The molecular structure of a substituted 2-norbornyl cation, 2-methoxy-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylium fluoroborate

Montgomery, L. K.; Grendze, M. P.; Huffman, John C.

doi:10.1021/ja00249a064

Cited by 21 publications

(4 citation statements)

References 2 publications

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“…Despite numerous attempts, a single-crystal x-ray structure determination of the parent 2norbornyl cation has remained elusive. Although crystalline 2-norbornyl salts have been obtained earlier (31), numerous attempts by various research groups to solve the x-ray structure failed (32,33). The structural characterization of related, but metrically and electronically rather different, norbornyl cation derivates (31)(32)(33)(34) Fully assigned vibrational spectra of samples from these crystals agree with prior measurements (16, 28) as well as with computations (figs.…”

Section: Arbocations Have Been Controversialmentioning

confidence: 99%

Crystal Structure Determination of the Nonclassical 2-Norbornyl Cation

Scholz

Himmel

Heinemann

et al. 2013

Science

115

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After decades of vituperative debate over the classical or nonclassical structure of the 2-norbornyl cation, the long-sought x-ray crystallographic proof of the bridged, nonclassical geometry of this prototype carbonium ion in the solvated [C7H11](+)[Al2Br7](-) • CH2Br2 salt has finally been realized. This achievement required exceptional treatment. Crystals obtained by reacting norbornyl bromide with aluminum tribromide in CH2Br2 undergo a reversible order-disorder phase transition at 86 kelvin due to internal 6,1,2-hydride shifts of the 2-norbornyl cation moiety. Cooling with careful annealing gave a suitably ordered phase. Data collection at 40 kelvin and refinement revealed similar molecular structures of three independent 2-norbornyl cations in the unit cell. All three structures agree very well with quantum chemical calculations at the MP2(FC)/def2-QZVPP level of theory.

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Section: Arbocations Have Been Controversialmentioning

confidence: 99%

Crystal Structure Determination of the Nonclassical 2-Norbornyl Cation

Scholz

Himmel

Heinemann

et al. 2013

Science

115

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“…The nearest α-CH···F distances are 2.83 and 2.99 Å. In the crystal structure of a substituted 2-norbornyl cation, the distance between cationic carbon and the fluorine atom of the BF 4 – counteranion is 3.41 Å and the shortest α-CH···F distance is 2.28 Å …”

Section: Resultsmentioning

confidence: 99%

Studies on the Origin of the Stabilizing Effects of Fluorinated Alcohols and Weakly Coordinated Fluorine-Containing Anions on Cationic Reaction Intermediates

Tian

2022

J. Org. Chem.

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Many synthetic methods that use fluorinated alcohols as solvents have been reported, and the fluorinated alcohols have been found to be crucial to the success of these methods. In addition, there have been reports indicating that adding a weakly coordinated fluorine-containing anion, such as BF 4− , PF 6 − , or SbF 6 − , to fluorinated alcohols can improve yields. The boosting effect of fluorinated alcohols is attributed mainly to hydrogen bond activation. A few studies have suggested that the very polar fluorinated alcohols can stabilize cationic reaction intermediates. However, how they do so and why weakly coordinated fluorine-containing anions improve yields have not been studied in depth. Here, we used quaternary ammonium cations, a quaternary phosphonium cation, and a triaryl-substituted carbocation as models for short-lived cationic intermediates and studied the possible interactions of these cations with fluorinated alcohols and BF 4 − , PF 6 − , or SbF 6 − . On the basis of the results, we propose that the C−F dipoles of fluorinated alcohols and the E−F dipoles (where E is B, P, or Sb) of weakly coordinated fluorinecontaining anions stabilized these cations by intermolecular charge−dipole interactions. We deduced that in the same fashion the C−F and E−F dipoles can thermodynamically stabilize cationic reaction intermediates.

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“…581 Conformers 322 and 323 were identified by calculation [MP2(fu)/6-31G* and MP2/6-31G*þZPE levels, respectively]. 630 It is a substituted 2-norbornyl cation and, indeed, the C(2)-C(1)-C(6) bond angle (98.8 ) and the C(1)-C(6) bond distance (1.603 Å) indicate s-bond charge delocalization, that is, the contribution of the 326b resonance form. The X-ray structure of a number of alkoxycarbenium ions has been determined.…”

Section: ð3:90þmentioning

confidence: 99%

“…ð3:148Þ Although experimental work on the parent square pyramidal (CH) 5 þ ion has not been reported, a dimethyl-substituted derivative 623 of the pyramidal ion 615, however, has been prepared by Masamune et al 1095,1096 and studied by 1 H and 13 C NMR spectroscopy. 630 631 632 (3.149)].…”

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confidence: 99%