Axial Haloketone Rule Pdf 14

The axial haloketone rule is a rule that predicts the sign and magnitude of the Cotton effect in the circular dichroism (CD) spectra of α-haloketones and related compounds. The rule states that a strong and inherently dissymmetric chromophore is formed when a halogen atom is attached to the α-carbon of a ketone in an axial position, and that the sign of the Cotton effect is determined by the configuration of the α-carbon. The rule was proposed by Klyne and Prelog in 1958 and has been applied to various types of compounds, such as lactones, cyclohexanones, and steroids. The rule is also useful for determining the absolute configuration of chiral molecules by comparing their CD spectra with those of known compounds.

The axial haloketone rule can be explained by considering the interaction between the lone pair electrons of the halogen atom and the π-electrons of the carbonyl group. When the halogen atom is in an axial position, it can overlap with the π-orbital of the carbonyl group, creating a n-π* transition that is responsible for the Cotton effect. The direction and extent of this overlap depend on the configuration of the α-carbon, which determines the sign and magnitude of the Cotton effect. For example, if the α-carbon has an R configuration, the overlap is constructive and the Cotton effect is positive, whereas if the α-carbon has an S configuration, the overlap is destructive and the Cotton effect is negative. The magnitude of the Cotton effect also depends on the electronegativity and size of the halogen atom, as well as other substituents on the molecule that may affect its conformation and electronic structure.

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The axial haloketone rule can be extended to other types of compounds that have a heteroatom attached to an α-carbon of a carbonyl group, such as lactones, esters, amides, and thioesters. The rule can also be applied to compounds that have a bridged ring system with a carbonyl group and a heteroatom in axial positions, such as gibberellins and dihydrocoronopilin. However, there are some exceptions and limitations to the rule, such as when there are multiple heteroatoms or carbonyl groups in the molecule, or when there are other factors that affect the CD spectra, such as solvent effects, temperature effects, or intermolecular interactions.

The axial haloketone rule is one of the most important rules in organic stereochemistry, as it provides a simple and reliable method for determining the absolute configuration of chiral molecules by using CD spectroscopy. The rule has been widely used in various fields of chemistry, such as natural products chemistry, medicinal chemistry, and synthetic chemistry. The rule has also been combined with other rules, such as the octant rule and the sector rule, to analyze more complex molecules with multiple chiral centers. The axial haloketone rule is a powerful tool for understanding and manipulating the molecular dissymmetry and chiroptical properties of organic compounds.

References

Klyne W., Prelog V., Experientia 1958, 14, 339-345.

Meguro H., Konno T., Tuzimura K., Agric. Biol. Chem. 1973, 37 (4), 945-947.

Watanabe Y., Kato S., Bull. Chem. Soc. Jpn. 1969, 42 (10), 2920-2925.

Watanabe Y., Kato S., Bull. Chem. Soc. Jpn. 1970, 43 (1), 1-6.

MacMillan J., Gaskin P., Zeevaart J.A.D., Tetrahedron Lett. 1971, 12 (48), 4127-4130.

Watanabe Y., Kato S., Bull. Chem. Soc. Jpn. 1972, 45 (3), 831-835.

Mason S.F., Quart. Rev. Chem. Soc. 1967, 21 (4), 527-560.

Watanabe Y., Kato S., Bull. Chem. Soc. Jpn. 1971, 44 (5), 1369-1374.

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