Indiana University Purdue University Indianapolis
Search:     Advanced search
print  Print
Showing: 1-30 of 46    »»

  • Half-chair
  • One of the two most stable conformations of cyclopentane. Three consecutive carbons in the half-chair conformation are coplanar. The fourth and fifth carbon lie, respectively, above and below the plane
  • Haloform reaction
  • The formation of CHX3 (X = Br, Cl, or I) brought about by cleavage of a methyl ketone on treatment with Br2, Cl2, I2 in aqueous base.  FIG
  • Halogenation
  • replacement of a hydrogen by a halogen. The most frequently encountered examples are the free radical halogenations of alkanes and the halogenations of arenes by electrophilic aromatic substitution
  • Halohydrin
  • A compound that contains both a halogen atom and a hydroxyl group. The term is most often used for compounds in which the halogen and the hydroxyl group are on adjacent atoms (vicinal halohydrins). The most commonly encountered halohydrins are chlorohydrins and bromohydrins
  • Halonium ion
  • A species that incorporates a positively charged halogen. Bridged halonium ions are intermediates in the addition of halogens to the double bond of an alkene.
  • Hammond's postulate
  • Principle used to deduce the approximate structure of a transition state. If two states, such as a transition state and an unstable intermediate derived from it, are similar in energy, they are believed to be similar in structure
  • Haworth formulas
  • Planar representations of furanose and pyranose forms of carbohydrates
  • Hückel's Rule
  • Completely conjugated planar monocyclic hydrocarbons possess special stability when the number of their π electrons = 4n + 2, where n is an integer
  • Heat of combustion
  • Heat evolved on combustion of a substance. It is the value of -∆H for the combustion reaction
  • Heat of formation
  • The value of ∆H for formation of a substance from its elements
  • Heat of hydrogenation
  • Heat evolved on hydrogenation of a substance. It is the value of -∆H for the addition of H2 to a multiple bond
  • Hell-Volhard-Zelinsky reaction
  • The phosphorus trihalide-catalyzed  α halogenations of a carboxylic acid: FIG
  • Hemiacetal
  • Product of nucleophilic addition of one molecule of an alcohol to an aldehyde or a ketone. Hemiacetals are compounds of the type  FIG
  • Hemiketal
  • A hemiacetal derived from a ketone
  • Henderson-Hasselbalch equation
  • An equation that relates degree of dissociation of an acid at a particular pH to its pKa  EQUATION
  • A 2D NMR technique that correlates the 1H chemical shift of a proton to the 13C chemical shift of the carbon to which it is attached. HETCOR stands for heteronuclear chemical shift correlation
  • Heteroatom
  • An atom in an organic molecule that is neither carbon nor hydrogen
  • Heterocyclic aromatic compound
  • A heterocyclic compound in which the ring that contains the heteroatom is aromatic
  • Heterocyclic compound
  • Cyclic compound in which one or more of the atoms in the ring are elements other than carbon. Heterocyclic compounds may or may not be aromatic
  • Heterogeneous reaction
  • A reaction involving two or more substances present in different phases. Hydrogenation of alkenes is a heterogeneous reaction that takes places on the surface of an insoluble metal catalyst
  • Heterolytic cleavage
  • Dissociation of a two-electron covalent bond in such a way that both electrons are retained by one of the initially bonded atoms
  • Hexose
  • A carbohydrate with six carbon atoms
  • High-density lipoprotein (HDL)
  • A protein that carries cholesterol from the tissues to the liver where it is metabolized. HDL is often called “good cholesterol”
  • Histones
  • Proteins that are associated with DNA in nucleosomes
  • Hofmann elimination
  • Conversion of a quaternary ammonium hydroxide, especially an alkyltrimethylammonium hydroxide, to an alkene on heating. Elimination occurs in the direction that gives the less substituted double bond. FIG
  • Hofmann rule
  • β-Elimination of quaternary ammonium hydroxides gives predominantly the alkene with the least substituted double bond
  • HOMO
  • Highest occupied molecular orbital (the orbital of highest energy that contains at least one of a molecule’s electrons)
  • Homogeneous hydrogenation
  • Hydrogenation of a double bond catalyzed by an organometallic compound that is soluble in the solvent in which the reaction is carried out
  • Homologous series
  • Group of structurally related substances in which successive members differ by a CH2 group
  • Homolytic cleavage
  • Dissociation of a two-electron covalent bond in such a way that one electron is retained by each of the initially bonded atoms
Department of Chemistry & Chemical Biology