Rearrangements comparison

Both for the phenylene-ring rotation and for the carbonate-group rearrangement comparison of the actual activation paths of the relaxation with possible... 

Comparison of the rates of rearrangement of 30 and 31 showed 30 to react faster by a factor of 18,000. This corresponds to about 14kcal/mol in the measured A/f, but is partially compensated for by a more favorable A5 for 31. In the corresponding... 

The bases most commonly used to effect rearrangement are hydroxides, alkoxides, alcoholic sodium bicarbonate and, in some instances, amines. In the rearrangement of a series of l,l-dibromo-2-keto-alkanes, where a direct comparison has been made between triethylamine and sodium methoxide, the amine has given slightly better results ... 

Benzodiazepinones also undergo rearrangement to isoindoles when treated with acetic anhydride and pyridine (Py). The diazepinone (81), for instance, gives l-phenyl-3-acetylisoindole (82) under these conditions. The structure of the product was established in this case by comparison with (82) prepared by acetylation of 1-phenyl-isoindole. The rearrangement may be formally represented by a... 

Assignment of the l,2,4-triazolo[l,5-c]pyrimidine structures to the products obtained from the previously described cyclizations and not the alternative [4,3-c] structures has been rationalized and corroborated on the basis of (a) preference of cyclization at the more nucleophilic triazole ring N2 rather than at its less nucleophilic N4 (65JOC3601 88JMC1014), (b) inability of the obtained products to undergo acid- or base-catalyzed Dimroth rearrangement, a property characteristic of the thermodynamically less stable [4,3-c] isomers (91JMC281), (c) comparison with unequivocally prepared... 

Claisen rearrangement, 1194-1195 dehydration, 622 elimination reactions, 393 oxidation, 625-626 radical reactions, 243-244 characteristics of, 162-164 comparison with laboratory reactions, 162-164 conventions for writing, 162. 190 energy diagram of, 161 reduction, 723-725 reductive animation, 932 substitution reactions, 381-383 Biological reduction, NADH and, 610-611... 

A comparison of the electron impact (El) and chemical ionization (Cl-methane) mass spectra of 1//-azepine-1-carboxylates and l-(arylsulfonyl)-l//-azepines reveals that in the El spectra at low temperature the azepines retain their 8 -electron ring structure prior to fragmentation, whereas the Cl spectra are complicated by high temperature thermal decompositions.90 It has been concluded that Cl mass spectrometry is not an efficient technique for studying azepines, and that there is no apparent correlation between the thermal and photo-induced rearrangements of 1//-azepines and their mass spectral behavior. 

Base-induced rearrangement of bicyclo[2.2.2]octane oxide 67 gives predominantly bicyclo[2.2.2]octanone 68 (Scheme 5.15), which once again indicates that close proximity between the carbenoid center and the C-H bond into which it may insert is important if such an insertion is to occur [30]. In comparison, the sense of product distribution is reversed for the related substrate bicyclo[2.2.2]octadiene oxide 70 on treatment with LDA [15, 22], alcohol 72 being the favored product. 

There is one further piece of kinetic evidence which throws light on an aspect of the benzidine rearrangement mechanism, and this is comparison of the rates of reaction of ring-deuterated substrates with the normal H compounds. If the final proton-loss from the benzene rings is in any way rate-determining then substitution of D for H would result in a primary isotope effect with kD < kH. This aspect has been examined in detail42 for two substrates, hydrazobenzene itself where second-order acid dependence is found and l,l -hydrazonaphthalene where the acid dependence is first-order. The results are given in Tables 2 and 3. 

For example /-butyl phenyl ether with aluminium chloride forms para-t-butyl phenol155. Often the de-alkylated phenol is also formed in considerable quantity. The reaction formally resembles the Fries and Claisen rearrangements. Like the Fries rearrangement the question of inter- or intramolecularity has not been settled, although may experiments based on cross-over studies156, the use of optically active ethers157 and comparison with product distribution from Friedel-Crafts alkylation of phenols158 have been carried out with this purpose in view. 

In the course of studying the bromination reactions of the bicyclic systems we noticed that the reaction temperature has a dramatic influence on the product distribution. Increasing of the temperature gives non-rearranged reaction products (refs. 1,2). For this reason, we submitted 1 to high temperature bromination. To a solution of 1 in decalin at 150 C was added a hot solution of bromine in decalin in one portion. The colour of bromine disappeared immediately. After silica gel chromatography followed by fractional crystallization we isolated four products 2-6 in yields 8, 35, 37, and 9 % respectively. The structure of these compounds has been elucidated on the basis of spectral data by iH NMR and NMR experiments and by comparison with those reported in the literature. Symmetrical endo-c/5-isomer 6 has been observed for the first time. Studies concerning the mechanism of syn-addition show that the syn-adduct can arise either from direct... 

Anion photoelectron spectroscopy [37, 38] amd photodetachment techniques [39] provide accurate information on electron detachment energies of negative ions. Ten closed-shell ainions considered here exhibit sharp peaks, indicative of minor or vanishing final-state nuclear rearrangements, in their photoelectron spectra. Comparisons between theory and experiment are straiightforward, for differences between vertical and adiabatic electron detachment energies (VEDEs and AEDEs, respectively) are small. 

Solution The comparisons will be made at the same k and same throughput (i.e., the same Q). Rearrange Equation (4.19) and take the Mh root to obtain... 

The analogous dimerization of alkynes over Fe(C0)5 is not applicable, so clearly a different route towards alkynylated derivatives of 25 was needed. Comparison of 25 to cymantrene suggests that metallation of the hydrocarbon ligand should be the route of choice for the synthesis of novel substituted cyclobutadienes. In the literature, addition of organolithium bases (MeLi, BuLi) to the CO ligands with concomitant rearrangement had been observed [25]. But the utilization of LiTMP (lithium tetramethylpiperidide, Hafner [26]) or sec-BuLi as effectively non-nucleophilic bases led to clean deprotonation of the cyclobuta-... 

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