Heterolytic Bond Dissociation Energies Research Articles

Gas phase heats of formation of alkyl immonium ions

Using an energy-resolved electron beam, the gas-phase heats of formation of [CH2NH2]+, [CH3CHNH2]+, [CH3NHCH2]+, [(CH3)2CNH2]+, [(CH3)2NCH2]+, [CH3CHNHCH3]+, [CH3CH2NHCH2]+, and [CH3CH2CHNH2]+ ions have been measured from their appearance energies in ionic dissociations. All of these ions can have a quaternary immonium structure as one of the canonical forms and are consequently more stable than other isomers. Introduction of the —NH2 group into a CH3+ ion brings about a decrease of over 4 eV in the heterolytic bond dissociation energy D(R+—H−), with slightly larger decreases for —NHR and —NR2 groups.

Some properties of heterolytic bond dissociation energies and their use as molecular parameters for rationalizing or predicting reactivity

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSome properties of heterolytic bond dissociation energies and their use as molecular parameters for rationalizing or predicting reactivityConstantinos G. ScrettasCite this: J. Org. Chem. 1980, 45, 2, 333–336Publication Date (Print):January 1, 1980Publication History Published online1 May 2002Published inissue 1 January 1980https://doi.org/10.1021/jo01290a026RIGHTS & PERMISSIONSArticle Views216Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (454 KB) Get e-Alerts Get e-Alerts

Linear Free Energy Relationships in Heterogeneous Catalysis. XIII. The Dehydration of Aliphatic Alcohols over Silica–Alumina

Abstract In order to survey the applicability of linear free-energy relationships to the catalytic dehydration of aliphatic alcohols, isopropyl alcohol and n-, s-, and t-butyl alcohols were dehydrated over silica–alumina at 54–166 °C. The dehydration was zero order in alcohol over the pressure range of 0.01 to 0.1 atm. The true activation energies were 32.0, 35.3, 31.7, and 29.9 kcal/mol for isopropyl alcohol and n-, s, and t-butyl alcohols, respectively. The zero-order rate constants were exclusively affected by the activation energy. A linear relationship was found between the true activation energy, as well as the logarithm of the zero-order rate constant, and the heterolytic bond dissociation energy for the C–O bond in alcohols, D(R+OH−). The activation energy increased and the rate constant decreased with an increase in the D(R+OH−). These correlations were explained in terms of the heterolytic fission of the C–O bond in the rate-determining step.

Carbenium ion stabilities in the gas phase and solution. An ion cyclotron resonance study of bromide transfer reactions involving alkali ions, alkyl carbenium ions, acyl cations, and cyclic halonium ions

Ion cyclotron resonance techniques are used to measure relative heterolytic bond dissociation energies D(R/sup +/ - Br/sup -/) in the gas phase for a series of alkali cations, alkyl carbenium ions, acyl cations, and cyclic halonium ions. D(R/sup +/ - Br/sup -/) for adamantyl cation is found to be less than for tert-butyl cation. A proton affinity for norbornene of D(B - H/sup +/) = 198.8 +- 2 kcal/mol is determined from which D(R/sup +/ - Br/sup -/) = 146.8 +- 2.3 kcal/mol is calculated for norbornyl cation, 16 kcal/mol less than for cyclopentyl cation. In several cases additional thermochemical data useful in assessing absolute D(R/sup +/ - Br/sup -/) heterolytic bond dissociation energies are provided by photoionization mass spectrometry. Relative enthalpies of solvation for carbenium ions are estimated via appropriate thermochemical cycles by combining the gas phase data with heats of ionization in a HSO/sub 3/F/SbF/sub 3/ medium. The results show that solvation enthalpies are related to ion size with smaller ions being better solvated. Relative stabilities of cyclic bromonium ions are the same in the gas phase and solution. Stability increases with increasing ring size and in the three-membered rings with methyl substitution. However, solvent has an appreciablemore » effect in attenuating the observed range.« less

ChemInform Abstract: EFFECTS OF ALKYL AND FLUOROALKYL SUBSTITUTION ON THE HETEROLYTIC AND HOMOLYTIC BOND DISSOCIATION ENERGIES OF PROTONATED AMINES

Chemischer InformationsdienstVolume 8, Issue 15 Physical Organic Chemistry ChemInform Abstract: EFFECTS OF ALKYL AND FLUOROALKYL SUBSTITUTION ON THE HETEROLYTIC AND HOMOLYTIC BOND DISSOCIATION ENERGIES OF PROTONATED AMINES R. H. STALEY, R. H. STALEYSearch for more papers by this authorM. TAAGEPERA, M. TAAGEPERASearch for more papers by this authorW. G. HENDERSON, W. G. HENDERSONSearch for more papers by this authorI. KOPPEL, I. KOPPELSearch for more papers by this authorJ. L. BEAUCHAMP, J. L. BEAUCHAMPSearch for more papers by this authorR. W. TAFT, R. W. TAFTSearch for more papers by this author R. H. STALEY, R. H. STALEYSearch for more papers by this authorM. TAAGEPERA, M. TAAGEPERASearch for more papers by this authorW. G. HENDERSON, W. G. HENDERSONSearch for more papers by this authorI. KOPPEL, I. KOPPELSearch for more papers by this authorJ. L. BEAUCHAMP, J. L. BEAUCHAMPSearch for more papers by this authorR. W. TAFT, R. W. TAFTSearch for more papers by this author First published: April 12, 1977 https://doi.org/10.1002/chin.197715036AboutPDF 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 No abstract is available for this article. Volume8, Issue15April 12, 1977 RelatedInformation

Photoionization mass spectrometry of the fluoromethylsilanes (CH3)nF4-nSi (n = 1-4)

Photoionization efficiency curves for molecular ions P/sup +/ and lowest energy fragments (P--CH/sub 3/)/sup +/ for the series of methyl and fluoro substituted silanes (CH/sub 3/)/sub n/F/sub 4-n/Si (n = 1-4) are reported for photon energy ranges extending from 1 to 2 eV above the respective parent thresholds. Adiabatic ionization potentials of 9.80 +- 0.03, 10.31 +- 0.04, 11.03 +- 0.03, and 12.48 +- 0.04 eV are determined for (CH/sub 3/)/sub 4/Si, (CH/sub 3/)/sub 3/SiF, (CH/sub 3/)/sub 2/SiF/sub 2/, and CH/sub 3/SiF/sub 3/, respectively, with appearance thresholds of 10.03 +- 0.04, 10.70 +- 0.04, 11.70 +- 0.03, and 13.33 +- 0.04 eV for siliconium ion fragments (CH/sub 3/)/sub 3/Si/sup +/, (CH/sub 3/)/sub 2/FSi/sup +/, (CH/sub 3/)F/sub 2/Si/sup +/, and F/sub 3/Si/sup +/ arising from CH/sub 3/ loss. These data are interpreted in terms of the thermochemistry of the various ionic and neutral silicon species. Derived heats of formation afford accurate calculation of fluoride affinities (heterolytic bond dissociation energies, D(R/sub 3/Si/sup +/--F/sup -/)) of 219.5, 237.3, 258.4, and 302.0 kcal/mol for the siliconium ions (CH/sub 3/)/sub 3/Si/sup +/, (CH/sub 3/)/sub 2/FSi/sup +/, (CH/sub 3/)F/sub 2/Si/sup +/, and F/sub 3/Si/sup +/, respectively. These values are 30 to 50 kcal/mol higher than themore » analogous carbonium ions.« less

Effects of alkyl and fluoroalkyl substitution on the heterolytic and homolytic bond dissociation energies of protonated amines

Effects of alkyl and fluoroalkyl substitution on the heterolytic and homolytic bond dissociation energies of protonated amines

Relative stabilities of carbonium ions in the gas phase and solution. Comparison of cyclic and acyclic alkylcarbonium ions, acyl cations and cyclic halonium ions

Carbonium ion stabilities were assessed by comparing their R-Br heterolytic bond dissociation energies. Preliminary data were tabulated for a series of carbonium ions using bromide affinities as reference. Heats of ionization of RBr in HSO/sub 3/F were obtained from the literature, and the heats of solvation for R/sup +/ + Br/sup +/ in HSO/sub 3/F were calculated and tabulated for the carbonium ions studied. The effect of solvation on relative carbonium ion stabilities can be estimated from the data. (DDA)

Hydration of CN−, NO2−, NO3−, and OH− in the Gas Phase

By measuring the A−(H2O)n−1 + H2O = A−(H2O)n equilibria in the gas phase and their temperature dependence, the equilibrium constants and ΔHn, n–1 and ΔSn, n–1 for some of the hydrates of NO2−, NO3−, CN−, and OH− were determined. Available thermochemical data are used for the evaluation of the total heats of hydration of the above ions. The total heats of hydration were then compared with the ΔH1,0. Relative to the total hydration energies the ΔH1,0 of the above ions were found larger than the ΔH1,0 of the halide ions.An approximate linear correlation was found to exist between ΔH1,0 of negative ions and the heterolytic bond dissociation energy D(A−–H+). With this relationship independent estimates for the electron affinities of NO2 and NO3 could be obtained.The ΔHn, n–1 of OH− were found in essential agreement with earlier measurements from this laboratory and in disagreements with recent measurements (Friedman) which gave much higher values.

Mass Spectrum, appearance potentials and bond dissociation energies of 1,1,1-trifluoroethane

The mass spectral cracking pattern of CH 3CF 3 and the appearance potentials of the ions CF 3 +, CH 3CF 2 +, CH 3CF 3 + have been determined. Heterolytic bond dissociation energies, D(R +F −), for the series CH 3CH 3-nF n ( n  1,2,3) and the C—C bond dissociation energy in CH 3CF 3 are reported, and the latter is discussed in relation to recent thermochemical and kinetic data.