Control of the rotational barrier and spatial disposition of the N-(2′-methylphenyl) group in succinimides by substituent and solvent effects

Kishikawa, Keiki; Yoshizaki, Kazumi; Kohmoto, Shigeo; Yamamoto, Makoto; Yamaguchi, Kentaro; Yamada, Kazutoshi

doi:10.1039/a605896e

Cited by 54 publications

(37 citation statements)

References 24 publications

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“…However, a number of observations suggested that the rotors could not rotate and interconvert within the crystals. This was also consistent with previous studies by Kishikawa 14 and Grossmann 15 that did not report any signs of interconversion of crystalline N-(o-tolyl) succinimides at room temperature. First, two crystals (17 and 19) contained crystallographically independent syn-and anti-conformers suggesting that the conformers were kinetically locked in the crystals.…”

supporting

confidence: 94%

“…To address these questions, the X-ray crystal structure and solution conformational ratios for a series of 30 molecular rotors based on an atropisomeric bicyclic N-(otolyl)succinimide framework were measured and compared ( Figure 1). The suitability of atropisomeric N-arylsuccinimides for studying the correlation between solid-state and solution structures was previously recognized by Verma, 13 Kishikawa,14 and Grossmann. 15 The rigid bicyclic framework fixes the position of most of the atoms, which greatly simplifies its conformational analysis.…”

mentioning

confidence: 94%

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Correlation between Solid-State and Solution Conformational Ratios in a Series of N-(o-Tolyl)Succinimide Molecular Rotors

Hwang

Maier

et al. 2015

Crystal Growth & Design

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The syn-anti conformational equilibrium of a library of 30 N-(o-tolyl)succinimide molecular rotors was measured in solution via 1 H NMR and in the solid-state via Xray crystallography. A strong correlation was observed between the solution and solid-state mole fractions of syn-conformers (χ syn ). All rotors, even those with a small conformational preference in solution (±0.15 kcal/mol), displayed the same conformation in their crystal structures. The conformational preferences in the crystals tended to be more pronounced with a predominance of all syn-or anti-structures. However, when the rotors had no conformational preference in solution, the conformational preferences in the crystal structures varied widely. X -ray crystallography is a powerful tool in modern chemistry and biochemistry for the determination of the three-dimensional structure of natural products, 1,2 rational drug design, 3,4 and the study of noncovalent interactions 5−7 and solid-form pharmaceuticals. 8,9 An important question in these studies is whether an X-ray crystal structure accurately reflects the conformation in solution. 10−12 Conversely, can the conformation in solution be used to predict the conformation in a crystal structure? To address these questions, the X-ray crystal structure and solution conformational ratios for a series of 30 molecular rotors based on an atropisomeric bicyclic N-(otolyl)succinimide framework were measured and compared ( Figure 1).The suitability of atropisomeric N-arylsuccinimides for studying the correlation between solid-state and solution structures was previously recognized by Verma, 13 Kishikawa, 14 and Grossmann. 15 The rigid bicyclic framework fixes the position of most of the atoms, which greatly simplifies its conformational analysis. The only major degree of rotational freedom is the C−N single bond connecting the o-tolyl rotor to the succinimide ring. Due to steric repulsion between the orthomethyl group of the rotor and the imide carbonyls, the N-tolyl and succinimide rings avoid the coplanar geometry. This leads to anti-and syn-atropisomers that are conformationally distinct due to the asymmetry of the succinimide ring arising from the fused bicyclic framework.In the course of our studies using molecular balances to measure weak noncovalent interactions, 16−23 we realized that we had access to a library of 30 N-(o-tolyl)succinimide rotors that displayed a wide range of anti-/syn-conformational ratios (Figure 2). This provided a unique opportunity to examine the correlation or lack of correlation between their solid-state and solution structures. By comparison, the scope of previous studies utilizing this framework 18,20,23 was based on a small number of structures (12−14) limiting the certainty and generality of the observed trends.We specifically focused on bicyclic N-(o-tolyl)succinimides with ortho-methyl groups because their atropisomers are generally bereft of the common factors that lead to differences in solid-state and solution structures. 24,25 First, the ortho-methyl group is nonpol...

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supporting

confidence: 94%

mentioning

confidence: 94%

Correlation between Solid-State and Solution Conformational Ratios in a Series of N-(o-Tolyl)Succinimide Molecular Rotors

Hwang

Maier

et al. 2015

Crystal Growth & Design

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“…The C-H---π contact of 2.81 Å and angle of 149.7° are in correlation with the literature reports and confirm the contribution of CH/π interaction to the molecular network between adjacent molecules [47][48][49][50]. The directionality and the CH/acceptor distance in this interaction are dependent on the strength of CH as a proton donor.…”

Section: Single Crystal X-ray Diffraction Studysupporting

confidence: 88%

Aluminium complexes bearing N,O-aminophenol ligands as efficient catalysts for the ring opening polymerization of lactide

Roymuhury

Chakraborty

Ramkumar

2015

European Polymer Journal

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“…Thus, the C–H/π interaction5 was favorable enough to partially balance the repulsive steric effect. Remarkably, the proportion of the Me‐ endo adduct increased when the N ‐aryl residue featured an electron‐withdrawing substituent X in the para position relative to the nitrogen atom, with the Me‐ endo /Me‐ exo ratio becoming 70:30 when X was a nitro group 4d. These results were explained in terms of a favorable Me/π interaction that was able to overcome the steric repulsion only if the H atoms were made “acidic” enough by suitable phenyl ring substitution with the X group 4d.…”

Section: Introductionmentioning

confidence: 99%

“…Remarkably, the proportion of the Me‐ endo adduct increased when the N ‐aryl residue featured an electron‐withdrawing substituent X in the para position relative to the nitrogen atom, with the Me‐ endo /Me‐ exo ratio becoming 70:30 when X was a nitro group 4d. These results were explained in terms of a favorable Me/π interaction that was able to overcome the steric repulsion only if the H atoms were made “acidic” enough by suitable phenyl ring substitution with the X group 4d. No isotope effect was observed on passing from R = CH 3 to R = CD 3 , with the two adducts showing roughly the same endo / exo ratio 4g.…”

Section: Introductionmentioning

confidence: 99%

Aliphatic C–H/π and Heteroatom/π Interactions in N‐Aryl‐3,4‐(9′,10′‐dihydroanthracene‐9′,10′‐diyl)succinimides

2014

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A series of N‐aryl‐3,4‐(9′,10′‐dihydroanthracene‐9′,10′‐diyl)succinimides have been synthesized as model compounds to study the interaction of an aromatic π system with aliphatic H atoms and heteroatoms such as oxygen, sulfur, and fluorine. The steric requirements of the rigid scaffold forces the N‐aryl residue and a benzene ring of the dihydroanthracenyl moiety to adopt an edge‐to‐face conformation in which one of the ortho‐substituents of the N‐aryl group interacts with the π system. The succinimides were generally obtained as mixtures of isomers and their ratios were considered as a function of the substitution pattern at the ortho positions of the N‐aryl residue. The experimentally observed ratios were in good agreement with those predicted computationally by DFT calculations at the BMK/cc‐pVDZ level of theory. From this study it was concluded that in these systems the aliphatic C–H/π interaction is mildly stabilizing and, to a certain extent, capable of overcoming unfavorable steric effects. On the other hand, the interaction of a π system with oxygen, sulfur, or fluorine atoms was destabilizing. When methyl or ethyl groups were allowed to compete with oxygen and fluorine for interaction with the benzene ring, C–H/π interactions were consistently observed to preferentially occur despite unfavorable steric effects.

show abstract

Control of the rotational barrier and spatial disposition of the N-(2′-methylphenyl) group in succinimides by substituent and solvent effects

Cited by 54 publications

References 24 publications

Correlation between Solid-State and Solution Conformational Ratios in a Series of N-(o-Tolyl)Succinimide Molecular Rotors

Correlation between Solid-State and Solution Conformational Ratios in a Series of N-(o-Tolyl)Succinimide Molecular Rotors

Aluminium complexes bearing N,O-aminophenol ligands as efficient catalysts for the ring opening polymerization of lactide

Aliphatic C–H/π and Heteroatom/π Interactions in N‐Aryl‐3,4‐(9′,10′‐dihydroanthracene‐9′,10′‐diyl)succinimides

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