Absolute configuration
The actual three-demensional arrangement of groups around a chirality center.
Acetal
The product of the addition of two equivalents of an alcohol to an aldehyde or a ketone.
Acetylide anion
A carbon nucleophile generated by treating 1-alkynes with a very strong base, such as sodium amide.
Achiral molecule
A molecule that is superimposable on its mirror image.
Acidity constant
An equilibirum constant for the reaction of an acid with water as a base; used as a measure of the strength of an acid. For a general acid, HA, the equation for Ka is
Ka = [A-][H3O+]/[HA].
Activation energy
The energy required to surmount the energy barrier separating reactants and products.
Acyl group
A carbonyl group with an attached alkyl group.
Addition polymer or chain-growth polymer
A polymer formed by a chain mechanism, where one initiatior molecule causes a large number of monomers to react to form one polymer molecule.
Addition reaction
A reaction that results in the addition of two groups to opposite ends of a multiple bond.
Alkaloid
A nitrogen-containing natural product that occurs primarily in higher plants and in some fungi, such as mushrooms.
Alkyl group
The part of a compound that has carbons that are only singly bonded to other carbons and hydrogens.
Alkylation reaction
A reaction that results in the attachment of an alkyl group to the reactant.
Allowed reaction
A pericyclic reaction that is energetically favorable because the electrons in the occupied M.O.'s do not increase in energy.
Allyl group
The CH2=CHCH2- group.
Alpha carbon
The carbon adjacent to a functional group; most commonly used to refer to the carbon adjacent to a carbonyl group.
Amorphous solid
A solid in which the individual molecules have a random arrangement; a glassy solid with no order in the arrangement of its molecules.
Amphoteric compound
A compound that can act as either an acid or a base.
Angle strain
Destabilization, usually found in compounds having three- or four-membered rings, that occurs when the orbitals of a bond do not point directly at each other, so the amount of overlap is decreased.
Annulene
A name sometimes given to rings that contain alternating single and double bonds in a Lewis structure.
Anomers
Diastereomers that are formed by cyclization of a carbohydrate with differing configurations at the new stereocenter.
Anti addition
The addition of groups to opposite sides of a double bond.
Anti conformation
Conformation in which the dihedral angle between two groups on adjacent atoms is 180 degrees
Anti elimination
Elimination of groups from a conformation in which the dihedral angle between them is 180 degrees. This is the preferred geometry for the E2 reaction.
Antiaromatic compound
A compound that is destabilized because of the presence of a conjugated cycle of p orbitals containing 4n electrons.
Antibonding M.O.
A M.O. that is higher in energy than the A.O.'s that combine to form it.
Anti-periplanar bonds
Bonds with a dihedral angle of 180 degrees.
Aprotic sovent
A solvent that does not have a H bonded to N or O and therefore cannot H bond.
Arenium ion
The carbocation formed by addition of an electrophile to a benzene derivative.
Aromatic compound
A compound that is especially stable because of the presence of a conjugated cycle of p orbitals containing 4n + 2 electrons.
Atactic polymer
A polymer with random configurations at its many stereocenters.
Atomic orbital
The region about the nucleus of an atom where, if the orbital contains an electron, the probability of finding an electron is very high.
Axial bond
In the chair formation of cyclohexane, a bond that is parallel to the axis of the ring.
Axial strain energy
The amount of destabilization caused by a group in the axial position in the chair conformation of cyclohexane.
Base ion
The most abundant ion in the mass spectrum.
Benzyl group
The PhCH2- group.
Benzyne
A highly reactive intermediate that has a benzene ring with a formal triple bond.
Boat conformation
The boat-shaped conformation of cyclohexane that has no angle strain but does have some steric strain and some torsional strain.
Bond disconnections
The imaginary process of breaking bonds at or near the functional groups in a compound during the process of retrosynthetic analysis.
Bond dissociation energy
The amount of energy that must be added in the gas phase to break the bond in a homolytic manner.
Bonding M.O.
A M.O. that is lower in energy than the A.O.'s that combine to form it.
Bromonium ion
A three-membered ring containging a positively charged bromine atom; an intermediate formed in the addition of bromine to an alkene.
Bonsted-Lowry acid
A proton donor.
Bronsted-Lowry base
A proton acceptor.
Cahn-Ingold-Prelog sequence rules
Rules that are used to assign priorities to groups attacted to a stereocenter so that the configuration of a compound can be designated.
Carbanion
A C with three bonds, an unshared pair of electrons, and a negative charge.
Carbene
A reactive species having a C with only two bonds and an unshared pair of electrons.
Carbenoid
An organometallic species that reacts like carbene.
Carbocation
A carbon with three bonds and a positive charge.
Carbohydrate
Naturally occuring compounds, often with the empirical formula C(H2O) that are polyhydroxy aldehydes or ketones and derivatives formed from these; includes sugars and starches.
Carbonyl group
A C=O bond.
Carboxy group
A carbonyl group with an attached hydroxy group.
Chain reaction
A reaction in which a reactive intermediate, such as a radical, reacts with a normal molecule, ultimately generating a molecule of product and regenerating the original reactive intermediate, which then causes another reaction cycle to occur. A chain reaction involves three steps: inititation, propagation, and termination.
Chain-growth polymer or addition polymer
A polymer formed by a chain mechanism, where one initiator molecule causes a large number of monomers to react to form one polymer molecule.
Chair conformation
The chair-shaped conformation of cyclohexane that has no angle strain and has no torsional strain because it is perfectly staggered about all the C-C bonds. It is strain free.
Chemical shift
The position of an absorption on the x-axis in an NMR spectrum; provides information about the local environment of the atom that is responsible for the absorption.
Chirality center
A carbon or other tetrahedral atom bonded to four different groups; a type of sterocenter.
Chiral molecule
A molecule that is not superimposable on its mirror image.
Chromophore
The part of a molecule that is responsible for the absorption of ultraviolet or visible light.
Cis-trans isomers
Stereoisomers that differ in the placement of groups on one side or the other of a double bond.
Codon
A series of three bases in a nucleic acid polymer that specifies a particular amino acid.
Concerted reaction
A reaction that occurs in one step.
Condensation polymer or step growth polymer
A polymer formed from monomers with two reactive functional groups by normal reactions, such as ester formation, between the functional groups.
Configuration
The three-dimensional arrangment of groups about a stereocenter in a molecule.
Conformation
A shape that a molecule can assume by rotation about a single bond.
Conformational analysis
Analysis of the energies of the various conformations of a compound.
Conjugate acid
The acid formed by protonation of a base in an acid-base reaction.
Conjugate addition or 1,4-addition
The addition of a nucleophile to the B-carbon of an a,B-unsaturated carbonyl compound.
Conjugate base
The base formed by the loss of a proton from an acid in an acid-base reaction.
Conjugated molecule
A molecule that has a series of overlapping parallel p orbitals on adjacent atoms.
Connectivity
The arrangement of bonded atoms in a structure.
Conrotation
Rotation of orbitals in the same direction in an electrocyclic reaction.
Constitutional isomers
Compounds that have the same molecular formula but a different arrangement (connectivity) of bonded atoms.
Coupling constant (Jax)
The separation between two adjacent peaks in a group of peaks that results from coupling in an NMR spectrum.
Covalent bonding
Bonding that results from atoms sharing electrons in order to arrive at the same number of electrons as a noble gas.
Cross-link
A group that connects separate polymer chains by covalent bonds.
Crystalline solid
A solid in which the individual molecules are arranged with a very high degree of order.
Cycloaddition reaction
A pericyclic reaction in which two molecules react to form two new sigma bonds between the end atoms of their pi systems, resulting in the formation of a ring.
Degenerate orbitals
Orbitals with the same energy.
Degree of unsaturation (DU)
The total number of multiple bonds plus rings in a compound. The DU is calculated by subtracting the actual number of H's in a compound from the maximum number of H's and dividing the results by 2.
Delocalized MO
A MO that extends around more than two atoms.
DEPT-NMR (distortionless enhancement by polarization transfer)
A technique used in 13C-NMR that allows the number of H's attached to each C to be determined.
Dextrorotatory (d) or (+)
Clock-wise rotation of plane-polarized light.
Diastereomers
Non-mirror-image stereoisomers.
1,3-Diaxial interaction
An interaction that destabilizes two axial groups on the same face of a cyclohexane ring because of steric crowding between them.
Dienophile
The species, most often an alkene or alkyne, that acts as the two-electron component in a Diels-Alder reaction.
Dihedral angle
The angle between the a marker group on the front atom and on the back atom of a Newman projection.
Dipolar ion or zwitterion
A neutral compound containing a covalently linked cation and anion.
Dipole moment (u)
The product of the amount of charge separation in a molecule x the distance of the charge separation.
Disaccharide
A carbohydrate formed from two monosaccharide units that are connected by a glycosidic bond.
Disrotation
Rotation of orbitals in opposite directions in an electrocyclic reaction.
Downfield
A chemical shift at a higher delta value in the NMR spectrum.
E
Letter used to designate the isomer of an alkene that has the high priority groups on opposite sides of the double bond.
E1 reaction or unimolecular elimination reaction
An elimination reaction that occurs in two steps through a carbocation intermediate.
E2 reaction or bimolecular elimination reaction
An elimination reaction that follows a concerted mechanism in which a base removes a proton simultaneously with the departure of the leaving group.
Eclipsed conformation
Conformation in which the bonds on one atom are directly in line with the bonds on the adjacent atom when a Newman projection is viewed.
Electrocyclic reaction
A pericyclic reaction that forms a sigma bond between the end atoms of a series of conjugated pi bonds within a molecule.
Electromagnetic spectrum
The range of electromagnetic radiation (light), from very energetic cosmic rays to low-energy radio waves.
Electronegativity
Electron-attracting ability of an atom.
Electronic transition
The excitation of an electron from an occupied MO to an antibonding MO.
Electrophile
An electron-poor species that seeks an electron rich site; similar to a Lewis acid.
Electrophilic addition reaction
A reaction that results in the addition of two groups, an electrophile and a nucleophile, to the carbons of a CC double or triple bond.
Electrophilic aromatic substitution
A reaction in which an electrophile is substituted for a hydrogen on an aromatic ring.
Elimination reaction
A reaction in which groups (most commonly a proton and a leaving group) are lost from an adjacent atoms, resulting in the formation of a double bond.
1,1-Elimination
An elimination of two groups from the same C to produce a carbene; also called alpha elimination
1,2-Eliminatinon
An elimination of two groups from adjacent atoms to produce a pi bond; also called beta elimination.
Enantiomers
Nonsuperimposable mirror-image stereoisomers.
Endergonic reaction
A reaction for which the change in standard Gibbs free energy is positive; the products are higher in energy than the reactants and the reaction favors the reactants at equilibrium.
Endothermic reaction
A reaction for which the enthalpy change is positive.
Enol
A compound with a hydroxy group attached to a CC double bond.
Enolate ion
A carbanion adjacent to a carbonyl group.