Chiral bis(benzo[1,2-b:4,3-b']dithiophene) atropisomers: experimental and theoretical investigations of the stereochemical and chiroptical properties

2021 ◽  
Author(s):  
Valentina Pelliccioli ◽  
Roberta Franzini ◽  
Giuseppe Mazzeo ◽  
Claudio Villani ◽  
Sergio Abbate ◽  
...  
Keyword(s):  
Single Bond ◽  
Hindered Rotation ◽  
Chiroptical Properties ◽  
Theoretical Investigations

Conformational chirality is a feature that may arise from the presence of a hindered rotation around a single bond that corresponds to a stereogenic axis. Atropisomers that feature such element...

Monomeres [(Me3Si)2CH]2Al-Te-Al[CH(SiMe3)2]2 mit gewinkelter Al-Te-Al-Gruppe / Monomeric [(Me3Si)2CH]2Al-Te-Al[CH(SiMe3)2] 2 with a Bent Al-Te-Al Group

1994 ◽  
Vol 49 (7) ◽  
pp. 931-934 ◽  
Author(s):  
Werner Uhl ◽  
Uwe Schütz
Keyword(s):  
Solid State ◽  
Bond Length ◽  
Title Compound ◽  
Single Bond ◽  
Hindered Rotation ◽  
Coordination Numbers ◽  
Mild Conditions ◽  
High Yields

AbstractTetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 with an Al-Al bond and Et3P+-Te- give under mild conditions the title compound R2Al-Te-AlR2 (R = CH(SiMe3)2) 2 in high yields. Due to the high steric shielding 2 is monomeric even in the solid state with an angled Al-Te-Al group (110.4°) and an Al-Te bond length of 254.9 pm as expected for a Al-T e single bond with the atoms in low coordination numbers. A hindered rotation of the bulky substituents is observed in solution probably caused by steric restrictions similar that in ana­logous compounds with Al-S-Al or Al-CH2-Al groups.

Hindered rotation around the N(sp2)-C(sp3) single bond in 2,4,6-trimethyl-N-alkylpyridinium cations:H DNMR analysist

Tetrahedron ◽  
1984 ◽  
Vol 40 (13) ◽  
pp. 2547-2553 ◽  
Author(s):  
Alexandru T. Balaban ◽  
Cornelia Uncuţ/a ◽  
Mihai Elian ◽  
Filip Chiraleu ◽  
Antonie Dinculescu
Keyword(s):  
Single Bond ◽  
Hindered Rotation

Gehinderte Ligandbewegungen in Übergangsmetallkomplexen, XXXVII [1]: Photoreaktion von Dekacarbonyldirhenium mit Phenylallen / Hindered Ligand Motions in Transition Metal Complexes, XXXVII [1]: Photoreaction of Decacarbonyldirhenium with Phenylallene

1990 ◽  
Vol 45 (6) ◽  
pp. 793-802 ◽  
Author(s):  
Cornelius G. Kreiter ◽  
Wolfgang Michels ◽  
Reiner Exner
Keyword(s):  
Molecular Structure ◽  
Solid State ◽  
Transition Metal ◽  
Transition Metal Complexes ◽  
Crystal And Molecular Structure ◽  
Dinuclear Complexes ◽  
Rotation Barrier ◽  
Single Bond ◽  
Hindered Rotation ◽  
X Ray

Decacarbonyldirhenium (1) and phenylallene (2) form upon UV irradiation four dinuclear complexes: Decacarbonyl-μ-η1:1-(3,4-diphenyl-1,5-hexadien-2,5-diyl)-dirhenium (3), enneacarbonyl-μ-ηl:3-(3-phenyl-2-propen-1,2-diyl)-dirhenium (4), octacarbonyl-μ-hydrido-μ-η1:2-(3-phenyl-1,2-propadien-l-yl)-dirhenium (5) and octacarbonyl-μ-η2:2-(phenyl-1,2-propadiene)-dirhenium (6). The thermolabile complex 4 looses CO and forms the phenylallene bridged compound 6. Similarly 5 is rearranged to 6 by transfer of the hydrido ligand to the 3-phenyl-1,2-propadien-1-yl bridge. The formation of 3 and 4 can be rationalized via pentacarbonyl-phenylpropenediyl-rhenium radicals which dimerize to give 3 or add pentacarbonylrhenium radicals, loose CO and form 4. The crystal and molecular structure of 3 was determined by X-ray structure analysis. In the solid state the molecule is present in the ± ap conformation. In solution at 233 K the ±ap, +sc, and –sc conformations are equally populated. By a hindered rotation around a CC single bond, the three conformers are interconverted with a rotation barrier of ΔG*258 = 52.3 ± 1 kJ · mol-1.

Proton Magnetic Resonance Studies of Rotational Isomerism in Halotoluene Derivatives. XI. Experimental and Theoretical Barriers to Rotation in α,α,2,4,6-Pentabromo-, α,α-Dibromo-2,4,6-trichloro-, and α,α-Dibromo-2,6-dichlorotoluene

1974 ◽  
Vol 52 (5) ◽  
pp. 849-854 ◽  
Author(s):  
James Peeling ◽  
Ludger Ernst ◽  
Ted Schaefer
Keyword(s):  
Energy Barrier ◽  
Proton Magnetic Resonance ◽  
Geometry Optimization ◽  
Activation Parameters ◽  
Rotational Isomerism ◽  
Partial Geometry ◽  
Single Bond ◽  
Hindered Rotation ◽  
Magnetic Resonance Studies ◽  
Potential Energy Barrier

Using rate constants determined from an analysis of the p.m.r. lineshape of the ring protons as a function of temperature, the activation parameters for the hindered rotation about the sp2–sp3 carbon–carbon single bond in α,α,2,4,6-pentabromotoluene dissolved in perchlorobutadiene are determined. Values of ΔG≠ for the analogous hindered rotations in α,α-dibromo-2,6-dichlorotoluene in toluene-d8, and for α,α-dibromo-2,4,6-trichlorotoluene in solutions of toluene-d8 and methylcyclohexane are also given. The results are compared with semiempirical potential energy barrier calculations employing partial geometry optimization. The agreement is satisfactory.

Magnetic non-equivalence of fluorine atoms of a trifluoromethyl group

1982 ◽  
Vol 60 (19) ◽  
pp. 2451-2455 ◽  
Author(s):  
Mohsin A. Khan ◽  
Donald F. Tavares ◽  
Arvi Rauk
Keyword(s):  
Methoxy Group ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Trifluoromethyl Group ◽  
Single Bond ◽  
Hindered Rotation ◽  
Geminal Coupling ◽  
Coupling Pattern ◽  
Derivatives Of

The three fluorine atoms of N,N-dialkyl amide and chloride derivatives of 2-methoxy-2-phenyl-3,3,3-trifluoropropanoic acid are magnetically nonequivalent below –60 °C and exhibit a clear ABC coupling pattern from which chemical shifts and geminal coupling constants are readily derived. The chemical shifts span a range of about 10 ppm and the geminal coupling constants average about 110 Hz. A five bond coupling of about 5 Hz is observed between the hydrogens of the methoxy group and one of the nonequivalent fluorine atoms of the trifluoromethyl group. Barriers to the hindered rotation about the single bond to the trifluoromethyl group are in the range 36–46 kJ/mol.

Observation of buttressing effect and hindered rotation about C(sp2)—C(sp2) single bond in styrenes coordinated to a ruthenium cation, Cp(diphosphine)Ru+

1996 ◽  
Vol 74 (11) ◽  
pp. 1936-1944
Author(s):  
Kenzo Ohkita ◽  
Hideo Asano ◽  
Hideo Kurosawa ◽  
Toshikazu Hirao ◽  
Yohko Miyaji ◽  
...  
Keyword(s):  
Variable Temperature ◽  
Phenyl Group ◽  
Shielding Effect ◽  
Single Bond ◽  
Conformational Isomerism ◽  
Nmr Studies ◽  
Hindered Rotation ◽  
Restricted Rotation ◽  
Conformational Isomers ◽  
Dominant Isomer

Complexes of (η5-cyclopentadienyl)(bis(di-p-tolylphosphino)ethane)ruthenium(II) cation with some styrenes containing meta or para substituants were prepared and their NMR spectra examined in detail. Variable-temperature NMR studies on the unsubstituted and para-substituted styrene analogues demonstrated occurrence of a restricted rotation about the C(sp2)—C(sp2) single bond of the styrenes where one of the ortho hydrogens of the styrene phenyl group receives a very large diamagnetic shielding effect by one of the phosphine tolyl groups. Similar studies on the meta-substituted styrene complexes showed existence of two unequally populated conformational isomers arising from the similar restricted rotation where the meta substituent in the dominant isomer was placed further away from the C=C group. The origin of such conformational isomerism was deduced to be the buttressing effect of the meta substituent transmitted via the ortho-hydrogen atom. Key words: buttressing effect, hindered rotation, Ru–styrene complex.

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