464,323 research outputs found
Laser flash photolysis study of substituent effects on the rate of 1, 2-H migration in a series of benzylchlorocarbenes
No full textLaser flash photolysis of para-substituted 3-chloro-3-benzyldiazirines in isooctane produces the corresponding carbenes, which react with pyridine to form ylides or undergo 1,2-H migration to form the (Z)- and (E)-beta-chlorostyrenes. The rate for the 1,2-H migration is determined by plotting the pseudo-first-order rate constants for the growth of the ylide vs [pyridine] and extrapolating to zero pyridine concentration. In the case of (p-chlorobenzyl)chlorocarbene, the carbene decay can be monitored directly at 310 nm, whereas in [p-(trifluoromethyl)benzyl]chlorocarbene, the 285-nm trace may bc analyzed as the sum of the absorption of the carbene and of the product beta-chlorostyrenes. A Hammett plot of the logarithms of the rate constants for 1,2-H migration vs sigma(p) values gave a rho-value of -1.0, consistent with a hydride-like 1,2-H shift to the carbene center. The rate constants for the cyclopropanation of carbenes with tetramethylethylene (TME) were determined. In particular, the cyclopropanation of (p-chlorobenzyl)chlorocarbene with TME gave a negative activation energy of -4.7 kcal mol-1.PT: J; CR: BONNEAU R, 1989, J AM CHEM SOC, V111, P5973 BONNEAU R, 1989, J PHYS CHEM-US, V93, P4802 CARMICHAEL I, 1986, J PHYS CHEM REF DATA, V15, P1 DOYLE MP, 1987, J ORG CHEM, V52, P1619 EVANSECK JD, 1990, J PHYS CHEM-US, V94, P5518 GOULD IR, 1985, TETRAHEDRON, V41, P1987 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 HO GJ, 1989, J AM CHEM SOC, V111, P6875 HOUK KN, 1984, J AM CHEM SOC, V106, P4291 JACKSON JE, 1989, J AM CHEM SOC, V111, P6874 JONES M, 1980, REACTIVE INTERMEDIAT, V2 JONES WM, 1980, REARRANGEMENTS GROUN KIRMSE W, 1971, CARBENE CHEM LAVILLA JA, 1989, J AM CHEM SOC, V111, P6877 LIU MTH, 1908, J ORG CHEM, V52, P4223 LIU MTH, 1985, J CHEM SOC CHEM COMM, P982 LIU MTH, 1987, CHEM DIAZIRINES, CH5 LIU MTH, 1989, J AM CHEM SOC, V111, P6873 LIU MTH, 1989, J CHEM SOC CHEM COMM, V12 LIU MTH, 1990, J AM CHEM SOC, V112, P3915 LIU MTH, 1992, J PHOTOCH PHOTOBIO A, V63, P115 MORGAN S, 1991, J AM CHEM SOC, V113, P2782 MOSS RA, 1986, J AM CHEM SOC, V108, P7028 MOSS RA, 1990, J AM CHEM SOC, V112, P5642 SCHAEFER HF, 1979, ACCOUNTS CHEM RES, V12, P288; NR: 25; TC: 27; J9: J AMER CHEM SOC; PG: 4; GA: HT801Source type: Electronic(1
1, 2-H shift in benzylchlorocarbene: isotope effect and influence of the solvent
No full textLaser flash photolysis of 3-chloro-3-benzyldiazirine and 3-chloro-3-(phenyldideuteriomethyl)diazirine in isooctane over the 60 to -80-degrees-C temperature range gives rise to curved Arrhenius plots for both 1,2-H and 1,2-D migration in benzylchlorcarbene. The k(H)/k(D) values increase smoothly from 0.87 to 2.62 when the temperature increases from -60 to +30-degrees-C. The k(H)/k(D) value is approximately 4 for most of the temperatures studied if a solvent correction is applied. Quantum mechanical tunnelling or the influence of the solvent may be a possible explanation for these observations.PT: J; CR: BONNEAU R, 1989, J AM CHEM SOC, V111, P5973 BONNEAU R, 1992, J PHOTOCH PHOTOBIO A, V68, P97 DIX EJ, 1993, J AM CHEM SOC, V115, P10424 EVANSECK JD, 1990, J PHYS CHEM-US, V94, P5518 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 JACKSON JE, 1994, ADV CARBENE CHEM JONES M, 1980, REACTIVE INTERMEDIAT, V2 KIRMSE W, 1971, CARBENE CHEM LIU MTH, 1984, TETRAHEDRON, V40, P887 LIU MTH, 1990, J AM CHEM SOC, V112, P3915 LIU MTH, 1992, J PHOTOCH PHOTOBIO A, V63, P115 LIU MTH, 1992, J PHYS ORG CHEM, V15, P285 LIU MTH, 1994, RES CHEM INTERMEDIAT, V20, P195 MODARELLI DA, 1992, J AM CHEM SOC, V114, P7034 MOSS RA, 1992, TETRAHEDRON LETT, V33, P4287 MOSS RA, 1994, ADV CARBENE CHEM MUROV SL, 1973, HDB PHOTOCHEMISTRY NICKON A, 1993, ACCOUNTS CHEM RES, V26, P84 SALIS GA, 1968, J PHYS CHEM-US, V72, P752 SANDER W, 1994, UNPUB SCHAEFER HF, 1979, ACCOUNTS CHEM RES, V12, P288 SCHOLLER WW, 1989, HOUBEN WEYL METHODEN, P41 SHIMANOUCHI T, 1972, TABLES MOL VIBRATION, V1 SUGIYAMA MH, 1992, J AM CHEM SOC, V114, P966 WIERLACHER S, 1993, J AM CHEM SOC, V115, P8943; NR: 25; TC: 20; J9: J PHOTOCHEM PHOTOBIOL A-CHEM; PG: 5; GA: PV021Source type: Electronic(1
Insertion of phenylchlorocarbenes in the C-H bonds of alkanes: measurement of the rate constants by laser flash photolysis
No full textPhenylchlorocarbenes, produced by photolysis of the parent diazirines, have a very limited lifetime in alkane solvents. The rate of disappearance of p-methyl- and p-chlorophenylchlorocarbenes has been measured in iso-octane, cyclohexane and n-hexane as well as in benzene for comparison. The rate constants of several processes (dimerization, addition to the diazirine, reaction with the solvent, etc. ) contributing to the disappearance of the phenylchlorocarbenes have been determined. The rate of reaction with the solvent, which is much lower in benzene than in alkanes and depends strongly on the nature of the alkane, is assumed to be an insertion of the carbene in the C-H bonds of the solvent. Consequences of this reaction on the chemistry of carbenes produced by continuous irradiation (or thermolysis) of diazirines in alkanes are briefly discussed.PT: J; CR: BENSASSON R, 1971, T FARADAY SOC, V67, P1904 BONNEAU R, 1986, NOUV J CHIM, V10, P425 BONNEAU R, 1991, PURE APPL CHEM, V63, P289 DOYLE MP, 1988, TETRAHEDRON LETT, V29, P5863 GOULD IR, 1985, TETRAHEDRON, V41, P1587 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 LIU MTH, 1987, CHEM DIAZIRINES LIU MTH, 1990, J CHEM SOC CHEM COMM, P1482 LIU MTH, 1992, J AM CHEM SOC, V114, P3604 LIU MTH, 1992, J ORG CHEM, V57, P2483 LIU MTH, 1992, J PHOTOCH PHOTOBIO A, V63, P115 LUTZ H, 1973, J PHYS CHEM-US, V77, P1758 MORGAN S, 1991, J AM CHEM SOC, V113, P2782 MOSS RA, 1990, J AM CHEM SOC, V112, P5642 MOSS RA, 1990, KINETICS SPECTROSCOP; NR: 15; TC: 11; J9: J PHOTOCHEM PHOTOBIOL A-CHEM; PG: 10; GA: JQ196Source type: Electronic(1
Effect of diazirine concentration on the reaction of 3-benzyl-3-chlorodiazirine with methanol
No full textPT: J; CR: GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 GRILLER D, 1982, J AM CHEM SOC, V104, P5549 LIU MTH, 1984, J CHEM SOC CHEM COMM, P1062 LIU MTH, 1985, J CHEM SOC CHEM COMM, P982 LIU MTH, 1985, J ORG CHEM, V50, P3218 LIU MTH, 1985, TETRAHEDRON LETT, V26, P3071 LIU MTH, 1986, J CHEM SOC PERK T 2, P1233 LIU MTH, 1986, J PHYS CHEM-US, V90, P75 LIU MTH, 1987, CHEM DIAZIRINES, V1, CH5 TOMIOKA H, 1984, J AM CHEM SOC, V106, P454 TOMIOKA H, 1986, J CHEM SOC CHEM COMM, P1364; NR: 11; TC: 5; J9: J CHEM SOC PERKIN TRANS 2; PG: 3; GA: L7207Source type: Electronic(1
Letter from A. F. Potter to John H. Page
No full textLetter from A. F. Potter to John H. Page referring his request to build a railway to the District Forester at Albuquerque, New Mexico
Difference based Ridge and Liu type Estimators in Semiparametric Regression Models
Get PDFWe consider a difference based ridge regression estimator and a Liu type estimator of the regression parameters in the partial linear semiparametric regression model, y = Xβ + f + ε. Both estimators are analysed and compared in the sense of mean-squared error. We consider the case of independent errors with equal variance and give conditions under which the proposed estimators are superior to the unbiased difference based estimation technique. We extend the results to account for heteroscedasticity and autocovariance in the error terms. Finally, we illustrate the performance of these estimators with an application to the determinants of electricity consumption in Germany.Difference based estimator; Differencing estimator, Differencing matrix, Liu estimator, Liu type estimator, Multicollinearity, Ridge regression estimator, Semiparametric model
Termolecular trapping of benzylchlorocarbene by methanol
No full textPT: J; CR: GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 GRILLER D, 1982, J AM CHEM SOC, V104, P5549 KIRMSE W, 1971, CARBENE CHEM LIU MTH, UNPUB LIU MTH, 1982, CHEM SOC REV, V11, P127 MOSS RA, 1973, CARBENES, V1 MOSS RA, 1975, CARBENES, V2 TOMIOKA H, 1984, J AM CHEM SOC, V106, P454 TURRO NJ, 1982, J AM CHEM SOC, V104, P1754; NR: 9; TC: 14; J9: J CHEM SOC CHEM COMMUN; PG: 3; GA: TF969Source type: Electronic(1
Shwachman-Diamond Syndrome Protein SBDS Maintains Human Telomeres by Regulating Telomerase Recruitment. Liu et al
No full textOriginal data of main figures including Western blot, Southern blot, immunofluorescence and TBE PAGE results were provided in .tif format. Selected panels were boxed. The detail of each lane was labeled and described in our paper (see Shwachman-Diamond Syndrome Protein SBDS Maintains Human Telomeres by Regulating Telomerase Recruitment. Liu et al)
on the thermal decomposition of diazirines
No full textPT: J; CR: BIGOT B, 1978, J AM CHEM SOC, V100, P6576 BRADLEY GF, 1977, J CHEM SOC P2, P1214 BRUNNER J, 1980, J BIOL CHEM, V255, P3313 DIDERICH G, 1972, HELV CHIM ACTA, V55, P2103 FLEMING I, 1980, FRONTIER ORBITALS OR GRILLER D, 1982, J AM CHEM SOC, V104, P5549 JENNINGS BM, 1976, J AM CHEM SOC, V98, P6416 LAHMANI F, 1976, J PHYS CHEM-US, V80, P2623 LANGANIS ED, 1983, J AM CHEM SOC, V105, P7457 LIU MTH, 1972, J PHYS CHEM-US, V76, P797 LIU MTH, 1973, CAN J CHEM, V51, P2393 LIU MTH, 1974, J CHEM SOC P2, P937 LIU MTH, 1977, CAN J CHEM, V55, P3596 LIU MTH, 1982, CHEM SOC REV, V11, P127 MOORE CB, 1964, J CHEM PHYS, V41, P3504 SCHMITZ E, 1965, CHEM BER, V98, P2509 SCHMITZ E, 1967, CHEM BER, V100, P2093 SCHMITZ E, 1971, 23RD INT C PUR ALL C, V2, P283 SHEPARD RA, 1967, J ORG CHEM, V32, P3197 SHILOV AE, 1968, TETRAHEDRON LETT, P4177 SMITH NP, 1979, J CHEM SOC P2, P213 SMITH RAG, 1975, J CHEM SOC P2, P686 SNYDER JP, 1972, TETRAHEDRON LETT, P4347 TAYLOR EC, 1979, CHEM REV, V79, P181 TURRO NJ, 1980, J AM CHEM SOC, V102, P7576 TURRO NJ, 1982, J AM CHEM SOC, V104, P1754 VOIGT E, 1975, CHEM BER, V108, P3326 ZOLLINGER H, 1978, ANGEW CHEM INT EDIT, V17, P141; NR: 28; TC: 8; J9: J CHEM SOC PERKIN TRANS 2; PG: 4; GA: A2035Source type: Electronic(1
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