O Chem Vocab

Absorption spectrum

A plot showing which wavelengths of electromagnetic radiation are absorbed by a compound, used in IR and UV-Vis spectroscopy to identify functional groups.

Alcohol

An organic compound containing a hydroxyl group (–OH) bonded to a saturated carbon atom.

Aldehyde

A carbonyl compound in which the carbonyl group (C=O) is bonded to at least one hydrogen atom

Alkane

A saturated hydrocarbon containing only single carbon–carbon bonds

Alkene

An unsaturated hydrocarbon containing at least one carbon–carbon double bond

Alkyl halide

An organic compound in which one or more halogen atoms (F, Cl, Br, I) are bonded to an sp3 carbon.

Alkyne

An unsaturated hydrocarbon containing at least one carbon–carbon triple bond

Allylic

Referring to a position or carbon atom adjacent to a carbon–carbon double bond.

Alpha (α) position

The carbon atom directly adjacent to a carbonyl group or other functional group in a molecule.

Amide

A carbonyl compound in which the carbonyl carbon is bonded to a nitrogen atom

Amine

An organic derivative of ammonia in which one or more hydrogen atoms are replaced by alkyl or aryl groups.

Anti-periplanar

A conformational relationship in which two substituents have a dihedral angle of 180°, required for E2 elimination.

Asymmetric stretching

A vibrational mode in IR spectroscopy in which two bonds stretch simultaneously but in opposite directions (one lengthens while the other shortens).

Atomic orbital

A mathematical function describing the probability of finding an electron in a specific region of space around an atom.

Bending

A vibrational mode in IR spectroscopy involving a change in bond angle rather than bond length.

Beta (β) position

The carbon atom one position removed from the alpha carbon (two carbons away from the principal functional group).

Beta elimination

A reaction in which atoms or groups on adjacent (alpha and beta) carbons are removed to form a pi bond

Bimolecular

A reaction step involving two species in the rate-determining step

Bond-line structures

A shorthand representation of organic molecules in which carbon atoms are shown as vertices and hydrogen atoms on carbon are implied.

Carboxylic acid

An organic compound containing a carboxyl group (–COOH)

Clockwise sequence, R

A stereodescriptor assigned when the three substituents of a chiral center decrease in priority in a clockwise direction (after the lowest-priority group points away)

Column chromatography

A separation technique in which a mixture is passed through a column packed with a stationary phase (e.g., silica) to separate compounds by their polarity.

Condensed structures

A structural representation of organic molecules that shows all atoms but omits most bond lines

Conjugated

Describing a system of alternating single and multiple bonds that allows for delocalization of pi electrons across multiple atoms.

Conjugated π bond

A pi bond that is part of a conjugated system, allowing electron delocalization over multiple atoms.

Constitutional isomer

Compounds with the same molecular formula but different connectivity (bonding order) of atoms.

Counter clockwise sequence, S

A stereodescriptor assigned when the three substituents of a chiral center decrease in priority in a counterclockwise direction (after the lowest-priority group points away)

Covalent bond

A chemical bond formed by the sharing of one or more pairs of electrons between two atoms.

Curved arrows

Arrow notation used in reaction mechanisms to show the movement of electron pairs from nucleophile to electrophile.

Dash

A bond representation in 3D structural drawings indicating a bond going behind the plane of the page.

Degenerate

Having the same energy level

Delocalization

The spreading of electron density (lone pairs or pi electrons) over multiple atoms through resonance or conjugation.

Delocalized lone pair

A lone pair that participates in resonance and is spread over more than one atom rather than residing on a single atom.

Dextrorotary

Describing an optically active compound that rotates plane-polarized light clockwise (to the right)

Diagnostic region

The region of an IR spectrum (above ~1500 cm⁻¹) that contains absorption bands characteristic of specific functional groups.

Diastereoisomer

Stereoisomers that are not mirror images of each other

Dihedral angle

The angle between two planes defined by four atoms in a chain

Dipole moment

A measure of the separation of positive and negative charge in a molecule

Dipole-dipole interactions

Intermolecular forces between polar molecules due to the attraction between partial positive and partial negative charges.

Disubstituted alkene

An alkene in which two carbon substituents (other than H) are attached to the double-bond carbons.

E1

A unimolecular elimination mechanism proceeding through a carbocation intermediate

E2

A bimolecular elimination mechanism occurring in a single concerted step

Eclipsed conformation

A conformation in which substituents on adjacent carbons are aligned when viewed in a Newman projection, maximizing torsional strain.

Electron density

A measure of the probability of finding an electron in a given region of space around a molecule.

Electrophile

An electron-deficient species (atom, ion, or molecule) that accepts an electron pair in a reaction

Electrostatic potential map

A color-coded map superimposed on a molecular structure showing the distribution of electron density/charge across the molecule.

Enantiomer

One of a pair of non-superimposable mirror-image stereoisomers

Equatorial position

A position on a cyclohexane ring in which a substituent points roughly outward from the ring, minimizing steric strain.

Ester

A carbonyl compound in which the carbonyl carbon is bonded to an –OR group

Ether

An organic compound in which an oxygen atom is bonded to two carbon groups

Fingerprint region

The region of an IR spectrum below ~1500 cm⁻¹ that contains complex overlapping bands unique to each compound, used for identification.

Fischer projections

A 2D representation of a 3D molecule in which horizontal bonds point toward the viewer and vertical bonds point away

Flagpole interaction

A steric interaction in the boat conformation of cyclohexane between substituents pointing straight up and straight down (the "flagpole" positions).

Formal charge

The charge assigned to an atom in a Lewis structure calculated as: valence electrons − nonbonding electrons − ½(bonding electrons).

Fractional distillation

A separation technique that separates mixtures of liquids with different boiling points by controlled heating and condensation.

Frequency

The number of wave cycles per unit time

Functional group

An atom or group of atoms within a molecule that is responsible for its characteristic chemical reactions and properties.

Gauche interactions

A steric interaction in a staggered conformation where two large substituents are 60° apart (gauche relationship), causing some strain.

Haworth projections

A flat hexagonal or pentagonal representation of cyclic sugar structures showing the stereochemistry of substituents (above or below the ring).

Heat of combustion

The energy released when one mole of a compound is completely burned in oxygen

Hofmann product

The less substituted alkene product formed preferentially in elimination reactions using a bulky base

Hydrophilic

"Water-loving"

Hydrophobic

"Water-fearing"

Induction

The polarization of electron density through sigma bonds due to an electronegative atom

Intermediate

A species that is formed and consumed during a multi-step reaction

Inversion of configuration

The reversal of spatial arrangement at a chiral center (R→S or S→R) that occurs during an SN2 reaction (Walden inversion).

Ketone

A carbonyl compound in which the carbonyl group is bonded to two carbon substituents

Leaving group

An atom or group that departs with the bonding electrons during a substitution or elimination reaction

Levorotary

Describing an optically active compound that rotates plane-polarized light counterclockwise (to the left)

Lewis structures

Diagrams showing the bonding and nonbonding (lone pair) electrons in a molecule using dots and lines.

Localized lone pair

A lone pair of electrons that remains on a single atom and does not participate in resonance delocalization.

Locant

A number used in IUPAC nomenclature to specify the position of a substituent or functional group on the parent chain.

London dispersion forces

Weak, temporary intermolecular forces arising from instantaneous fluctuations in electron distribution

Lone pair

A pair of valence electrons on an atom that is not involved in bonding

Loss of leaving group

A mechanistic step in which a leaving group departs from the substrate, often generating a carbocation intermediate (as in SN1/E1).

Mechanism

A step-by-step description of the bond-breaking and bond-forming events that convert reactants to products in a chemical reaction.

Meso compound

A molecule with multiple chiral centers that is achiral overall due to an internal plane of symmetry

Methyl shift

A 1,2-shift in which a methyl group migrates with its bonding electrons to an adjacent carbocation, forming a more stable carbocation.

Mirror image

The reflection of a molecule

Molecular dipole moment

The vector sum of all individual bond dipoles in a molecule

Multiple chirality centers

The presence of more than one chiral (stereogenic) center in a single molecule, giving rise to diastereomers.

Newman projections

A way to depict the conformation about a carbon–carbon single bond by viewing along the bond axis

Nucleophile

An electron-rich species (atom, ion, or molecule) that donates an electron pair to an electrophile in a reaction

Nucleophilic attack

The mechanistic step in which a nucleophile donates electrons to an electrophilic center, forming a new covalent bond.

Nucleophilic centers

The electron-rich sites in a molecule (lone pairs, pi bonds, or negatively charged atoms) that can act as nucleophiles.

Observed rotation

The actual rotation of plane-polarized light measured by a polarimeter for a given sample

Octet rule

The tendency of main-group atoms to gain, lose, or share electrons to achieve a valence shell with eight electrons.

Optically active

Describing a compound that rotates plane-polarized light

Optically pure

Describing a sample consisting of a single enantiomer (100% ee)

Parent chain

The longest continuous carbon chain in a molecule, used as the basis for IUPAC naming of alkanes and other compounds.

Partial negative charge (δ-)

A slight negative charge on an atom due to unequal electron sharing in a polar covalent bond.

Partial positive charge (δ+)

A slight positive charge on an atom due to unequal electron sharing in a polar covalent bond.

Partially condensed structures

A structural representation between full bond-line and fully condensed

Petroleum

A naturally occurring mixture of hydrocarbons found underground

Phenol

An aromatic compound in which a hydroxyl group (–OH) is directly attached to a benzene ring.

Pi bond

A covalent bond formed by the sideways overlap of p orbitals above and below the internuclear axis

Plane of symmetry

An imaginary plane that bisects a molecule into two mirror-image halves

Plane polarized light

Light in which the electric field oscillates in only one plane

Polar aprotic solvent

A polar solvent that lacks O–H or N–H bonds and cannot donate hydrogen bonds

Polar covalent

A covalent bond in which electrons are shared unequally due to a difference in electronegativity between the bonded atoms.