Introduction to Organic Chemistry

• Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon-containing compounds, which include not only hydrocarbons but also compounds with any number of other elements, including hydrogen, nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur
• It overlaps with many areas including medicinal chemistry, biochemistry, organometallic chemistry, and polymer chemistry
• Organic compounds are pervasive, fundamental components of many products including plastics, drugs, petrochemicals, food, explosives, paints, and adhesives

Core Principles

• Distinguished by carbon's ability to catenate, i.e., form chains and rings with other carbon atoms
• Carbon is tetravalent and readily forms stable covalent bonds with other atoms including H, O, N, and halogens
• The structure of an organic molecule is defined by its carbon skeleton and the functional groups attached to that skeleton
• Functional groups are specific arrangements of atoms that impart characteristic chemical properties to the molecule
• Isomerism is common, where different compounds have the same molecular formula but different structural formulas and arrangements of atoms leading to different properties

Nomenclature

• IUPAC nomenclature provides a systematic way to name organic compounds
• It involves identifying the parent chain, numbering the carbons, identifying and naming substituents, and then assembling the name
• Common nomenclature, using trivial names, is still used, particularly for simple and commonly encountered compounds

Classes of Organic Compounds

• Alkanes: Saturated hydrocarbons with single bonds only (general formula CₙH₂ₙ₊₂)
• Alkenes: Unsaturated hydrocarbons with at least one carbon-carbon double bond (general formula CₙH₂ₙ)
• Alkynes: Unsaturated hydrocarbons with at least one carbon-carbon triple bond (general formula CₙH₂ₙ₋₂)
• Alcohols: Contain a hydroxyl group (-OH) attached to a carbon atom
• Ethers: Contain an oxygen atom bonded to two alkyl or aryl groups (R-O-R')
• Aldehydes: Contain a carbonyl group (C=O) bonded to at least one hydrogen atom
• Ketones: Contain a carbonyl group (C=O) bonded to two alkyl or aryl groups
• Carboxylic Acids: Contain a carboxyl group (-COOH)
• Esters: Contain a carboxyl group where the hydrogen is replaced by an alkyl or aryl group (-COOR)
• Amines: Contain a nitrogen atom with one, two, or three alkyl or aryl groups
• Amides: Contain a nitrogen atom bonded to a carbonyl group

Reactions

• Addition Reactions: Typically occur with unsaturated compounds, where atoms or groups add to the molecule, saturating it
• Elimination Reactions: Atoms or groups are removed from the molecule, resulting in the formation of a multiple bond
• Substitution Reactions: One atom or group is replaced by another atom or group
• Rearrangement Reactions: The structure of the molecule is altered
• Redox Reactions: Involve the transfer of electrons; oxidation is loss of electrons, reduction is gain of electrons

Mechanisms

• Reaction mechanisms describe the step-by-step sequence of elementary reactions by which an overall chemical change occurs
• They involve the movement of electrons, often depicted using curved arrows
• Reactive intermediates include carbocations, carbanions, and free radicals

Spectroscopy

• Nuclear Magnetic Resonance (NMR): Provides information about the carbon-hydrogen framework of a molecule
• Infrared (IR) Spectroscopy: Provides information about the functional groups present in a molecule
• Mass Spectrometry (MS): Provides information about the molecular weight and fragmentation pattern of a molecule
• UV-Vis Spectroscopy: Provides information about the electronic transitions in a molecule

Acids and Bases

• Brønsted-Lowry acids are proton donors, and Brønsted-Lowry bases are proton acceptors
• Lewis acids are electron-pair acceptors, and Lewis bases are electron-pair donors
• Acidity is determined by the stability of the conjugate base
• Factors that affect acidity include electronegativity, size, resonance, and inductive effects

Aliphatic Compounds

• Alkanes are relatively unreactive due to the strength and nonpolarity of C-C and C-H bonds
• Alkenes and alkynes undergo addition reactions at their multiple bonds
• Reactions of alkanes typically involve free radical mechanisms

Stereochemistry

• Stereoisomers have the same connectivity but different spatial arrangement of atoms
• Enantiomers are stereoisomers that are non-superimposable mirror images
• Chiral molecules are non-superimposable on their mirror images and contain one or more stereocenters, typically a carbon atom bonded to four different groups
• Diastereomers are stereoisomers that are not mirror images
• Optical activity is the ability of a chiral molecule to rotate the plane of plane-polarized light
• A racemic mixture is a mixture containing equal amounts of both enantiomers, resulting in no net optical rotation
• Meso compounds contain stereocenters but are achiral due to internal symmetry

Aromatic Compounds

• Aromatic compounds are cyclic, planar, and conjugated systems that exhibit exceptional stability
• Benzene is the archetypal aromatic compound
• Aromaticity is determined by Hückel's rule (4n+2 π electrons)
• Aromatic compounds undergo electrophilic aromatic substitution reactions

Alkyl Halides

• Alkyl halides contain a halogen atom bonded to an alkyl group
• They undergo nucleophilic substitution and elimination reactions
• SN1 reactions proceed through a carbocation intermediate and are unimolecular
• SN2 reactions proceed through a concerted mechanism and are bimolecular
• Elimination reactions (E1 and E2) compete with substitution reactions

Alcohols, Ethers and Epoxides

• Alcohols can be primary, secondary, or tertiary, depending on the number of carbon atoms bonded to the carbon bearing the -OH group
• Alcohols can be converted to alkyl halides, alkenes, and other functional groups
• Ethers are relatively unreactive, but can be cleaved under strongly acidic conditions
• Epoxides are cyclic ethers that are highly reactive due to ring strain and undergo ring-opening reactions

Aldehydes and Ketones

• Aldehydes and ketones undergo nucleophilic addition reactions at the carbonyl carbon
• They can be reduced to alcohols and oxidized to carboxylic acids (for aldehydes)
• Common reactions include Grignard reactions, Wittig reactions, and aldol reactions

Carboxylic Acids and Derivatives

• Carboxylic acids are acidic due to the resonance stabilization of carboxylate anion
• Derivatives include esters, amides, acid halides, and anhydrides
• Derivatives undergo nucleophilic acyl substitution reactions
• Esters can be formed by Fischer esterification
• Amides are the most stable carboxylic acid derivatives

Amines

• Amines are basic due to the lone pair on the nitrogen
• They can be primary, secondary, or tertiary, or quaternary ammonium salts
• Amines undergo reactions with acids, alkyl halides, and aldehydes/ketones

Biomolecules

• Carbohydrates: Polyhydroxy aldehydes or ketones, which are the primary source of energy for living organisms
• Lipids: Fats, oils, and waxes, which are important for energy storage, insulation, and cell structure
• Proteins: Polymers of amino acids, which perform a wide variety of functions in living organisms
• Nucleic Acids: DNA and RNA, which store and transmit genetic information

Organic chemistry is the study of carbon-containing compounds and their properties. Carbon's ability to form chains and rings is a core principle. Organic compounds are fundamental components of plastics, drugs, and food.