J. Cieślak, J. Jankowska, M. Sobkowski, M. Wenska, J. Stawinski, A. Kraszewski
The reaction of nucleoside H-phosphonate monoesters with phenols in the presence of a condensing agent, followed by oxidation of the in-situ-generated aryl nucleoside H-phosphonate diesters with iodine–water or with elemental sulfur, provides a new, ‘one-pot’, efficient entry to nucleoside phosphate or nucleoside phosphorothioate diesters bearing diverse aryl moieties.
h -膦酸核苷单酯与苯酚在冷凝剂存在下的反应，随后用碘水或单质硫氧化原位生成的芳基h -膦酸核苷二酯，提供了一种新的，“一锅”，高效的进入磷酸核苷或硫代核苷二酯，含有不同的芳基部分。
{"title":"Aryl H-phosphonates. Part 13. A new, general entry to aryl nucleoside phosphate and aryl nucleoside phosphorothioate diesters","authors":"J. Cieślak, J. Jankowska, M. Sobkowski, M. Wenska, J. Stawinski, A. Kraszewski","doi":"10.1039/B109373H","DOIUrl":"https://doi.org/10.1039/B109373H","url":null,"abstract":"The reaction of nucleoside H-phosphonate monoesters with phenols in the presence of a condensing agent, followed by oxidation of the in-situ-generated aryl nucleoside H-phosphonate diesters with iodine–water or with elemental sulfur, provides a new, ‘one-pot’, efficient entry to nucleoside phosphate or nucleoside phosphorothioate diesters bearing diverse aryl moieties.","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"41 1","pages":"31-37"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74817878","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Banwell, K. Jolliffe, David T. J. Loong, K. Mcrae, Filisaty Vounatsos
The enantiomerically pure cis-1,2-dihydrocatechol 7, which is obtained by microbial oxidation of chlorobenzene, has been converted, via a sequence of reactions including ring-closing metathesis and Yamaguchi lactonisation steps, into the natural product (−)-cladospolide A (1).
{"title":"A chemoenzymatic synthesis of the 12-membered macrolide (−)-cladospolide A","authors":"M. Banwell, K. Jolliffe, David T. J. Loong, K. Mcrae, Filisaty Vounatsos","doi":"10.1039/B110018A","DOIUrl":"https://doi.org/10.1039/B110018A","url":null,"abstract":"The enantiomerically pure cis-1,2-dihydrocatechol 7, which is obtained by microbial oxidation of chlorobenzene, has been converted, via a sequence of reactions including ring-closing metathesis and Yamaguchi lactonisation steps, into the natural product (−)-cladospolide A (1).","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"95 1","pages":"22-25"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72887400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Moira Ambrosi, A. Batsanov, N. Cameron, B. G. Davis, J. Howard, R. Hunter
Methacrylate derivatives bearing β-D-glucopyranoside and β-D-galactopyranoside residues are synthesised by glycosylation of 2-hydroxyethyl methacrylate (HEMA) with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide and 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide, respectively. β-Selectivity in the glycosylation reactions is ensured by neighbouring-group participation of acetyl groups at O-2 in the glycosyl donors. 2-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucosyloxy)ethyl methacrylate (AcGlcEMA, 1a) was obtained as a crystalline solid and its crystal structure was determined by single-crystal X-ray diffraction. Deprotected polymers are synthesised in two parallel ways; either polymerisation of the protected monomers and subsequent deacetylation of the resulting polymers, or polymerisation of the previously deprotected monomers. The number- and weight-average relative molecular masses of both the protected and deprotected polymers are determined by size exclusion chromatography (SEC). Absolute molecular masses are obtained using the previously estimated refractive-index increments, dn/dc. It is found that polymerisation of deprotected monomers leads to polymers of well-defined composition, in contrast to the deacetylation of protected polymers.
采用2-羟乙基甲基丙烯酸酯(HEMA)与2,3,4,6-四- o -乙酰-α- d -葡萄糖吡喃基溴和2,3,4,6-四- o -乙酰-α- d -半乳糖吡喃基溴糖基化法制备了含有β- d -葡萄糖吡喃苷残基的甲基丙烯酸酯衍生物。糖基化反应中的β-选择性是通过糖基供体中O-2位置乙酰基的邻基参与来保证的。得到2-(2 '，3 '，4 '，6 ' -四- o -乙酰基-β- d -葡萄糖氧基)甲基丙烯酸乙酯(AcGlcEMA, 1a)为结晶固体，并通过单晶x射线衍射测定其晶体结构。去保护聚合物以两种平行的方式合成;受保护单体的聚合和随后产生的聚合物的去乙酰化，或先前去保护单体的聚合。采用尺寸排除色谱法测定了受保护和未受保护聚合物的相对分子质量。绝对分子质量由先前估计的折射率增量dn/dc得到。研究发现，与受保护的聚合物的去乙酰化相反，脱保护单体的聚合会产生具有明确组成的聚合物。
{"title":"Influence of preparation procedure on polymer composition: synthesis and characterisation of polymethacrylates bearing β-D-glucopyranoside and β-D-galactopyranoside residues","authors":"Moira Ambrosi, A. Batsanov, N. Cameron, B. G. Davis, J. Howard, R. Hunter","doi":"10.1039/B108421F","DOIUrl":"https://doi.org/10.1039/B108421F","url":null,"abstract":"Methacrylate derivatives bearing β-D-glucopyranoside and β-D-galactopyranoside residues are synthesised by glycosylation of 2-hydroxyethyl methacrylate (HEMA) with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide and 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide, respectively. β-Selectivity in the glycosylation reactions is ensured by neighbouring-group participation of acetyl groups at O-2 in the glycosyl donors. 2-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucosyloxy)ethyl methacrylate (AcGlcEMA, 1a) was obtained as a crystalline solid and its crystal structure was determined by single-crystal X-ray \u0000diffraction. Deprotected polymers are synthesised in two parallel ways; either polymerisation of the protected monomers and subsequent deacetylation of the resulting polymers, or polymerisation of the previously deprotected monomers. The number- and weight-average relative molecular masses of both the protected and deprotected polymers are determined by size exclusion chromatography (SEC). Absolute molecular masses are obtained using the previously estimated refractive-index increments, dn/dc. It is found that polymerisation of deprotected monomers leads to polymers of well-defined composition, in contrast to the deacetylation of protected polymers.","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"7 1","pages":"45-52"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82260553","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The rate constants of the oxidation of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPPD) are measured in water by means of stopped-flow techniques using different inorganic ions, like Fe(CN)63−, MnO4−, Co(NH3)63+, Ru(OH)3+6. The rates do not depend on the different oxidation potentials, but can be correlated well with calculated rate constants from the Marcus cross-relation. The electron self-exchange rates of the inorganic oxidants range over nine orders of magnitude. Measurements were performed at T = 293 K within a pH-range of 7–9.
{"title":"Application of Marcus cross-relation to mixed inorganic–organic redox couples. A stopped-flow study of the oxidation of N,N,N′,N′-tetramethyl-p-phenylenediamine with various oxidants","authors":"G. Grampp, S. Landgraf, D. Sabou, D. Dvoranová","doi":"10.1039/B104564B","DOIUrl":"https://doi.org/10.1039/B104564B","url":null,"abstract":"The rate constants of the oxidation of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPPD) are measured in water by means of stopped-flow techniques using different inorganic ions, like Fe(CN)63−, MnO4−, Co(NH3)63+, Ru(OH)3+6. The rates do not depend on the different oxidation potentials, but can be correlated well with calculated rate constants from the Marcus cross-relation. \u0000 The electron self-exchange rates of the inorganic oxidants range over nine orders of magnitude. Measurements were performed at T \u0000= 293 K within a pH-range of 7–9.","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"4 1","pages":"178-180"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86621255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Y. Kondo, H. Takezawa, T. Katsura, S. Nakanishi, Xinyu Chen
Rate constants and activation parameters for the reactions of the 2-nitrobenzoate and 2,6-dichlorobenzoate ions with ethyl iodide have been determined in acetonitrile–methanol mixtures. The activation parameters for the two reactions indicated different responses to solvent compositions. Single-ion enthalpies of transfer for the two anions have also been determined in the same solvent mixtures and on the basis of the results single-ion enthalpies of transfer for the transition-state anion for the two reactions have also been calculated and separated into their components. By empirical analysis of the transfer enthalpies due to the “more physical” interaction for the transition-state anion, ΔtHPHYSAN→MeOH (TS−), the approach of solvent molecules to the α-carbon atom and the central carbon atom in carboxylate group in the carboxylate ion, together with the number of partial dipoles in the anion, have been suggested to account for the various transfer enthalpies.
{"title":"Solvation and nucleophilic reactivity of 2-nitrobenzoate and of 2,6-dichlorobenzoate ions in acetonitrile–methanol mixtures","authors":"Y. Kondo, H. Takezawa, T. Katsura, S. Nakanishi, Xinyu Chen","doi":"10.1039/B108197G","DOIUrl":"https://doi.org/10.1039/B108197G","url":null,"abstract":"Rate constants and activation parameters for the reactions of the 2-nitrobenzoate and 2,6-dichlorobenzoate ions with ethyl iodide have been determined in acetonitrile–methanol mixtures. The activation parameters for the two reactions indicated different responses to solvent compositions. Single-ion enthalpies of transfer for the two anions have also been determined in the same solvent mixtures and on the basis of the results single-ion enthalpies of transfer for the transition-state anion for the two reactions have also been calculated and separated into their components. By empirical analysis of the transfer enthalpies due to the “more physical” interaction for the transition-state anion, ΔtHPHYSAN→MeOH (TS−), the approach of solvent molecules to the α-carbon atom and the central carbon atom in carboxylate group in the carboxylate ion, together with the number of partial dipoles in \u0000the anion, have been suggested to account for the various transfer enthalpies.","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"302 1","pages":"77-82"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87954854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semi-empirical calculations on 4-hydroxy-3-(3′,4′-methylenedioxyphenyl)-5,6,7-trimethoxycoumarin, a natural product recently isolated from Millettia griffoniana, show low rotational barriers for the C(3)–C(1′) bond (19.9 kJ mol−1) and for the inversion of the out-of-plane central 6-methoxy group (9.7 kJ mol−1). The structure of this compound is confirmed by its synthesis in 4 steps from 3,4,5-trimethoxyphenol in 37% overall yield, the key step being the ligand-coupling reaction of the 4-hydroxycoumarin 9 with 3,4-methylenedioxyphenyllead triacetate.
{"title":"On the optical activity of the 3-aryl-4-hydroxycoumarin isolated from Millettia griffoniana: molecular modelling and total synthesis","authors":"S. Combes, J. Finet, D. Siri","doi":"10.1039/B108707J","DOIUrl":"https://doi.org/10.1039/B108707J","url":null,"abstract":"Semi-empirical calculations on 4-hydroxy-3-(3′,4′-methylenedioxyphenyl)-5,6,7-trimethoxycoumarin, a natural product recently isolated from Millettia griffoniana, show low rotational barriers for the C(3)–C(1′) bond (19.9 kJ mol−1) and for the inversion of the out-of-plane central 6-methoxy group (9.7 kJ mol−1). The structure of this compound is confirmed by its synthesis in 4 steps from 3,4,5-trimethoxyphenol in 37% overall yield, the key step being the ligand-coupling reaction of the 4-hydroxycoumarin 9 with 3,4-methylenedioxyphenyllead triacetate.","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"58 1","pages":"38-44"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86816323","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
W. Bowman, Colin F. Bridge, P. Brookes, M. Cloonan, D. Leach
A novel cascade cyclisation protocol has been developed which ‘zips up’ two rings to form new tetracycles. In the protocol, treatment of vinyl bromides and iodides with hexamethylditin (Me3Sn˙) yields intermediate vinyl radicals which undergo 5-exo cyclisation onto nitrile groups to yield intermediate iminyl radicals. The iminyl radicals can undergo 6-endo cyclisation (or 5-exo followed by neophyl rearrangement) to yield tetracyclic π-radicals which lose hydrogen (H˙) in an H-abstraction step. Methyl radicals, generated from the breakdown of trimethylstannyl radicals (Me3Sn˙), are proposed as a possible H-abstractor for this final oxidative step. The protocol has been used to synthesise the tetracyclic rings A–D (tetracycle indolizino[1,2-b]quinolin-9(11H)-one) of the anticancer alkaloids camptothecin, mappicine, nothapodytine B and nothapodytine A. The protocol has also been applied to the synthesis of analogues of camptothecin in which ring A has been replaced by thiophene (8,10-dihydrothieno[2′,3′:5,6]pyrido[2,3-a]indolizin-8-one) and ring D by pyrrole (10H-pyrrolizino[1,2-b]quinoline) and benzene (11H-indeno[1,2-b]quinolin-11-one).
{"title":"Cascade radical synthesis of heteroarenes via iminyl radicals","authors":"W. Bowman, Colin F. Bridge, P. Brookes, M. Cloonan, D. Leach","doi":"10.1039/B108323F","DOIUrl":"https://doi.org/10.1039/B108323F","url":null,"abstract":"A novel cascade cyclisation protocol has been developed which ‘zips up’ two rings to form new tetracycles. In the protocol, treatment of vinyl bromides and iodides with hexamethylditin (Me3Sn˙) yields intermediate vinyl radicals which undergo 5-exo cyclisation onto nitrile groups to yield intermediate iminyl radicals. The iminyl radicals can undergo 6-endo cyclisation (or 5-exo followed by neophyl rearrangement) to yield tetracyclic π-radicals which lose hydrogen (H˙) in an H-abstraction step. Methyl radicals, generated from the breakdown of trimethylstannyl radicals (Me3Sn˙), are proposed as a possible H-abstractor for this final oxidative step. The protocol has been used to synthesise the tetracyclic rings A–D (tetracycle indolizino[1,2-b]quinolin-9(11H)-one) of the anticancer alkaloids camptothecin, mappicine, nothapodytine B and nothapodytine A. The protocol has also \u0000been applied to the synthesis of analogues of camptothecin in which ring A has been replaced by thiophene (8,10-dihydrothieno[2′,3′:5,6]pyrido[2,3-a]indolizin-8-one) and ring D by pyrrole (10H-pyrrolizino[1,2-b]quinoline) and benzene (11H-indeno[1,2-b]quinolin-11-one).","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"56 1","pages":"58-68"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79163649","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xian‐Wen Wei, A. G. Avent, O. Boltalina, J. M. Street, R. Taylor
Various pyrrolidinofullerenes (both mono- and bis-addition products) have been isolated from the reaction between toluene solutions of C60F18, N-methyl-2-aminoethanoic acid (sarcosine) and either formaldehyde or benzaldehyde. Both mono- and bis-addition products were obtained and either partially of fully characterised. The main mono-addition product from the reaction with formaldehyde was also obtained from reactions with the other aldehydes, indicating that formaldehyde may be present in sarcosine, or generated from it through in situ oxidation by the fullerene. The main mono-addition product from reaction of C60F18 with toluene solutions of sarcosine and benzaldehyde was obtained also in the absence of benzaldehyde. This anomaly was traced to the presence of benzaldehyde (0.05%) in HPLC grade toluene, which may be increased by oxidation of toluene during the reaction conditions.
从C60F18 - n -甲基-2-氨基乙醇酸(肌氨酸)的甲苯溶液与甲醛或苯甲醛反应中分离出多种吡咯烷二富勒烯(单加成和双加成产物)。得到了单加成产物和双加成产物，并进行了部分或完全表征。与甲醛反应的主要单加成产物也可以从与其他醛的反应中得到，这表明甲醛可能存在于肌氨酸中，或者由它通过富勒烯的原位氧化而产生。在不含苯甲醛的情况下，C60F18与肌氨酸和苯甲醛的甲苯溶液反应得到了主要的单加成产物。这种异常可以追溯到HPLC级甲苯中存在苯甲醛(0.05%)，这可能是由于反应条件下甲苯的氧化而增加的。
{"title":"Products from the reaction of C60F18 with sarcosine and aldehydes: the Prato reaction","authors":"Xian‐Wen Wei, A. G. Avent, O. Boltalina, J. M. Street, R. Taylor","doi":"10.1039/B106877F","DOIUrl":"https://doi.org/10.1039/B106877F","url":null,"abstract":"Various pyrrolidinofullerenes (both mono- and bis-addition products) have been isolated from the reaction between toluene solutions of C60F18, N-methyl-2-aminoethanoic acid (sarcosine) and either formaldehyde or benzaldehyde. Both mono- and bis-addition products were obtained and either partially of fully characterised. The main mono-addition product from the reaction with formaldehyde was also obtained from reactions with the other aldehydes, indicating that formaldehyde may be present in sarcosine, or generated from it through in situ oxidation by the fullerene. The main mono-addition product from reaction of C60F18 with toluene solutions of sarcosine and benzaldehyde was obtained also in the absence of benzaldehyde. This anomaly was traced to the presence of benzaldehyde (0.05%) in HPLC grade toluene, which may be increased by oxidation of toluene during the reaction conditions.","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"13 1","pages":"47-52"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88780623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tertiary (2-propyl)cyclopentyl and (2-propyl)cyclohexyl carbocations were investigated by 13C NMR spectroscopy in superacid solution. Both ions undergo fast nondegenerate 1,2-hydride shifts to the corresponding 2-cycloalkyl-2-propyl cations. The direction of these equilibria depends on the size of the ring. The more stable isomer of the (2-propyl)cyclopentyl cation has the formal positive charge at the endocyclic carbon atom, while the more stable isomer of the (2-propyl)cyclohexyl cation has the formal charge at the exocyclic carbon atom. The dynamic NMR results were confirmed by NMR spectroscopic measurement of the equilibrium isotope effects and rationalized by quantum chemical calculations.
{"title":"Nondegenerate equilibrium in (2-propyl)cycloalkyl cations. Comparison of (2-propyl)cyclopentyl and (2-propyl)cyclohexyl cation using 13C NMR spectroscopy, equilibrium isotope effects and quantum chemical calculations","authors":"H. Siehl, V. Vrek, O. Kronja","doi":"10.1039/B107756B","DOIUrl":"https://doi.org/10.1039/B107756B","url":null,"abstract":"Tertiary (2-propyl)cyclopentyl and (2-propyl)cyclohexyl carbocations were investigated by 13C NMR spectroscopy in superacid solution. Both ions undergo fast nondegenerate 1,2-hydride shifts to the corresponding 2-cycloalkyl-2-propyl cations. The direction of these equilibria depends on the size of the ring. The more stable isomer of the (2-propyl)cyclopentyl cation has the formal positive charge at the endocyclic carbon atom, while the more stable isomer of the (2-propyl)cyclohexyl cation has the formal charge at the exocyclic carbon atom. The dynamic NMR results were confirmed by NMR spectroscopic measurement of the equilibrium isotope effects and rationalized by quantum chemical calculations.","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"11 1","pages":"106-113"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88830808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A series of seven alkyl-substituted benzonitriles was investigated as a model for small steric effects (van der Waals tension) excluding any steric inhibition due to resonance. The energies were calculated at a B3LYP/6-311+G(d,p) level and the gas-phase basicities of some compounds were measured by Fourier-transform ion cyclotron resonance. Substituent effects were evaluated separately for neutral molecules and protonated forms by means of isodesmic reactions, and dissected into polar and steric effects by comparing ortho and para derivatives. One or two ortho methyl groups have a relatively small steric effect operating almost exclusively in the protonated form which leads to weakened basicity. An ortho tert-butyl group exerts a strong steric effect both in the protonated and nonprotonated forms, manifested also in a rather strong distortion of geometry. The effect on basicity is then a small difference of two large values and is base strengthening. Acid–base properties are in such cases a poor measure of substituent effects and cannot be interpreted in simple terms.
{"title":"Small steric effects in isolated molecules: alkyl-substituted benzonitriles","authors":"O. Exner, S. Böhm, M. Decouzon, J. Gal, P. Maria","doi":"10.1039/B104856M","DOIUrl":"https://doi.org/10.1039/B104856M","url":null,"abstract":"A series of seven alkyl-substituted benzonitriles was investigated as a model for small steric effects (van der Waals tension) excluding any steric inhibition due to resonance. The energies were calculated at a B3LYP/6-311+G(d,p) level and the gas-phase basicities of some compounds were measured by Fourier-transform ion cyclotron resonance. Substituent effects were evaluated separately for neutral molecules and protonated forms by means of isodesmic reactions, and dissected into polar and steric effects by comparing ortho and para derivatives. One or two ortho methyl groups have a relatively small steric effect operating almost exclusively in the protonated form which leads to weakened basicity. An ortho tert-butyl group exerts a strong steric effect both in the protonated and nonprotonated forms, manifested also in a rather strong distortion of geometry. The effect on basicity is then a small difference of two large values and is base strengthening. Acid–base properties are in such cases a poor measure of substituent effects and cannot be interpreted in simple terms.","PeriodicalId":17267,"journal":{"name":"Journal of The Chemical Society-perkin Transactions 1","volume":"19 1","pages":"168-172"},"PeriodicalIF":0.0,"publicationDate":"2002-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75324986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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