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What is the effect of an electron withdrawing group on the acidity of carboxylic acid?
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Mills Baker
What is the effect of an electron withdrawing group on the acidity of carboxylic acid?
Well, I invite you to compare the [math]pK_{a}[/math] values of [math] ext{acetic acid}[/math], [math]H_{3}C-C(=O)OH[/math], [math] ext{chloro-acetic acid}[/math], [math]ClH_{2}C-C(=O)OH[/math], and [math] ext{dichloro-acetic acid}[/math], [math]Cl_{2}HC-C(=O)OH[/math]… and [math] ext{trichloro-acetic acid}[/math], [math]Cl_{3}C-C(=O)OH[/math]
These are respectively, [math]4.76[/math], [math]2.86[/math], [math]1.35[/math], and [math]0.71[/math] ….
Now is this an electronic effect…? Likely not, given that an entropy effect dominates … the LARGER, chloro-substituted acids are LESS-CHARGE dense, and the anion in aqueous solution is LESS polarizing…
Well, I invite you to compare the [math]pK_{a}[/math] values of [math]ext{acetic acid}[/math], [math]H_{3}C-C(=O)OH[/math], [math]ext{chloro-acetic acid}[/math], [math]ClH_{2}C-C(=O)OH[/math], and [math]ext{dichloro-acetic acid}[/math], [math]Cl_{2}HC-C(=O)OH[/math]… and [math]ext{trichloro-acetic acid}[/math], [math]Cl_{3}C-C(=O)OH[/math]
These are respectively, [math]4.76[/math], [math]2.86[/math], [math]1.35[/math], and [math]0.71[/math] ….
Now is this an electronic effect…? Likely not, given that an entropy effect dominates … the LARGER, chloro-substituted acids are LESS-CHARGE dense, and the anion in aqueous solution is LESS polarizing…
Electron withdrawing groups help stabilize the negatively charged carboxylate anion by helping to distribute the negative charge over more of the anion. The more stable the carboxylate anion, the stronger the acid.
This can be achieved through Inductive effect, which diminishes rapidly with distance from the carboxylate. Proximity and electronegativity influence the inductive effect. Resonance also influences acidity, thus, a carboxylic acid attached in close proximity to a Benzene group, will stabilize that anion charge nicely, and make it more acidic.
Electron withdrawing groups help stabilize the negatively charged carboxylate anion by helping to distribute the negative charge over more of the anion. The more stable the carboxylate anion, the stronger the acid.
This can be achieved through Inductive effect, which diminishes rapidly with distance from the carboxylate. Proximity and electronegativity influence the inductive effect. Resonance also influences acidity, thus, a carboxylic acid attached in close proximity to a Benzene group, will stabilize that anion charge nicely, and make it more acidic.
Well, I invite you to compare the [math]pK_{a}[/math] values of [math] ext{acetic acid}[/math], [math]H_{3}C-C(=O)OH[/math], [math] ext{chloro-acetic acid}[/math], [math]ClH_{2}C-C(=O)OH[/math], and [math] ext{dichloro-acetic acid}[/math], [math]Cl_{2}HC-C(=O)OH[/math]… and [math] ext{trichloro-acetic acid}[/math], [math]Cl_{3}C-C(=O)OH[/math]
These are respectively, [math]4.76[/math], [math]2.86[/math], [math]1.35[/math], and [math]0.71[/math] ….
Now is this an electronic effect…? Likely not, given that an entropy effect dominates … the LARGER, chloro-substituted acids are LESS-CHARGE dense, and the anion in aqueous solution is LESS polarizing…
Well, I invite you to compare the [math]pK_{a}[/math] values of [math]ext{acetic acid}[/math], [math]H_{3}C-C(=O)OH[/math], [math]ext{chloro-acetic acid}[/math], [math]ClH_{2}C-C(=O)OH[/math], and [math]ext{dichloro-acetic acid}[/math], [math]Cl_{2}HC-C(=O)OH[/math]… and [math]ext{trichloro-acetic acid}[/math], [math]Cl_{3}C-C(=O)OH[/math]
These are respectively, [math]4.76[/math], [math]2.86[/math], [math]1.35[/math], and [math]0.71[/math] ….
Now is this an electronic effect…? Likely not, given that an entropy effect dominates … the LARGER, chloro-substituted acids are LESS-CHARGE dense, and the anion in aqueous solution is LESS polarizing…
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Electron withdrawing groups help stabilize the negatively charged carboxylate anion by helping to distribute the negative charge over more of the anion. The more stable the carboxylate anion, the stronger the acid.
This can be achieved through Inductive effect, which diminishes rapidly with distance from the carboxylate. Proximity and electronegativity influence the inductive effect. Resonance also influences acidity, thus, a carboxylic acid attached in close proximity to a Benzene group, will stabilize that anion charge nicely, and make it more acidic.
Electron withdrawing groups help stabilize the negatively charged carboxylate anion by helping to distribute the negative charge over more of the anion. The more stable the carboxylate anion, the stronger the acid.
This can be achieved through Inductive effect, which diminishes rapidly with distance from the carboxylate. Proximity and electronegativity influence the inductive effect. Resonance also influences acidity, thus, a carboxylic acid attached in close proximity to a Benzene group, will stabilize that anion charge nicely, and make it more acidic.
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