Acidity and polarity of surrounding environment

[Monkeymaniac]

---

Members don't see this ad.

In TBR biology book (Bio - Section VII - passage problem 55), it is stated that dissociating hydrogen of a carboxyl group is more favored in polar environment.

I guess it's due to the solvent molecules pulling the H of the carboxyl towards them, which makes the O-H bond (of carboxyl) weaker. Is this correct?

But then the book also states that having a negative charge in vicinity of the H of O-H stablizes the carboxyl group (by the negative charge interacting with the partial postiive on the H). It also states that the carboxyl group is stablized by hydrogen bonding in the polar environment.

Don't these ideas contradict each other? How does the polar environment make dissociation more favorable and stabilizes the carboxyl group at the same time? Isn't stabilizing supposed to make O-H bond more strong and thus make it less susceptible to proton dissociation?

 

[boaz]

.

I don't have the book in front of me, so I can only speak from heresay. Take my words with a few grains of salt.

In TBR biology book (Bio - Section VII - passage problem 55), it is stated that dissociating hydrogen of a carboxyl group is more favored in polar environment.

The dissociated carboxyl group is more polar than the nondissociated. Therefore the former will be more stable in a polar solvent than in a nonpolar solvent.

I guess it's due to the solvent molecules pulling the H of the carboxyl towards them, which makes the O-H bond (of carboxyl) weaker. Is this correct?

No. It's mainly because of the stability of the PRODUCTS of dissociation, as above.

But then the book also states that having a negative charge in vicinity of the H of O-H stablizes the carboxyl group (by the negative charge interacting with the partial postiive on the H). It also states that the carboxyl group is stablized by hydrogen bonding in the polar environment.

On the molecule, or separately in the solution?

 

[Monkeymaniac]

On the molecule, or separately in the solution?

Thank you. I meant separately in the solution.

 

[boaz]

Does it say that it stabilizes it more than the dissociated form?