Correlated Rotations and Unusual Fluorescence Properties ofperi-Substituted, Axially Chiral Naphthyl Ketones

Abstract

The dynamics of the two rotors in 8-(dimethylamino)naphthyl ketones possessing a tetrahedral amino group and a trigonal planar carbonyl group has been investigated by 1 H NMR spectroscopy. The dynamic system is described by an aryl−nitrogen and an aryl−carbonyl rotation and a possible amine inversion. As the two rotors, which are twisted in the ground state, are tightly interlocked, the question arises of how strongly the processes might be correlated and how strongly the electrostatic interactions would influence the barriers. In the case of the isopropyl, tert-butyl, and benzyl ketones, the rotors are coupled sufficiently strongly that correlated rotations become energetically preferred over independent rotations of the individual groups. For the methyl and trimethoxyphenyl ketone, the Ar−N and Ar−C barriers could be distinguished because of the lesser degree of inter-

Artificial Molecular Rotors

“…More comprehensive treatments of the static and dynamic stereochemistry of alkyl groups can be found in several reviews. ,,, Other systems, such as tetraalkylethylenes, tetracycloalkylethylenes, tetracycloalkylmethanes, ortho -disubstituted benzenes, , alkylated propenals, alkylated adamantanes, and 8-(dimethylamino)naphthyl ketones, have also been studied for correlated rotation of the alkyl or related fragment. A number of groups have also investigated cogwheeling of alkyl groups from a computational standpoint. − Pophristic and Goodman calculated the “gearing” (correlated disrotation) and “antigearing” (rotation in phase) in dimethyl ether.…”

“…More comprehensive treatments of the static and dynamic stereochemistry of alkyl groups can be found in several reviews. 194,197,198,300 Other systems, such as tetraalkylethylenes, 301 tetracycloalkylethylenes, 302 tetracycloalkylmethanes, 303 ortho-disubstituted benzenes, 304,305 alkylated propenals, 306 alkylated adamantanes, 307 and 8-(dimethylamino)naphthyl ketones, 308 have also been studied for correlated rotation of the alkyl or related fragment. A number of groups have also investigated cogwheeling of alkyl groups from a computational standpoint.…”

Characterization of the restricted rotation of the dimethyl groups in chemically N-terminal C13-labeled antifreeze glycoproteins: A temperature-dependent study in water to ice through the supercooled state

“…The rotational barrier between the 60° and the other two minima are larger and not easily surmounted at room temperature. Another possible way to reach the 60° structure is by inversion of the amine nitrogen (seeFigure 8) from the -150° structure27 . The energy barrier from the -150° structure and the inversion transition state structure is 6.4 kcal/mol.…”

A Redox-Mediated Molecular Brake: Dynamic NMR Study of 2-[2-(Methylthio)phenyl]isoindolin-1-one and S-Oxidized Counterparts

“…Examination in models of the N−Ar rotation reveals a severe steric interaction during the passage of the ortho substituents over the carbonyl group during rotational interconversion of enantiomers. Transition-state nitrogen pyramidalization to avoid steric interactions during rotational motion has been reported .…”