Cryptoclastic diastereotopism: NMR evidence for the chirotopicity of the methyl group in (.alpha.-deuterio-o-chlorotoluene)chromium tricarbonyl

Restelli, A.; Siegel, Jay S.

doi:10.1021/ja00029a050

Cited by 19 publications

(19 citation statements)

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“…The spectrum may be simulated by using the following parameters: |J HH | = 14.7 ± 0.3 Hz, ∆δ = 8.0 ± 0.4 ppb. These are consistent with the literature [31].…”

Section: Methodssupporting

confidence: 94%

“…Of these, the one expected to provide rapid CH 2 D rotation is (α-deuterio-ochlorotoluene)chromium tricarbonyl (I), see Figure 1. A small chemical shift difference of ∆δ 8.0 ppb between the CH 2 D protons has been observed in this compound, and has been attributed to a significant interaction between the orbitals of the chromium centre and those of the CH 2 D carbon, combined with the chiral environment provided by the ortho-Cl substituent [31].…”

Section: Introductionmentioning

confidence: 67%

“…In monodeuterated methyl groups, a small chemical shift difference ∆δ may exist between the two protons, providing that: (1) the rotamer populations of the CH 2 D group are not exactly equal, and (2) the local molecular environment is chiral, so that a significant chemical shift difference exists between the protons in a given rotamer. These conditions have been shown to be satisfied in a variety of molecular systems [29][30][31].…”

Section: Introductionmentioning

confidence: 92%

“…To the best of our knowledge, chemical inequivalence between CH 2 D protons has only been described so far in three chemical compounds [29][30][31]. Of these, the one expected to provide rapid CH 2 D rotation is (α-deuterio-ochlorotoluene)chromium tricarbonyl (I), see Figure 1.…”

Section: Introductionmentioning

confidence: 99%

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Long-lived nuclear spin states in rapidly rotating CH 2 D groups

Elliott

Brown

Dumez

et al. 2016

Journal of Magnetic Resonance

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Although monodeuterated methyl groups support proton long-lived states, hindering of the methyl rotation limits the singlet relaxation time. We demonstrate an experimental case in which the rapid rotation of the CH 2 D group extends the singlet lifetime but does not quench the chemical shift difference between the CH 2 D protons, induced by the chiral environment. Proton singlet order is accessed using Spin-Lock Induced Crossing (SLIC) experiments, showing that the singlet relaxation time T S is over 2 minutes, exceeding the longitudinal relaxation time T 1 by a factor of more than 10. This result shows that proton singlet states may be accessible and long-lived in rapidly rotating CH 2 D groups.

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“…The spectrum may be simulated by using the following parameters: |J HH | = 14.7 ± 0.3 Hz, ∆δ = 8.0 ± 0.4 ppb. These are consistent with the literature [31].…”

Section: Methodssupporting

confidence: 94%

Section: Introductionmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Long-lived nuclear spin states in rapidly rotating CH 2 D groups

Elliott

Brown

Dumez

et al. 2016

Journal of Magnetic Resonance

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“…We failed to access the CH 2 D singlet state in both of these cases: the chemical inequivalence of the CH 2 D protons is presumably too small to exploit. Apart from unusual circumstances [53], hyperconjugation between a lone pair on a neighbouring atom (such as N) and the methyl C-H/D bonds seems to be a requirement for obtaining a sufficient chemical shift difference of a few ppb or more. At the time of writing we have not attempted these experiments on other chiral compounds containing a X-CH 2 D moiety, where X is an atom other than N possessing a long pair, such as P, O or S.…”

Section: Relaxation Analysismentioning

confidence: 99%

Long-lived nuclear spin states in monodeuterated methyl groups

Elliott

Brown

Dumez

et al. 2016

Phys. Chem. Chem. Phys.

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It is possible to access long-lived nuclear singlet order in monodeuterated methyl groups, in the case that a significant chemical shift difference exists between the CH 2 D protons. This occurs when the local environment is chiral, and the CH 2 D rotamers have different populations. An experimental demonstration is presented for the case of N-CH 2 D-2-methylpiperidine. The ratio of the singlet relaxation time constant T S to the longitudinal relaxation time constant T 1 is found to be equal to 3.1 ± 0.1, over a wide range of temperatures, solvents, and magnetic fields. The longest observed value of T S approaches 1 minute. The relaxation mechanisms of the long-lived state are discussed, and a modified model of the CH 2 D geometry is proposed to explain the observed ratio of T S to T 1 .

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Chiral Atropisomeric Indenocorannulene Bowls: Critique of the Cahn–Ingold–Prelog Conception of Molecular Chirality

et al. 2018

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Chiral corannulenes abound, but suffer generally from configurational lability associated with bowl-to-bowl inversion, [1] thus obviating questions of stereogenicity and stereoelement construction. [2] In contrast, peri-annulated corannulenes show greatly increased barriers for bowl-to-bowl inversion;s pecifically indenocorannulenes invert on at ime scale too slow to observe by normal NMR methods and raise the possibility of creating chiral atropisomeric bowl-shaped aromatics. [3] Twom ethods for preparing indenocorannulene from simple 2-haloarylcorannulenes-silyl cation C-F activation, [4] and Pd-mediated C-Cl activation [5] -enable the synthesis of an arrayo fs uch chiral atropisomeric indenocorannulenes. [6] Resolution of the enantiomers by high-performance liquid chromatography over chiral support phases motivates the study of chiroptical properties,the assignment of absolute "Cartesian" configuration, and the assessment of configurational stability. [7] These studies bring into question any systematic assignment of nontrivial stereoelements (i.e.not the molecule in its entirety) and refute any assertion of congruence between "Cahn-Ingold-Prelog elements" and the physical or "Cartesian" basis of chirality. Theminimum-energystaticbowlformofindenocorannulenemanifests bilateral (C s )symmetry.All of the hydrogen atoms are chirotopic (local symmetry C 1 )and therefore replacement of any single hydrogen atom by anon-hydrogen atom lowers the symmetry of the molecule to C 1 .T his study focuses on chiral molecules resulting from substitutions to the indeno six-membered ring.Iodocorannulene couples efficiently with av ariety of 2haloarylboronic acids to provide the immediate synthetic precursors to indenocorannulenes 1a-1f(Scheme 1). Fluoro precursors were subjected to silyl cation C-F activation/ coupling,whereas chloro precursors underwent Pd-catalyzed C-Cl activation/coupling.A lthough both methods cleanly provide product, the yields for Pd-catalyzed C-Cl activation/ coupling are in general higher (80 %v s. 40 %, see the Supporting Information) and the reaction is less sensitive to moisture and oxygen.Indenocorannulenes in general embody useful photophysical and electrochemical properties.C ompared to corannulene with af irst reduction potential of À2.49 V, the parent monoindenocorannulene has af irst reduction potential of À2.06 Va nd azaindenocorannulene 1f has af irst reduction potential of À2.00 V. [8] Clearly the effect of introducing an indeno annulation (ca. 0.5 V) outweighs the modulating influence of simple substituents (< 0.1 V). Across the series,the optical spectra display absorption peaks around 270 nm and 300-350 nm, and one broad emission peak at about 580 nm (ca. 100 nm width at half-height). Quantum efficiencies are routinely observed to be less than 1%.Indenocorannulenes are predicted to have high barriers and low rates for bowl inversion. [3] As such, one expects the products of the reactions described above,m onosubstituted derivatives 1a-1f, to be nonfluxional racemic mixtures. HPLC over ac hi...

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Cryptoclastic diastereotopism: NMR evidence for the chirotopicity of the methyl group in (.alpha.-deuterio-o-chlorotoluene)chromium tricarbonyl

Cited by 19 publications

References 0 publications

Long-lived nuclear spin states in rapidly rotating CH 2 D groups

Long-lived nuclear spin states in rapidly rotating CH 2 D groups

Long-lived nuclear spin states in monodeuterated methyl groups

Chiral Atropisomeric Indenocorannulene Bowls: Critique of the Cahn–Ingold–Prelog Conception of Molecular Chirality

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