Racemization Barriers of Helicenes:  A Computational Study<sup>1</sup>

Janke, Roland H.; Haufe, Günter; Würthwein, Ernst‐Ulrich; Borkent, J. H.

doi:10.1021/ja950774t

Cited by 218 publications

(174 citation statements)

References 29 publications

Supporting

Mentioning

161

Contrasting

Unclassified

Order By: Relevance

“…The racemization proves that their molecules are flexible; theoretical studies on the racemization barriers indicate that a methyl in position 1 of a pentaor hexahelicene raises the barrier to a value comparable with that of hexa-or heptahelicene, respectively [23].…”

mentioning

confidence: 90%

Heliphenes and Related Structures

Balaban

Vollhardt

2011

TOOCJ

View full text Add to dashboard Cite

This review discusses from a qualitative viewpoint three-dimensional structures (hydrocarbons and carbon allotropes) that can be obtained from the 4,6,12-archimedean tiling of the Euclidean plane (graphenylene net) or that are related to subgraphs derived from the graphenylene net, insisting on helical structures called [n]heliphenes with alternating 4-and 6-membered conjugated rings. Analogies with benzenoid [n]helicenes allow proposals for non-planar heliphenerelated structures that have yet to be explored.

show abstract

mentioning

confidence: 90%

Heliphenes and Related Structures

Balaban

Vollhardt

2011

TOOCJ

View full text Add to dashboard Cite

show abstract

“…The right-handed helical structure (moving from up to down) is assigned the name (P)-enantiomer, whereas the left-handed helical structure (moving from up to down) is designated the (M)-enantiomer, according to the CahnIngold-Prelog rule (Figure 6b). This type of helicene tends to give configurationally stable enantiomers as the racemization process is expected to go through the highly energetic, strained Cssymmetrical transition state [37]. Along with this thermodynamic stability of enantiomers, helicenes also exhibit notable enhanced (chir)optical properties, making them suitable candidates for chiral auxiliaries and other chirogenic processes.…”

Section: Chiral (Configurationally Stable) Helicenesmentioning

confidence: 99%

Helicene-Based Chiral Auxiliaries and Chirogenesis

Hasan

Borovkov

2017

Symmetry

View full text Add to dashboard Cite

Helicenes are unique helical chromophores possessing advanced and well-controlled spectral and chemical properties owing to their diverse functionalization and defined structures. Specific modification of these molecules by introducing aromatic rings of differing nature and different functional groups results in special chiroptical properties, making them effective chiral auxiliaries and supramolecular chirogenic hosts. This review aims to highlight these distinct structural features of helicenes; the different synthetic and supramolecular approaches responsible for their efficient chirality control; and their employment in the chirogenic systems, which are still not fully explored. It further covers the limitation, scope, and future prospects of helicene chromophores in chiral chemistry.

show abstract

“…S1 in the SI for a depiction). 19,20 The geometries and W1-F12 reference value for tetrahelicene have been taken from Karton; 38 all other reference values have been determined for this work at the DLPNO-CCSD(T)/CBS level.…”

Section: The Inv24 Test Setmentioning

confidence: 99%

“…18 The majority of papers on this topic have been published in the 1990s; [19][20][21] however, also in very recent times, joint experimental-computational studies have been conducted. 22,23 More recently, the experimental and computational interest in inversion barriers has moved to bowl-shaped molecules, such as corannulene, [24][25][26][27][28][29] sumanene and its derivatives, [29][30][31][32] and other bowl-shaped hydrocarbons, including some derived from fullerene fragments.…”

Section: Introductionmentioning

confidence: 99%

The INV24 test set: how well do quantum-chemical methods describe inversion and racemization barriers?

Goerigk

Sharma

2016

Can. J. Chem.

View full text Add to dashboard Cite

For years, there has been ongoing interest in experimentally and theoretically understanding inversion and racemization processes. However, to the best of our knowledge, there has been no computational study that systematically investigated how well low-level quantum-chemical methods predict inversion barriers. Herein, we provide an answer to this question and we present the INV24 benchmark set of 24 high-level, ab initio inversion barriers. INV24 covers inversion in triatomics, in pyramidal molecules, in one cyclic system, and in various helical and bowl-shaped compounds. Our results indicate that previously applied DFT approximations combined with small basis sets are not reliable enough and that at least a triple-basis is needed for meaningful results. Moreover, we show that intramolecular London dispersion influences the barriers by 2 kcal/mol or more and that dispersion corrections should always be applied to DFT results. With our analysis of 34 DFT approximations, we can reproduce the well-known Jacob's Ladder scheme with (meta-)generalized-gradient-approximation methods underestimating barriers and global-hybrid DFT functionals performing better. Range-separated hybrids or Minnesota-type hybrids are not particularly superior to more conventional methods, such as B3LYP-D3. The by far best results are achieved with dispersioncorrected double hybrids, which give results below the chemical accuracy target of 1 kcal/mol. They also outperform wavefunction second-order perturbation theory approaches and we recommend using them whenever possible. Given that our systematic study of INV24 is the first of its kind, our findings have the potential to change common practice in this field and they will guide future investigations of inversion processes.Key words: barrier heights, chemical inversion, racemization barriers, benchmarking, density functional theory, wave-function theory.Résumé : Depuis des années, il y a un intérêt pour comprendre de manière expérimentale et théorique les processus d'inversion et de racémisation. Cependant, à notre connaissance, aucune étude computationnelle n'a évalué de manière systématique la précision des méthodes de chimie quantique de bas niveau pour prédire les barrières d'inversion. Dans le cadre des présents travaux, nous offrons une réponse à cette question et présentons la base de référence INV24 de 24 barrières d'inversion ab initio de haut niveau. L'application de la base INV24 couvre l'inversion des systèmes triatomiques dans les molécules pyramidales, dans un système cyclique et dans divers composés hélicoïdaux et de forme concave. Nos résultats indiquent que les approximations de DFT appliquées antérieurement, combinées avec des bases de petite taille, ne sont pas assez fiables et qu'une base tripleest minimalement requise pour que les résultats soient significatifs. De plus, nous montrons que la dispersion intramoléculaire de London a une incidence de 2 kcal/mol ou plus sur les barrières et que les résultats de DFT doivent toujours être corrigés pour tenir compte...

show abstract

Racemization Barriers of Helicenes: A Computational Study¹

Cited by 218 publications

References 29 publications

Heliphenes and Related Structures

Heliphenes and Related Structures

Helicene-Based Chiral Auxiliaries and Chirogenesis

The INV24 test set: how well do quantum-chemical methods describe inversion and racemization barriers?

Contact Info

Product

Resources

About

Racemization Barriers of Helicenes: A Computational Study1

Cited by 218 publications

References 29 publications

Heliphenes and Related Structures

Heliphenes and Related Structures

Helicene-Based Chiral Auxiliaries and Chirogenesis

The INV24 test set: how well do quantum-chemical methods describe inversion and racemization barriers?

Contact Info

Product

Resources

About

Racemization Barriers of Helicenes: A Computational Study¹