- NMR Spectroscopy of Organolithium Compounds, Part XVI. The Aggregation Behaviour of Butyllithium, Phenyllithium, and Lihtium Diisopropylamide in Dimethoxy- and Diethoxymethane
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Keywords: Organolithium compounds, aggregation behavior, 6Li NMR, 13C NMR.The aggregation behaviour of butyllithium (BuLi), phenyllithium (PhLi), and lithium diisopropylamide (LDA) in dimethoxy- and diethoxymethane (methylal and ethylal, respectively) has been studied by NMR spectroscopy using the isotropic fingerprint method and 13C,6Li as well as 15N,6Li spin-spin coupling constants.In both solvents, LDA exists as a dimer, while BuLi forms a tetramer, PhLi forms a dimer in methylal, whereas two major aggregates exist in ethylal.Due to solvent viscosity at lower temperatures, their structure could not be determined.
- Bergander, Klaus,He, Runxi,Chandrakumar, Narayanan,Eppers, Oswald,Guenther, Harald
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- Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance
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A low-coordinate, high spin (S = 3/2) organometallic iron(I) complex is a catalyst for the isomerization of alkenes. A combination of experimental and computational mechanistic studies supports a mechanism in which alkene isomerization occurs by the allyl mechanism. Importantly, while substrate binding occurs on the S = 3/2 surface, oxidative addition to an η1-allyl intermediate only occurs on the S = 1/2 surface. Since this spin state change is only possible when the alkene substrate is bound, the catalyst has high immunity to typical σ-base poisons due to the antibonding interactions of the high spin state.
- Lutz, Sean A.,Hickey, Anne K.,Gao, Yafei,Chen, Chun-Hsing,Smith, Jeremy M.
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supporting information
p. 15527 - 15535
(2020/10/20)
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- Regioselective deuteration of alcohols in D2O catalysed by homogeneous manganese and iron pincer complexes
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We report a convenient and cost-effective protocol for the regioselective deuteration of primary and secondary alcohols using Earth abundant homogeneous first row transition metal pincer catalysts. D2O is utilized as both a deuterium source and a solvent, allowing for a benign inexpensive process. Depending on the metal selected (Mn or Fe), a high degree of deuterium incorporation was observed selectively either at the α and β position (Mn) or exclusively at the α position (Fe), for primary alcohols. This simple, efficient, and cost-effective protocol for alcohol C-H bond deuteration constitutes a powerful tool for the large scale synthesis of deuterated molecules.
- Kar, Sayan,Goeppert, Alain,Sen, Raktim,Kothandaraman, Jotheeswari,Surya Prakash
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supporting information
p. 2706 - 2710
(2018/07/05)
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- Synthesis of sequentially deuterated 1-n-Butyl-3-methylimidazolium ionic liquids
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Deuterium isotopologues of the ionic liquid (IL) 1-n-butyl-3- methylimidazolium chloride ([C4mim]Cl) sequentially labeled on the C-1″, C-1′, C-2′, C-3′, and C-4′ positions of the N-alkyl groups were prepared following a strategy that minimizes
- Khrizman, Alexander,Cheng, Hiu Yan,Moyna, Guillermo
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experimental part
p. 401 - 407
(2012/07/13)
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- Experimental and theoretical study of tunable 1,3-lithium shift of proparglie/allem lie species, transmetallation and Pd-catalyzed crosscoupling reactions
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The highly selective tuning of the isomerization from 1-arylalka1,2-dien-l- yllithium to l-arylalka-1,2dien-3-yllithium has been realized in the deprotonation of 1-arylalk-l-yne (conditions A and B) and carbolithiation of l-arylbut-3-en-l-yne with alkyllithium (conditions C and D). Subsequent transmetallation and Pd-catalyzed Negishi coupling reactions afforded 1,1-diaryl or 1,3-diaryl alienes with high selectivity. Deuterium-labeling cross experiments indicated that an intermolecular lithiation process occurred in both 1,3-lithium shift conditions (conditions B and D). 1-Arylalka1,2-diene was confirmed experimentally to be the intermediate. A computational study at the B3LYP level for the isomerization indicated that the acidity of H at the 3-position is higher than that of the H at the 1-position of 1phenyl-l,2-butadiene. Under conditions B, (Pr2NH acts as a proton carrier to finish the 1,3-lithium shift. The overall activation barrier for the rate-determining step in the solvated models is ≈ 21.0 kcal mol-1, indicating that the isomerization is reasonable at room temperature. For the isomerization under conditions D, DFT calculations indicated that the addition of TMEDA (tetramethylethylenediamine) and HMPA (hexamethylphosphoramide) changes the global minimum of the system; among the possible mechanisms (P1-P5) considered, the mechanism catalyzed by dilithiated species (P5) is the most probable one. The overall activation barriers for isomerization in THF and TMEDA solvated models are 22.6 and 19.7 kcal mol-1, respectively, proving that the isomerization may proceed at RT in THF or at -78°C with TMEDA, due to the fact that the solvation of the additives may increase the concentration of 1-phenyl1,2-butadienyllithium monomer by a deaggregation effect.
- Zhao, Jinbo,Liu, Yu,He, Qiwen,Li, Yuxue,Ma, Shengming
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scheme or table
p. 11361 - 11372
(2010/05/18)
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- Cryptoregiochemistry of a Brassica napus fatty acid desaturase (FAD3): A kinetic isotope effect study
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α-Linolenic acid ((Z,Z,Z)-octadeca-9,12,15-trienoic acid) is biosynthesized by a series of regio- and stereoselective dehydrogenation reactions which are catalyzed by a set of enzymes known as fatty acid desaturases. As part of ongoing research into the mechanism of these remarkable catalysts, we have examined the cryptoregiochemistry (site of initial oxidation) of extraplastidial ω - 3 desaturation as it occurs in the commercially important plant Brassica napus (oilseed rape or canola). The individual deuterium kinetic isotope effects associated with the C-H bond cleavages at C-15 and C-16 of a thiaoleoyl analogue were measured using a convenient in vivo yeast expression system. Competition experiments using appropriately deuterium-labelled 7-thia substrates revealed a large kinetic isotope effect (KIE) (kH/kD = 7.5 ± 0.4) for the C-H bond-breaking step at C-15 while the C-H bond cleavage at C-16 was found to be insensitive to deuterium substitution (kH/kD = 1.0 ± 0.14). These results point to C-15 as the site of initial oxidation in ω - 3 desaturation since the first chemical step in this type of reaction is rupture of a strong, unactivated C-H bond - an energetically difficult process which typically exhibits a large KIE.
- Savile,Reed,Meesapyodsuk,Covello,Buist
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p. 1116 - 1121
(2007/10/03)
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- Site-selective deuterium labeling of the tetrabutylammonium cation
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Four separate selectively deuterated samples of tetrabutylammonium iodide have been prepared in which each one of the four nonequivalent alkyl carbons is separately and fully deuterated. These samples were prepared for nuclear magnetic resonance (NMR) studies of the aggregation of ion pairs in low polarity solvents.
- Heinsen, Melissa J.,Pochapsky, Thomas C.
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p. 473 - 480
(2007/10/03)
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- Intermediacy of ion neutral complexes in the fragmentation of short-chain dialkyl sulfides
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The main fragmentation processes after electron ionization of butyl methyl and butyl ethyl sulfides are rationalized by the intermediacy of the ion neutral complex [RSH · methylcyclopropane](+·) as demonstrated by extensive labeling and collision activation studies.
- Filsak,Budzikiewicz
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p. 601 - 610
(2007/10/03)
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- Tritiated chiral alkanes as substrates for soluble methane monooxygenase from Methylococcus capsulatus (Bath): Probes for the mechanism of hydroxylation
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The tritiated chiral alkanes (S)-[1-2H1, 1-3H]ethane, (R)-[1-2H1, 1-3H]ethane, (S)-[1-2H1, 1-3H]butane, (R)[1-2H1, 1-3H]but
- Valentine, Ann M.,Wilkinson, Barrie,Liu, Katherine E.,Komar-Panicucci, Sonja,Priestley, Nigel D.,Williams, Philip G.,Morimoto, Hiromi,Floss, Heinz G.,Lippard, Stephen J.
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p. 1818 - 1827
(2007/10/03)
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- Side-chain Effects on the Fragmentation Behaviour of Alkylthiophenes
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The processes leading to the fragment ions formed from alkylthiophene molecule ions by benzylic cleavage without and with transfer of one hydrogen from the side-chain to the ring and the influence of additional methyl groups on the relative importance of these two fragmentation reactions were investigated.
- Lange, D.,Budzikiewicz, H.
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p. 432 - 438
(2007/10/02)
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- Reactions of Ionized Dibutyl Ether
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The reactions of ionized di-n-butyl ether are reported and compared with those of ionized n-butyl sec-butyl and di-sec-butyl ether.The main fragmentation of metastable (CH3CH2CH2CH2)O+. is C2H5. loss (ca. 85percent), but minor amounts (2-4percent of CH3., C4H7., C4H9., C4H10 and C4H10O are also eliminated.In contrast, C2H5. elimination is of much lower abundance (20 and 4percent, respectively) from metastable CH3CH2CH2CH2OCH(CH3)CH2CH3+. and 2O+., which expel mainly C2H6 and CH3. (35percent-55percent).Studies on collisional activation spectra of the C6H13O+ oxonium ions reveal that C2H5. loss from (CH3CH2CH2CH2)2O+. gives the same product, (CH3CH2CH2CH2+O=CHCH3) as that formed by direct cleavage of CH3CH2CH2CH2OCH(CH3)CH2CH3+..Elimination of C2H5. from (CH3CH2CH2CH2O+. is interpreted by means of a mechanism in which a 1,4-H shift to the oxygen atom initiates a unidirectional skeletal rearrangement to CH3CH2CH2CH2OCH(CH3)CH2CH3+., which than undergoes cleavage to CH3CH2CH2CH2+O=CHCH3 and C2H5..Further support for this mechanism is obtained from considering the collisional activation and neutralization-reionization mass spectra of the (C4H9)2O+. species and the behaviour of the labelled analogues of the (CH3CH2CH2CH2)2O+..The rate of ethyl radical loss is suppressed relative to those of alternative dissociations by deuteriation at the γ-position of either or both butyl substituents.Moreover, C2H5. loss via skeletal rearrangement and fragmentation of the unlabelled butyl group in CH3CH2CH2CH2OCH2CH2CD2CH3+. occurs approximately five times more rapidly than C2H4D. expulsion via isomerization and fission of the labelled butyl substituent.These findings indicate that the initial 1,4-hydrogen shift is influenced by a significant isotope effect, as would be expected if this step is rate limiting in ethyl radical loss.
- Bowen, Richard D.,Suh, Dennis,Terlouw, Johan K.
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p. 791 - 805
(2007/10/02)
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- Unimolecular Reactions of Isolated Organic Ions: the Chemistry of the Oxonium Ions CH3CH2CH2CH2(+)O=CH2 and CH3CH2CH2CH=O(+)CH3
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The reactions of the metastable oxonium ions CH3CH2CH2CH2(+)O=CH2 and CH3CH2CH2CH=O(+)CH3 are reported and discussed.Both these isomers of C5H11O(+) expel predominantly CH2O (75 - 90percent of the metastable ion current), a moderate amount of C3H6 (5-15percent), a minor amount of CH3OH (2-8percent) and a very small proportion of H2O (0.5-3percent).All these processes give rise to Gaussian metastable peaks.The kinetic energy releases associated with fragmentation of these oxonium ions are similar, but slightly larger for dissociation of CH3CH2CH2CH=O(+)CH3.The behaviour of labelled analogues confirms that the reactions of CH3CH2CH2CH2(+)O=CH2 and CH3CH2CH2CH=O(+)CH3 are closely related, but subtly different.Elimination of CH2O and C3H6 is intelligible by means of mechanisms involving CH3CH(+)CH2CH2OCH3.This open-chain cation is accessible to CH3CH2CH2CH2(+)O=CH2 by a 1,5-H shift and to CH3CH2CH2CH=O(+)CH3 by two consecutive 1,2-H shifts (or, possibly, a direct 1,3-H shift).The rates of these 1,2-, 1,3- and 1,5-H shifts are compared with one another and also with the rates of CH2O and C3H6 loss from each of the two oxonium ions.The 1,5-H shift that converts CH3CH(+)CH2CH2OCH3 formed from CH3CH2CH2CH=O(+)CH3 into CH3CH2CH2CH2(+)O=CH2 prior to CH2O elimination is essentially unidirectional.In contrast, the corresponding step converting C5H11O(+) ions generated as CH3CH2CH2CH2(+)O=CH2 into CH3CH(+)CH2CH2OCH3 competes effectively with expulsion of CH2O and C3H6.The implications of the latter finding for the degree of concert in the hydrogen transfer and carbon-carbon bond fission steps in alkene losses from oxonium ions via routes that are formally isoelectronic with the retro 'ene' pericyclic process are emphasized.
- Bowen, Richard D.,Derrick, Peter J.
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p. 1197 - 1209
(2007/10/02)
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- Isotope effects in nucleophilic substitution reactions VI. The effect of ion pairing on the transition state structure of SN2 reactions.
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Spectroscopic and conductivity studies of sodium thiophenoxide solutions in four different solvents and the secondary α-deuterium kinetic isotope effects found in the presence of 15-crown-5-ether demonstrate that the secondary α-deuterium kinetic isotope effect and transition state structure for the SN2 reaction between sodium thiophenoxide and n-butyl chloride are significantly different, depending on whether the ionic reactant is a solvent-separated ion-pair complex or a free ion.In all three solvents in which the form of the ionic reactant changes, a smaller isotope effect and tighter transition state are found for the reaction with the ion-pair complex.
- Westaway, Kenneth Charles,Lai, Zhu-gen
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p. 1263 - 1271
(2007/10/02)
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- Pseudo One-Step Cleavage of C-C Bonds in the Decomposition of Ionized Carboxyclic Acids. Radical Like Reactions in Mass Spectrometry
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Metastable molecular ions of hexanoic acid (1) decompose unimolecularly to C2H5. and protonated methacrylic acid (5-H+)(92percent rel. abund.).Investigation of the mechanism reveals that 1) the branched cation radical 11 must be regarded as the essential intermediate in the course of the rearrangement/dissociation reaction and 2) the process commences with intramolecular hydrogen transfer from either C-3 or C-5 to the ionized carbonyl oxygen ("hidden" hydrogen migration).Hydrogen transfer from C-4, which would correspond to the well-known McLafferty rearrangement, is of no importance in the C2H5.-elimination from 1.The same conclusion applies for various alternative mechanisms, as for example a SRi type reaction, 1 -> 2-H+.The gas phase chemistry of the cation radical of 1, and in particular the hydrogen exchange processes between the methylene groups C-2/C-3 and C-5/C-6, is in surprisingly close correspondence to the chemistry of free alkyl radicals. - The syntheses of various 13C and 2H-labelled model compounds are described.
- Weiske, Thomas,Schwarz, Helmut
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p. 323 - 347
(2007/10/02)
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- A ready Access to Primary Alcohols
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Base catalysed hydrogen-deuterium exchange in the now readily available sulphonium salts, followed by nucleophilic displacement by acetate ion, leads to the labeled acetates which are then hydrolysed.
- Badet, Bernard,Julia, Marc,Sarrazin, Claire-Anne
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