MCAT Organic Chemistry Review


Answers to Concept Checks

·        3.1

·        3.2

1.    Bonding orbitals are more stable than antibonding orbitals. Therefore, antibonding orbitals have higher energy than bonding orbitals.

2.    The differences would be in bond length (shorter in double bond than single), bond energy (higher in double bond than single), and molecular rigidity (higher in double bond than single).

3.    Triple bond > double bond > σ bond > π bond. Remember that while an individual π bond is weaker than a σ bond, bond strength is additive. Therefore, double bonds are stronger than single, and triple bonds are stronger still.

·        3.3

1.    sp orbitals have 50% s character and 50% p character; sp2 has 33% s character and 67% p character; and sp3 has 25% s character and 75% p character.

2.    Resonance structures differ in their placement of electrons in hybridized p-orbitals and require bond conjugation to delocalize electrons in a molecule. The true electron density is a weighted average of the resonance structures of a given compound, favoring the most stable structures.