Studies in Stereochemistry. XXXIV. Variation of Carbonium Ion Structure with Variation in Origin

1963 ◽  
Vol 85 (9) ◽  
pp. 1257-1263 ◽  
Author(s):  
Donald J. Cram ◽  
Melville R. V. Sahyun
Keyword(s):  
Ion Structure ◽  
Carbonium Ion

scholarly journals A Kinetic and Thermodynamic Behavioral Comparison of Observable Secondary and Tertiary 2-Norbornyl Cations

1975 ◽  
Vol 53 (13) ◽  
pp. 1891-1900 ◽  
Author(s):  
R. Haseltine ◽  
N. Wong ◽  
T. S. Sorensen ◽  
A. J. Jones
Keyword(s):  
Model Systems ◽  
Suitable Model ◽  
Absolute Rate ◽  
Free Energies ◽  
Ion Structure ◽  
Hydride Shift ◽  
Carbonium Ion ◽  
Carbenium Ion ◽  
Rearrangement Processes ◽  
Rate Comparison

By analyzing various rearrangement processes, one can deduce the relative stabilities of the following 2-norbornyl cations (kcal/mol): 1,2-dimethyl, 0; 2-methyl, 1; 1-methyl, 6.5; and the parent 2-norbornyl, 8.5. Secondary 2-norbornyl cations have been assigned a "carbonium ion" structure and tertiary a "carbenium ion" structure. Using suitable model systems, an absolute rate comparison has been made of all three common rearrangement processes in the tertiary systems ("carbenium") with those already measured for the 2-norbornyl cation ("carbonium"). The activation free energies, ΔG≠, (in kcal/mol) were: Wagner–Meerwein (WM) shift: tertiary, < 4; secondary, < 4; endo-6,2-hydride shift: tertiary, 7.2; secondary, 5.8; exo-3,2-hydride shift: tertiary, 6.6; secondary, 11.4. A discussion of the structure of tertiary and secondary 2-norbornyl cations emphasizes the following points: (i) a rationalization of the rapid endo-6,2-hydride shift observed in norbornyl cations does not necessitate a protonated nortricyclene ("carbonium ion") postulate; (ii) on the basis of the results for acyclic cations and the 1,2-dimethyl-2-norbornyl cation, one would not expect to "freeze out" the WM shift in an equilibrating 2-norbornyl cation structure; (iii) the formation of nortricyclenes may be related to a partial C6—C2 bond in the ions; and (iv) the structure of the observable secondary 2-norbornyl cation probably involves partial C6—C2 bonding but, in our opinion, this does not require a symmetrical static formulation.

Simple theoretical models of elimination reactions on polar catalysts; Dehydration reactivity of secondary alcohols on acidic and basic catalysts

1985 ◽  
Vol 50 (4) ◽  
pp. 920-929 ◽  
Author(s):  
Jiří Sedláček
Keyword(s):  
Experimental Data ◽  
Quantum Chemical ◽  
Theoretical Models ◽  
Aliphatic Alcohols ◽  
Secondary Alcohols ◽  
Carbonium Ion ◽  
Dehydration Reactions ◽  
Aromatic Alcohols ◽  
Basic Catalysts ◽  
Simple Models

CNDO/2 calculations for simple models of adsorption and dehydration reactions of secondary aliphatic and aromatic alcohols on polar catalysts are presented. The models involve selected stages of elimination mechanisms of various types (E1, E2 and E1cB elimination). Calculated quantum chemical quantities were correlated with reported experimental data. It is shown that reactivities for the series of substituted phenylethanols correlate very well with the ease of carbonium ion formation. In the case of aliphatic alcohols, calculated quantities correlate generally with the reactivities on SiO2 and are in anticorrelation with the reactivities on Al2O3.NaOH.

Solvolysis of 1,2-dimethyl-exo-2-benzonorbornenyl derivatives. Direct evidence for a classical carbonium ion

1974 ◽  
Vol 96 (24) ◽  
pp. 7602-7603 ◽  
Author(s):  
Harlan L. Goering ◽  
Chiu-Shan Chang ◽  
John V. Clevenger
Keyword(s):  
Direct Evidence ◽  
Carbonium Ion

Thermochemistry of Organic and Heteroorganic Species. Part IX. Photoionization Studies of Isomerization and Fragmentation of Polysubstituted Cyclopropenes: Phenyl-Substituted Cyclopropenes

2000 ◽  
Vol 6 (1) ◽  
pp. 53-64 ◽  
Author(s):  
V.V. Takhistov ◽  
I.N. Domnin ◽  
D.A. Ponomarev
Keyword(s):  
Mass Spectrometry ◽  
Enthalpy Of Formation ◽  
Good Alternative ◽  
Enthalpies Of Formation ◽  
Isodesmic Reactions ◽  
Ion Structure ◽  
Photoionization Mass Spectrometry ◽  
General Methodology ◽  
Fragment Ions ◽  
The Enthalpy Of Formation

Ionization and appearance energies of some fragment ions from 1,2,3-trimethy1-3-phenyl-, 3-methyl-1,2,3-triphenyl-, 1,2-diphenyl-3-methoxycarbonyl-, 1,2,3-triphenyl-3-methoxycarbonyl- and 1,3,3-triphenyl-2-methoxycarbonyl-cyclopropenes were measured by photoionization mass spectrometry. It was shown that in none of these compounds did the fragment ions possess the expected stable substituted cyclopropenium ion structure. Accordingly, possible schemes of molecular ion isomerization are given. The enthalpies of formation of nearly 50 substituted cyclopropenium ions, and ions of related structure, were estimated using series of isodesmic reactions. This publication, together with the previous works of the authors in this Journal, demonstrates the general methodology for estimation of the enthalpy of formation for even-electron ions. It is suggested that the present methodology can provide a good alternative to other estimation or computation procedures applied to the thermochemistry of ions.

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