Introduction to Organic Chemistry and Molecular Structure

Vocabulary flashcards covering hybridization, organic chemical reactions, physical properties, functional groups, and structural/stereoisomerism based on the introductory organic chemistry text.

Modern Organic Chemistry

The branch of chemistry dedicated to the study of compounds containing carbon atoms, established historically in 1828 when Friedrich Wöhler synthesized urea ($H_2N-CO-NH_2$) from ammonium cyanate ($NH_4CNO$).

$sp^3$ Hybridization

Orbital hybridization where one $2s$ orbital combines with three $2p$ orbitals, forming four equivalent hybrid orbitals with tetrahedral geometry, bond angles of $109.5^\times$ ($109.5^\text{o}$), bond lengths of $1.54\,\text{Å}$, and bond energies of $348\,kJ\,mol^{-1}$.

$\sigma$ (Sigma) Bond

A strong, highly stable covalent bond formed by the direct, frontal (axial) overlap of atomic or hybrid orbitals along the internuclear axis.

$sp^2$ Hybridization

Orbital hybridization involving one $s$ orbital and two $p$ orbitals, producing three coplanar hybrid orbitals directed toward the vertices of an equilateral triangle with $120^\circ$ bond angles, leaving one unhybridized $p$ orbital perpendicular to the plane.

$\pi$ (Pi) Bond

A covalent bond formed by the lateral (sideways) overlap of two unhybridized $p$ orbitals above and below the molecular plane; it is weaker than a $\sigma$ bond and responsible for carbon-carbon multiple bonds.

$sp$ Hybridization

Orbital hybridization combining one $s$ orbital and one $p$ orbital, forming two linear hybrid orbitals oriented at $180^\circ$, while leaving two unhybridized $p$ orbitals perpendicular to each other and to the hybrid axis.

Hydrocarbons

Organic compounds containing exclusively carbon and hydrogen atoms, classified into aliphatic (acyclic or alicyclic) and aromatic compounds.

Functional Group

A specific atom or group of atoms within an organic molecule that determines its characteristic physical properties and chemical reactivity.

Topological (Skeletal) Formula

A highly schematic molecular representation that uses line segments to display only the carbon skeleton, omitting explicit carbon and hydrogen symbols unless attached to functional groups.

Empirical Formula

A chemical formula that defines the simplest whole-number ratio of atoms of each element present in a compound (e.g., $CH_2O$ for glucose).

Reaction Mechanism

The detailed step-by-step sequence of elementary process stages detailing electron movement, bond breaking, bond formation, and intermediate species created during a chemical reaction.

Homolytic Cleavage

The symmetrical breaking of a covalent bond where each fragment retains one bonding electron, generating highly reactive, neutral species with unpaired electrons known as radicals.

Heterolytic Cleavage

The asymmetrical breaking of a polar covalent bond where the more electronegative atom retains both bonding electrons, yielding a negatively charged anion and a positively charged cation.

Electrophile

An electron-deficient chemical species bearing a full or partial positive charge, or an incomplete valence octet (e.g., $H^+$ , $BF_3$ , $AlCl_3$), that accepts electron pairs from nucleophiles.

Nucleophile

An electron-rich chemical species possessing a full or partial negative charge, or an available unshared electron pair (e.g., $Cl^-$ , $NH_3$ , $OH^-$), that donates electrons to electrophiles.

Addition Reaction

A characteristic reaction of unsaturated compounds in which two reactant molecules combine to form a single product by breaking a $\pi$ bond and forming two new $\sigma$ bonds.

Elimination Reaction

A reaction in which two substituent groups are removed from a molecule without replacement, resulting in the formation of a double/triple bond or a ring system.

Rearrangement Reaction

A reaction in which the carbon skeleton of a molecule undergoes structural reorganization through the migration of an atom, bond, or group from one site to another without changing overall formula.

Hydrophilic Functional Groups

Polar functional groups (e.g., $-OH$, $-COOH$, $-NH_2$) capable of participating in hydrogen bonding with water, thereby imparting water solubility.

Hydrophobic Groups

Nonpolar molecular regions (e.g., $-CH_3$, $-(CH_2)_nCH_3$, $-C_6H_5$) that cannot form hydrogen bonds with water and reduce water solubility.

Structural (Constitutional) Isomers

Compounds that share identical molecular formulas but differ in the connectivity and arrangement of their constituent atoms (includes chain, position, and functional group isomerism).

Conformational Isomers (Rotamers)

Stereoisomers that can freely interconvert through rotation around single C-C $\sigma$ bonds without breaking chemical bonds.

Geometric Isomerism

A form of configurational stereoisomerism caused by restricted rotation around double bonds or rings; cis isomers have substituents on the same side, while trans isomers have them on opposite sides.

Stereocenter (Chiral Center)

An asymmetric carbon atom ($C^*$) bonded to four completely different atoms or groups of atoms, imparting chirality to the molecule.

Enantiomers

A pair of chiral configurational stereoisomers that are non-superimposable mirror images of each other, displaying identical achiral physical properties but opposing optical and biological activity.