Eclipsed conformation
In chemistry an eclipsed conformation is a conformation in which two substituents X and Y on adjacent atoms A, B are in closest proximity, implying that the torsion angle X–A–B–Y is 0°.[1] Such a conformation can exist in any open chain, single chemical bond connecting two sp3-hybridised atoms, and it is normally a conformational energy maximum. This maximum is often explained by steric hindrance, but its origins sometimes actually lie in hyperconjugation (as when the eclipsing interaction is of two hydrogen atoms).
Organic chemistry
In the example of ethane in Newman projection it shows that rotation around the carbon-carbon bond is not entirely free but that an energy barrier exists. The ethane molecule in the eclipsed conformation is said to suffer from torsional strain and by a rotation around the carbon carbon bond to the staggered conformation around 12.5 kJ/mol of torsional energy is released.
Inorganic chemistry
As established by X-ray crystallography, octachlorodimolybdate(II) anion ([Mo2Cl8]4-) has an eclipsed conformation. This sterically unfavorable geometry is given as evidence for a quadruple bond between the Mo centers.[2]
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See also
References
- ^ Eliel, Ernest L.; Wilen, Samuel H. (1994). Stereochemistry of Organic Compounds. Wiley. p. 1197. ISBN 978-0-471-01670-0.
- ^ Brignole, A. B.; Cotton, F. A.; Dori, Z. (1972). Rhenium and Molybdenum Compounds Containing Quadruple Bonds. Inorg. Synth. Inorganic Syntheses. Vol. 13. pp. 81–89. doi:10.1002/9780470132449.ch15. ISBN 978-0-470-13244-9.