- Photolysis of matrix-isolated acetyl chloride and infrared spectrum of the 1:1 molecular complex of hydrogen chloride with ketene in solid argon
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Acetyl chloride in an argon matrix decomposed on irradiation to generate ketene and hydrogen chloride, which formed the ketene...HCl complex.The fundamental vibrational frequency of HCl in the complex was observed at 2679 cm-1, i.e. 191 cm-1 below the frequency of the corresponding HCl monomer in solid argon.The fundamental frequency of DCl in the ketene-d2...DCl complex formed by photolysis of acetyl chloride-d3 was observed at 1939 cm-1, i.e. 140 cm-1 below the frequency of the corresponding DCl monomer in solid argon.
- Kogure, N.,Ono, T.,Suzuki, E.,Watari, F.
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Read Online
- Formamide catalyzed activation of carboxylic acids-versatile and cost-efficient amidation and esterification
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A novel, broadly applicable method for amide C-N and ester C-O bond formation is presented based on formylpyrrolidine (FPyr) as a Lewis base catalyst. Herein, trichlorotriazine (TCT), which is the most cost-efficient reagent for OH-group activation, was employed in amounts of ≤40 mol% with respect to the starting material (100 mol%). The new approach is distinguished by excellent cost-efficiency, waste-balance (E-factor down to 3) and scalability (up to >80 g). Moreover, high levels of functional group compatibility, which includes acid-labile acetals and silyl ethers, are demonstrated and even peptide C-N bonds can be formed. In comparison to reported amidation procedures using TCT, yields are considerably improved (for instance from 26 to 91%) and esterification is facilitated for the first time in synthetically useful yields. These significant enhancements are rationalized by activation by means of acid chlorides instead of less electrophilic acid anhydride intermediates.
- Huy, Peter H.,Mbouhom, Christelle
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p. 7399 - 7406
(2019/08/20)
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- "Meta elimination," a diagnostic fragmentation in mass spectrometry
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The diagnostic value of the "ortho effect" for unknown identification by mass spectrometry is well known. Here, we report the existence of a novel "meta effect," which adds to the repertoire of useful mass spectrometric fragmentation mechanisms. For example, the meta-specific elimination pathway described in this report enables unequivocal identification of meta isomers from ortho and para isomers of carboxyanilides. The reaction follows a specific path to eliminate a molecule of meta-benzyne, from the anion produced after the initial decarboxylation of the precursor. Consequently, in the CID spectra of carboxyanilides, a peak for the (R-CO-NH)- anion is observed only for the meta isomers. For example, the peaks observed at m/z 58, 86, 120, 128, and 170 from acetamido-, butamido-, benzamido, heptamido-, and decanamido-benzoates, respectively, were specific only to the spectra of meta isomers.
- Attygalle, Athula B.,Nishshanka, Upul,Weisbecker, Carl S.
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experimental part
p. 1515 - 1525
(2012/05/05)
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- Raman spectroscopy of n-pentyl methyl ether and deuterium labelledanalogues
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The Raman spectra of n-pentyl methyl ether, C5H 11OCH3, and six selectively deuteriated analogues arereported and discussed. Correlations between the observed ν(sp 3CH)stretching and bending bands and the position of the deuterium atoms in thealkyl chain are developed and refined. Similar progress is possible inassociating specific skeletal vibrations with bands in the Raman spectra. Therelevance of this study to improving the assignment of bands in the Ramanspectra of larger systems of biological interest is highlighted. Copyright
- Bowen, Richard D.,Edwards, Howell G. M.,Farwell, Dennis W.,Morgan, Sara E
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scheme or table
p. 1725 - 1734
(2012/04/04)
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- New transition-state models and kinetics of elimination reactions of tertiary alcohols over aluminum oxide
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A new transition-state model was developed in order to justify the anti intramolecular E2 elimination with cis (Z)-preference over pure alumina and interinolecular E2 elimination with trans (E)-preference over doped alumina. The reactions of model compounds 1,2,3-triphenyl-2-propanol (1), 1,2-diphenyl-2-propanol (2), and 3,3,3-trideuterio-1,2-diphenyl-2-propanol (3) with aluminum oxides with a pH range of 4.5-9.5 and thorium oxide in the temperature range of 200-350 °C in 2-hexanol have been investigated. Over acidic alumina (pH = 4.5 ±0.5), the ratio of E-isomer to Z-isomer (E/Z ? 2) for 2 was found to remain unchanged in this temperature range. At 300 °C, however, Saytzeff elimination favored Hofmann. Over pure alumina the E/Z ratio was equal to 0.650 (2-alkene/1-alkene = 0.750). At equilibrium, the E/Z ratio for 2 was equal to 4.5 with the formation of trace amounts of Hofmann adducts. The ratio of Saytzeff to Hofmann elimination was found to be pH independent. Any decrease in pH caused a slight increase in the E/Z ratio. The average primary kinetic isotope effect (kH/kD) for elimination at 230 °C was equal to 3.775 ± 0.227. The ratio of E/Z over thorium oxide at 300 and 350 °C was similar to that of aluminum oxide at 300 °C, but the Saytzeff elimination was surprisingly favored over Hofmann! The energy of activation (Ea), entropy of activation (AS?), selectivity, isotope effect (kH/kD), and semiempirical calculation (AM1) all agreed with concerted E2 elimination.
- Dabbagh,Salehi, J. Mohammad
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p. 7619 - 7627
(2007/10/03)
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- Mechanism of Propene and Water Elimination from the Oxonium Ion CH3CH=O+CH2CH2CH3
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The site-selectivity in the hydrogen transfer step(s) which result in propene and water loss from metastable oxonium ions generated as CH3CH=O+CH2CH2CH3 have been investigated by deuterium-labelling experiments.Propene elimination proceeds predominantly by transfer of a hydrogen atom from the initial propyl substituent to oxygen.However, the site-selectivity for this process is inconsistent with β-hydrogen transfer involving a four-centre transition state.The preference for apparent α- or γ-hydrogen transfer is interpreted by a mechanism in which the initial propyl cation accessible by stretching the appropriate bond in CH3CH=O+CH2CH2CH3 isomerizes unidirectionally to an isopropyl cation, which then undergoes proton abstraction from either methyl group +CH2CH2CH3 CH3CH=O---+CH2CH2CH3 +CH(CH3)2> + CH3CH=CH2>>.This mechanism involving ion-neutral complexes can be elaborated to accommodate the minor contribution of expulsion of propene containing hydrogen atoms originally located on the two-carbon chain.Water elimination resembles propene loss insofar as there is a strong preference for selecting the hydrogen atoms from the α- and γ-positions of the initial propyl group.The bulk of water loss is explicable by an extension of the mechanism for propene loss, with the result that one hydrogen atom is eventually transferred to oxygen from each of the two methyl groups in the complex +CH(CH3)2>.This site-selectivity is strikingly different from that (almost random participation of the seven hydrogen atoms of the propyl substituent) encountered in the corresponding fragmentation of the lower homologue CH2=O+CH2CH2CH3.This contrast is explained in terms of the differences in the relative energetics and associated rates of the cation rearrangement and hydrogen transfer steps.
- Bowen, Richard D.,Suh, Dennis,Terlouw, Johan K.
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p. 119 - 130
(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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- Syntheses of racemic and both chiral forms of cyclopropane-1,2-d2 and cyclopropane-1-13C-1,2,3-d3
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The racemic and both chiral forms of cyclopropane-1,2-d2 and cyclopropane-1-13C-1,2,3-d3 have been prepared efficiently through sequences based on trans-1,2-bis(methoxycarbonyl)cyclopropanes. These diesters have been prepared in racemic form with 1,2-d2 labeling and with 3-13C-1,2,3-d3 labeling. The labeled diesters have been resolved to provide both chiral forms, and the racemic or resolved diesters have been converted to the corresponding specifically labeled racemic or chiral cyclopropanes through a two-step sequence involving reduction and decarbonylation. The chemical, isotopic, geometrical, and chiral quality of the labeled cyclopropanes in both sets of isomers is estimated to be quite high and strictly comparable.
- Baldwin, John E.,Cianciosi, Steven J.
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p. 9401 - 9408
(2007/10/02)
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- The Mechanism of Ethylene Elimination from the Oxonium Ions CH3CH2CH=O+CH2CH3 and (CH3)2C=O+CH2CH3
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The reactions of the metastable oxonium ions CH3CH2CH=O+CH2CH3 and (CH3)2C=O+CH2CH3 are reported and discussed.Various mechanisms for ethylene elimination, which is the principal dissociation route for these ions, are considered.It is shown by means of 2H-labelling experiments and analysis of collision-induced dissociation spectra that routes involving ion-neutral complexes pre-empt 'conventional' mechanisms for these processes.In contrast, the behaviour of the lower homologues CH3CH2CH=OR+ and (CH3)2C=OR+ (R = H, CH3) is consistent with the operation of 'conventional' mechanisms for ethylene expulsion.This contrast is interpreted in energetic terms.The significance of these results for the chemistry of homologous and analogous 'onium' ions containing a Z+-R function (Z = O, S, NH, NCH3; R= CnH2n+1, n 2) is explained.
- Bowen, Richard D.,Derrick, Peter J.
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p. 1033 - 1039
(2007/10/02)
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- Stereochemistry of the of tryptophan catalyzed by 4-(γ, γ-dimethylallyl)tryptophan synthase from claviceps, the first pathway-specific enzyme in ergot alkaloid biosynthesis
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The first pathway-specific reaction in ergot alkaloid biosynthesis, the isoprenylation of tryptophan catalyzed by 4-(γ, γ-dimethylallyl)tryplophan (DMAT) synthase, involves displacement of the allyic pyrophosphate moiety by C-4 of the ring with inversion of configuration at C-l of dimethylallyl pyrophosphate (DMAPP). The of the allylic double bond is retained, and no scrambling of labeled hydrogens between the two methyl groups is observed in the reaction. Ooccurrence of 8-10% scrambling of a 13C from C-2 lable from of mevalonate C-7 and C-l7 of elymoclavine was confirmed, and it was shown (i) that this scrambling must take place in the formation of DMAPP from mevalonate and (ii) that it is unrelated to another partial scrambling of label, between the two hydrogens derived from C-5 of mevalonate, also observed in ergot alkaloid formation. The results are fully consistent with a mechanism for DMAT synthase involving direct attack of DMAPP on C-4 of the indole, possibly through a stabilized allylic carbocation or ion pair as intermediate.
- Shibuya,Chou,Fountoulakis,Hassam,Kim,Kobayashi,Otsuka,Rogalska,Cassady,Floss
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p. 297 - 304
(2007/10/02)
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- Carbon-carbon bond forming reactions of rhenium enolates with terminal alkynes. Evidence for an alkyne C-H oxidative addition mechanism and observation of highly stereoselective base-catalyzed proton transfer reactions in rhenium metallacycles
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The acetonitrile-substituted complexes fac-(MeCN)(OC)3(PPh3)ReCH(R2)CO(R1) (4, R1 = OEt R2 = H; 5, R1 = OEt R2 = Me) and the chelating amide complex 6 react with terminal alkynes (R3 C≡CH) to afford five-membered metallacycles 7-9 The metallacycles possess an exocyclic double bond which exists in the less thermodynamically stable Z stereochemistry, in which the alkyl group R3 is oriented proximate to the metal center. These complexes rearrange in the presence of a Lewis base to form the endocyclic isomers 10-12. The structure of the metallacycle 10g was determined by a single-crystal X-ray diffraction study. Labeling studies demonstrated that the 1,3-hydrogen shift involved in this rearrangement is intramolecular and stereospecific with respect to the rhenium center, even though it is mediated by an external reagent. Deuterium incorporation into the 7-position of the endo metallacycles can also be induced by base and once again occurs stereospecifically (anti to the phosphine ligand). Treatment of the metallacycles with acid results in removal of the metal and yields the unsaturated esters as a mixture of stereo- and regioisomers. Kinetic studies demonstrated that the reaction of 4 with terminal alkynes involves reversible dissociation of the coordinated acetonitrile to form an unsaturated intermediate 29 (R1 = CO2Et) This intermediate reacts faster with more electron-rich alkynes (HC≡CCMe3) than electron-deficient alkynes (HC≡CCO2Me) and displays a R3C≡CH/R3C≡CD kinetic isotope effect kH/kD of 2.0. On the basis of these results and information about reactions of related rhenium complexes, we suggest that formation of the metallacycles is best accommodated by the mechanism shown in Scheme VIII: insertion of 29 into the alkyne C-H bond leading to a 7-coordmate rhenium acetylide hydride 31, 1,3-migration of the hydride to the acetylide β-carbon, providing vinylidene complex 32, and then migration of the enolate ligand to the a-carbon of the vinylidene group, giving the exo metallacycle.
- Stack, Jeffrey G.,Simpson, Robert D.,Hollander, Frederick J.,Bergman, Robert G.,Heathcock, Clayton H.
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p. 2716 - 2729
(2007/10/02)
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- Reactions of Isolated Organic Ions. Alkene Loss from the Immonium Ions CH3CH=N+HC2H5 and CH3CH=N+HC3H7
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The slow unimolecular reactions of metastable CH3CH=N+HR ions are reported and discussed in energetic and mechanistic terms.These immonium ions eliminate an alkene (R-H) derived by hydride abstraction from the incipient carbonium ion R+.This reaction is interpreted as occurring via an ion-dipole complex comprising the incipient carbonium ion co-ordinated to CH3CH=NH, followed by rearrangement to another complex in which (R-H) and CH3CH=NH are bound to a common proton. 2H-Labelling experiments show a different specificity in the hydrogen abstraction step for R = ethyl and R = n-propyl: transfer of a deuterium atom from the β-carbon predominates when R = CH2CD3, but CH3CH=N+HCD2CH2CH3 expels a substantial proportion of C3H5D.The behaviour of the CH3CH=N+HR ions is compared with that of their CH2=N+HR homologues.An analysis is presented of the influence of the structure of R on the properties of the associated ion-dipole complexes.
- Bowen, Richard D.
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p. 913 - 918
(2007/10/02)
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- Ion-Neutral Complexes as Intermediates in the Decompositions of C5H10O2.+ Isomers
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Ionized pentanoic acid, 3-methylbutanoic acid, and the enol isomer of ionized isopropyl acetate are shown to pass in part through common intermediates before decomposing to CH3C.HC(OH)2+ (7) and the "McLafferty + 1" ion CH3C(OH)2+ (10).The H transfer to form the methyl of CH3C(OH)2+ and the joining of two CH2 groups to form the C-C bond in the ethylene eliminated to produce CH3C.HC(OH)2+ are both attributed to reactions of the ion-neutral complex .H2C(OH)2+>.The McLafferty + 1 ion is also formed, especially from ionized esters, by another pathway in which complexes may or may not be intermediates.The intermediacy of the ion-neutral complexes is supported by energetic considerations, isotope effects, and the decomposition patterns of labeled ions.The latter correlate with a preference for hydrogen transfer from the end carbons of the C3 partner in other reactions proposed to be complex-mediated.Unification of the McLafferty rearrangement, the McLafferty + 1 rearrangement, and the McLafferty rearrangement with charge reversal by a common initial γ-hydrogen rearrangement followed by dissociation or isomerization in ion-neutral complexes is proposed.Group migration by 1,2-shifts, possibly by dissociation to form a double bond in one partner in an ion-neutral complex followed by addition at the opposite end of the double bond, is shown to be a general reaction of ions in the gas phase.
- McAdoo, David J.,Hudson, Charles E.,Skyiepal, Mark,Broido, Ellen,Griffin, Lawrence L.
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p. 7648 - 7653
(2007/10/02)
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- Methoxychlorocarbene. Matrix Spectroscopy and Photochemistry
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Irradiation of 3-chloro-3-methoxydiazirine matrix isolated in argon or nitrogen at 10 K gives methoxychlorocarbene.The carbene was observed by IR and UV spectroscopy.Deuterium and 18O labeling indicated significant C-O double bond character in the carbene, which was exhibited in an intense IR absorption at ca. 1300 cm-1.The time evolution and wavelength dependence of the IR bands indicate two geometric isomers for the carbene, with distinct IR absorptions.The cis-carbene shows a significantly lower energy C-Cl stretch than the trans, consistent with an anomeric interaction.Irradiation of the carbene gives acetyl chloride, ketene, and HCl in argon matrices.In nitrogen, small amounts of CO and methylchloride are also observed.Several mechanisms are proposed to explain the photochemical results.
- Kesselmayer, Mark A.,Sheridan, Robert S.
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- Synthesis of Some Deuterated Aromatic Mesomorphic Compounds Used in Broad-Line 2H-NMR Studies
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Twenty-one deuterated mesogens of the following types: HOAB (perdeuterated chains), 4-alkoxybenzoic acids (perdeuterated chain and acid deuteron), 7S5 and 8S5 (perdeuterated alkoxy chain), 4-alkoxybenzylidene-4'-alkylanilines (2 or 4 deuterons in the aniline ring, 2-α-deuterons on the alkyl chain and perdeuterated alkyl or alkoxy chain) and TBBA (perdeuterated alkyl chains or anil deuterons) were prepared for use in broad-line 2H-NMR by using standard literature methods.The required 4-alkoxybenzoic acids, aldehydes and anilines with perdeuterated chains were prepared by alkylation of the appropriate 4-substituted phenol.The acid proton in the 4-alkoxybenzoic acids were replaced with a deuteron either by basic hydrolysis of the ester or acid chloride or by base-catalyzed exchange on the acid.Two deuterons were incorporated into the aniline ring ortho to the amino group by exchange in dilute H2SO4.Four ring deuterons, two α-chain deuterons or a perdeuterated chain were incorporated into 4-alkylanilines by the following sequence of steps: Friedel-Crafts acylation of benzene with an acid chloride, catalytic reduction, Friedel-Crafts acylation with oxalyl chloride, hydrolysis in base and a Schmidt rearrangement in H2SO4.New deuteration equipment was designed for the catalytic reduction using deuterium.IR NMR and MS were used to determine the deuterium content of these compounds.Small differences in mesophase transition temperatures were observed for mesogens containing perdeuterated alkyl or alkoxy chains.
- Neubert, Mary E.
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p. 327 - 374
(2007/10/02)
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- Reinvestigation of a Synthesis of (R,S)-Mevalonolactone
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An n.m.r. study of the reaction of 3-hydroxy-3-methylpentane-1,5-dioic acid (5) with excess of acetic anhydride is described.It has shown that 3-hydroxy-3-methylpentane-1,5-dioic acid anhydride (2), previously described by Scott and Shishido as an intermediate in their synthesis of mevalonolactone, is formed only transiently, along with 3-acetoxy-3-methylpentane-1,5-dioic acid (6).Both intermediates eventually give 3-acetoxy-3-methylpentane-1,5-dioic acid anhydride (3).To obtain (R,S)-mevalonolactone, sodium borohydride reduction of 3-hydroxy-3-methylpentane-1,5-dioic acid anhydride (2), prepared from the diacid (5) and N,N-dicyclohexylcarbodi-imide, is shown to be better than reduction of 3-acetoxy-3-methylpentane-1,5-dioic acid anhydride (3).
- Lewer, Paul,MacMillan, Jake
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p. 1417 - 1420
(2007/10/02)
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- SYNTHESIS AND NMR SPECTRA OF 2,2,2,-TRIDEUTERIOETHYLARSINE AND 2,2,2-TRIDEUTERIOETHYLCYCLOPENTAARSINE
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Pentakis(2,2,2-trideuterioethyl)cyclopentaarsine (PDECA) was synthesized by the reaction of 2,2,2-trideuterioethylarsine with dibenzylmercury.Variable temperature NMR spectra in C6D6 are interpreted in terms of fast pseudorotation.NMR and mass spectra and synthesis of 2,2,2-trideuterioethylarsine are also described.
- Rheingold, A. L.,Natarajan, S.
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p. 119 - 124
(2007/10/02)
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- Acyl Transfer Reactions in the Gas Phase. Ion-Molecule Chemistry of Vinyl Acetate
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An ion cyclotron resonance study of the ion-molecule reactions of vinyl acetate with methanol in the gas phase has revealed the formation of structurally different ions having the composition of protonated vinyl acetate.Deuterium-labeled reactants (CD3CO2CH=CH2 with CH3OH or CD3OD) gave product ions showing incorporation of up to two deuteriums in the vinyl group, indicating coexistence and interconversion of O-protonated and C-protonated vinyl acetate.Evidence was also obtained for a third MH+ ion for which the proposed structure is protonated 3-oxobutanal.This ion is believed to be formed by attack of CH3CO+ at the terminal vinylic carbon with loss of the ester acyl group as ketene.The ion reacts with methanol to give m/z 101 by loss of water.In contrast, protonated vinyl acetate reacts with methanol by an acyl transfer process to give (AcOCH3)H+, m/z 75.The related ion chemistry of vinyl propanoate, vinyl 2,2-dimethylpropanoate, and isopropenyl acetate is also described.Each of the acyl transfer reactions observed is consistent with formation of intermediate acylium ion complexes rather than tetracovalent addition complexes.Attempts were made to generate tetracovalent intermediates by an independent route from ortho esters of vinyl acetate.Dissociation of the ortho ester CH3C(OCH=CH2)2(OCH3) to dioxacarbocations was the dominant reaction, but the product ions were unreactive with H2O, CH3OH, or t-C4H9OH.The mechanistic implications of these results are discussed.
- Kim, Jhong K.,Caserio, Marjorie C.
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p. 4624 - 4629
(2007/10/02)
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