What Determines C-F Bond Length Order?

In summary, the conversation discusses factors to consider when measuring bond lengths, such as lone pair-bond pair repulsions, interactions between H and F atoms, and C-H and C-F bond interactions. The example given shows how these factors affect the bond length in CF3. The conversation also mentions that the correct answer to the question is B), which is the reverse of what was expected.
  • #1
utkarshakash
Gold Member
854
13

Homework Statement


Choose correct order of C-F bond length
A)C-HF2<C-H2F<C-F3
B)C-F3<C-HF2<C-H2F
C)C-F3<C-H2F<C-HF3
D)C-HF2<C-F3<C-H2F

The Attempt at a Solution



What factors should I look for while measuring bond lengths?
 
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  • #2
You can take Lone Pair-Bond pair repulsions, Interaction of H and F (due to their size difference), F F interactions, and probably C-H C-F Bond interaction.
 
  • #3
AGNuke said:
You can take Lone Pair-Bond pair repulsions, Interaction of H and F (due to their size difference), F F interactions, and probably C-H C-F Bond interaction.

Can you please show through an example?
 
  • #4
Two C-F bonds will repel each other, thus they will try to maximize their angle, but their repulsion with lone pair is even greater, hence they will be forced to elongate themselves in order to face minimal repulsion from each other and the lone pair.

Try to work on this.
 
  • #5
AGNuke said:
Two C-F bonds will repel each other, thus they will try to maximize their angle, but their repulsion with lone pair is even greater, hence they will be forced to elongate themselves in order to face minimal repulsion from each other and the lone pair.

Try to work on this.

If I follow through this reasoning, then CF3 will have maximum C-F bond length because it suffers more repulsion as compared to others.
 
  • #6
Might be. But you should check around the internet for factual data before putting your vote in my "theory".

See, I am assuming that you are preparing for college entrance exam (JEE).
 
  • #7
AGNuke said:
Might be. But you should check around the internet for factual data before putting your vote in my "theory".

See, I am assuming that you are preparing for college entrance exam (JEE).

Yes. I'm preparing for JEE and they won't ask questions where factual data is required. But what I wanted to say is that the correct answer is B) which is just the reverse of what I expected.
 
  • #8
Well, what can I say, I'd need to dig up some lost info on this one.
 

FAQ: What Determines C-F Bond Length Order?

What is a C-F bond length?

A C-F bond length refers to the distance between the carbon atom and the fluorine atom in a molecule. It is a measure of the strength and stability of the bond between these two atoms.

How is C-F bond length determined?

C-F bond length is typically determined using spectroscopic techniques, such as infrared or nuclear magnetic resonance (NMR) spectroscopy. These methods allow scientists to measure the distance between the carbon and fluorine atoms in a molecule.

What factors affect C-F bond length?

The main factors that affect C-F bond length are the electronegativity of the atoms involved and the presence of any nearby functional groups. As fluorine is highly electronegative, it tends to pull electrons towards itself, resulting in a shorter bond length.

How does C-F bond length impact the properties of a molecule?

The C-F bond is one of the strongest bonds in organic chemistry, making molecules containing this bond highly stable. This also makes them resistant to chemical reactions, which can be useful in certain applications, such as in pharmaceuticals.

Is there a trend in C-F bond length across the periodic table?

Yes, there is a general trend of decreasing C-F bond length as you move down a group in the periodic table. This is due to the increasing atomic size and decreasing electronegativity of the atoms involved.

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