Polar Covalent Bonds Acids and Bases

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Organic Bases

Have an atom with a lone pair of electrons that can bond to H+

Nitrogen-containing compounds derived from ammonia are the most common organic bases

Oxygen-containing compounds can react as bases when with a strong acid or as acids with strong bases

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Acids and Bases: The Lewis Definition

Lewis acids are electron pair acceptors and Lewis bases are electron pair donors

Brønsted acids are not Lewis acids because they cannot accept an electron pair directly (only a proton would be a Lewis acid)

The Lewis definition leads to a general description of many reaction patterns but there is no scale of strengths as in the Brønsted definition of pKa

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Lewis Acids and the Curved Arrow Formalism

The Lewis definition of acidity includes metal cations, such as Mg2+

They accept a pair of electrons when they form a bond to a base

Group 3A elements, such as BF3 and AlCl3, are Lewis acids because they have unfilled valence orbitals and can accept electron pairs from Lewis bases

Transition-metal compounds, such as TiCl4, FeCl3, ZnCl2, and SnCl4, are Lewis acids

Organic compounds that undergo addition reactions with Lewis bases (discussed later) are called electrophiles and therefore Lewis Acids

The combination of a Lewis acid and a Lewis base can shown with a curved arrow from base to acid

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Illustration of Curved Arrows in Following Lewis Acid-Base Reactions

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Lewis Bases

Lewis bases can accept protons as well as Lewis acids, therefore the definition encompasses that for Brønsted bases

Most oxygen- and nitrogen-containing organic compounds are Lewis bases because they have lone pairs of electrons

Some compounds can act as both acids and bases, depending on the reaction

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Molecular Models

Organic chemistry is 3-D space

Molecular shape is critical in determining the chemistry a compound undergoes in the lab, and in living organisms

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Noncovalent Interactions

Several types:

Dipole-dipole forces

Dispersion forces

Hydrogen bonds

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Dipole-Dipole

• Occur between polar molecules as a result of electrostatic interactions

among dipoles

• Forces can be attractive of repulsive depending on orientation of the