Foundations of Organic Chemistry: Structure, Reactivity, and Purification Flashcards

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Carbon tetravalence

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Carbon forms four covalent bonds due to four valence electrons, enabling a vast variety of organic structures. This tetravalence underpins the diversity of organic chemistry.

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Hybridization

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Hybridization mixes atomic orbitals to form new orbitals: $sp^3$, $sp^2$, and $sp$ correspond to tetrahedral, trigonal planar, and linear geometries respectively. Hybridization explains molecular shape and bonding patterns.

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Sigma bond

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A sigma ($\sigma$) bond is formed by head-on overlap of orbitals and allows free rotation about the bond axis. It is the primary bond in single bonds between atoms.

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Pi bond

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A pi ($\pi$) bond arises from side-by-side overlap of p orbitals and exists in double and triple bonds along with a sigma bond. Pi bonds restrict rotation and contribute to regions of electron density above and below the bond axis.

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Bond-line formula

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The bond-line (skeletal) formula omits carbon and hydrogen labels on carbons, showing the carbon skeleton as lines. It simplifies drawing complex organic molecules while retaining connectivity information.

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Wedge-dash notation

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Wedge (solid) and dash (hashed) bonds indicate three-dimensional orientation: wedge toward the viewer, dash away from the viewer. This notation is essential for representing stereochemistry.

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Functional group

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A functional group is a specific atom arrangement that imparts characteristic chemical properties to a molecule, such as alcohols, aldehydes, ketones, and amines. Reactivity is often dictated by the functional group present.

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IUPAC nomenclature

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IUPAC nomenclature systematically names compounds by selecting the longest parent chain, assigning locants, and using appropriate prefixes and suffixes for substituents and functional groups. This yields unambiguous names correlating to structure.

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Ortho/meta/para

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Ortho (o-), meta (m-), and para (p-) describe relative positions of two substituents on a benzene ring: 1,2-; 1,3-; and 1,4- respectively. These prefixes are commonly used for disubstituted benzenes.

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Structural isomerism

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Structural isomerism occurs when compounds share a molecular formula but differ in atom connectivity, including chain, position, and functional group isomerism. Different connectivities lead to distinct properties.

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Stereoisomerism

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Stereoisomerism involves isomers with the same connectivity but different spatial arrangements, such as geometric (cis/trans) and optical (chiral) isomers. These differences can dramatically affect biological activity.

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Homolytic cleavage

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Homolytic cleavage splits a covalent bond so each atom retains one electron, generating two radicals. It commonly occurs under heat or photochemical conditions.

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Heterolytic cleavage

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Heterolytic cleavage results in both bonding electrons going to one atom, forming a cation and an anion (e.g., carbocation and carbanion). This pathway is common in polar reactions involving nucleophiles and electrophiles.

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Nucleophile

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A nucleophile is an electron pair donor that attacks electron-deficient centers; examples include $OH^-$ and $NH_3$. Nucleophiles form bonds by donating electrons to electrophiles.

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Electrophile

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An electrophile is an electron pair acceptor that seeks electron density; examples include $H^+$ and carbocations. Electrophiles react with nucleophiles during many organic reactions.

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Inductive effect

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The inductive effect is electron withdrawal or donation through sigma bonds due to differences in electronegativity. It influences acidity, basicity, and stability of reaction intermediates.

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Resonance

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Resonance delocalizes electrons across adjacent p orbitals, stabilizing molecules or intermediates by distributing charge. Resonance structures are contributing forms of a resonance hybrid.

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Hyperconjugation

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Hyperconjugation stabilizes carbocations via donation of electron density from adjacent C–H or C–C sigma bonds into an empty p orbital. It is sometimes called 'no-bond resonance' and affects reactivity trends.

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Chromatography

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Chromatography separates mixture components using a stationary phase and a mobile phase, with forms including adsorption (TLC, column) and partition (paper) chromatography. It is widely used for purification and analysis.

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Crystallization

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Crystallization purifies solids by dissolving an impure sample in hot solvent and cooling to form purer crystals; impurities stay in the mother liquor. Multiple recrystallizations can increase purity.

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Distillation types

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Distillation separates liquids by boiling point differences: simple (large Δbp), fractional (small Δbp), reduced-pressure (for high-boiling or decomposing liquids), and steam (for steam-volatile compounds). Choice depends on volatility and stability.

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Lassaigne's test

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Lassaigne's test involves fusing an organic sample with sodium to convert N, S, halogens, and P into ionic forms that are detectable in aqueous extracts. It is a classic qualitative method for heteroatom detection.