Organic Chemistry: Structure, Bonding, and Groups

• Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon-containing compounds.

Key Concepts in Organic Chemistry

• Carbon's unique ability to form stable covalent bonds with itself and other elements is foundational.
• Organic molecules are primarily composed of carbon and hydrogen atoms, but also include nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur.
• The arrangement of atoms and bonds in a molecule determines its properties and reactivity.

Bonding in Organic Compounds

• Carbon forms four covalent bonds.
• Single, double, and triple bonds between carbon atoms are common.
• Sigma (σ) bonds are formed by end-on overlap of atomic orbitals.
• Pi (π) bonds are formed by sideways overlap of p orbitals.

Functional Groups

• Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.
• Alkanes contain only single bonds, while alkenes contain at least one double bond, and alkynes contain at least one triple bond.
• Alcohols contain a hydroxyl group (-OH), ethers contain an oxygen atom bonded to two alkyl or aryl groups (R-O-R'), and amines contain a nitrogen atom bonded to alkyl or aryl groups.
• Aldehydes contain a carbonyl group (C=O) with at least one hydrogen atom attached, ketones contain a carbonyl group bonded to two alkyl or aryl groups, and carboxylic acids contain a carboxyl group (-COOH).
• Esters are derivatives of carboxylic acids where the hydrogen atom of the carboxyl group is replaced by an alkyl or aryl group (R-COO-R').
• Amides contain a nitrogen atom bonded to a carbonyl group.

Isomerism

• Isomers are molecules with the same molecular formula but different structural or spatial arrangements.
• Structural isomers have different connectivity of atoms.
• Stereoisomers have the same connectivity but different spatial arrangements.
• Enantiomers are non-superimposable mirror images.
• Diastereomers are stereoisomers that are not enantiomers.
• Cis-trans isomers (geometric isomers) occur when there is restricted rotation around a bond (e.g., double bonds or cyclic structures).

Nomenclature

• IUPAC nomenclature provides a systematic way to name organic compounds that is universally understood.
• Identify the parent chain, which is the longest continuous chain of carbon atoms.
• Number the carbon atoms in the parent chain to give the lowest possible numbers to substituents.
• Name and number the substituents.
• Combine the substituent names, numbers, and parent chain name into a single name.
• Functional groups have specific suffixes and prefixes.

Alkanes

• Alkanes are saturated hydrocarbons with the general formula CnH2n+2.
• They are relatively unreactive due to the strong C-C and C-H bonds.
• Alkanes undergo combustion, halogenation, and cracking reactions.
• Cycloalkanes are cyclic alkanes with the general formula CnH2n.

Alkenes and Alkynes

• Alkenes are unsaturated hydrocarbons with at least one carbon-carbon double bond.
• Alkynes are unsaturated hydrocarbons with at least one carbon-carbon triple bond.
• Alkenes and alkynes are more reactive than alkanes due to the presence of π bonds.
• They undergo addition reactions, such as hydrogenation, halogenation, hydrohalogenation, and hydration.
• Markovnikov's rule states that in the addition of HX to an alkene, the hydrogen atom adds to the carbon atom with more hydrogen atoms already attached.

Aromatic Compounds

• Aromatic compounds are cyclic, planar molecules with a delocalized π electron system.
• Benzene is the most common aromatic compound.
• Aromatic compounds undergo electrophilic aromatic substitution reactions, such as halogenation, nitration, sulfonation, and Friedel-Crafts alkylation and acylation.
• Substituents on the aromatic ring can be activating or deactivating, and ortho-, para-, or meta-directing.

Reactions

• Addition reactions involve the addition of atoms or groups of atoms to a molecule, typically at a multiple bond.
• Elimination reactions involve the removal of atoms or groups of atoms from a molecule, typically forming a multiple bond.
• SN1 reactions are unimolecular nucleophilic substitution reactions that proceed through a carbocation intermediate.
• SN2 reactions are bimolecular nucleophilic substitution reactions that occur in one step.
• Electrophilic Aromatic Substitutions (EAS) involve the substitution of an atom (usually hydrogen) on an aromatic ring by an electrophile.
• Oxidation reactions involve an increase in the oxidation state of a carbon atom, while reduction reactions involve a decrease in the oxidation state.

Stereochemistry

• Chirality refers to the property of a molecule that is non-superimposable on its mirror image (enantiomer).
• A chiral center is a carbon atom bonded to four different groups.
• Enantiomers have identical physical properties except for the direction in which they rotate plane-polarized light.
• A racemic mixture is a mixture containing equal amounts of both enantiomers.
• Optical activity is the ability of a chiral molecule to rotate plane-polarized light.
• Diastereomers have different physical properties.
• Meso compounds contain chiral centers but are achiral due to internal symmetry.
• The Cahn-Ingold-Prelog (CIP) priority rules are used to assign R and S configurations to chiral centers.

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 environment of atoms in a molecule.
• Chemical shift is the position of a signal in an NMR spectrum, which is influenced by the electronic environment of the atom.
• Splitting of NMR signals is caused by spin-spin coupling between neighboring atoms.
• Infrared (IR) spectroscopy provides information about the functional groups present in a molecule based on the absorption of infrared radiation.
• Characteristic IR absorption bands are associated with specific functional groups.
• Mass spectrometry (MS) provides information about the molecular weight and fragmentation pattern of a molecule.
• The molecular ion peak (M+) corresponds to the molecular weight of the compound.
• Fragmentation patterns can provide clues about the structure of the molecule.
• Ultraviolet-Visible (UV-Vis) spectroscopy provides information about the electronic transitions in a molecule.
• UV-Vis spectroscopy is often used to study conjugated systems and aromatic compounds.