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  • E- Stereochemical
  • descriptor used when higher ranked substituents are on opposite sides of a double bond
  • E-Z notation for alkenes
  • System for specifying doublebond configuration that is an alternative to cis-trans notation. When higher ranked substituents are on the same side of the double bond, the configuration is Z. When higher ranked substituents are on opposite sides, the configuration is E. Rank is determined by the Chn-Ingold-Prelog system. LINK
  • E1
  • See Eliminations unimolecular (E1) mechanism. LINK
  • E2
  • See Eliminations bimolecular (E2) mechanism. LINK
  • Eclipsed conformation
  • Conformations in which bonds on adjacent atoms are aligned with one another. For example, the C-H bonds indicated in the structure shown are eclipsed. Fig
  • Edman degradation
  • Method for determining the N-Terminal amino acid of a peptide of protein. It involves treating the material with phenyl isothiocyanate (C6H5N=C=S), cleaving with acid, and then identifying the phenylthiohydantoin (PTH derivative) produced.
  • Elastomer
  • A synthetic polymer that possesses elasticity.
  • Electromagnetic radiation
  • Various forms of radiation propagated at the speed of light. Electromagnetic radiation includes (among other) visible light; infrared, ultraviolet, and microwave radiation: and radio waves, cosmic rays and X-rays.
  • Electron affinity
  • Energy change associated with the capture of an electron by an atom
  • Electron count
  • The number of electrons assigned to an individual atom in a Lewis structure. It is equal to the sum of the electrons in unshared pairs associated with the atom and one-half the number of electrons in its covalent bonds.
  • Electron impact
  • Method for producing positive ions in mass spectrometry whereby a molecule is bombarded by high-energy electrons.
  • Electron-releasing group
  • An atom or group that increases the electron density around another atom by an inductive or resonance effect.
  • Electron-withdrawing group
  • An atom or group that decreases the electron density around another atom by an inductive or resonance effect (Link)
  • Electronegativity
  • A measure of the ability of an atom to attract the electrons in a covalent bond toward itself. Fluorine is the most electronegative element
  • Electronic effect
  • An effect on structure or reactivity that is attributed to the change in electron distribution that a substituent causes in a molecule.
  • Electrophile
  • A species (ion or compound) that can act as a Lewis acid, or electron pair acceptor; an “electron seeker.” Carbocations are one type of electrophile.
  • Electrophilic addition
  • Mechanism of addition in which the species that first reacts with the multiple bond is an electrophile (“electron seeker”)
  • Electrophilic aromatic substitution
  • Fundamental reaction type exhibited by aromatic compounds. An electrophilic species (E+) replaces one of the hydrogens of an aromatic ring. FIG
  • Electrophoresis
  • Method for separating substances on the basis of their tendency to migrate to a positively or negatively charged electrode at a particular pH
  • Electrostatic attraction
  • Force of attraction between oppositely charged particles.
  • Electrostatic potential map
  • The charge distribution in a molecule represented by mapping the interaction energy of a point positive charge with the molecule’s electric field on the van der Walls surface.
  • Elementary step
  • A step in a reaction mechanism in which each species shown in the equation for this step participates in the same transition state. An elementary step is characterized by a single transition state.
  • Elements of unsaturation
  • See index of hydrogen deficiency LINK
  • Elimination bimolecular (E2) mechanism
  • Mechanism for elimination of alkyl halides characterized by a transition state in which the attacking base removes a proton at the same time that the bond to the halide leaving group is broken.
  • Elimination unimolecular (E1) mechanism
  • Mechanism for elimination characterized by the slow formation of a carbocation intermediate followed by rapid loss of a proton from the carbocation to form the alkene.
  • Elimination-addition mechanism
  • Two-stage mechanism for nucleophilic aromatic substitution. In the first stage, an aryl halide undergoes elimination to form an aryne intermediate. In the second stage, nucleophilic addition to the aryne yields the product of the reaction.
  • Enamine
  • Product of the reaction of a secondary amine and an aldehyde or a ketone. Enamines are characterized by the general structure FIG
  • Enantiomeric excess
  • Difference between the percentage of the major enantiomer present in a mixture and the percentage of its mirror image. An optically pure material has an enantiomeric excess of 100%. A racemic mixture has an enantiomeric excess of zero
  • Enantiomers
  • Stereoisomers that are related as an object and its nonsuperimposable mirror image.
  • Enantioselective synthesis
  • Reaction that converts an achiral or racemic starting material to a chiral product in which one enantiomer is present in excess of the other.
Department of Chemistry & Chemical Biology