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Deuteration, activated

The present writer (136) attempted to explain this discrepancy in terms of a balance between hyperconjugative retardation and inductive acceleration by the heavier isotope. Only the inductive effect should manifest itself in the meba position, and strong support for the inductive interpretation was provided by Suhr and Zollinger (174), who found, by painstaking chromatographic analysis of the products of nitration of toluene and toluene-ads in nitromethane at 20°C., that methyl deuteration activates the meta position to an extent of kn/kj) = 0.94. The total rate was the same, within experimental error, and and there were no significant effects on nitration in the ortho and para positions. The latter point was recently confirmed with toluene-af by Eastham et al. (175). [Pg.211]

The mechanism of the PdCh-catalyzed Cope rearrangement has been studied by use of the partially deuterated 1.5-diene 53[46], The coordination of Pd(II) activates the alkene, and cyclization (carbopalladation) takes place to... [Pg.534]

Decomposition. Acetaldehyde decomposes at temperatures above 400°C, forming principally methane and carbon monoxide [630-08-0]. The activation energy of the pyrolysis reaction is 97.7 kj/mol (408.8 kcal/mol) (27). There have been many investigations of the photolytic and radical-induced decomposition of acetaldehyde and deuterated acetaldehyde (28—30). [Pg.50]

In theory two carbanions, (189) and (190), can be formed by deprotonation of 3,5-dimethylisoxazole with a strong base. On the basis of MINDO/2 calculations for these two carbanions, the heat of formation of (189) is calculated to be about 33 kJ moF smaller than that of (190), and the carbanion (189) is thermodynamically more stable than the carbanion (190). The calculation is supported by the deuterium exchange reaction of 3,5-dimethylisoxazole with sodium methoxide in deuterated methanol. The rate of deuterium exchange of the 5-methyl protons is about 280 times faster than that of the 3-methyl protons (AAF = 13.0 kJ moF at room temperature) and its activation energy is about 121 kJ moF These results indicate that the methyl groups of 3,5-dimethylisoxazole are much less reactive than the methyl group of 2-methylpyridine and 2-methylquinoline, whose activation energies under the same reaction conditions were reported to be 105 and 88 kJ moF respectively (79H(12)1343). [Pg.49]

Isothiazole-4,5-dicarboxylic acid, 3-phenyl-dimethyl ester synthesis, S, 150 Isothiazole-5-glyoxylic acid ethyl ester reduction, 6, 156 Isothiazole-4-mercurioacetate reactions, 6, 164 Isothiazole-5-mercurioacetate reactions, 6, 164 Isothiazoles, 6, I3I-I75 acidity, 6, 141 alkylation, 6, 148 aromaticity, S, 32 6, 144-145 basicity, 6, I4I biological activity, 6, 175 boiling points, 6, I43-I44, 144 bond fixation, 6, 145 bond orders, 6, I32-I34 calculated, 6, 133 bromination, S, 58 6, 147 charge densities, 6, 132-134 cycloaddition reactions, 6, 152 desulfurization, S, 75 6, 152 deuteration, S, 70... [Pg.683]

Further evidence for a bromine-bridged radical comes from radical substitution of optically active 2-bromobutane. Most of the 2,3-dibromobutane which is formed is racemic, indicating that the stereogenic center is involved in the reaction. A bridged intermediate that can react at either carbon can explain the racemization. When the 3-deuterated reagent is used, it can be shown that the hydrogen (or deuterium) that is abstracted is replaced by bromine with retention of stereochemistry These results are also consistent with a bridged bromine radical. [Pg.709]

Enolizalion of conjugated or /3,y-unsatiirated enones and dienones in O-deiiterated solvents facilitates the introduction of deuterium labels into positions as far as three and five carbon atoms away from a given ketone function. Exchange of the activated hydrogens in androst-4-en-3-one (12) provides a good illustration of the potential of this method. Saturation of the double bond (section V) in the deuterated enone (13) followed by back exchange of the a-deuteriums (section II-B) proves to be an excellent method for the preparation of 6,6-d2-5a-androstan-3-one (15). ... [Pg.152]

During the course of base-catalyzed exchange in O-deuterated alcohols, the vinylic hydrogen in the a position to the ketone is replaced by deuterium, in addition to the hydrogens activated by enolization. Thus, under these conditions the exchange of androst-l-en-3-one (16, R = H) gives a trideuterio derivative (18) instead of the expected 4,4-d2 analog (16, R = D). " (For other examples see compounds 13, 19, 21, 23, 26 and 27.) Incorporation of this deuterium is due to rapidly reversible alcohol addition (16 -+17) and elimination (17 18) which competes with the enolization step. " ... [Pg.152]

Optical rotation data have been used in two different ways to study tautomerism. The rate of racemization at an optically active carbon atom gives an upper limit for the rate at which the other tautomeric form is produced rates of halogenation and deuteration can sometimes be used in a similar way. [Pg.338]

A distinction between these four possibilities can be made on the basis of the kinetic isotope effect. There is no isotope effect in the arylation of deuterated or tritiated benzenoid compounds with dibenzoyl peroxide, thereby ruling out mechanisms in which a C5— bond is broken in the rate-determining step of the substitution. Paths (ii) and (iii,b) are therefore eliminated. In path (i) the first reaction, Eq. (6), is almost certain to be rate-determining, for the union of tw o radicals, Eq. (7), is a process of very low activation energy, while the abstraction in which a C—H bond is broken would require activation. More significant evidence against this path is that dimers, Arz, should result from it, yet they are never isolated. For instance, no 4,4 -dinitrobiphenyl is formed during the phenylation of... [Pg.136]

The symmetric series provides functional cyclohexadienes, whereas the non-symmetric one serves to build deuterated and/or functional arenes and tentacled compounds. In both series, several oxidation states can be used as precursors and provide different types of activation. The complexes bearing a number of valence, electrons over 18 react primarily by electron-transfer (ET). The ability of the sandwich structure to stabilize several oxidation states [21] also allows us to use them as ET reagents in stoichiometric and catalytic ET processes [18, 21, 22]. The last well-developed type of reactions is the nucleophilic substitution of one or two chlorine atoms in the FeCp+ complexes of mono- and o-dichlorobenzene. This chemistry is at least as rich as with the Cr(CO)3 activating group and more facile since FeCp+ activator is stronger than Cr(CO) 3. [Pg.50]

A kinetic study of the deuteration of pyridones and quinolones by deuterated sulphuric acid yielded the data in Table 148sl0. For the 4-pyridones, the rapid rise in rate with increasing acidity in strongly basic solutions, and the levelling off in rate at about H0 = 0 is consistent with reaction on the free base as is the small negative entropy of activation. The similarity in rate between 4-pyridone and its 1-methyl derivative shows reaction to take place on the form (XII) and not (XIII), viz. [Pg.231]

Nesmeyanov et a/.545 used a mixture of ferrocene, deuterated trifluoroacetic acid and benzene in the molar ratios 1 2 20 in a preliminary investigation of the reactivity of ferrocene and its derivatives. At 25 °C, rate coefficients were 1,620 x 10-7 (ferrocene) and 19.3 xlO-7 (acetylferrocene). In a subsequent publication by Alikhanov and Shatenshtein543 these values were altered to 1,600 x 10-7 and 1.5 x 10 7, respectively, and a value of 0.77 x 10"7 added for 1,1-diacetylferrocene. Under the same conditions, toluene gave a value of 0.3 x 10-7 so that the activating effects of these compounds relative to benzene can be approximately determined. [Pg.249]

The occurrence of proton transfer reactions between Z)3+ ions and CHa, C2H, and NDZ, between methanium ions and NH, C2HG, CzD , and partially deuterated methanes, and between ammonium ions and ND has been demonstrated in irradiated mixtures of D2 and various reactants near 1 atm. pressure. The methanium ion-methane sequence proceeds without thermal activation between —78° and 25°C. The rate constants for the methanium ion-methane and ammonium ion-ammonia proton transfer reactions are 3.3 X 10 11 cc./molecule-sec. and 1.8 X 70 10 cc./molecule-sec., respectively, assuming equal neutralization rate constants for methanium and ammonium ions (7.6 X 10 4 cc./molecule-sec.). The methanium ion-methane and ammonium ion-ammonia sequences exhibit chain character. Ethanium ions do not undergo proton transfer with ethane. Propanium ions appear to dissociate even at total pressures near 1 atm. [Pg.284]

The extent or nature of solvent-solute interactions may be different in the deuterated and nondeuterated solvents this may change the energies of the transition state, and hence the activation energy of the reaction. These are secondary isotope effects. Two physical models for this third factor have been constructed. ... [Pg.300]

A particularly interesting case is when a set of hydrogens which are chemically equivalent in the unionized molecule become inequivalent in the positive ion. Obvious examples are Jahn-Teller active molecules, but the same phenomenon may be found also in Jahn-Teller inactive systems. Since deuteration fcr practical reasons must be done before ionization, it may happen that a single deuterated molecule may produce several inequivalent isomers of the radical cation, e.g., upon irradiation. This will obviously influence the recorded ESR spectrum. [Pg.340]

We have previously in a number of papers [1-5] investigated these effects ft -both the Jahn-Teller inactive molecule n-butane [1] and the Jahn-Teller active molecules ethane, cyclopropane, and cyclohexane [2-5]. The choice of systems was largely dictated by the availability of experimental results [5-8]. New experiments being performed on selectively deuterated benzene have motivated a closer theoretical study of this system, and a first presentation of these investigations is given in the present paper. [Pg.340]

The proposed catalytic cycle is shown in Scheme 31. Hence, FeCl2 is reduced by magnesium and subsequently coordinates both to the 1,3-diene and a-olefin (I III). The oxidative coupling of the coordinated 1,3-diene and a-olefin yields the allyl alkyl iron(II) complex IV. Subsequently, the 7i-a rearrangement takes place (IV V). The syn-p-hydride elimination (Hz) gives the hydride complex VI from which the C-Hz bond in the 1,4-addition product is formed via reductive elimination with regeneration of the active species II to complete the catalytic cycle. Deuteration experiments support this mechanistic scenario (Scheme 32). [Pg.53]

II. 5 kcal.mole (activation energy), and —15 cal.deg . mole (activation entropy) for deuterated solvent the corresponding values are 9.1 l.mole sec , 13.2 kcal.mole S and —10.2 cal.deg . mole... [Pg.99]

The reactions have also been studied in deuterated media, the corresponding values of the terms 3 and k are 8.56x10 mole.l . sec and 1.02x10 mole. l . sec (at 24.9 °C, n = 2.2 M perchlorate media) an overall activation... [Pg.137]


See other pages where Deuteration, activated is mentioned: [Pg.101]    [Pg.50]    [Pg.249]    [Pg.582]    [Pg.659]    [Pg.831]    [Pg.855]    [Pg.863]    [Pg.222]    [Pg.628]    [Pg.160]    [Pg.163]    [Pg.290]    [Pg.23]    [Pg.226]    [Pg.66]    [Pg.7]    [Pg.117]    [Pg.195]    [Pg.235]    [Pg.250]    [Pg.258]    [Pg.277]    [Pg.218]    [Pg.287]    [Pg.289]    [Pg.899]    [Pg.207]    [Pg.154]    [Pg.139]   
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