Stable carbocations. 204. Rearrangement and equilibria of ions formed from side-chain substituted .beta.-phenylethyl chlorides under stable ion conditions

Oláh, George A.; Spear, Robert J.; Forsyth, David

doi:10.1021/ja00450a035

Cited by 31 publications

(6 citation statements)

References 6 publications

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“…The NPA-derived charges indicate that the halogens in 7Br and 7Cl bear substantial positive charge. GIAO shifts for the spirocyclic carbons in 7Br , 7Cl , and 7F (δ 73, 71, and 70 ppm) are in close range to the experimental value for this carbon in the parent phenonium ion (no double bond in the three-membered ring), reported at δ 68.8 ppm by Olah et al in 1977 …”

Section: Resultssupporting

confidence: 82%

Intermediates of Halogen Addition to Phenylethynes and Protonation of Phenylethynyl Halides. Open Halovinyl Cations, Bridged Halonium, or Phenyl-Bridged Ions: A Substituent Effect Study by DFT and GIAO-DFT

Okazaki

Laali

2006

J. Org. Chem.

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Formation of alpha-phenyl-beta-halovinyl cation, beta-phenyl-alpha-halovinyl cation, as well as the halogen-bridged and the spirocyclic phenyl-bridged cations as intermediates of protonation of phenylethynyl halides or by halogen addition to phenylethynes was evaluated by DFT at B3LYP/6-31+G(d) and, for comparison in representative cases, by B3LYP/6-311++G(d,p). Relative stabilities of the resulting minima were gauged as a function of substituents on the phenyl group with p-OH, p-OMe, p-H, p-CF3, p-CN, and p-NO2 and with p-OMeH+, p-NO2H+, and p-N2+. In the majority of cases, the alpha-aryl-beta-halovinyl cations were identified as the most likely intermediates, irrespective of X and for most R groups. For R = p-N2+ (with X = Br and Cl), R = CNH+ (with X = Cl), and R = MeOH+ (with X = Br), the corresponding beta-aryl-alpha-halovinyl cations become more stable than alpha-aryl-beta-halovinyl cations (but in most cases with a relatively small stability difference). Whereas competitive formation of the spirocyclic aryl bridged cations via this route appears remote, with R = N2+ and R = NO2H+ as substituents (with X = Br), cyclic halonium ions could intervene, since their relative stabilities are within approximately 4 kcal/mol of the lowest energy vinyl cations. Geometrical features, GIAO NMR chemical shifts, and NPA-derived charges were used to gain insight into the structural/electronic features in the resulting mono and dications. The study provides a basis for stable ion and solvolytic/kinetic studies on a series of substituted phenylethynyl halides that are being synthesized.

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Section: Resultssupporting

confidence: 82%

Intermediates of Halogen Addition to Phenylethynes and Protonation of Phenylethynyl Halides. Open Halovinyl Cations, Bridged Halonium, or Phenyl-Bridged Ions: A Substituent Effect Study by DFT and GIAO-DFT

Okazaki

Laali

2006

J. Org. Chem.

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“…Thus at M σ the HOMO(H 2 )−LUMO(C 6 H 5 + ) interaction between the fragments is augmented by a strong back-bonding through the LUMO(H 2 )− NHOMO(C 6 H 5 + ) interaction (see Figure a) which leads to the cleavage of the H−H bond and makes possible the formation of the two C−H bonds from which the hydrogen molecule will be eliminated. It is interesting to note here that a related important structure is the nonclassical form of the phenonium ion . Figure displays the contour plots of the MOs of the C 6 H 7 + supermolecule reflecting the interaction between (a) the HOMO of H 2 and the LUMO of C 6 H 5 + , and (b) between the LUMO of H 2 and the NHOMO of C 6 H 5 + .…”

Section: Resultsmentioning

confidence: 99%

A Theoretical Study of the H₂ Elimination from C₆H₇⁺: An Example of the Role of Back-Donation in Carbocation Chemistry

1997

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C 6 H 7 + has been investigated by using the ab initio method at MP2-FC/6-31G* level and single point calculations on the MP2 geometries at the MP4(SDTQ)-FC/6-31G* level. The most stable structure located corresponds to the benzenium ion C 6 H 7 + in which a proton is bonded to one of the carbon atoms of the benzene ring and an extension of the delocalization has taken place to include the attached proton, the π-electron density distribution being basically allylic in agreement with experimental findings. Two transition structures (TSs) for hydrogen scrambling were found on the C 6 H 7 + PES. The first one corresponds to the peripheral migration of a proton in the benzenium ion and determines an energy barrier of 7.8 kcal/mol at MP2 level (10.8 at MP4//MP2 level) in good agreement with experimental data. The second scrambling TS corresponds to the interchange of the two hydrogen atoms bonded to the same carbon atom in the ring of the benzenium ion and presents an energy barrier of 59.2 kcal/mol at MP2 level (62.6 at MP4//MP2 level). The H 2 -elimination is an endoergic process that proceeds through a very late TS and an intermediate very close in energy to it that finally renders the products, C 6 H 5 + + H 2 , without any energy barrier. The activation energy for this process (70.3 and 70.1 kcal/mol at MP2 and MP4//MP2 levels, respectively) is practically its endoergicity (71.1 kcal/mol at MP2 level and 70.8 kcal/mol at MP4//MP2 level) in accordance with the experimental finding of null energy release as relative motion between the fragments. A configuration analysis of the wave function of C 6 H 7 + along the reaction coordinate for H 2 -elimination clearly shows that the back-donation from the NHOMO of C 6 H 5 + to the LUMO of H 2 plays a fundamental role in the bonding structure of the benzenium ion. The H 2 elimination takes place through deactivation of the back-bonding at an early stage in the process.

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“…In sharp contrast to the phenonium ion intermediate B in Scheme 1, the rapid Sc(OTf) 3 -catalyzed ring-opening allylation of the cyclopropane in E with 2a from either site, prior to the formation of the open-chain 1-arylethan-1-yl cation intermediate through the slow rearrangement (1,2-hydride shift) of 2-arylethan-1-yl cation intermediate, would proceed to give the linear allylated products 8d–8g without the formation of the branched allylated products (vide supra) (Scheme 2). 27…”

Section: Results and Discussionmentioning

confidence: 99%

Homogeneous Sc(OTf)₃-Catalyzed Direct Allylation Reactions of General Alcohols with Allylsilanes

et al. 2018

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Homogeneous Sc(OTf) 3 used in nitromethane showed excellent catalytic activity for the direct allylation reactions of general alcohols including benzylic, propargylic, allylic, and some aliphatic alcohols with allyltrimethylsilane under mild and neutral reaction conditions. Metal-free β-silyl-substituted carbocations are intermediates generated by the highly oxophilic Sc(OTf) 3 -assisted rapid removal of a hydroxyl group in alcohols, which is supported by the result that allylation of ( R )-1-(naphthalen-2-yl)ethan-1-ol with allytrimethylsilanes using the Sc(OTf) 3 catalyst combined with ( R )- or ( S )-[1,1′-binaphthalene]-2,2′-diol ligands gave only racemic 2-(pent-4-en-2-yl)naphthalene in quantitative yield. The present study resolves the argument about the uncertain catalytic activity of Sc(OTf) 3 .

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Stable carbocations. 204. Rearrangement and equilibria of ions formed from side-chain substituted .beta.-phenylethyl chlorides under stable ion conditions

Cited by 31 publications

References 6 publications

Intermediates of Halogen Addition to Phenylethynes and Protonation of Phenylethynyl Halides. Open Halovinyl Cations, Bridged Halonium, or Phenyl-Bridged Ions: A Substituent Effect Study by DFT and GIAO-DFT

Intermediates of Halogen Addition to Phenylethynes and Protonation of Phenylethynyl Halides. Open Halovinyl Cations, Bridged Halonium, or Phenyl-Bridged Ions: A Substituent Effect Study by DFT and GIAO-DFT

A Theoretical Study of the H₂ Elimination from C₆H₇⁺: An Example of the Role of Back-Donation in Carbocation Chemistry

Homogeneous Sc(OTf)₃-Catalyzed Direct Allylation Reactions of General Alcohols with Allylsilanes

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Stable carbocations. 204. Rearrangement and equilibria of ions formed from side-chain substituted .beta.-phenylethyl chlorides under stable ion conditions

Cited by 31 publications

References 6 publications

Intermediates of Halogen Addition to Phenylethynes and Protonation of Phenylethynyl Halides. Open Halovinyl Cations, Bridged Halonium, or Phenyl-Bridged Ions: A Substituent Effect Study by DFT and GIAO-DFT

Intermediates of Halogen Addition to Phenylethynes and Protonation of Phenylethynyl Halides. Open Halovinyl Cations, Bridged Halonium, or Phenyl-Bridged Ions: A Substituent Effect Study by DFT and GIAO-DFT

A Theoretical Study of the H2 Elimination from C6H7+: An Example of the Role of Back-Donation in Carbocation Chemistry

Homogeneous Sc(OTf)3-Catalyzed Direct Allylation Reactions of General Alcohols with Allylsilanes

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A Theoretical Study of the H₂ Elimination from C₆H₇⁺: An Example of the Role of Back-Donation in Carbocation Chemistry

Homogeneous Sc(OTf)₃-Catalyzed Direct Allylation Reactions of General Alcohols with Allylsilanes