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1.
The solvolysis rates and products of the 6endo-R-substituted 2endo-norbornyl toluenesulfonates 6a – 6i have been determined. The rates of 6a – 6g correlate with the inductive constants σ the 6endo-substituents and are not related to the size of the latter. It is therefore concluded that polar rather than steric effects control the exo/endo-rate ratios of norbornyl sulfonates. Products are derived mainly from rearranged 6exo-R-norbornyl cations when the substituent is an electron donor and from unrearranged 6endo-R-substituted cations when the substituent is an electron acceptor. 相似文献
2.
The solvolysis rates and products of several 7-anti-substituted 2-endo-norbornyl p-toluenesulfonates 11 have been determined and compared with those of the previously reported 6-exo-substituted 2-exo-norbornyl p-toluenesulfonates 1. Although the number of bonds between the substituent and the reaction site is the same in the two series, the inductive effect of the substitutents is transmitted far more strongly in the 6-exo-2-exo-series 1 than in the 7-anti-2-endo-series 11 ; i.e. their inductivities differ widely. It is concluded that through space induction involves graded bridging of the substituent-bearing C-atom to the incipient cationic center at C(2) and that this involves differential bridging strain. The different reactivities of unsubstituted 2-exo- and 2-endo-norbornyl derivatives can then be ascribed to a stereoelectronic effect. 相似文献
3.
The Synthesis and Hydrolysis of 6-exo-Substituted 2-Methyl-2-exo-norbornyl and 2-Methyl-2-endo-norbornyl 2,4-Dinitrophenyl Ethers The synthesis of the title compounds and their hydrolysis products in aqueous dioxane are described. Upon hydrolysis, the 2-exo-ethers 1 (X=N2phO) as well as the 2-endo-ethers 2 (X=N2phO) yield the corresponding 2-methyl-2-exo-norbornanols 3 only. Therefore, the 2-exo-ethers react with retention of configuration at C(2), the 2-endo-ethers 2 with inversion at C(2). 相似文献
4.
The solvolysis rates and products of several 1-substituted 2exo- and 2-endo-norbornyl p-toluenesulfonates 7 and 8 , respectively, have been determined. Hydrolyses of these epimeric tosylates yielded rearranged products in varying amounts, except when the substituent was COOCH3 or CN. The logarithms of the rate constants (log k) for the endo-series 8 correlated linearly with the corresponding inductive constants σ with a reaction constant ρI of ?1.24. On the other hand, log k values for the exo-series 7 appear to fit two regression lines, the first line (ρI = ?1.90) defined by the tosylates that ionize, with rearrangement, to the tertiary cations 11 , the second (ρI = ?1.86) by the tosylates 7 (R = H, COOCH3, and CN) that ionize to an asymmetrically bridged secondary cation 19 . These results confirm the unique participation of C(6) with a ρI of ?2.00 in the ionization of 2-exo-nor-bornyl tosylate. 相似文献
5.
Walter Fischer Cyril A. Grob Georg Von Sprecher Adrian Waldner 《Helvetica chimica acta》1980,63(4):928-937
The Hydrolysis of 6 exo -Substituted 2 exo - and 2 endo -Norbornyl p -Toluenesulfonates. Norbornane Series. Part 3 Hydrolysis of the 6exo-substituted 2exo- and 2endo-norbornyl p-toluenesulfonates 1b - 1 and 2b - 1 , respectively, in 70% dioxane led to different amounts of the following products: Unrearranged 2exo-norbornanols 3 and norbornenes 5 , accompanied in somes cases by small amounts of the rearranged Rendo-epimers 4 and 6 and by norticyclenes 7 . When the 6exo-substituent was a nucleophilic group as in 1e - 1 and 2e - 1 , various amounts of tricyclic products were also formed by endo-cyclization. These results show that the 2exo- and 2endo-esters 1 and 2 , respectively, react by way of different intermediates. In cases where the 6exo-substituent was an n-electron donor, as in 1m - r and 2m - r , quantitative fragmentation to (3-cyclopentenyl)acetaldehyde (13) occurred. 相似文献
6.
‘Bare’ FeO+ reacts in the gas phase with norbornane with collision efficiency, and the most prominent cationic products correspond to [FeC5H6]+ (32%), [FeC7H8]+ (19%), [FeC3H6O]+ (19%) and [FeC6H6]+ (14%), which are structurally characterized by ligand exchange as well as collision-induced dissociation experiments. Circumstantial evidence is provided which indicates that the complexes [FeC5H6]+, [FeC7H8]+, and [FeC6H6]+ originate from an Fe(norbornene)+ intermediate which itself is formed by elimination of H2O from the [FeO(norbornane)]+ encounter complex. Although the reactions are preceded and/or accompanied by partial H/D exchange, the isotope distribution in the productions clearly points to a preferential endo-attack of bare FeO+, with an endo/exo-ratio of ca. 10.3 and kinetic isotope effects kH/kD for the endo-abstraction of 2.4 and of 7.7 for approaching an exo-C? H bond. The preferred endo-approach of bicyclo[2.2.1]heptane by ‘bare’ FeO+ is in distinct contrast to the P-450-mediated or the iron(III)porphyrin-catalyzed hydroxylation of this substrate which favor reactions at the exo-face. 相似文献
7.
γ, δ-Unsaturated diazoketones undergo acid catalysed hydrolysis accompanied by cyclisation; the latter is favoured by suitable geometry (cyclopentenes) and by substitution by methyl groups. If both are present, rate enhancement by anchimeric assistance has been observed. Hydrolysis of 4-diazoacetyl-cyclopentene ( 1 ) yields a product mixture similar to that formed during solvolysis of 5-oxo-norbornyl-2-endo brosylate (23) and quite different from that of the exo isomer. The results are interpreted in terms of a common intermediate, the 5-oxo-2-norbornyl carbonium ion. Solvent participation in the transition state, i. e. partial SN 2 character, is implied by the entropies of activation and by the action of an added nucleophile (Br?). In superstrong acids, a different type of cyclisation takes place, involving the carbonyl oxygen and the protonated C? C double bond and forming tetrahydropyrane derivatives. 相似文献
8.
The reactions of 2exo- and 2endo-norbornyl bromide ( 1e and 2e , respectively) in 90% ethanol with a large excess of potassium hydroxide, and of 2exo-norbornyl p-toluenesulfonate (1g) with excess sodium thiophenolate in methyl cellosolve, have been studied. They obey the first order rate law and are zero order with respect to the base-nucleophile. However, the ratio of 1,2- and 1,3-elimination to exo-substitution products depends strongly on the base-nucleophile concentration. Ion pair intermediates are indicated. The extreme inertness of 2-norbornyl derivatives in displacement reactions is due to severe steric hindrance of rearside nucleophilic attack, a feature they have in common with other bi- and tricyclic molecules bearing nucleofugal groups adjacent to one or two bridgehead atoms. 相似文献
9.
The buffered (AcOK) acetolyses of exo, (11) and endo-5, 6-dimethylidene-2-norbornyl brosylate (12) yielded exo5, 6-dimethylidene-2-norbornyl (16) and (3-methylidene-2-nortricyclyl)methyl acetates (18) . Endo-5, 6-dimethylidene-2-norbornyl (17) and 2-methylidene-3-tricyclo [3.2.1.03,6]octyl acetates (20) could not be detected. The titrimetric rate constants of the acetolysis of 11 (kt(exo)=4.49 ± 0.02) · 10?5 s?1 at 25°, ΔH≠=23.6 ±0.7 kcal mol?1, ΔS≠=0.7 ±2 calmol?1 K?1 and 12 (kt(endo)=1.9 ±0.08) · 10?9 s?1 at 25°, ΔH≠=27 ±1 kcal mol?1, ΔS≠=-8 ±2.5 calmol?1 K?1) were measured and compared with the polarimetric rate constants (kα/k(exo)=6.8 at 25°,(kα/k(exo)=1.0 at 121°) of the buffered acetolyses of the optically active brosylates (+)- 11 and (+)- 12 . Neither a common-ion (KOBs) nor a special ion effect (LiClO4) on kt(endo) could be detected, although external return might well intervene as some exo-5,6-dimethylidene-2-norbornyl tosylate (21) was formed upon solvolysis in the presence of KOTs. Acetolysis of (+)- 11 yielded completely racemized products, whereas (+)- 12 led to incomplete racemization. The buffered acetolysis of exo-(3exo-D)-5,6-dimethylidene-2-norbornyl brosylate (24) furnished (3exo-D)-( 26 :37.5%), exo-(7syn-D)-5,6-dimethylidene-2-norbornyl brosylate (27 : 37.5%) and [(5anti-D)-3-methylidene-2-nortricyclyl]methyl acetates (28 : 25 %). The acetolysis of endo-(2exo-D)-5,6-dimethylidene-2-norbornyl brosylate (25) yielded (2endo-D)-( 29 : 54%), exo-(1-D)-5,6-dimethylidene-2-norbornyl ( 30 : 36%) and [(6-D)-3-methylidene-2-nortricyclyl]methyl acetates ( 31 : 10%). Product analysis and deuterium label distribution was established by a combination of GC., 1H-NMR., 2H-{1H}-NMR. and MS. techniques. The results are rationalized by invoking anchimerically assisted ionization of the exo-brosylate 11 to symmetrical ion-pairs (cyclopropylcarbinyl cation intermediates) which undergo internal (and probably also external) return. Acetolysis of the endo-brosylate 12 is not anchimerically assisted and leads initially to non-symmetrical ion pairs. These evolve to symmetrical ion pair intermediates or, to a minor extent, are intercepted by solvent. 相似文献
10.
Detlef Schrder Ralf Wesendrup Christoph A. Schalley Waltraud Zummack Helmut Schwarz 《Helvetica chimica acta》1996,79(1):123-132
Ion/molecule reactions of ‘bare’ FeO+ with linear and branched aliphatic alcohols have been examined by Fourier-transform ion-cyclotron resonance mass spectrometry. Depending on the chain length of the alcohol, three different types of reactions can be distinguished: (i) Oxidation of the alcohols in the α-positions, to yield the corresponding carbonyl-Fe+ complexes, involves an initial O? H bond activation of the alcohol resulting in the formation of RO? Fe+? OH as the central intermediate. (ii) The formation of Fe(OH), concomitant by loss of the corresponding neutral alkenes, competes with the generation of neutral OFeOH and a carbocation R+. These couples point to the existence of an intracomplex acid-base equilibrium and are connected with each other by a proton transfer from either acid to the other, e.g. i-C3H + OFeOH?C3H6 + Fe(OH). The process is driven by the Lewis acidity of FeO+ and starts with the abstraction of a hydroxide anion from the alcohol. (iii) For longer alcohols, e.g. pentanol, functionalization of non-activated C? H bonds which are remote from the O functionality is observed. Here, the OH group of the alcohol serves as an anchor, which directs the reactive metal-oxide cation toward a particular site of the hydrocarbon chain. 相似文献
11.
Photoelectron spectra of endo- and exo-cyclopropano-norbornene ( = endo- and exo-tricyclo[3.2.1.02.4]octa-6-ene) show that a significant homoconjugation exists between the π-orbital of the double bond and the symmetric Walsh-es-orbital of the cyclopropane ring in the exo-isomer, whereas the interaction is negligeable in the endo-derivative. 相似文献
12.
The solvolysis products of the stereoisomeric 6-cyano-2-norbornyl p-toluene sulfonates 1 - 4 (R ? CN) in dioxane/water 7 : 3 have been determined. In contrast to an earlier report the 6exo-cyano-2exo-norbornyl p-toluenesulfonate ( 1 ; R?CN) yields 30% of the 2endo-alcohol 9 (R?CN) beside the 2exo-alcohol 10 and the norbornenes 12 and 13. The results confirm that - I substituents at C(6) reduce 1,3-bridging in the intermediate norbornyl cation and hence its rate of rearrangement. The relatively high rate constants for some 6-fluoro- and 6-cyano-2exo norbornyl p-toluenesulfonates are ascribed to C, C-hyperconjugation assisted by the conjugative effects of the 6-fluoro and cyano substituents. 相似文献
13.
D. C. DeJongh S. R. Shrader R. G. Isakson N. A. LeBel J. H. Beynon 《Journal of mass spectrometry : JMS》1969,2(9):919-922
The photoionization, as well as the electron-impact, mass spectra of exo-and endo-norbornyl bromide and of exo-and endo-8-bromobicyclo[3.2.1]octane show that exo-Br loss is more facile than endo-Br loss in formation of C7H11⊕ and C8H13⊕, respectively. The relative intensity values are compared with solvolysis data from the same systems. 相似文献
14.
Rolf Bielmann Marcus Christen Peter Flury Cyril A. Grob 《Helvetica chimica acta》1983,66(7):2154-2164
A comparison of the solvolysis rates of the substituted 2-exo- and 2-endo -norbornyl p-toluenesulfonates 1, 2, 3 and 4 and the substituted 1- and 2-adamantyl sulfonates 9 and 10 , respectively, in 80% ethanol and 97% trifluoroethanol has shown that the sensitivity of rates to the I-effect of substituents, i.e. the inductivity of these compounds, varies strongly with structure, configuration and solvent. In 97% trifluoro-ethanol, a solvent of low nucleophilicity and high ionizing power, the inductivities of the 2-endo-norbornyl p-toluenesulfonates 2 and 4 as well as the inductivities of the adamantyl derivatives 9 and 10 were larger than in 80% ethanol. In contrast, the inductivity of the 2-exo-norbornyl p-toluenesulfonates 1 was practically unchanged. It was, therefore, concluded that the transition states for the former compounds are not, or only weakly, bridged, whereas the transition states for the 2-exo-norbornyl p-tolu-enesulfonates 1 involve graded bridging by C (6). These results confirm that, due to differential bridging strain, 2-norbornyl cations are anisotropic to polar effects. 相似文献
15.
Walter Fischer Cyril A. Grob Reinhard Hanreich Georg von Sprecher Adrian Waldner 《Helvetica chimica acta》1981,64(7):2298-2311
The solvolysis rates and products of the 6-exo-substituted 2-exo- 1a - 1u , and 2-endo-norbornyl p-toluenesulfonates 2a - 2u , have been determined. In general, the rate constants for 1 and 2 (log k) correlate well with the inductive constants σ of the substitutents at C(6); however, their sensitivity to σ is much larger in the 2-exo-series 1 than in the 2-endo-series 2 . This differential transmission of polar effects is the cause of decreasing 2-exo/2-endo rate ratios from 2388 for R = t-C4H9 to 0.37 for R = Br, i. e. with increasing electron attraction by the substituent. The high sensitivity of the rate constants for the 2-exo-p-toluenesulfonates 1 to σ indicates an unusually strong inductive interaction between C(6) and the incipient cationic center at C(2). This interaction is ascribed to the participation of the pentacoordinate C(6)-atom, i. e. to 1,3-bridging, a consequence of steric hindrance of nucleophilic solvent participation in norbornanes. Donor substituents enhance 1,3-bridging, lead to faster reactions and to the formation of 2-exo substitution products. Conversely, acceptor substituents reduce 1,3-bridging, decrease rates and facilitate the formation of 2-endo substitution products. Graded 1,3-bridging is discussed in the light of Winstein's nonclassical ion concept. 相似文献
16.
Raymond J. Abraham Steven M. Coppell Robert Ramage 《Magnetic resonance in chemistry : MRC》1974,6(12):658-662
The 1H NMR spectra of 2-exo-hydroxymethyl-3-endo-methylnorbornene and the corresponding 2-endo-3-exo isomer have been completely assigned with the aid of lanthanide reagents. This enabled a full analysis of the unusual spectrum of 2-exo-hydroxy-methyl-3-endo-methylnorbornene to be undertaken, confirming the proposed structure. The ΔEu values for 2-exo-hydroxymethyl-3-endo-methylnorbornene and the 2-endo-3-exo-isomer have been used to test the effect of rotational averaging on the calculated pseudo contact shifts. Good agreement is obtained for a dynamic model in which the Eu atom exchanges between two sites on the oxygen atom of the OH bond, and in which the rotational equilibrium about the CH? CH2OH bond is explicitly considered. 相似文献
17.
Francesco Fuso Cyril A. Grob Pawel Sawlewicz Guo Wei Yao 《Helvetica chimica acta》1986,69(8):2098-2107
The solvolysis rates and products of 4- and 5-exo-substituted 2-exo- and 2-endo-norbornyl tosylates 9 and 10 , respectively, are reported. The logarithms of the rate constants (log k) correlate linearly with the inductive constants σ for the substituents. A comparison of the reaction constants p1 for the 4-, 5-, 6-, and 7-substituted 2-exo- and 2-endo-tosylates 9 , 10 , 1 , and 2 respectively, indicates that inductivity is higher for 2-exo-ionization than for 2-endo-ionization in all series. This observation is attributed to the more favorable alignment of neighbouring C-atoms for dorsal participation in exo-ionization, especially, in the case of C(6). 相似文献
18.
The solvolysis rates and products of the tertiary 2-methyl-2-exo- and -2-endo-norbornyl 2,4-dinitrophenyl ethers 1 and 2 , (X = 2,4-(NO2)22C6H3O) have been determined. The different sensitivities of the rates of these ethers to the inductive effect of substituents at C(6) indicate that graded bridging of C(2) by C(6) occurs in the ionization of the exo-ethers 1 , not, however, in the ionization of the endo-ethers 2. In both cases hydrolysis leads to 2-methyl-2-exo-norbornanols only. Consequently, substitution takes place with retention at C(2) in the exo-series 1 and with inversion at C(2) in the endo-series 2. It is concluded that stereoelectronic and polar effects, rather than steric bulk effects, determine the high exo/endo rate ratios of the parent norbornyl derivatives 1a and 2a . 相似文献
19.
Low temperature (?130° to ?110°) addition of exo-norborn-5-en-2-ol ( 7 ) to excess HSO3F in SO2CIF yielded a mixture of exo-5-(fluorosulfonyloxy)-exo-2- and endo-2-norbornylhydroxonium ions ( 9+10 ) under kinetic control that was different from the mixture of 9+10 obtained by addition of endo-norborn-5-en-2-ol ( 8 ) to HSO3F under kinetic control. These mixtures differed from the mixture of 9+10 observed at higher temperature (?80° to ?60°) (thermodynamic control). Addition of 3-nortricyclanol ( 23 ) or exo-2, 3-epoxynorbornane ( 24 ) to HSO3F at -?120° ± 10° yielded a mixture containing the exo-2-(fluorosulfonyloxy)-anti-7- and syn-7-norbornylhydroxonium ions ( 26+27 ) as major adducts. Qualitative rates of the isomerization of 26+27 to the more stable ions 9+10 and of the isomerization 9 ? 10 were evaluated. The solvolysis of 9+10 in HSO3F yielded the exo-2, exo-5- and exo-2, endo-5-norbornanediyl bis (fluorosulfates) ( 21+22 ). Norbornadiene and quadricyclane added 2 equivalents of HSO3F and furnished kinetically a mixture of exo-2, anti-7- and exo-2, syn-7-norbornanediyl bis (fluorosulfates) ( 36+37 ) as major adducts. The latter 36+37 were isomerized into a kinetic mixture of the more stable isomers 21+22 . The rates of these isomerizations were compared. The use of DSO3F and (exo-2-D)-norborn-5-en-2-ol ( 15 ) confirmed that heterolyses of the fluorosulfates were responsible for the observed isomerization; elimination-addition processes occurred but much more slowly. The results are interpreted in terms of substituted classical and σ-bridged secondary 2-norbornyl cation intermediates. It appears that the electron withdrawing substituents FSO3 and H2O+ (HO) destabilize the σ-bridged 2-norbornyl cation more at C(5) than C(7). If the σ-bridged ions 5-Z substituted at C(5) by Z = FSO3 or H2O+ (HO) are transition states in the isomerization of the corresponding classical ions 3-Z, 4-Z , the free enthalpy difference between the ‘non-classical’ σ-bridged ion and the classical ions is not higher than the energy barrier to the quenching of the latter intermediates by FSO in HSO3F/SO2CIF. 相似文献
20.
Yasuhiro Matoba Takashi Kagayama Yasutaka Ishii Masaya Ogawa 《Magnetic resonance in chemistry : MRC》1981,17(2):144-147
The 13C NMR spectra of a series of epoxides derived from endo- and exo-dicyclopentadiene and their partially hydrogenated compounds were determined to examine the substituent effects arising from the introduction of the oxirane ring in comparison with those found in other ring systems. The 13C signals of some epoxides were assigned by using lanthanide shift reagents. Characteristic substituent effects exerted by an oxirane ring were demonstrated. Marked steric γ-effects of ?8—13 ppm were observed at the bridge carbon signal in the bicyclo[2.2.1]heptane skeleton. Differences were found in the substituent effects between endo- and exo-dicyclopentadiene epoxides, and have been discussed in relation to the molecular geometry. 相似文献