pKa Values and Acidity in Organic Chemistry

Flashcards covering key pKa values and the effects of electron withdrawing and donating groups on acidity.

Alkane C-H

pKa value of 51-55, indicating low acidity.

Alkene C-H

pKa value of 42, indicating low acidity.

Alkyne C-H

pKa value of 25, indicating moderate acidity.

Ammonia/Amines (N-H)

pKa value of 35-38, indicating moderate acidity.

Water/Alcohols (O-H)

pKa value of 16, indicating higher acidity.

Thiols (H3CS-H)

pKa value of 10, indicating higher acidity.

Phenol (C6H5O-H)

pKa value of 10, indicating higher acidity.

Aliphatic RNH3+

pKa value of 11, indicating moderate acidity.

Aromatic ArNH3+

pKa value of 5, indicating higher acidity.

Carboxylic Acid (RCOO-H)

pKa value of 3.2, indicating strong acidity.

HF

pKa value of -7, indicating very strong acidity.

HCl

pKa value of -8, indicating very strong acidity.

HBr

pKa value of -9.9, indicating very strong acidity.

HI

pKa value of -10, indicating very strong acidity.

α-Hydrogens

pKa value of 18-20, indicating moderate acidity.

Ketone/Aldehyde (CH3CHO)

pKa value of 25, indicating moderate acidity.

Esters (CH3COOR)

pKa value of 30, indicating low acidity.

Amides (CH3CONR2)

pKa value of 30, indicating low acidity.

Nitriles (CH3CN)

pKa value of 9, indicating moderate acidity.

β-Diketone (RCOCH2COR)

pKa value of 11, indicating moderate acidity.

β-Ketoester (RCOCH2COOR)

pKa value of 13, indicating moderate acidity.

β-Diester (ROCOCH2COOR)

pKa value of 5, indicating higher acidity.

Electron withdrawing groups

Increase acidity and decrease pKa (e.g., -NO2, -F).

Electron donating groups

Decrease acidity and increase pKa (e.g., -OMe).