Ranking Protons in order of Increasing Acidity Using pKa Values | Summary and Q&A

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February 10, 2023
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Ranking Protons in order of Increasing Acidity Using pKa Values

TL;DR

Carnosine is a dipeptide with specific amino acids. By considering the pKa values, the proton acidity can be ranked accordingly.

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Questions & Answers

Q: What is carnosine and what is it composed of?

Carnosine is a dipeptide made up of the amino acids beta-alanine and histidine.

Q: How does the pKa of a regular carboxylic acid compare to that of an amino acid?

The pKa of a regular carboxylic acid is around 4-5, but the pKa of a carboxylic acid in an amino acid is lower, about 2-3.

Q: What is the pKa of a protonated amine in most cases?

Protonated amines typically have a pKa around 10, but for amino acids, it's slightly lower, around 9-10.

Q: What is the pKa of the alpha proton adjacent to the carbonyl group in an amide?

The pKa of this proton is around 30 in the context of an amide, while it would be lower for a ketone or an ester.

Q: How does the pKa of a proton near a double bond in an alkane carbon compare to that in carnosine?

The pKa of a proton near a double bond in an alkane carbon is high, but in carnosine, due to possible delocalization, it could range from 40 to 60.

Q: What is the pKa value of the hydrogen atom on the imidazole ring in histidine?

The pKa value of the hydrogen atom on the imidazole ring in histidine is approximately 6-7.

Q: Which proton is ranked as the least acidic in carnosine?

Proton C is ranked as the least acidic proton in carnosine.

Q: What is the most acidic proton in carnosine?

The carboxylic acid proton is the most acidic proton in carnosine.

Summary & Key Takeaways

  • Carnosine is a dipeptide composed of beta-alanine and histidine, known for its antioxidant properties.

  • The pKa values of the different protons in carnosine vary due to the presence of specific groups and atoms.

  • By considering the pKa values, the protons in carnosine can be ranked in order of increasing acidity.

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