Captodative Substitution Research Articles

Conformation of C‐1‐Substituted Pyranos‐1‐yl and Pyranosan‐5‐yl Radicals Evidence for a Quasi‐Homo‐Anomeric Stabilization Effect

Acetylated 1‐cyano‐ and 1‐chloro‐pyranos‐1‐yl radicals and 5‐acetoxycarbonyl‐, 5‐methoxycarbonyl‐, and 5‐unsubstituted pyranosan‐5‐yl radicals were generated from the corresponding bromides by bromine abstraction with trimethyltin radicals. The conformation of these radicals, as deduced from the ESR hyperfine splittings, is explained by the combined action of a quasi‐anomeric and a homo‐anomeric stabilization effect. A captodative substitution pattern of the radical center does not influence the conformations.

Substituent effects on the strength of single bonds and in free-radical chemistry

The C-X and C-C bond dissociation energies of organic compounds can be explained in terms of the stabilization energies of these species and the corresponding radical (s). The lowest C-H bond strengths correspond to the so-called captodative radicals due to their relatively large stabilization energy. These species being most commonly transient, dehydrodimerization reactions are generally favoured by captodative substitution. On the other hand, the lowest C-C bond strengths correspond to species highly destabilized by steric strain or polar interactions. However, in many cases, the stabilization energy of the corresponding radicals plays also an important role in the thermal stability of substituted (cyclo)alkanes.

ChemInform Abstract: Captodative Substitution and Cyclopropane Geometry. Part 5. X‐Ray Structure of Five New Compounds (I) and Asymmetry Parameters of the Substituents

ChemInformVolume 19, Issue 41 Physical Organic Chemistry ChemInform Abstract: Captodative Substitution and Cyclopropane Geometry. Part 5. X-Ray Structure of Five New Compounds (I) and Asymmetry Parameters of the Substituents B. TINANT, B. TINANT Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorS. WU, S. WU Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorJ.-P. DECLERCQ, J.-P. DECLERCQ Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorM. VAN MEERSSCHE, M. VAN MEERSSCHE Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorW. MASAMBA, W. MASAMBA Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorA. DE MESMAEKER, A. DE MESMAEKER Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorH. G. VIEHE, H. G. VIEHE Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this author B. TINANT, B. TINANT Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorS. WU, S. WU Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorJ.-P. DECLERCQ, J.-P. DECLERCQ Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorM. VAN MEERSSCHE, M. VAN MEERSSCHE Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorW. MASAMBA, W. MASAMBA Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorA. DE MESMAEKER, A. DE MESMAEKER Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this authorH. G. VIEHE, H. G. VIEHE Lab. Chim. Phys. Cristallogr., Univ. Cathol. Louvain, B-1348 Louvain-la-Neuve, Belg.Search for more papers by this author First published: October 11, 1988 https://doi.org/10.1002/chin.198841060Read 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 onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue41October 11, 1988 RelatedInformation

ChemInform Abstract: Thermal Reactions of Donor‐Acceptor Systems. Part 3. Captodative Olefins in Normal and Inverse Diels‐Alder Reactions.

AbstractAlkenes with captodative substitution such as (I) may act as dienophiles in Diels‐Alder reactions with normal and inverse electron demand.

Captodative olefins in normal and inverseDiels‐AlderReactions

AbstractOlefins with captodative substitution are reactive dienophiles inDiels‐Alderreactions with normal and inverse electron demand. This is shown for reactions of 2‐(tert‐butylthio)acrylonitrile (1) with various dienes and heterodienes,e.g.1,3‐cyclohexadiene, hexachloro‐1, 3‐cyclopentadiene, acrolein, methacrolein, and methyl vinyl ketone (Schemes 2and3). In case of the hetrodienes, 3,4‐dihydro‐2H‐pyrans are formed beside small amounts of tetrahydrothiophenes; however, with methyl vinyl ketone, both reaction pathways are equally followed. The high reactivity of captodative olefins inDiels‐Alderreactions are rationalized on the basis ofSustmann's FMO model under consideration of Viehe's concept of captodative substitution of alkenes.

ChemInform Abstract: Hydrogen Abstraction from Primary Amines. Substituent Effects on the Carbon‐Nitrogen Bond Rotation Barriers in Aminoalkyl Radicals

Hydrogen abstraction by t-butoxyl radicals from primary amines RCH2NH2(R = H, Me, Et, Pri, or But) gave mainly α-aminoalkyl radicals which were observed by e.s.r. spectroscopy. The barriers to rotation about the C–N bonds were determined from exchange broadening. For 2-fluoro- and 2-chloro-ethylamine the initial α-aminoalkyl radical lost hydrogen halide to give a mixture of syn- and anti-1-aza-allyl radicals. In contrast, the 1-amino-2,2,2-trifluoroethyl radical was stable under the same experimental conditions. The α-amino radicals formed on hydrogen abstraction from the methyl and t-butyl esters of glycine and the t-butyl ester of alanine were also examined. The stabilisation energy of the α-aminomethyl radical was estimated from the C–N bond rotation barriers of the aminoalkyl radicals. The pattern of stabilisation was found to be consistent with an extra stabilisation in radicals with captodative substitution.

Captodative substitution and cyclopropane geometry. Part 5. X-Ray structure of five new compounds and asymmetry parameters of the substituents

Five new captodative (cd) substituted cyclopropanes have been synthesized and their structures determined from X-ray diffraction data. These are cis-1,2-dicyano-1,2-dimethyl-(1), trans-1,2-dicyano-1,2-bisethoxycarbonyl-(2), cis-1,2-dicyano-1,2-dimethoxy-(3), trans-1,2-dicyano-1,2-bismethylthio-(4), and trans-1,2-dicyano-1,2-bis(dimethylamino)-cyclopropane (5). These structures have been solved by direct methods and refined by least-squares using 865, 1 332, 766, 1 075, and 1 341 reflections respectively, to R 0.062, 0.041, 0.044, 0.031, and 0.049. This work completes former results and permits the discussion of the influence of polar substituents on cyclopropane geometry in relation to their reported ease of cis–trans isomerization. The effect on ring bond lengths is small but significant: in both captodative and dicapto-substitution, the distal ring bond is shortened and vicinal bonds are lengthened. Mean distal-bond shortenings are proposed for SR, OR, and NR2; the values calculated for C=N, C=O, and phenyl agree with published data. The particular facile isomerization of cd cyclopropanes appears best explained, not as the consequence of a destabilized ground state but rather as increased spin delocalization in the transition state.

Captodative substitution and cyclopropane geometry. VI. Structure of dimethyl cis-1,2-bis(phenylthio)-1,2-cyclopropanedicarboxylate

Captodative substitution and cyclopropane geometry. VI. Structure of dimethyl cis-1,2-bis(phenylthio)-1,2-cyclopropanedicarboxylate

ChemInform Abstract: Captodative Substituent Effects. Part 26. Allylic Radicals with Captodative Substitution: Easy Homolysis of 1,5‐Hexadienes.

AbstractThe equilibration of allyl radicals such as (I) with captodative substitution and their 1,5‐hexadiene dimers such as (II) is investigated.

Electron delocalisation and stabilisation in substituted amino- and hydroxypropynyl radicals

A series of aminopropynes, RCCCH2NH2(R = H, Me, But, Me3Si), RCCCH2N(SiMe3)2, and hydroxypropynes RCCCH2OH (R = H, Me, But, Me3Si, CF3, and EtO2C), were prepared and the corresponding α-aminopropynyl and α-hydroxypropynyl radicals were examined by e.s.r. spectroscopy. For the first series, the C–N bond rotation barriers were determined from the exchange broadening in the spectra and hence radical stabilisation energies were estimated. The spin distribution in these series indicated an extra delocalisation in radicals with captodative substitution.

Hydrogen abstraction from primary amines. Substituent effects on the carbon–nitrogen bond rotation barriers in aminoalkyl radicals

Hydrogen abstraction by t-butoxyl radicals from primary amines RCH2NH2(R = H, Me, Et, Pri, or But) gave mainly α-aminoalkyl radicals which were observed by e.s.r. spectroscopy. The barriers to rotation about the C–N bonds were determined from exchange broadening. For 2-fluoro- and 2-chloro-ethylamine the initial α-aminoalkyl radical lost hydrogen halide to give a mixture of syn- and anti-1-aza-allyl radicals. In contrast, the 1-amino-2,2,2-trifluoroethyl radical was stable under the same experimental conditions. The α-amino radicals formed on hydrogen abstraction from the methyl and t-butyl esters of glycine and the t-butyl ester of alanine were also examined. The stabilisation energy of the α-aminomethyl radical was estimated from the C–N bond rotation barriers of the aminoalkyl radicals. The pattern of stabilisation was found to be consistent with an extra stabilisation in radicals with captodative substitution.

ChemInform Abstract: Effects of the Captodative Substitution. Part 34. Dienophilic Properties of Captodative Olefins: Diels‐Alder Cycloadditions of α‐Methylthio‐acrylonitrile and Transformation of the Adducts.

AbstractCycloaddition reactions of the title compound (V) with the dienes (I)‐(IV) yields the adducts indicated in the scheme.

ChemInform Abstract: Effects of the Captodative Substitution. Part 33. Dienophilic Properties of Captodative Olefins: Influence of the Steric Dimensions of α‐Alkylthioacrylonitriles on the Stereoselectivity of Diels‐Alder Reactions.

AbstractThe cycloaddition of cyclopentadiene (I) with the nitriles (II) occurs spontaneously to give mixtures of the adducts (III) and (IV).

Allylic radicals with captodative substitution : Easy homolysis of 1,5-hexadienes.

Dissociation of the new 1,3,4,6-captodative substituted 1,5-hexadienes 1 to 1,3-bis-captodative allylic radicals 4 has been observed around room temperature. Dissociation enthalpies ΔH vary from 8 to 25 Kcal/mol. In contrast the dimer 3a of the 1,3-bis-dicapto allylic tetraester radical dissociates to 6a only around 140°C (ΔH = 38.1 Kcal/mol). The replacement of one of the olefinic ester groups on carbons 1 and 6 in 3a by a donor substituent (without influencing the crowding around the central C-C bond), such as in 2a and b lowers ΔH from 38.1 to 24.0 and 28.2 Kcal/mol respectively. These results demonstrate the synergy for radical stabilisation by captodative substitution.

ChemInform Abstract: CAPTO‐DATIVE SUBSTITUTION AND CYCLOPROPANE GEOMETRY. PART 1. COMPARISON BETWEEN CAPTO‐DATIVE AND DI‐CAPTO SUBSTITUTION EFFECTS ON CYCLOPROPANE GEOMETRY; AN X‐RAY DIFFRACTION STUDY

Chemischer InformationsdienstVolume 16, Issue 33 Physical Organic Chemistry ChemInform Abstract: CAPTO-DATIVE SUBSTITUTION AND CYCLOPROPANE GEOMETRY. PART 1. COMPARISON BETWEEN CAPTO-DATIVE AND DI-CAPTO SUBSTITUTION EFFECTS ON CYCLOPROPANE GEOMETRY; AN X-RAY DIFFRACTION STUDY B. TINANT, B. TINANTSearch for more papers by this authorS. WU, S. WUSearch for more papers by this authorJ. P. DECLERCQ, J. P. DECLERCQSearch for more papers by this authorM. VAN MEERSSCHE, M. VAN MEERSSCHESearch for more papers by this authorA. DE MESMAEKER, A. DE MESMAEKERSearch for more papers by this authorW. MASAMBA, W. MASAMBASearch for more papers by this authorR. MERENYI, R. MERENYISearch for more papers by this authorH. G. VIEHE, H. G. VIEHESearch for more papers by this author B. TINANT, B. TINANTSearch for more papers by this authorS. WU, S. WUSearch for more papers by this authorJ. P. DECLERCQ, J. P. DECLERCQSearch for more papers by this authorM. VAN MEERSSCHE, M. VAN MEERSSCHESearch for more papers by this authorA. DE MESMAEKER, A. DE MESMAEKERSearch for more papers by this authorW. MASAMBA, W. MASAMBASearch for more papers by this authorR. MERENYI, R. MERENYISearch for more papers by this authorH. G. VIEHE, H. G. VIEHESearch for more papers by this author First published: August 20, 1985 https://doi.org/10.1002/chin.198533059AboutPDF 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. Volume16, Issue33August 20, 1985 RelatedInformation

ChemInform Abstract: CAPTO‐DATIVE SUBSTITUTION AND CYCLOPROPANE GEOMETRY. PART 2. X‐RAY STRUCTURE OF CIS‐1,2‐DICYANO‐1,2‐BIS(PHENYLTHIO)CYCLOPROPANE, C17H12N2S2

Chemischer InformationsdienstVolume 16, Issue 33 Physical Organic Chemistry ChemInform Abstract: CAPTO-DATIVE SUBSTITUTION AND CYCLOPROPANE GEOMETRY. PART 2. X-RAY STRUCTURE OF CIS-1,2-DICYANO-1,2-BIS(PHENYLTHIO)CYCLOPROPANE, C17H12N2S2 B. TINANT, B. TINANTSearch for more papers by this authorJ. P. DECLERCQ, J. P. DECLERCQSearch for more papers by this authorM. VAN MEERSSCHE, M. VAN MEERSSCHESearch for more papers by this author B. TINANT, B. TINANTSearch for more papers by this authorJ. P. DECLERCQ, J. P. DECLERCQSearch for more papers by this authorM. VAN MEERSSCHE, M. VAN MEERSSCHESearch for more papers by this author First published: August 20, 1985 https://doi.org/10.1002/chin.198533060Read 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. Volume16, Issue33August 20, 1985 RelatedInformation

Capto-dative substitution and cyclopropane geometry. Part 1. Comparison between capto-dative and di-capto substitution effects on cyclopropane geometry; an X-ray diffraction study

To study capto-dative (cd) and di-capto (cc′) substitution effects on cyclopropane geometry the crystal and molecular structures of the following three cyclopropane derivatives have been determined from X-ray diffraction data: 2-t-butylthio-1-r,2-t-dicyano-1-methoxycarbonylcyclopropane(I); 2-t-butylthio-1-r, 2-t-dicyano-1-phenylthiocyclopropane (II); and 2-t-butylthio-1-r,2-t-dicyano-1-phenylcyclo-propane (III). These structures have been solved by direct methods and refined by least-squares using 1 572, 3 729, and 1 768 reflections, respectively, to R= 4.7, 6.4, and 4.0%. In both capto-dative. and di-capto substitution, the distal ring bond is shortened, but the vicinal bonds are lengthened. Although a long C(1)–C(2) ring bond is observed in each compound, this bond is the most stretched one in molecule (I) for which the highest activation energy of thermal cis–trans isomerisation was determined.

Captodative substituent effects — Part XXXI olefins with captodative substitution in [2+2] cycloadditions

Olefins with captodative substitution are excellent partners in [2+2] cycloadditions leading to cyclobutane derivatives. The reaction rates increase with the radical stabilising power of the substituents. Thio- and selenoalkyl(aryl) substituted gemdifluoroolefins allow the synthesis of new cyclobutane derivatives.

Couplage okydatif facile d'anions substitues captodativement

Carbanions carrying captodative substitution are readily oxidized to their dimers.

The capto-dative substituent effect on benzylic radicals ESR hyperfine splittings. An evaluation of the extra stabilization based upon spin delocalization

Appropriate hyperfine splittings in ESR spectra of disubstituted (cyano/methoxy) benzylic radicals were compared with the corresponding values of monosubstituted ones. On the basis of the dependence of radical stabilization on spin delocalization, it is concluded that captodative substitution implies a synergetic substituent effect on radical stabilization. On the contrary, an antagonistic effect is observed in the case of two identical substituents.