| van't Hoff's law | In stereochemistry, all optically active substances have one or more multivalent atoms united to four different atoms or radicals so as to form in space an unsymmetrical arrangement, the osmotic pressure exerted by any substance in very dilute solution is the same that it would exert if present as gas in the same volume as that of the solution; or, at constant temperature, the osmotic pressure of dilute solutions is proportional to the concentration (number of molecules) of the dissolved substance; i.e., the osmotic pressure, π, in dilute solutions is π = RTσci, where R is the universal gas constant, T is the absolute temperature, and ci is the molar concentration of solute i, the rate of chemical reactions increases between two-and three-fold for each 10캜 rise in temperature. (05 Mar 2000) |
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| van't Hoff's theory | That substances in dilute solution obey the gas laws. Compare: van't Hoff's law. (05 Mar 2000) |
| ellis-van creveld syndrome | <radiology> Chondro-ectodermal dysplasia, hereditary (especially seen in Amish of Pennsylvania), polydactyly (100%), congenital heart disease (60%), abnormalities of cutaneous appendages (skin, hair, nails) More info: Ellis-van Creveld syndrome (12 Dec 1998) |
| exon trapping vincent van buren | <molecular biology, technique> A technique used to identify vector. The vector has two exons that are normal, splicedtogether in a transcript.Fragments of DNA can be inserted into the intron, and when the insert is an exon, the exon is splicedinto the transcript, thereby giving a longer transcript that can be detected by Northern blotanalysis. (09 Oct 1997) |
| Le Bel-van't Hoff rule | The number of stereoisomers of an organic compound is 2n where n represents the number of asymmetric carbon atoms (unless there is an internal plane of symmetry). A corollary of their simultaneously announced conclusions, in 1874, that the most probable orientation of the bonds of a carbon atom linked to four groups or atoms is toward the apexes of a tetrahedron, and that this accounted for all then-known phenomena of molecular asymmetry (which involved a carbon atom bearing four different atoms or groups). See: stereoisomerism. (05 Mar 2000) |
| Lobry de Bruyn-van Ekenstein transformation | The conversion of glucose to fructose and mannose in dilute alkali by enolization adjacent to the carbonyl group to form an enediol, a reaction analogous to certain biochemical transformations. (05 Mar 2000) |