Conformational Space and Dynamic Stereochemistry of Overcrowded Homomerous Bistricyclic Aromatic Enes − A Theoretical Study

Biedermann, P. Ulrich; Stezowski, John J.; Agranat, Israel

doi:10.1002/1099-0690(200101)2001:1<15::aid-ejoc15>3.0.co;2-0

Cited by 97 publications

(50 citation statements)

References 108 publications

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“…An analogous two-step enantiomerization process via an anti-folded intermediate was found in 2 [5,12]. The closest nonbonding contacts in C 1ta E is r(Cl 1 · · ·H 8 ) = 180.6 pm, while r(H 8 · · ·Cl 1 ) = 343.3 pm (PM3).…”

mentioning

confidence: 57%

“…and 2,2 -dimethylbifluorenylidene are 79.5 and 84.6 kJ/mol, respectively [5,12]. and 2,2 -dimethylbifluorenylidene are 79.5 and 84.6 kJ/mol, respectively [5,12].…”

Section: Figurementioning

confidence: 97%

“…They have been classified into homomerous BAEs (1, X = Y) and heteromerous BAEs (1, X = Y) [3]. These systems are attractive substrates for the study of the ground state properties and dynamic stereochemistry of overcrowded polycyclic aromatic enes [5]. Bifluorenylidene (2), the smallest BAE, is a fullerene fragment and a potential starting material for the preparation of buckybowls [6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

“…The syntheses of diindeno [1,2,3,4-defg; 1 ,2 ,3 ,4 -mnop]-chrysene (3) from 2 and its 1,1 -dibromo derivative by flash vacuum pyrolysis (FVP) have been reported [10,11]. The controversial dynamic stereochemistry of 2 has been elucidated [5,12]. The BAEs (1), including 2, are overcrowded in the fjord regions on both sides of the central ene (C 9 = C 9 ).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Stereochemistry of ( E )- and ( Z )-1,1′-Dichlorobifluorenylidenes, Substituted Overcrowded Fullerene Fragments

Pogodin

Cohen²,

Biedermann³

et al. 2002

Enantiomer

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X-ray crystallographic and semiempirical PM3 and AM1 studies of 1,1'-dichlorobi-9H-fluoren-9-ylidene (5) are reported. The X-ray molecular structure of (Z)-5 indicated an approximately C2 symmetric conformation with pure twist around C9 = C9' of 40.4 degrees. The fjord regions are somewhat overcrowded: r(C8...C8') = 315.3 pm, r(Cl(1)...Cl(1') = 341.7 pm, r(C(8)...H(8')) = 259.0 pm. The four chlorine atoms of two neighboring molecules of (Z)-5 form a chain. The PM3 calculations showed that the global minimum of 5 is the C2 symmetric twisted conformation t(E)-5, which is 2.4 kJ/mol more stable than its diastereomer C2-t(Z)-5. The corresponding AM1 relative stability is reversed: C2-t(Z)-5 is 1.1 kJ/mol more stable than C2-t(E)-5. The pure twists of t(Z)-5 and t(E)-5 are 37.0 degrees and 37.2 degrees (PM3) and 40.5 degrees and 39.1 degrees (AM1). The corresponding (E) --> (Z) (PM3) and (Z) --> (E) (AM1) energy barriers of diastereomerization are 80.6 kJ/mol (PM3) and 75.8 kJ/mol (AM1). Two anti-folded local minima conformations C2-a(Z)-5 and C(i)-a(E)-5 were found to be 21.2 and 29.5 kJ/mol (PM3) and 25.8 and 35.2 kJ/mol (AM1) less stable than t(E)-5. The syn-folded conformations C(S)-s(Z)-5 and C2-s(E)-5 are transition states for the enantiomerization processes of C2-tz-5 and C2-tE-5, respectively, and lay 79.8 and 94.1 kJ/mol (PM3) and 108.3 and 107.4 kJ/mol (AM1) higher in energy than their corresponding twisted conformations. An alternative pathway for enantiomerization of C2-t(E)-5 via the anti-folded achiral intermediate C(i)-a(E) has a barrier of 56.0 kJ/mol (PM3) and 68.5 (AM1). An alternative pathway for enantiomerization of C2-t(Z)-5 via C2-t(E) and C(i)-a(E) has a barrier of 80.6 (PM3) and 75.8 (AM1) kJ/mol.

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mentioning

confidence: 57%

“…and 2,2 -dimethylbifluorenylidene are 79.5 and 84.6 kJ/mol, respectively [5,12]. and 2,2 -dimethylbifluorenylidene are 79.5 and 84.6 kJ/mol, respectively [5,12].…”

Section: Figurementioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Stereochemistry of ( E )- and ( Z )-1,1′-Dichlorobifluorenylidenes, Substituted Overcrowded Fullerene Fragments

Pogodin

Cohen²,

Biedermann³

et al. 2002

Enantiomer

Self Cite

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“…1, and has also been observed for other second-generation motors 26,55 and structurally related bistricyclic aromatic enes like dithioxanthylene and dixanthylene. 76 In the syn-folded conformation, the stator and rotator point toward the same side of the olefinic plane, whereas they point toward opposite sides in the antifolded conformation. As a result, the latter conformation exhibits less steric overcrowding in the fjord regions than the former, and lies lower in energy.…”

Section: Syn-and Anti-folded Isomers Of Motormentioning

confidence: 99%

Computational design of faster rotating second-generation light-driven molecular motors by control of steric effects

Oruganti

Fang

Durbeej

2015

Phys. Chem. Chem. Phys.

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We report a systematic computational investigation of the possibility to accelerate the rate-limiting thermal isomerizations of the rotary cycles of synthetic light-driven overcrowded alkene-based molecular motors through modulation of steric interactions.Choosing as reference system a second-generation motor known to accomplish rotary motion in the MHz regime and using density functional theory methods, we propose a three-step mechanism for the thermal isomerizations of this motor and show that variation of the steric bulkiness of the substituent at the stereocenter can reduce the (already small) free-energy barrier of the rate-determining step by a further 15−17 kJ mol -1 . This finding holds promise for future motors of this kind to reach beyond the MHz regime. Furthermore, we demonstrate and explain why one particular step is kinetically favored by decreasing and another step is kinetically favored by increasing the steric bulkiness of this substituent, and identify a possible back reaction capable of impeding the rotary rate.3

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Enhanced Emission by Restriction of Molecular Rotation

Hong¹

2013

Aggregation-Induced Emission: Fundamentals

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Conformational Space and Dynamic Stereochemistry of Overcrowded Homomerous Bistricyclic Aromatic Enes − A Theoretical Study

Cited by 97 publications

References 108 publications

Stereochemistry of ( E )- and ( Z )-1,1′-Dichlorobifluorenylidenes, Substituted Overcrowded Fullerene Fragments

Stereochemistry of ( E )- and ( Z )-1,1′-Dichlorobifluorenylidenes, Substituted Overcrowded Fullerene Fragments

Computational design of faster rotating second-generation light-driven molecular motors by control of steric effects

Enhanced Emission by Restriction of Molecular Rotation

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