Exam 2 Study Guide: Organic Compounds, Chemical Reactions, and Carbohydrates

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Chapter 4: Introduction to Organic Compounds

Recognizing and Interconverting Structural Representations

Organic compounds can be represented in several ways, each providing different levels of detail about the molecule's structure.

Lewis Structures: Show all atoms, bonds, and lone pairs explicitly.
Condensed Structural Formulas: Group atoms together to simplify the structure, omitting some or all bonds.
Line (Skeletal) Drawings: Represent carbon chains as lines; carbon and hydrogen atoms are often implied.
Interconversion: Practice converting between these representations to understand molecular structure.
Example: Butane can be drawn as a Lewis structure, condensed as CH3CH2CH2CH3, or as a zig-zag line with four carbons.

Functional Groups and Families

Functional groups are specific groups of atoms within molecules that determine the chemical properties of those molecules.

Common Functional Groups: Alcohols (-OH), Aldehydes (-CHO), Ketones (C=O), Carboxylic acids (-COOH), Amines (-NH2), Halides (–X), etc.
Families: Compounds are classified by their functional groups (e.g., alcohols, alkanes, alkenes, alkynes, etc.).
Example: Ethanol contains an alcohol functional group.

Naming Simple Compounds

Systematic naming (IUPAC) allows chemists to communicate structures unambiguously.

Alkanes: Saturated hydrocarbons with only single bonds. Named with the suffix -ane (e.g., methane, ethane).
Cycloalkanes: Ring structures with the prefix cyclo- (e.g., cyclopentane).
Haloalkanes: Alkanes with halogen substituents (e.g., chloromethane).
Example: 2-chloropropane is a haloalkane with a chlorine on the second carbon.

Isomers

Isomers are compounds with the same molecular formula but different structures or spatial arrangements.

Structural Isomers: Differ in the connectivity of atoms.
Conformers: Differ by rotation around single bonds.
Cis-Trans (Geometric) Isomers: Occur in alkenes and cyclic compounds due to restricted rotation.
Example: But-2-ene has cis and trans isomers.

Chiral Centers

A chiral center (stereocenter) is a carbon atom bonded to four different groups, leading to non-superimposable mirror images (enantiomers).

Chirality: Important in biological systems; enantiomers can have different biological effects.
Example: Lactic acid has a chiral center at the central carbon.

Saturated and Unsaturated Hydrocarbons & Fatty Acids

Hydrocarbons and fatty acids are classified based on the presence of double or triple bonds.

Saturated: Only single bonds (alkanes, saturated fatty acids).
Unsaturated: Contain double (alkenes) or triple (alkynes) bonds; unsaturated fatty acids have one or more C=C bonds.
Example: Oleic acid is a monounsaturated fatty acid.

Cis & Trans Unsaturated Fatty Acids

Unsaturated fatty acids can have cis or trans configurations at the double bond.

Cis: Hydrogen atoms on the same side; naturally occurring; cause a bend in the chain, lowering melting point.
Trans: Hydrogens on opposite sides; often produced industrially; straighter chains, higher melting point.
Physical Effect: Cis fats are typically liquid at room temperature; trans fats are more solid.

Chapter 5: Chemical Reactions

Energy Terms

Chemical reactions involve changes in energy, described by several key terms.

Enthalpy (ΔH): Heat content of a system; negative for exothermic, positive for endothermic reactions.
Entropy (ΔS): Measure of disorder or randomness.
Endothermic: Absorbs heat (ΔH > 0).
Exothermic: Releases heat (ΔH < 0).
Endergonic: Requires input of free energy (ΔG > 0).
Exergonic: Releases free energy (ΔG < 0).
Equation:

Reaction Energy Graphs

Energy diagrams show the progress of a reaction and the energy changes involved.

Endothermic: Products have higher energy than reactants.
Exothermic: Products have lower energy than reactants.
Activation Energy (Ea): The energy barrier that must be overcome for a reaction to proceed.

Kinetics: Factors Affecting Rate

The rate of a chemical reaction depends on several factors:

Concentration of reactants
Temperature
Presence of a catalyst
Surface area (for solids)

Reversible and Irreversible Reactions

Reversible: Can proceed in both directions; reach equilibrium.
Irreversible: Proceed to completion in one direction.

Classification of Reactions

Chemical reactions can be classified by the changes that occur:

Synthesis (Combination): Two or more substances combine to form one product.
Decomposition: One substance breaks down into two or more products.
Exchange: Atoms or groups are exchanged between molecules.
- Single Displacement: One element replaces another.
- Double Displacement: Exchange of groups between two compounds.
Combustion: Reaction with oxygen producing heat and light (often CO2 and H2O).
Condensation: Two molecules combine with loss of a small molecule (often water).
Hydrolysis: Splitting of a molecule by addition of water.
Addition: Atoms added to a double or triple bond (e.g., hydrogenation, hydration).

Predicting Products of Reactions

Combustion: Hydrocarbon + O2 → CO2 + H2O
Condensation: Alcohol + acid → ester + water
Hydrolysis: Ester + water → acid + alcohol
Addition: Alkene + H2 (hydrogenation) → alkane; Alkene + H2O (hydration) → alcohol

Redox Reactions

Redox (reduction-oxidation) reactions involve the transfer of electrons.

Oxidation: Loss of electrons (increase in oxidation state).
Reduction: Gain of electrons (decrease in oxidation state).
Oxidizing Agent: Causes oxidation; is reduced.
Reducing Agent: Causes reduction; is oxidized.
Example: In the reaction Zn + Cu2+ → Zn2+ + Cu, Zn is oxidized, Cu2+ is reduced.

Chapter 6: Carbohydrates – Life's Sweet Molecules

Classification of Carbohydrates

Carbohydrates are classified by the number of sugar units.

Monosaccharides: Single sugar units (e.g., glucose, fructose).
Disaccharides: Two monosaccharides linked (e.g., sucrose, lactose).
Oligosaccharides: 3–10 monosaccharide units.
Polysaccharides: Many monosaccharide units (e.g., starch, cellulose, glycogen).

Common Disaccharides

Disaccharide	Monosaccharide Components
Sucrose	Glucose + Fructose
Lactose	Glucose + Galactose
Maltose	Glucose + Glucose

Classification of Alcohols

Alcohols are classified by the number of carbon atoms attached to the carbon bearing the -OH group.

Primary (1°): -OH on a carbon attached to one other carbon.
Secondary (2°): -OH on a carbon attached to two other carbons.
Tertiary (3°): -OH on a carbon attached to three other carbons.

Characterizing Carbohydrates by Functional Group and Carbon Number

Aldose: Contains an aldehyde group.
Ketose: Contains a ketone group.
Number of Carbons: Triose (3), Tetrose (4), Pentose (5), Hexose (6).
Example: Glucose is an aldohexose; fructose is a ketohexose.

Fischer Projections and Stereochemistry

Fischer projections are two-dimensional representations of three-dimensional molecules, useful for depicting sugars.

Enantiomers: Non-superimposable mirror images.
Epimers: Differ at only one chiral center.
D- and L- Stereoisomers: Based on the configuration at the chiral center farthest from the carbonyl group.
Diastereomers: Stereoisomers that are not mirror images.
Number of Stereoisomers: where n = number of chiral centers.

Ring Forms of Glucose and Other Aldohexoses

Monosaccharides with five or more carbons can cyclize to form ring structures.

Alpha (α) and Beta (β) Anomers: Differ in the configuration at the anomeric carbon (C1 in glucose).
Example: α-D-glucopyranose vs. β-D-glucopyranose.

Oxidation and Reduction Products of Aldoses

Oxidation: Aldoses can be oxidized to form aldonic acids (at C1) or uronic acids (at C6).
Reduction: Aldoses can be reduced to form sugar alcohols (alditols).
Example: Glucose oxidized to gluconic acid; reduced to sorbitol.

Glycosidic Bonds

Glycosidic bonds link monosaccharide units in disaccharides and polysaccharides.

Hemiacetal: Formed when a monosaccharide cyclizes.
Acetal: Formed when a second alcohol reacts with the hemiacetal carbon.
Alpha (α) and Beta (β) Glycosidic Bonds: Based on the configuration at the anomeric carbon.
Example: Maltose has an α(1→4) glycosidic bond.

Common Polysaccharides

Polysaccharide	Monomer	Linkage	Function
Starch	Glucose	α(1→4), α(1→6)	Energy storage in plants
Glycogen	Glucose	α(1→4), α(1→6)	Energy storage in animals
Cellulose	Glucose	β(1→4)	Structural in plants