The Letter "E" in Chemistry

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E1 reaction - A first - order elimination reaction. This means that there is only one reactant concentration that effects the rate of reaction.

E2 Reaction - A second - order elimination reaction. This means that the concentration of two reactants impact the rate of the reaction.

E Conformation - The conformation of a carboxylic acid or carboxylic acid derivative in which the carbonyl oxygen and the substituent bonded to the carboxyl oxygen or nitrogen are on opposite sides of the single bond.

E isomer - A geometric isomer in which the highest priority substituent groups are located on opposite sides of a double bond.

Eclipsed Conformation - The conformation in which the bonds on adjacent carbons are positioned directly on top of each other when viewed in a Newman Projection.

Edman's Reagent - This reagent, phenyl isothiocyanate, is used to determine the N - terminal amino acid in a polypeptide.

Effective Molarity - The molarity required of a reagent in an intermolecular reaction that would result in it having the same rate as an intermolecular reaction.

Effective Nuclear Charge - The apparent nuclear charge exerted on a particular electron, equal to the actual nuclear charge minus the effect of electron repulsion.

Effusion - The passage of a gas through a tiny hole into an evacuated chamber.

Elastomer - A polymer that is able to return to its original shape after being stretched.

Electrolysis - A process that involves forcing a current through a cell to cause a non spontaneous chemical reaction to occur.

Electrolyte - A material that dissolves in water to give a solution that conducts an electric current.

Electrolytic Cell - A cell that uses electrical energy to produce a chemical change that would otherwise not occur spontaneously.

Electrolytic Reaction - A reaction in which a (pi) bond in the reactant is lost so that a cyclic compound with a new (sigma) bond can be formed.

Electromagnetic radiation - Radiant energy that exhibits wavelike behavior and travels through space at the speed of light in a vacuum.

Electron - A negatively charged particle that moves around the nucleus of the atom.

Electron affinity - The energy change associated with the addition of an electron to a gaseous atom.

Electron capture - A process in which one of the inner - orbital electrons in an atom is captured by the nucleus.

Electron sink - A site to which electrons can be delocalized.

Electronegative element - An element that readily gains an electron.

Electronegativity - The tendency of an atom in a molecule to attract/pull shared electrons to itself.

Electronic transition - Promotion of an electron from it HOMO to its LUMO

Electrophile - Meaning "electron - loving" in Greek - this term describes an atom or molecule that is electron - deficient resulting in its reactivity with electron rich atoms or molecules.

Electrophilic Addition Reaction - An addition reaction in which the species that facilitates the reaction in an electrophile.

Electrophilic Aromatic Substitution - A reaction in which an electrophile substitutes for a hydrogen in an aromatic ring.

Electrophilic Catalysis - Catalysis in which the species that facilitates the reaction is an electrophile.

Electropositive element - An element that readily loses an electron.

Electrostatic attraction - Attractive force between opposite charges.

Electrostatic catalysis - A reaction in which the catalyst stabilizes the charge on one substance with an opposite charge.

Element - A substance that cannot be decomposed into simpler substances by chemical or physical means.

Elemental analysis - The determination of the relative amounts of the different elements in a compound.

Elementary step - A reaction whose rate law can be written from its molecularity

(alpha) - Elimination - The removal of two atoms or groups from the same carbon.

(beta) - Elimination - The removal of two atoms or groups from adjacent carbons.

Elimination reaction - A reaction that involves the elimination of atoms (or molecules) from a compound.

Empirical formula - The simplest whole number ratio of atoms in a compound

Enamine - an (alpha, beta) - unsaturated tertiary amine.

Enantiomers - Isomers that are nonsuperimposable mirror images of one another.

Enatiomeric excess - The amount of excess of one enantiomer in a mixture that contains an enantiomeric pair.

Enantiomerically pure - A sample that contains only one enantiomer

Enantioselective reaction - A reaction that forms the excess of one enantiomer.

Enantiotopic hydrogens - Two hydrogens that are bonded to a carbon that is bonded to two other nonidentical groups.

Endergonic reaction - A reaction with a positive change in free energy.

Endo - A substituent that has a closer proximity to the longer or more unsaturated bridge.

Endopeptidase - An enyme that hydrolyzes a peptide that is not at the end of a peptide chain.

Endothermic reaction - A reaction in which the products are higher in energy than the reactants.

Endpoint - The point in a titration at which the indicator changes color.

Enediol rearrangement - Interconversion of an aldose and one or more ketosis

Enolization - Keto - enol interconversion

Enthalpy - A property of a system equal to E+PV, where E is the internal energy of the system, P is the pressure of the system, and V is the volume of the system. At constant pressure, where only PV work is allowed, the change in enthalpy equals the heat energy.

Enthalpy of fusion - The enthalpy change that occurs to melt a solid at its melting point.

Entropy - A measure related to the probability of observing a particular microstate for a given system. The greater the possible way of arranging the atoms/molecules in a system the greater the associated entropy.

Enzyme - A large molecule, usually a protein, that catalyzes biological reactions.

Epimerization - Changing the configuration of an asymmetric center by removing a proton from it and then reprotonating the molecule at the same site.

Epimers - Monosaccharides that differ in configuration at only one carbon.

Epoxidation - Formation of an epoxide

Epoxide - An ether in which the oxygen is incorporated into a three - membered ring.

Epoxy resin - A substance that is formed by the mixing of a low - molecular - weight prepolymer with a compound that forms a cross - linked polymer.

Equatorial bond - A bond of the chair conformer of cyclohexane that comes out of the ring such that it makes an obtuse angle with the axial bond. This bond angle is a more stable position for bulky substituents than the axial position.

Equilibrium constant - The ratio of products to reactants at equilibrium or the ratio of the rate constants for the forward and reverse reactions.

Equilibrium expression - The expression (from the law of mass action) obtained by multiplying the product concentrations and dividing by the multiplied reactant concentrations, with each concentration raised to a power represented by the coefficient in the balanced equation.

Equilibrium position - A particular set of equilibrium concentrations.

Equivalence point - The point in a titration when enough titrant has been added to react exactly with the substance in solution being titrated.

Erythro enantiomers - In Fischer Projection, the pair of enantiomers with the same groups on the same side.

Excited - state electronic configuration - The electronic configuration that results when an electron in the ground state electronic configuration has been moved to a higher energy orbital due to an increase in its energy.

Exergonic reaction - A reaction with a negative change in free energy.

Exhaustive methylation - A reaction of an amine with excess methyl iodide to form a quaternary ammonium iodide.

Exo - A substituent that is located at a closer proximity to the shorter or more saturated bridge.

Exopeptidase - An enzyme that hydrolyzes a peptide bond at the end of a peptide chain.

Exothermic - A reaction in which more energy is released than is required to initiate the reaction.

Extrusion reaction - A reaction in which a neutral molecule (e.g. nitrogen, carbon dioxide, etc.) is eliminated from a molecule.