The Letter "D" in Chemistry

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Dalton's Law of Partial Pressures - The total pressure for a mixture of gases in a container, is equal to the sum of the pressures that each gas would exert individually.

Deactivating substituent - A substituent that decreases the reactivity of an aromatic ring. Electron - withdrawing substituents deactivate aromatic rings toward electrophilic attack, and electron - donating substituents deactivate aromatic rings toward nucleophilic attack.

Deamination - The loss of ammonia.

Decarboxylation - The loss of carbon dioxide

Degenerate orbitals - A group orbitals that have the same energy level.

Dehydration - The loss of water

Dehydrogenase - An enzyme that catalyzes an oxidation reaction by removing hydrogen from the substrate.

Dehydrogenation reaction - A reaction in which two hydrogen atoms are removed from adjacent carbons of a saturated hydrocarbon, giving an unsaturated hydrocarbon.

Dehydrohalogenation - The elimination of a proton and a halide ion.

Delocalization - Electrons in a molecule are not localized between a pair of atoms but are able to move throughout the molecule.

Delocalization energy - The extra stability a compound achieves as a result of having delocalized energy.

Denaturation - The breaking down of the tertiary structure of a protein resulting in the loss of its function.

Denitrification - The return of nitrogen from decomposed matter to the atmosphere by bacteria that change nitrates to nitrogen gas.

Deoxygenation - The removal of an oxygen from a reactant

Deoxyribonucleic acid (DNA) - A nucleotide polymer that has a double - helical structure with complementary bases on the two strands. Whose major functions are protein synthesis and the storage and transport of generic information.

Deoxyribonucleotide - A nucleotide in which the sugar component is D - 2' deoxyribose

Deoxy sugar - A sugar in which one of the OH groups has been replaced by an H.

Depurination - The elimination of a purine ring.

Desalination - The process that results in the removal of dissolved salts from an aqueous solution.

Detergent - A salt of a sulfonic acid.

Deuterium kinetic isotope effect - Ratio of the rate constant obtained for a compound containing hydrogen and the rate constant obtained for an identical compound in which one or more of the hydrogens have been replaced by deuterium

Dextrorotary - The enantiomer that rotates polarized light in a clockwise direction

Dialysis - A phenomenon in which a semipermeable membrane allows transfer of both solvent molecules and small solute molecules and ions.

Diamagnetism - A type of magnetism, associated with paired electrons, that causes a substance to be repelled from the inducing magnetic field.

Diastereomer - A configurational stereoisomer that is not an enantiomer.

Diastereotopic hydrogens - Two hydrogens bonded to a carbon that when replaced in turn with a deuterium, result in a pair of diastereomers.

Dieckmann condensation - An intramolecular Claisen condensation

Dielectric constant - A measure how well a solvent can insulate opposite charges from one another

Diels - Alder reaction - a [4+2] cycloaddition reaction

Diene - A hydrocarbon with two double bonds

Dienophile - An alkene that reacts with a diene in a Diels - Alder reaction

Differential rate law - An expression that gives the rate of a reaction as a function of concentrations.

Diffraction - The scattering of light from a regular array of points or lines, producing constructive and destructive interference.

Diffusion - An entropy driven process in which atoms or molecules move from a region of high concentration to a region of low concentration resulting in a uniform distribution of particles.

(beta) - diketone - A ketone with a second carbonyl group at the (beta) position

Dilution - The addition of the solvent to a solution in order to lower the solute concentration.

Dimer - A molecule formed by the joining of two identical monomers.

Dinucleotide - Two nucleotides linked by phosphodiester bonds

Dipeptide - Two amino acids linked by an amide bond.

Dipole - Dipole attraction - An intermolecular force resulting from the attraction between the positive and negative ends of polar molecules that are in close proximity to each other.

Dipole Moment - A measure of the separation of charge in a bond or in a molecule

Direct displacement mechanism - A reaction in which the nucleophile displaces the leaving group in a single step.

Direct substitution - Substitution at the carbon that was bonded to the leaving group.

Disaccharide - A sugar formed from two monosaccharides joined by a glyoside linkage.

Disproportionation reaction - Transfer of a hydrogen atom by a radical to another radical, forming an alkane and an alkene.

Disrotary ring closure - Achieves head - to - head overlap of p orbitals by rotating the orbitals in the opposite direction.

Dissociation energy - The amount of energy required to break a bond, or the amount of energy released when a bond is formed.

Dissolving - metal reaction - A reduction is brought about by the use of sodium or lithium metal dissolved in liquid ammonia.

Disulfide linkage - An S - S bond that stabilizes the tertiary structure of some proteins.

Doping - Adding or removing electrons from a polymer with conjugated double bonds.

Double bond - A sigma and pi bond shared between two atoms

Doublet - An NMR signal that is split into two peaks

Doublet of doublets - An NMR signal that is split into four peaks of approximately equal heights. This is caused by splitting a signal into a doublet by one hydrogen and into another doublet by another, nonequivalent, hydrogen.