An effective fragment model is developed to treat solvent effects on chemical properties and reactions. The solvent, which might consist of discrete water molecules, protein, or other material, is treated explicitly using a model potential that incorporates electrostatics, polarization, and exchange repulsion effects. The solute, which one can most generally envision as including some number of solvent molecules as well, is treated in a fully ab initio manner, using an appropriate level of electronic structure theory. In addition to the fragment model itself, formulae are presented that permit the determination of analytic energy gradients and, therefore, numerically determined energy second derivatives (hessians) for the complete system. Initial tests of the model for the water dimer and water-formamide are in good agreement with fully ab initio calculations.

AbstractThe nitrogen centers of pyridine, quinoline, pyrrole anion, carbazole anion, and acetonitrile possess, in each case, two energetically non‐equivalent electron pairs: one, a non‐bonding orbital, lies in the molecular plane or on the bond axis; the other is part of a π‐type orbital, and is perpendicular to the molecular plane or the bond axis. Simple molecular orbital considerations predict that the π‐type orbital will always be the higher lying and, therefore, the preferred donor orbital in a HOMO‐LUMO controlled frontier molecular orbital interaction with the HOMO and LUMO of an electrophilic reagent. This stereoelectronic effect seems to have been observed experimentally in the case of carbazole anion, but not in the cases of quinoline or acetonitrile (present work). The reasons for the different behavior of these nucleophiles have been analyzed using the semi‐empirical procedure AMI. It is pointed out that the lower lying non‐bonding orbital can control the stereochemical course of the reaction when HOMO‐HOMO interactions dominate. This will occur when the non‐equivalent electron pairs of the nucleophile lie close to the HOMO of the electrophilic reagent, as is the case in the reactions of pyridine, quinoline, and acetonitrile with methyl choride or trimethyloxonium cation. Transition structures for N‐methylation of acetonitrile and pyrrole anion have been located and are, respectively, linear and planar. However, a 45° bend of the pyrrole transition structure leads to only a 29‐fold rate retardation at 25°C, compared to the 300‐fold retardation calculated for acetonitrile.

AbstractThe bicyclobutane radical cation (I) is studied by ab initio UHF/SCF at the 3‐21G level (α = 115°‐180°).

AbstractThe carbonitriles (Ia) and (Ib) exhibit 100% syn stereospecific addition across the central bond (linear Hammett correlation with σ+).

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCoupling of internal motions in bicyclobutane radical cation. The effect of a positive charge on a radical centerShmaryahu Hoz, Harold Basch, and Drora CohenCite this: J. Am. Chem. Soc. 1987, 109, 22, 6891–6892Publication Date (Print):October 1, 1987Publication History Published online1 May 2002Published inissue 1 October 1987https://doi.org/10.1021/ja00256a074Request reuse permissionsArticle Views54Altmetric-Citations9LEARN 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 (283 KB) Get e-Alertsclose Get e-Alerts

The novel [4,4]-sigmahaptotropic rearrangement II → IV, in which a σ-bonded group and a Fe(CO)3 unit exchange bonding sites antarafacially across a four carbon skeleton, has been shown by kinetic data to involve a concerted, non-synchronous, one step process. First order rate constants for the rearrangement at 23°C are k 1.25 × 10−6 s−1 (acetone) and k 2.2 × 10−5 s−1 (methanol), with activation parameters ΔH# 21 kcal mol−1 and ΔS# −15 e.u. (acetone). The moderate value of the ratio of k in methanol to that in acetone, viz. 18, indicates that although a minor charge separation develops upon activation, no intermediate is formed. The least motion pathway mechanism is shown to involve a Berry pseudorotation about the metal, which maintains the bonding interaction between the metal and the organic fragment orbitals during the rearrangement. Topologically this rearrangement corresponds to a [σ2a + (σ2s + π2a)] thermally allowed pericyclic reaction. The structure of the rearranged complex IV was determined by single-crystal X-ray diffraction.

Chemischer InformationsdienstVolume 17, Issue 27 Physical Organic Chemistry ChemInform Abstract: Binding of Pt(NH3)32+ to Nucleic Acid Bases H. BASCH, H. BASCHSearch for more papers by this authorM. KRAUSS, M. KRAUSSSearch for more papers by this authorW. J. STEVENS, W. J. STEVENSSearch for more papers by this authorD. COHEN, D. COHENSearch for more papers by this author H. BASCH, H. BASCHSearch for more papers by this authorM. KRAUSS, M. KRAUSSSearch for more papers by this authorW. J. STEVENS, W. J. STEVENSSearch for more papers by this authorD. COHEN, D. COHENSearch for more papers by this author First published: July 8, 1986 https://doi.org/10.1002/chin.198627066Read the full textAboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue27July 8, 1986 RelatedInformation

Chemischer InformationsdienstVolume 17, Issue 4 Physical Inorganic Chemistry ChemInform Abstract: Electronic and Geometrie Structures of Pt(NH3)22+, Pt(NH3)2Cl2, Pt(NH3)3X, and Pt(NH3)2XY (X, Y: H2O, OH-) H. BASCH, H. BASCHSearch for more papers by this authorM. KRAUSS, M. KRAUSSSearch for more papers by this authorW. J. STEVENS, W. J. STEVENSSearch for more papers by this authorD. COHEN, D. COHENSearch for more papers by this author H. BASCH, H. BASCHSearch for more papers by this authorM. KRAUSS, M. KRAUSSSearch for more papers by this authorW. J. STEVENS, W. J. STEVENSSearch for more papers by this authorD. COHEN, D. COHENSearch for more papers by this author First published: January 28, 1986 https://doi.org/10.1002/chin.198604001AboutPDF 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. Volume17, Issue4January 28, 1986 RelatedInformation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCyclobutane-bicyclobutane system. 11. Mechanism and stereochemistry of general acid-catalyzed additions to bicyclobutaneShmaryahu Hoz, Mordechai Livneh, and Drora CohenCite this: J. Org. Chem. 1986, 51, 24, 4537–4544Publication Date (Print):November 1, 1986Publication History Published online1 May 2002Published inissue 1 November 1986https://pubs.acs.org/doi/10.1021/jo00374a009https://doi.org/10.1021/jo00374a009research-articleACS PublicationsRequest reuse permissionsArticle Views421Altmetric-Citations21LEARN 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 InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNucleophilic vinylic substitution. A theoretical studyDrora. Cohen, Rony. Bar, and Sason S. ShaikCite this: J. Am. Chem. Soc. 1986, 108, 2, 231–240Publication Date (Print):January 1, 1986Publication History Published online1 May 2002Published inissue 1 January 1986https://doi.org/10.1021/ja00262a008Request reuse permissionsArticle Views160Altmetric-Citations33LEARN 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 (1 MB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The cycloaddition reactions of (carbomethoxy)maleic anhydride (CMA) with (η4-cycloheptatriene)Fe(CO)3 and with uncoordinated cycloheptatriene were investigated. Both reactions are highly stereospecific and give single Diels-Alder adducts. The structure of the metal-bonded adduct X was determined by single-crystal X-ray diffraction. A full analysis of the 1H and 13C NMR spectra of X is described. The corresponding uncomplexed adduct XI was obtained by Diels-Alder reaction of CMA with norcaradiene. The unusual Diels-Alder periselectivity and the stereochemical consequences of the 4 + 2 cycloaddition to X are best rationalized in terms of a concerted reaction controlled by secondary orbital interactions in the transition state.

The reaction of tricarbonyl(tropone)iron with tetracyanoethylene (TCNE) was reinvestigated. Two primary cycloadducts, the 3 + 2 and 4 + 2 isomers are formed in a 96/4 ratio. The second order rate constant for the reaction is k 4.4 × 10−2 M−1 s−1 (at 24°C, in acetone) with a free activation energy of ΔG# 19.2 kcal mol−1 The 3 + 2 cycloadduct undergoes a facile sigmahaptotropic rearrangement to the formal 5 + 2 adduct with rate constants of k 3.8 × 10−10 s−1 (24°C, acetone) and k 5.1 × 10−4 s−1 (24°C, methanol), and with activation parameters ΔH# 20 kcal mol−1 and ΔS# −7 e.u. (acetone). The kinetic results suggest that both the cycloaddition and the rearrangment are concerted, nonsynchronous, one-step reactions, involving a slightly polar transition state. Frontier molecular orbital considerations imply that the 3 + 2 and 4 + 2 cycloadditions are symmetry allowed reactions. The structural reorganization which takes place in the [3,3]-sigmahaptotropic rearrangement suggests that the metal migration proceeds by way of a Berry pseudorotation, and the simultaneous 1,3-sigmatropic shift occurs with configuration retention at the migrating carbon. A detailed molecular orbital analysis of the rearrangement is given.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe .pi. nucleophilicity: the effect of charge delocalization on the efficiency of internal displacements in ElcB reactionsShmaryahu Hoz, Zeev Gross, and D. CohenCite this: J. Org. Chem. 1985, 50, 6, 832–836Publication Date (Print):March 1, 1985Publication History Published online1 May 2002Published inissue 1 March 1985https://pubs.acs.org/doi/10.1021/jo00206a022https://doi.org/10.1021/jo00206a022research-articleACS PublicationsRequest reuse permissionsArticle Views87Altmetric-Citations12LEARN 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 InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

The cycloaddition of ketenes R1R2CCO (R1 = Me, R2 = Ph; R1 = R2 = Ph; R1 = Ph, R2 = p-tolyl) (III) and tricarbonyl(η4-cycloheptatriene)iron (II) at room temperature gave regiospecifically the cyclobutanones IV, in which the carbonyl is bonded to the uncoordinated terminal of the conjugated triene. Tricarbonyl(η4-cyclooctatetraene)iron, VI, similarly reacts with dipenylketene to give the regioisomeric cyclobutanone VIII. Single crystal X-ray analysis of tricarbonyl[(η-2,3,4,5)-9-methyl-9-phenylbicyclo[5.2.0]nonan-2,4-dien-8-one]iron (IVa) confirmed the presence of the phenyl group at the endo position, providing a stereochemical evidence for a concerted 2s + 2a cycloaddition mechanism. The adducts IV undergo cyclobutanone ring cleavage catalyzed by acid to give the isomeric ketones VII. The diaryl adducts (IVb and IVc) rearrange thermally to the σ,π-allylic complexes IX, which may also be obtained directly upon heating cycloheptatriene complex II and the diarylketenes.

The equilibrium geometry of ground state HO−2 (1A′) has been determined by an ab initio multiconfiguration self-consistent field gradient optimization method using 14 active space molecular orbitals in a double zeta+polarization+(two different) diffuse Gaussian function basis sets. The calculated geometry is R(O–O)=1.498 Å, R(O–H)=0.962 Å, and ∠HOO=99.8°. For comparison purposes, parallel results were also obtained for the ground states of O, O−, O2, O−2 , and HO2. For a given basis set the calculated adiabatic electron affinities of O, O2, and HO2 are all found to differ by a constant value ±0.05 eV relative to their respective experimental values, suggesting that the errors in the molecular cases are essentially atomic in nature.

Chemischer InformationsdienstVolume 14, Issue 28 Physical Organic Chemistry ChemInform Abstract: EXCITED ELECTRONIC STATES OF OPTICALLY ACTIVE SUBSTITUTED ETHYLENE OXIDES: (-)-(S)-2-METHYLOXIRANE AND (-)-(S,S)-2,3-DIMETHYLOXIRANE D. COHEN, D. COHENSearch for more papers by this authorM. LEVI, M. LEVISearch for more papers by this authorH. BASCH, H. BASCHSearch for more papers by this authorA. GEDANKEN, A. GEDANKENSearch for more papers by this author D. COHEN, D. COHENSearch for more papers by this authorM. LEVI, M. LEVISearch for more papers by this authorH. BASCH, H. BASCHSearch for more papers by this authorA. GEDANKEN, A. GEDANKENSearch for more papers by this author First published: July 12, 1983 https://doi.org/10.1002/chin.198328054AboutPDF 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. Volume14, Issue28July 12, 1983 RelatedInformation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEthylene and acetylene complexes of the silver atomDrora Cohen and Harold BaschCite this: J. Am. Chem. Soc. 1983, 105, 23, 6980–6982Publication Date (Print):November 1, 1983Publication History Published online1 May 2002Published inissue 1 November 1983https://pubs.acs.org/doi/10.1021/ja00361a050https://doi.org/10.1021/ja00361a050research-articleACS PublicationsRequest reuse permissionsArticle Views71Altmetric-Citations15LEARN 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 InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts