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Hydrogen-bond basicity pKHB scale of aldehydes and ketones

1998; Royal Society of Chemistry; Issue: 1 Linguagem: Inglês

10.1039/a704427e

2050-8239

François Besseau, Maryvonne Luçon, Christian Laurence, M. Berthelot,

Organic Chemistry Cycloaddition Reactions

The thermodynamic hydrogen-bond basicity scale pKHB (logarithm of the formation constant of 4-fluorophenol–aldehyde or ketone complexes in CCl4 at 298 K) has been determined for aldehydes, aliphatic ketones, cycloalkanones, diketones and quinones, halogenated ketones, pyrones and related compounds, acetophenones, benzophenones and various other conjugated ketones. The relationship between pKHB and a spectroscopic scale of basicity is obscured by the presence of two stereoisomeric complexes. In the R1COMe series the electronic and steric effects of the alkyl R1 almost cancel out, whereas steric effects prevail in R1COR2. Among alkyl substituents the 1-adamantyl is the most electron-donating. In cycloalkanones the basicity sequence with ring size is 4 < 11 ∼ 12 ∼ 15 < 5 < 6 < 7 < 8. Quantitative structure–basicity relationships have been established in the aromatic 3- and 4-XC6H4COMe and the aliphatic XCOMe series. Intramolecular hydrogen bonding causes a basicity decrease in acetylacetone. Hydrogen bonding sites are discussed.