Chem 1110 Exam 3 Study Guide: Stereochemistry, Chemical Reactions, Carbohydrates, and States of Matter

Chapter 4: Stereochemistry and Chirality

Stereochemistry Overview

Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. It is crucial for understanding the properties and reactivity of organic compounds.

• Stereoisomers: Compounds with the same molecular formula and connectivity but different spatial arrangements.

• Chiral Center: Typically a tetrahedral carbon atom bonded to four different substituents, leading to non-superimposable mirror images.

• Enantiomers: Stereoisomers that are non-superimposable mirror images of each other. They have identical physical properties except for their interaction with plane-polarized light and reactions in chiral environments.

Key Points:

• To recognize a chiral center, look for a carbon atom with four different groups attached.

• Practice drawing tetrahedral centers in 3D to visualize chirality.

• Enantiomers differ in optical activity: one rotates plane-polarized light to the right (dextrorotatory), the other to the left (levorotatory).

Example: The two enantiomers of lactic acid differ only in the spatial arrangement around the central carbon atom.

Chapter 5: Chemical Reactions and Thermodynamics

Redox Reactions

Redox (reduction-oxidation) reactions involve the transfer of electrons between species. They are fundamental to both inorganic and organic chemistry.

• OIL RIG: "Oxidation Is Loss, Reduction Is Gain" (of electrons).

• LEO the lion says GER: "Lose Electrons = Oxidation; Gain Electrons = Reduction".

• Organic redox: Oxidation of alkanes to carbon dioxide involves stepwise addition of oxygen or removal of hydrogen.

Thermodynamics and Reaction Types

• Exothermic Reaction: Releases heat to the surroundings ($\Delta H < 0$).

• Endothermic Reaction: Absorbs heat from the surroundings ($\Delta H > 0$).

• Gibbs Free Energy ($\Delta G$): Determines spontaneity of a reaction.

• Exergonic: $\Delta G < 0$, spontaneous.

• Endergonic: $\Delta G > 0$, nonspontaneous.

• Activation Energy ($E_a$): Minimum energy required for a reaction to proceed.

Equation:

$\Delta G = \Delta H - T\Delta S$

Reaction Kinetics and Mechanisms

• Reaction Coordinate Diagram: Visualizes energy changes during a reaction.

• Calorimetry: Measurement of heat flow in chemical reactions.

• Factors Affecting Rate: Concentration, temperature, catalysts, and surface area.

• Catalysts and Enzymes: Lower activation energy, increasing reaction rate without being consumed.

Types of Chemical Reactions

• Synthesis (Combination): Two or more reactants form one product.

• Decomposition: One reactant breaks into two or more products.

• Exchange Reactions: Atoms or groups are exchanged between molecules (single and double replacement).

• Chemical Equilibrium: Forward and reverse reactions occur at the same rate; concentrations remain constant.

Organic Reaction Types

• Condensation: Two molecules combine with loss of a small molecule (often water).

• Hydrolysis: Breaking a bond by adding water.

• Hydrogenation: Addition of hydrogen to unsaturated bonds (e.g., alkenes).

• Hydration: Addition of water to a molecule.

• Markovnikov’s Rule: In addition of HX to an alkene, the hydrogen attaches to the carbon with more hydrogens already attached.

Example: Hydrogenation of ethene to ethane using a nickel catalyst.

Chapter 6: Carbohydrates – Structure and Function

Classification and Nomenclature

• Monosaccharides: Simple sugars; classified by number of carbons (triose, tetrose, pentose, hexose).

• D-Glucose, D-Mannose, D-Fructose: Important hexose monosaccharides; know their structures.

• Cyclic Structure of Glucose: Glucose forms a six-membered ring (pyranose) in solution.

Types of Carbohydrates

• Monosaccharides: Single sugar units.

• Disaccharides: Two monosaccharides linked by a glycosidic bond.

• Oligosaccharides: 3–10 monosaccharide units.

• Polysaccharides: Many monosaccharide units (e.g., starch, cellulose).

Aldose vs Ketose

• Aldose: Monosaccharide with an aldehyde group (e.g., glucose).

• Ketose: Monosaccharide with a ketone group (e.g., fructose).

Fischer Projections and Stereochemistry

• Fischer Projection: 2D representation; horizontal lines = bonds projecting out, vertical lines = bonds projecting back.

• D vs L Carbohydrates: Based on the configuration of the chiral carbon farthest from the carbonyl group.

• Enantiomer vs Diastereomer: Enantiomers are non-superimposable mirror images; diastereomers are not mirror images.

Biological Importance

• Glycolysis: Metabolic pathway converting glucose to pyruvate, generating ATP.

• Anomers and Anomeric Carbon: Isomers differing at the new chiral center formed on ring closure (α and β forms).

• Glycosidic Bond: Covalent bond joining carbohydrate molecules; named by the carbons involved (e.g., α(1→4)).

Polysaccharides

• Amylose vs Amylopectin: Amylose is unbranched; amylopectin is branched.

• Glycogen: Storage polysaccharide in animals; highly branched.

• Cellulose: Structural polysaccharide in plants; β(1→4) linkages.

• Chitin: Structural polysaccharide in arthropods and fungi.

Chapter 7: States of Matter and Attractive Forces

Gas Laws and Pressure

• Pressure: Force exerted per unit area by gas particles colliding with container walls.

• Kinetic Molecular Theory: Explains gas behavior based on particle motion.

Law	Equation	Variables
Boyle’s Law	$P_1V_1 = P_2V_2$	Pressure (P), Volume (V)
Charles’s Law	$\frac{V_1}{T_1} = \frac{V_2}{T_2}$	Volume (V), Temperature (T in K)
Gay-Lussac’s Law	$\frac{P_1}{T_1} = \frac{P_2}{T_2}$	Pressure (P), Temperature (T in K)
Combined Gas Law	$\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$	P, V, T

Boiling Points and Attractive Forces

• Boiling Point: Temperature at which vapor pressure equals atmospheric pressure.

• Vapor Pressure: Pressure exerted by a vapor in equilibrium with its liquid.

• Types of Attractive Forces:

  • London Dispersion Forces

  • Dipole-Dipole Interactions

  • Hydrogen Bonding

  • Ionic Bonds

  • Ion-Dipole Forces

• Intramolecular vs Intermolecular Forces: Intramolecular are within molecules; intermolecular are between molecules.

• Predicting Boiling Points: Stronger intermolecular forces lead to higher boiling points.

Solubility and Molecular Interactions

• Golden Rule of Solubility: "Like dissolves like"—polar solvents dissolve polar solutes, nonpolar dissolve nonpolar.

• Hydrophilic vs Hydrophobic: Hydrophilic = water-loving (polar); hydrophobic = water-fearing (nonpolar).

• Hydration: Interaction of water molecules with ions or polar molecules.

• Amphipathic Compounds: Molecules with both hydrophilic and hydrophobic regions (e.g., phospholipids).

Biological Membranes and Lipids

• Micelle: Spherical arrangement of amphipathic molecules in water.

• Bilayer/Vesicle: Double-layered structure forming the basis of cell membranes.

• Fluid Mosaic Model: Describes the dynamic and heterogeneous structure of cell membranes.

• Steroid Molecule Identification: Steroids have a characteristic four-ring structure.

• Cholesterol: Essential component of cell membranes; precursor to steroid hormones.

• Dietary Lipids: Fats are solid at room temperature (saturated); oils are liquid (unsaturated).

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard chemistry curriculum.