Carbocations have a positively charged carbon atom and are strong Lewis acids, while carbanions have a negatively charged carbon atom and are strong Lewis and Brønsted bases. Electrophiles seek electrons while nucleophiles seek positively charged nuclei. Electrophiles and nucleophiles participate in substitution, addition, and acid-base reactions. Curved arrows in reaction mechanisms show the direction of electron flow, not atom movement. Acidity constants (Ka) and pKa values quantify acid strength, with smaller Ka and larger pKa values indicating stronger acids. The conjugate base of a stronger acid is weaker, as its conjugate acid will have a larger pKa.

1. Carbocations and Carbanions
Carbocation: Ionic species with positively charged carbon atom
Carbanion: Ionic species with negatively charged carbon atom
Carbocations are strong Lewis acids while carbanions are strong
bases (both Lewis and Brønsted)

2. Electrophiles and Nucleophiles
Electrophile: species that seeks electrons (negatively charged center)
Nucleophile: species that seeks nuclei (positively charged center
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Electrophiles and Nucleophiles in substitutions and additions
Electrophiles and Nucleophiles in acid–base reactions

3. Mechanism of Reaction & Curved Arrow
Curved arrow: shows the direction of electron flow, not the movement of atoms
In resonance Structures
In drawing reaction mechanisms

4. The Strength of Acid / Base: Ka and pKa
Acidity constant of acetic acid:
At 25 °C, Ka = 1.76 x 10-5
Acidity constant of of any acid:
Acidity and pKa:
(analogous to for hydroxonium ion concentration)
For acetic acid:

5. The Strength of Acid / Base: Ka and pKa

6. Predicting the Strength of Acid / Base
Can we predict the relative basicity of two bases ?
The stronger the acid, the weaker will be its conjugate base.
(The larger the pKa of the conjugate acid, the stronger the base)