Introduction to Organic Chemistry

• Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon-containing compounds, which may contain many other elements, including hydrogen, nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur
• It is concerned with the synthesis of new molecules and the study of the properties of organic compounds, including their physical and chemical properties, and the evaluation of chemical reactivity.

Core Principles

• Carbon's unique ability to form stable covalent bonds with itself and other elements allows for an immense diversity of organic compounds
• Organic molecules are three-dimensional, and their shapes influence their physical and chemical properties
• Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules
• The understanding of reaction mechanisms is central to organic chemistry, describing how reactions occur at the molecular level.

Nomenclature

• IUPAC nomenclature provides a systematic way to name organic compounds based on their structure.
• Common names are still used for some well-known compounds.
• Naming involves identifying the parent chain, numbering the carbons, identifying substituents, and arranging them alphabetically.

Alkanes

• Alkanes are hydrocarbons containing only single bonds.
• They are relatively unreactive and undergo combustion and halogenation reactions.
• Cycloalkanes are alkanes containing a ring of carbon atoms.
• Isomers are molecules with the same molecular formula but different structural formulas and properties.

Alkenes and Alkynes

• Alkenes contain one or more carbon-carbon double bonds.
• Alkynes contain one or more carbon-carbon triple bonds.
• Alkenes and alkynes are more reactive than alkanes due to the presence of pi bonds.
• They undergo addition reactions, where new atoms or groups of atoms are added across the multiple bond.
• Markovnikov's rule states that in the addition of a protic acid HX to an alkene, the acid hydrogen (H) becomes attached to the carbon with more hydrogens, and the halide (X) group to the carbon with fewer hydrogens.

Stereochemistry

• Stereoisomers are molecules with the same connectivity but different spatial arrangements of atoms.
• Enantiomers are stereoisomers that are non-superimposable mirror images of each other.
• Chirality refers to the property of a molecule that is non-superimposable on its mirror image, often due to a carbon atom bonded to four different groups.
• A chiral center (stereocenter) is an atom, typically carbon, bonded to four different groups.
• Diastereomers are stereoisomers that are not mirror images of each other.
• Optical activity is the ability of chiral molecules to rotate plane-polarized light.
• Meso compounds contain chiral centers but are achiral due to an internal plane of symmetry.
• Racemic mixtures contain equal amounts of both enantiomers and are optically inactive.

Functional Groups

• Alcohols contain a hydroxyl (-OH) group bonded 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) with one hydrogen atom attached to the carbonyl carbon.
• Ketones contain a carbonyl group (C=O) with two alkyl or aryl groups attached to the carbonyl carbon.
• Carboxylic acids contain a carboxyl group (-COOH).
• Esters are derivatives of carboxylic acids where the hydrogen of the carboxyl group is replaced by an alkyl or aryl group.
• Amines contain a nitrogen atom with one or more alkyl or aryl groups attached.
• Amides are derivatives of carboxylic acids where the hydroxyl group is replaced by an amine group.

Reactions

• Addition reactions involve adding atoms or groups of atoms to a molecule, typically across a multiple bond.
• Substitution reactions involve replacing one atom or group of atoms with another.
• Elimination reactions involve removing atoms or groups of atoms from a molecule, often forming a double or triple bond.
• Oxidation reactions involve an increase in the oxidation state of a carbon atom, often by adding oxygen or removing hydrogen.
• Reduction reactions involve a decrease in the oxidation state of a carbon atom, often by adding hydrogen or removing oxygen.

Spectroscopy

• Spectroscopy is the study of the interaction of electromagnetic radiation with matter.
• Nuclear magnetic resonance (NMR) spectroscopy provides information about the structure and bonding of organic molecules by analyzing the magnetic properties of atomic nuclei.
• Infrared (IR) spectroscopy identifies functional groups in a molecule based on their characteristic absorption frequencies.
• Mass spectrometry (MS) determines the molecular weight and fragmentation pattern of a molecule.
• Ultraviolet-visible (UV-Vis) spectroscopy studies the electronic transitions in molecules, particularly those with conjugated pi systems.

Aromatic Compounds

• Aromatic compounds are cyclic, planar molecules with a delocalized pi electron system that obeys Hückel's rule (4n+2 pi electrons).
• Benzene is the most common aromatic compound.
• Aromatic compounds undergo electrophilic aromatic substitution reactions, where an electrophile replaces a hydrogen atom on the aromatic ring.
• Common electrophilic aromatic substitution reactions include halogenation, nitration, sulfonation, and Friedel-Crafts alkylation and acylation.

Important concepts

• Resonance describes the delocalization of electrons in molecules and ions, represented by multiple resonance structures.
• Inductive effects are the electronic effects transmitted through sigma bonds due to electronegativity differences between atoms.
• Hyperconjugation is the stabilizing interaction between sigma bonds and adjacent empty or partially filled p orbitals or pi orbitals.

Reaction Mechanisms

• SN1 reactions are unimolecular nucleophilic substitution reactions that proceed through a carbocation intermediate and favor tertiary substrates in protic solvents.
• SN2 reactions are bimolecular nucleophilic substitution reactions that occur in a single step and favor primary substrates in aprotic solvents.
• E1 reactions are unimolecular elimination reactions that proceed through a carbocation intermediate and favor tertiary substrates in protic solvents.
• E2 reactions are bimolecular elimination reactions that occur in a single step and require a strong base and favor the formation of the more substituted alkene (Zaitsev's rule).

Acids and Bases

• Bronsted-Lowry acids are proton donors, and Bronsted-Lowry bases are proton acceptors.
• Lewis acids are electron pair acceptors, and Lewis bases are electron pair donors.
• The strength of an acid is measured by its pKa value; lower pKa values indicate stronger acids.
• Factors affecting acidity include electronegativity, size, resonance, and inductive effects.

Radical Reactions

• Radicals are species with unpaired electrons.
• Radical reactions involve initiation, propagation, and termination steps.
• Radical halogenation of alkanes is a common radical reaction.
• Antioxidants inhibit radical reactions by scavenging radicals.

Polymers

• Polymers are large molecules composed of repeating structural units called monomers.
• Addition polymers are formed by the direct addition of monomers to each other.
• Condensation polymers are formed by the elimination of a small molecule, such as water, between monomers.
• Common polymers include polyethylene, polypropylene, polystyrene, and polyvinyl chloride (PVC).