Secondary Cations Research Articles

ChemInform Abstract: MOLECULAR ORBITAL THEORY OF THE ELECTRONIC STRUCTURE OF MOLECULES. 36. A THEORETICAL STUDY OF SEVERAL α‐SUBSTITUTED VINYL CATIONS

The cy-ethynylvinyl (4), n-ethenylvinyl (5), a-cyclopropylvinyl (6), and a-phenylvinyl (7) cations have been investigated by SCF-MO ab initio methods, using both the STO-3G and the 4-31G basis sets. The cations 5,6, and 7 are more stable in perpendicular conformations (5a, 6a, and 7a, respectively) where the interaction between the cationic orbital and the HOMO of the substituent is maximized. The calculated rotation barriers around the C+-substituent bonds are 22.2, 15.8, and 24.7 kcal/mol for 5,6, and 7, respectively, approximateiy half the barrier in the corresponding primary alkyl cations. The efficiency of the n substituent in stabilizing the vinyl cation follows the order CsH5 > c-CsH5 N HC=CHz >> C=CH = CH3 >> H. The ability of the substituents to donate electrons to the empty cationic orbital follows the order C6H5 > CH=CH* > C=CH > c-C~H~ > CH3 > H. No correlation is found between the total charge at the cationic center or the corresponding populations of the formally empty p orbital and the stability of the cation. The cations vinyl (21, a-methylvinyl (3), and 6 have stabilities which are intermediate between those of the corresponding primary and secondary alkyl cations. However, the r-stabilized cations, 4,5, and 7 are of comparable stability to the corresponding primary alkyl cations. Corresponding substituted ethyl cations are 12-17 kcal/mol more stable than the vinyl cations, suggesting that, for the groups examined here, substituent effects are inherently similar for alkenyl and for alkyl cations. The proton affinities of substituted acetylenes and olefins are comparable, with the olefins being 1-5 kcal/mol more basic.

Hyperconjugation and the angular dependence of .beta.-deuterium isotope effects

A method for the correlation of the magnitude of kinetic secondary ..beta..-deuterium isotope effects in solvolytic reactions with the conformation of the reaction transition states is proposed. An empirical angular correlation was developed and several secondary and tertiary carbocation species were analyzed. Good agreement between the observed and calculated isotope effects was found for all cases where the secondary substrate reacts by the same mechanism as the corresponding tertiary ..cap alpha..-Me derivative. This makes the described method a convenient probe for the geometry of solvolytic transition states. The possibility of making deductions about the involvement of anchimeric and/or nucleophilic participation in the solvolysis of secondary substrates is discussed. The absence of hyperconjugative stabilization of secondary cations appears to be the major factor responsible for high (greater than 10/sup 6/) CH/sub 3//H rate ratios.

Conformation et reactivite de derives (4.n.0) bicycliques a jonction trans—XXIV: Trifluoroéthanolyse du phényl-4a et du méthyl-4a tosyloxy-3a bicyclo (4.2.0) octane trans. mise en évidence d'une réaction d'élimination à partir d'union phénonium

Rate constants and reaction products for trifluoroethanolysis of transfused 4a-phenyl 3a-tosyloxy bicyclo (4.2.0) octane 1 and 4a-methyl 3a-tosyloxy bicyclo(4.2.0) octane 1' are reported. As for methanolysis, this reaction occurs through the E 1(ip) process. Nevertheless, first-formed secondary cations are rearranged before reacting, by hydride migration for 1 and 1', and phenyl migration for 1. Reaction products result from solvent or leaving group basic and nucleophilic attack on tertiary ions, and phenonium ion for 1. Elimination via phenonium ion has been established by the characterisation of a rearranged olefin (with equatorial phenyl). A mechanism for this elimination reaction is proposed.

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

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.

Primary‐secondary hydride transfer between secondary alkyl cations and neopentane: Difference in reactivity between isopropyl cation and cyclopentyl cation

Recueil des Travaux Chimiques des Pays-BasVolume 89, Issue 8 p. 857-860 Short Communication Primary-secondary hydride transfer between secondary alkyl cations and neopentane: Difference in reactivity between isopropyl cation and cyclopentyl cation† H. Hogeveen, H. Hogeveen Koninklijke/Shell-Laboratorium, AmsterdamSearch for more papers by this authorC. J. Gaasbeek, C. J. Gaasbeek Koninklijke/Shell-Laboratorium, AmsterdamSearch for more papers by this author H. Hogeveen, H. Hogeveen Koninklijke/Shell-Laboratorium, AmsterdamSearch for more papers by this authorC. J. Gaasbeek, C. J. Gaasbeek Koninklijke/Shell-Laboratorium, AmsterdamSearch for more papers by this author First published: 1970 https://doi.org/10.1002/recl.19700890811Citations: 9 † H. Hogeveen and C. F. Roobeek, “Chemistry and Spectroscopy in Strongly Acidic Solutions”, XXXV. Part XXXIV, in press. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume89, Issue81970Pages 857-860 RelatedInformation

STUDY OF PHOTOLUMINESCENCE IN GLASS*

The influence of composition and temperature on the fluorescence of glasses containing uranium and glasses containing cuprous oxide and stannous oxide was investigated. Secondary cations reduce the fluorescence of uranium in the glasses studied, depending to a certain extent on the electrostatic conditions they produce in the glass structure. The intensity of fluorescence as well as the structure of the spectrum diminishes in the order of phosphate, silicate, and borate glasses of equivalent compositions, which shows that fluorescence is favored by increase of oxygen in the glass structure without increasing the interfering secondary cations. Raising the temperature greatly diminishes the intensity of the fluorescence as well as the structure of the spectrum of glasses containing uranium. The fluorescence of the glasses containing cuprous oxide and stannous oxide as activators seems to be favored by increase in lime and increase in silica. These glasses possess appreciable phosphorescence, which appears to be enhanced by increase in silica and decrease in lime. A peculiar property of this type of luminescent glass is a maximum which it exhibits in its fluorescence-temperature relation-ship. There are indications that electrons are set free from the excited centers (copper atoms or small groups of copper atoms), which wander about in the glass structure.