Organic Chemistry: Core Principles

• Organic chemistry involves the study of carbon-containing compounds' structure, properties, composition, reactions, and preparation; these compounds may include hydrogen, nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur.
• Compounds typically excluded are salts, carbonates, oxides, and carbon allotropes.

Key Concepts in Organic Chemistry

• Molecular properties are defined by the structure, including atomic arrangement and bonding types.
• Carbon forms stable covalent bonds with itself and other elements to create myriad molecules.
• Functional groups, specific atom groups within molecules, dictate characteristic chemical reactions.
• Isomers are same-formula molecules with differing atomic arrangements.
  • Structural isomers are isomers with different connectivity.
  • Stereoisomers share connectivity but differ in spatial arrangement.
• Reaction mechanisms detail stepwise elementary reactions showing chemical transformation.

Core Principles

• Carbon is tetravalent, typically forming four covalent bonds.
• Catenation describes carbon's ability to form chains and rings.
• Polarity arises from electronegativity differences, leading to polar bonds.
• Resonance is electron delocalization in molecules, enhancing stability.

Nomenclature

• Organic compounds are named using the IUPAC nomenclature which is the standard.
• The IUPAC nomenclature gives systematic names based on structure.
• Key steps are identifying the parent chain, identifying functional groups and substituents, and parent chain numbering for locant assignment.

Classes of Organic Compounds

• Alkanes:
  • Saturated hydrocarbons featuring single bonds.
  • The general formula is CₙH₂ₙ+₂.
• Alkenes:
  • Unsaturated hydrocarbons possessing at least one carbon-carbon double bond.
  • General formula: CₙH₂ₙ.
• Alkynes:
  • Unsaturated hydrocarbons with at least one carbon-carbon triple bond.
  • The general formula is CₙH₂ₙ₋₂.
• Alcohols:
  • Characterized by a hydroxyl (-OH) group bonded to a carbon atom.
  • The general formula is R-OH.
• Ethers:
  • Contain an oxygen atom bonded to two alkyl or aryl groups.
  • The general formula is R-O-R'.
• Aldehydes:
  • Contain a carbonyl group (C=O) bonded to at least one hydrogen atom.
  • The general formula is R-CHO.
• Ketones:
  • Contain a carbonyl group (C=O) bonded to two alkyl or aryl groups.
  • The general formula is R-CO-R'.
• Carboxylic Acids:
  • Featuring a carboxyl group (-COOH).
  • The general formula is R-COOH.
• Esters:
  • Carboxylic acid derivatives where the acidic hydrogen is replaced by an alkyl or aryl group.
  • The general formula is R-COOR'.
• Amines:
  • Contain a nitrogen atom bonded with one, two, or three alkyl or aryl groups.
  • The general formulas are R-NH₂, R₂-NH, R₃-N.
• Amides:
  • Carboxylic acid derivatives with the hydroxyl group replaced by an amine.
  • The general formula is R-CO-NR'R''.
• Aromatic Compounds:
  • Characterized by a benzene ring or related structure containing delocalized π electrons.

Functional Groups

• Hydroxyl Group (-OH):
  • Present in alcohols and phenols.
  • Increases water solubility.
• Carbonyl Group (C=O):
  • Found in aldehydes, ketones, carboxylic acids, esters, and amides.
  • Polar, influencing reactivity.
• Carboxyl Group (-COOH):
  • Found in carboxylic acids.
  • Capable of hydrogen bonding.
• Amino Group (-NH₂):
  • Present in amines.
  • Basic, accepting protons.
• Ether Linkage (C-O-C):
  • Found in ethers.
  • Relatively unreactive.
• Ester Linkage (RCOOR'):
  • Present in esters.
  • Susceptible to hydrolysis.

Types of Organic Reactions

• Addition Reactions:
  • Two or more molecules combine into a larger one.
  • Common in unsaturated compounds.
• Elimination Reactions:
  • Atoms/groups are removed from a molecule, forming a multiple bond or a ring.
• Substitution Reactions:
  • One atom or group is replaced by another.
  • Common in alkyl halides and aromatic compounds.
• Rearrangement Reactions:
  • Atoms and bonds within a molecule are reorganized.

Reaction Mechanisms

• Nucleophilic Substitution (SN1 and SN2): Nucleophiles replace leaving groups.
• Elimination Reactions (E1 and E2): Removal of atoms/groups to form alkenes.
• Addition Reactions: Reactants add to multiple bonds, such as electrophilic and nucleophilic addition.

Isomerism

• Structural Isomers:
  • Same molecular formula, different connectivity.
  • Example: butane vs. isobutane (methylpropane).
• Stereoisomers:
  • Same molecular formula, same connectivity, different spatial arrangement.
  • Enantiomers: non-superimposable mirror images.
  • Diastereomers: stereoisomers that are not enantiomers.
  • Geometric isomers (cis/trans): different arrangement around a double bond or ring.

Acids and Bases in Organic Chemistry

• Brønsted-Lowry Acids and Bases: Donate and accept protons, respectively.
• Lewis Acids and Bases: Accept and donate electron pairs, respectively.
• Acidity factors: electronegativity, resonance, inductive effects.

Spectroscopy

• Techniques used to determine the structure and properties of organic compounds.
• NMR Spectroscopy (Nuclear Magnetic Resonance): gives information on the carbon-hydrogen framework of a molecule
• IR Spectroscopy (Infrared): Identifies functional groups.
• Mass Spectrometry (MS): Molecular weight and fragmentation pattern determination.
• UV-Vis Spectroscopy: Analyzes electronic transitions.

Purification Techniques

• Distillation: Separates liquids based on boiling points.
• Recrystallization: Purifies solids based on solubility differences.
• Extraction: Separates compounds based on solubility in different solvents.
• Chromatography: Separates compounds based on differential adsorption on a stationary phase, including Thin Layer Chromatography (TLC), Gas Chromatography (GC), and High-Performance Liquid Chromatography (HPLC).

Key Reaction Types

• Electrophilic Aromatic Substitution:
  • Electrophiles replace hydrogen on an aromatic ring.
  • Common examples: halogenation, nitration, sulfonation, Friedel-Crafts alkylation, and acylation.
• Nucleophilic Acyl Substitution:
  • Nucleophiles replace leaving groups bonded to a carbonyl carbon.
  • Common examples: esterification, amidation, and hydrolysis of esters.
• Grignard Reactions:
  • Carbon-carbon bond formation via Grignard reagent (R-MgX) addition to carbonyl compounds.
• Wittig Reaction:
  • Aldehydes and ketones converted to alkenes using a Wittig reagent (phosphorus ylide).
• Diels-Alder Reaction:
  • A [4+2] cycloaddition between a diene and a dienophile to form a cyclic adduct.
• Reduction Reactions:
  • Decrease the oxidation state of a molecule via hydrogen addition or oxygen removal.
  • Common reducing agents: LiAlH₄, NaBH₄, H₂/metal catalyst.
• Oxidation Reactions:
  • Increase the oxidation state of a molecule via oxygen addition or hydrogen removal.
  • Common oxidizing agents: KMnO₄, CrO₃.
• Polymerization Reactions:
  • Small molecules (monomers) combine to form large molecules (polymers).
  • Addition polymerization and condensation polymerization are the two main types.

General Reaction Principles

• Thermodynamics:
  • Studies energy changes in chemical reactions.
  • Gibbs free energy (ΔG) determines spontaneity (ΔG < 0 for spontaneous reactions).
• Kinetics:
  • Studies reaction rates.
  • The reaction rate depends on activation energy (Ea) and temperature.
  • Catalysts lower activation energy and increase reaction rate.