Chapter 4: Organic Molecules and Nomenclature

Representations of Molecules

Organic molecules can be represented in several ways, each providing different levels of structural detail and utility for chemical analysis.

• Molecular Formula: Shows the number and type of atoms in a molecule (e.g., C2H6).

• Condensed Formula: Groups atoms to show connectivity without displaying all bonds (e.g., CH3CH3).

• Lewis/Expanded Structure: Displays all atoms and bonds, including lone pairs.

• Skeletal Structure: Uses lines to represent carbon chains; hydrogens on carbons are implied.

Example: Ethanol can be written as C2H6O (molecular), CH3CH2OH (condensed), or as a full Lewis structure.

Functional Group Identification

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

• Alkanes: Saturated hydrocarbons (single bonds only).

• Alkenes: Hydrocarbons with at least one double bond.

• Alkynes: Hydrocarbons with at least one triple bond.

• Alcohols: Contain an -OH group.

• Amine: Contain an -NH2, -NHR, or -NR2 group.

• Ether: Contain an R-O-R' linkage.

• Alkyl Halide: Contain a halogen (F, Cl, Br, I) attached to an alkyl group.

• Aromatic: Contain a benzene ring (non-carbonyl).

• Amides, Carboxylic Acids, Aldehydes, Ketones, Esters: All contain a carbonyl group (C=O) with different attachments.

IUPAC Naming

The International Union of Pure and Applied Chemistry (IUPAC) system provides rules for naming organic compounds.

• Alkanes, Alkenes, Alkynes: Named based on the longest carbon chain and the type of bonds present.

• Alcohols, Alkyl Halides, Ketones, Carboxylic Acids, Aldehydes: Functional group suffixes and prefixes are used (e.g., -ol for alcohols, -al for aldehydes).

Example: 2-butanol: four-carbon chain with an -OH on the second carbon.

Bond Length vs. Bond Strength

• Bond Length: The distance between the nuclei of two bonded atoms. Shorter bonds are generally stronger.

• Bond Strength: The energy required to break a bond. Triple bonds are stronger and shorter than double or single bonds.

Alkyl and Halogen Substituent Naming

• Alkyl Groups: Methyl (CH3-), Ethyl (C2H5-), Propyl (C3H7-), etc.

• Halogen Substituents: Chloro-, Bromo-, Fluoro-, Iodo-.

Isomers

• Structural Isomers: Same molecular formula, different connectivity.

• Stereoisomers: Same connectivity, different spatial arrangement.

Stereoisomers: Cis/Trans and Chirality

• Cis/Trans Isomers: Occur in alkenes and cyclic structures; cis = same side, trans = opposite sides.

• Chiral Molecules: Molecules with a non-superimposable mirror image, often due to a chiral center (carbon with four different groups).

• Enantiomers: Pair of chiral molecules that are non-superimposable mirror images.

Fatty Acid Nomenclature

• Omega Designation: Indicates the position of the first double bond from the methyl end (omega carbon).

• X:X Designation: Number of carbons : number of double bonds (e.g., 18:1).

• Saturated: No double bonds.

• Monounsaturated: One double bond.

• Polyunsaturated: More than one double bond.

Extra Credit Functional Groups

• Thiols: Contain -SH group.

• Sulfides: Contain R-S-R' linkage.

• Disulfides: Contain R-S-S-R' linkage.

• Phenols: Aromatic ring with an -OH group.

Chapter 5: Thermochemistry and Organic Reactions

Enthalpy (ΔH)

Enthalpy is a measure of the total heat content of a system at constant pressure.

• Exothermic Reaction: Releases heat; ΔH < 0.

• Endothermic Reaction: Absorbs heat; ΔH > 0.

Free Energy (ΔG)

Gibbs free energy determines the spontaneity of a reaction.

• ΔG < 0: Spontaneous (exergonic).

• ΔG > 0: Non-spontaneous (endergonic).

Equation:

Increasing Reaction Rate

• Increase temperature.

• Increase concentration of reactants.

• Add a catalyst.

Categories of Organic Reactions

• Synthesis: Two or more reactants combine to form one product.

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

• Exchange/Displacement: Atoms or groups are exchanged between molecules.

Specific Types of Reactions

• Redox (Inorganic and Organic): Involves transfer of electrons.

• Combustion: Reaction with O2 producing CO2 and H2O.

• Addition Reactions: Atoms are added to double or triple bonds (e.g., hydration, hydrogenation).

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

• Hydrolysis: Breaking a bond using water.

Example: Hydration of an alkene forms an alcohol.

Chapter 6: Carbohydrates

Classification of Carbohydrates

• Monosaccharides: Single sugar units (e.g., glucose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose).

• Oligosaccharides: 3-10 monosaccharide units.

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

Alcohol Classification

• Primary Alcohol: -OH group attached to a carbon with one other carbon.

• Secondary Alcohol: -OH group attached to a carbon with two other carbons.

• Tertiary Alcohol: -OH group attached to a carbon with three other carbons.

Monosaccharide Nomenclature

• Triose: 3 carbons.

• Tetrose: 4 carbons.

• Pentose: 5 carbons.

• Hexose: 6 carbons.

Aldose vs. Ketose

• Aldose: Monosaccharide with an aldehyde group.

• Ketose: Monosaccharide with a ketone group.

Stereochemistry of Monosaccharides

• Diastereomers: Stereoisomers that are not mirror images.

• Enantiomers: Non-superimposable mirror images.

• Epimers: Differ at only one chiral center.

Anomeric Carbon and Cyclic Forms

• Anomeric Carbon: The carbon derived from the carbonyl carbon (C1 in aldoses) that becomes chiral in the cyclic form.

• Fischer to Cyclic (Hemiacetal): The anomeric carbon bonds to an -OH group, forming a ring.

• Alpha/Beta Anomers: If the -OH on the anomeric carbon is down (alpha) or up (beta) in the Haworth projection.

Reducing Sugars

• Monosaccharides and some disaccharides can act as reducing agents due to a free anomeric carbon.

Glycosidic Bond Formation

• Two monosaccharides join via condensation, forming a glycosidic bond (alpha or beta, with specific carbon numbering).

Polysaccharides: Storage and Structure

• Storage: Starch (plants: amylose and amylopectin), Glycogen (animals).

• Structure: Cellulose (plants), Chitin (arthropods).

• Amylose: Linear chains of glucose with α(1→4) bonds.

• Amylopectin: Branched chains with α(1→4) and α(1→6) bonds.

• Cellulose: Linear chains with β(1→4) bonds.

• Chitin: Similar to cellulose but with N-acetylglucosamine units.

• Glycogen: Highly branched, α(1→4) and α(1→6) bonds.

ABO Blood Typing and Oligosaccharides

• Blood types are determined by oligosaccharide antigens on red blood cells.

• Type O is the universal donor; type AB is the universal acceptor.

Heparin

• Heparin is a polysaccharide that acts as an anticoagulant (prevents blood clotting).

Extra Credit: Fischer and Haworth Projections

• Conversion between Fischer (linear) and Haworth (cyclic) projections is important for understanding carbohydrate structure.

Chapter 7.1: Gas Laws

Pressure Unit Conversions

Pressure can be measured in several units. Common conversions include:

Boyle’s Law (Conceptual)

• At constant temperature, the pressure and volume of a gas are inversely related.

Charles’ Law (Conceptual)

• At constant pressure, the volume of a gas is directly proportional to its absolute temperature.

Gay-Lussac’s Law (Conceptual)

• At constant volume, the pressure of a gas is directly proportional to its absolute temperature.

Extra Credit: Calculations Using Gas Laws

• Use the provided formulas to solve for unknown variables when given three of the four quantities (e.g., P, V, T).