Chem 464: Gen Chem & Org Chem Review

Study Notes

VSEPR (Valence Shell Electron Pair Repulsion) Theory determines local geometries around atoms in molecules by predicting shapes based on electron pairs.
Common orbital hybridizations include:
- sp: linear geometry
- sp2: trigonal planar geometry
- sp3: tetrahedral geometry
- sp3d: trigonal bipyramidal geometry
- sp3d2: octahedral geometry
Electronegativity varies among elements in the periodic table, impacting bond polarity and molecular stability.
Non-covalent interactions play crucial roles in molecular biology, including:
- Hydrogen bonds: important for DNA and protein structure
- Van der Waals interactions: weak forces that contribute to molecular interactions
- Cation-π interactions: involve positively charged ions interacting with electron-rich pi systems
Resonance structures illustrate multiple ways of representing electron distribution in molecules, influenced by electronegativity. Examples include:
- Carbonyl group
- Carboxylate group
- Amide bond
Oxidation states in organic molecules depend on relative electronegativities, guiding the understanding of redox reactions.

Nucleophiles are electron-rich species that donate electrons to electron-deficient groups (electrophiles). They can be negatively charged or possess lone pairs.
Electrophiles are electron-deficient species attracted to nucleophiles. They may be positively charged or feature an incomplete valence shell, enhancing their electron-accepting nature.
Lone pairs refer to pairs of electrons localized on one atom, contributing to the reactivity and bonding characteristics of molecules.
Leaving groups are atoms or groups that are expelled during substitution or displacement reactions. These groups should be stable upon departure.
Amines serve as nucleophiles in their free base form, with primary amines being the most nucleophilic, followed by secondary and tertiary amines, which face steric hindrance.
- Typical pKa of ammonium is around 9-10; at physiological pH (~7.0), most amines exist as protonated ammonium salts.
- N-H bonds are highly polar, and nitrogen's lone pairs form hydrogen bonds, influencing solubility and reactivity.
Example Reactions:
- Ethylamine Hydrochloride: a primary amine that is both basic and nucleophilic.
- Tris Hydrochloride: a tertiary amine that is basic but not nucleophilic due to steric hindrance.