Acidity in organic compounds and hybridization

In summary, the conversation is about labeling and arranging acidic hydrogens in compounds based on their electronegativity. The most electronegative element will have the most acidic hydrogen, and the order of increasing acidity can be determined by looking at the electronegativities of the carbons in the compound. The more electronegative the carbon, the more acidic the hydrogen attached to it will be.
  • #1
kirsten_2009
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2

Homework Statement


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Label the acid hydrogen in each of the following compounds and arrange them in order of increasing acidity and explain the trend.

Homework Equations



N/A

The Attempt at a Solution



I'm not quite sure what the question means by "label" the acidic hydrogen but I believe the most acidic hydrogen is the one closest to the most electronegative element, correct? I labeled them in the image with red but not sure if this is the conventional way of doing it or if I'm missing something? It just seems strange.

I would arrange them: C<B<A with A being the most acidic.

Why? My reasoning is that because the carbon with the triple bond is sp hybridized which means that 50% of its hybrid orbital is "s" character and since "s" orbitals are closer to the nucleus; they have a better capability of handling the negative charge left behind when the proton dissociates and thus forms a more stable conjugate base...same reasoning for the other two...thoughts? Thanks.
 
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  • #2
I think you've done the labeling part right. Yes, the most acidic hydrogen is the one closest to the most electronegative element.

For the 'which is more acidic part', I'd suggest you look at the electronegativities of the three carbons. Which carbon atom is more electronegative and why? More the electronegativity, more the acidity.
 
  • #3
Hello,

Thanks for the reply. What would make a carbon more electronegative? Aren't atoms of the same element equally electronegative? If anything, I guess, wouldn't the triple bond be the most electronegative? If that's the case, why would it be more electronegative? Thanks!
 
  • #4
I studied this 5 years back so these concepts are a bit foggy. But consider a C-C single bond. It has 3 H atoms attached to it. Carbon being more electronegative than hydrogen will pull the 6 electrons (2 from each covalent bond) towards it. It won't pull the electrons

In case of C=C double bond, the carbon has only 2 H atoms attached to it. So it will pull only 4 electrons towards it.

By that logic, the single bond carbon (C-C) will be the more electronegative one. Makes sense?
 
  • #5


Thank you for your question. Your reasoning is correct regarding the sp hybridization of the carbon atom and its ability to stabilize the negative charge in the conjugate base. However, there are a few other factors that also contribute to the acidity of a compound.

One important factor is the electronegativity of the atom that the acidic hydrogen is attached to. The more electronegative the atom, the more stable the conjugate base will be, making the compound more acidic. In this case, compound A has a chlorine atom attached to the acidic hydrogen, making it more acidic than compound B, which has a carbon atom attached to the acidic hydrogen.

Another factor is the size of the atom that the acidic hydrogen is attached to. Smaller atoms are better able to stabilize the negative charge in the conjugate base, making the compound more acidic. In this case, compound A has a smaller chlorine atom attached to the acidic hydrogen compared to compound B, which has a larger carbon atom attached to the acidic hydrogen.

Based on these factors, the correct order of increasing acidity would be: B < C < A, with compound A being the most acidic due to its sp hybridization and the small, electronegative chlorine atom attached to the acidic hydrogen.
 

1. What is the relationship between acidity and hybridization in organic compounds?

The acidity of an organic compound is largely determined by the hybridization state of the atom with the acidic hydrogen. Generally, the more s-character in the hybrid orbital, the more acidic the compound will be. This is because the s-orbital is closer to the nucleus and allows for better overlap with the proton, making it easier to remove.

2. How does hybridization affect the shape of organic compounds?

Hybridization plays a crucial role in determining the shape of organic compounds. The type of hybridization (e.g. sp3, sp2, sp) dictates the number and orientation of the bonds around an atom, which in turn determines the overall geometry of the molecule. For example, sp3 hybridized atoms will have a tetrahedral shape, while sp2 hybridized atoms will have a trigonal planar shape.

3. Can you explain the concept of resonance in relation to organic compounds?

Resonance is a phenomenon where electrons in a molecule are delocalized, or spread out over multiple atoms, leading to the stabilization of the molecule. In organic compounds, resonance can occur when there are multiple ways to draw the Lewis structure for a molecule, with each structure having the same overall charge. The actual structure of the molecule is a blend of all the resonance structures, resulting in increased stability.

4. How does the electronegativity of atoms influence the acidity of organic compounds?

The electronegativity of an atom can significantly impact its acidity in organic compounds. This is because electronegative atoms have a greater ability to attract electrons towards themselves, making it easier to remove the acidic hydrogen. For example, in a carboxylic acid, the presence of an electronegative oxygen atom makes the compound more acidic compared to a hydrocarbon with the same number of carbons and hydrogens.

5. Can you give an example of how hybridization affects the reactivity of organic compounds?

Yes, an example of this is seen in the difference in reactivity between alkenes and alkynes. Alkenes have sp2 hybridized carbon atoms, while alkynes have sp hybridized carbon atoms. The increased s-character in alkynes leads to a shorter and stronger bond, making them more reactive compared to alkenes. This is why alkynes are more prone to undergo addition reactions, while alkenes are more likely to undergo substitution reactions.

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