Paper
Reactivities of stable rotamers. XI. Rotamer distributions and some addition reactions to the carbonyl in 9-(2-(substituted carbonyl)-1-naphthyl)fluorene rotamers.
Published Oct 1, 1982 · R. Saito, M. Ōki
Bulletin of the Chemical Society of Japan
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Abstract
Rotational isomers (sp and ap) of several 9-[2-(substituted carbonyl)-1-naphthyl]fluorenes where the substituent is methyl, phenyl, hydroxyl, methoxyl, 1-imidazolyl, or others have been obtained as stable entities. Barriers to rotation in these compounds were ca. 26.5 kcal for the process sp→ap but those for the reverse (ap→sp) were dependent on the substituent, ranging from 23.8 to 25.3 kcal/mol at 55 °C. The difference is reflected in the populations of rotamers: if the substituent is a hydroxyl, the sp/ap value becomes as large as ca. 20. The relative instability of the ap form was attributed to twisting of the carbonyl plane from that of naphthalene. Infrared spectra support the twisting. Addition reactions to the carbonyl occur smoothly in the sp conformation but they do not occur to a detectable extent in the ap conformation, if the substituent on the carbonyl is larger than hydrogen. The results are attributed to the steric effect of the fluorene ring.
Stable rotamers of 9-[2-(substituted carbonyl)-1-naphthyl]fluorene show varying barriers to rotation, with a hydroxyl substituent causing a large sp/ap value, and addition reactions to the carbony
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