hey Woelen, I am very grateful for your response. It helped me a lot! Now, I am more confident in answering questions to my colleagues. Of course, I'll give credits especially to you. Thanks again!

[Gilded]

Hmm, interesting. And it makes sense to me too! By the way as opposed to alcohols, is there some sort of specific name for compounds such as this, or is it just something-hydroxyl?

[woelen]

I would call this compound trifluoro hydroxy methane. Maybe the name trifluoromethanol can be used as well.

[aamera]

1. No. inductive effect will not decrease the O's electronegativity. It will only decrease the electron density on oxygen atom ,& will make it electron deficient. Oxygen will in turn attract the shared pair of electron b/w O_H to compensate its elctron deficiency.H will be easy to remove as H+.

2. yes this bond weakened.because of less sharing of H for shared electron pair.

[A.J.]

1. No. inductive effect will not decrease the O's electronegativity. It will only decrease the electron density on oxygen atom ,& will make it electron deficient. Oxygen will in turn attract the shared pair of electron b/w O_H to compensate its elctron deficiency.H will be easy to remove as H+.

2. yes this bond weakened.because of less sharing of H for shared electron pair.

 

Hey Aamera, thanks for your add-ups. I'm thankful that you have the same conclusion that I have. After Woelen gave me his ideas, I thought that I shouldn't say that the electronegativity is decreased but I should say that electron density is the one decreased instead. For number 2, you said the exact same thing that I was thinking. Now, I am even more confident. Thanks for the help, guys! I appreciate it!