| Le Bel, Joseph Achille | <person> French chemist, 1847-1930. See: Le Bel-van't Hoff rule. (05 Mar 2000) |
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| 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) |
| bel | Unit expressing the relative intensity of a sound. The intensity in bels is the logarithm (to the base 10) of the ratio of the power of the sound to that of a reference sound. Ordinarily, the reference sound is assumed to be one with a power of 10-16 watts per sq cm, approximately the threshold of a normal human ear at 1000 Hz. Origin: A.G. Bell, Scottish-U.S. Scientist, 1847-1922 (05 Mar 2000) |
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