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  • Para
  • Term describing a 1,4 relationship between substituents on a benzene ring
  • Paraffin hydrocarbons
  • An old name for alkanes and cycloalkanes
  • Partial rate factor
  • In electrophilic aromatic substitution, a number that compares the rate of attack at a particular ring carbon with the rate of attack at a single position of benzene.
  • Pauli exclusion principle
  • No two electrons can have the same set of four quantum numbers. An equivalent expression is that only two electrons can occupy the same orbital, and then only when they have opposite spins.
  • PCC
  • Abbreviation for pyridinium dichromate (C5H5NH+ ClCrO3-) When used in a anhydrous medium, PCC oxidizes primary alcohols to aldehydes and secondary alcohols to ketones.
  • PDC
  • Abbreviation for pyridinium dichromate (C5H5NH)22+Cr2O72- Used in same manner and for same purposes as PCC link
  • Pentose
  • A carbohydrate with five carbon atoms
  • Peptidase
  • An enzyme that catalyzes the hydrolysis of amide bonds in a peptide or protein.
  • Peptide
  • Structurally, a molecule composed of two or more α-amino acids joined by peptide bonds
  • Peptide bond
  • An amide bond between the carboxyl group of one α-amino acid and the amino group of another FIG
  • Pericyclic reaction
  • A reaction that proceeds through a cyclic transition state
  • Period
  • A horizontal row of the periodic table
  • Peroxide
  • A compound of the type ROOR
  • Peroxide effect
  • Reversal of regioselectivity observed in the addition of hydrogen bromide to alkenes brought about by the presence of peroxides in the reaction mixture
  • Phase-transfer catalysis
  • Method for increasing the rate of chemical reaction by transporting an ionic reactant from an aqueous phase where it is solvated and less reactive to an organic phase where it is solvated and is more reactive. Typically, the reactant is an anion that is carried to the organic phase as it quaternary ammonium salt
  • Phenols

  • Family of compounds characterized by a hydroxyl substituent on an aromatic ring as in ArOH. Phenol is also the name of the parent compound, C6H5OH
  • Phenyl group
  • The group FIG It is often abbreviated C6H5-
  • Phosphatidic acid
  • A compound of the type shown, which is an intermediate in the biosynthesis of triacylglycerols. FIG
  • Phosphatidylcholine
  • One of a number of compounds of the type FIG
  • Phosphodiester
  • Compound of the type shown, especially when R and R’ are D-ribose or 2-deoxy-D-ribose. FIG
  • Phospholipid
  • A diacylglycerol bearing a cholinephosphate “head group” Also known as phosphatidylcholine.
  • Photochemical reaction
  • A chemical reaction that occurs when light is absorbed by a substance
  • Photon
  • Term for an individual “bundle” of energy, or particle, of electromagnetic radiation
  • Pi (?) bond
  • A bond in which the electron distribution is concentrated above and below the internuclear axis, rather than along it as in a σ bond. In organic chemistry π bonds are most often associated with a side-by-side overlap of p orbital’s on adjacent atoms that are already connected by a σ bond.
  • Pi (?) electron
  • Electrons in a π bond or a π orbital
  • PIN
  • Acronym for the name of a compound designated as it “preferred IUPAC name”
  • pKa
  • A measure of acid strength defied as –log Ka .The stronger the acid, the smaller the value of pKa
  • Planck's constant
  • Constant of proportionality (h) in the equation E = hv, which relates the energy (E) to the frequency (v) of electromagnetic radiation
  • Plane of symmetry
  • A plane that bisects an object, such as a molecule, into two mirror-image halves; also called a mirror plane. When a line is drawn from any element in the object perpendicular to such a plane and extend an equal distance in the opposite direction, a duplicate of the element is encountered.
  • Pleated β sheet
  • Type of protein secondary structure characterized by hydrogen bonds between NH and C=O groups of adjacent parallel peptide chains. The individual chains are in an extended zigzag conformation.
Department of Chemistry & Chemical Biology