189,181 research outputs found
Kinetic and spectroscopic properties of carbene-diazirine ylides
No full textThe formation of a metastable carbene-diazirine ylide (CDY), characterized by an UV absorption spectrum in the range of 270-290 nm and yielding azine by rearrangement, is shown to be a general process in the photolysis of diazirines. However, the yield of formation and the lifetime of CDY greatly depend on the system considered. The decreasing value of the rate constant of the reaction, carbene + diazirine --> CDY, from similar to 10(9) M-1 s(-1) for singlet dialkylcarbenes, Ad: (adamantylidene) and BCN: (bicyclo[3.3.1]non-9-ylidene), to similar to 10(8) M-1 s(-1) for benzylchlorocarbene and to similar to 10(6) M-1 s(-1) for cyclopropyl and phenylchlorocarbenes, reflects the decreasing reactivity of these carbenes. The lifetime of these ylides is determined by the value of the activation energy barrier for their rearrangement to azine, E-a approximate to 15.5 kcal/mol for dialkylcarbenes, approximate to 11.5 kcal/mol fur alkylchlorocarbenes, and <10 kcal/mol for phenylchlorocarbene. This decrease of E-a is related to the strong stabilization of the azine when proceeding from CR2=N-N=CR2 to Ph-CCl=N-N=CCl-Ph. Another mechanism for the formation of azine, by a second-order reaction of the diazo isomer of the diazirine, is clearly identified in the case of photolysis of the BCN(N-2) diazirine.PT: J; CR: BONNEAU R, 1989, J AM CHEM SOC, V111, P5974 BONNEAU R, 1992, J PHOTOCH PHOTOBIO A, V68, P97 BONNEAU R, 1997, PURE APPL CHEM, V69, P979 BONNEAU R, 1998, J PHOTOCH PHOTOBIO A, V116, P9 BRINKER UH, 1998, ADV CARBENE CHEM, V2 DOYLE MP, 1987, J ORG CHEM, V52, P1619 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 JACKSON JE, 1988, J AM CHEM SOC, V110, P5595 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 LIU MTH, 1994, INT J CHEM KINET, V26, P1179 LIU MTH, 1994, J PHOTOCH PHOTOBIO A, V84, P133 LIU MTH, 1994, RES CHEM INTERMEDIAT, V20, P195 LIUEAU R, 1989, J PHYS CHEM-US, V93, P7300 MERRER DC, 1998, J ORG CHEM, V63, P3010 MOSS RA, 1990, J AM CHEM SOC, V112, P1638 MOSS RA, 1990, J AM CHEM SOC, V112, P5642 OIDA S, 1967, CHEM PHARM BULL, V15, P545 OIDA S, 1968, CHEM PHARM BULL, V16, P654 SHUSTOV GV, 1999, CAN J CHEM, V77, P540 TURRO NJ, 1980, J AM CHEM SOC, V102, P7576; NR: 22; TC: 8; J9: J PHYS CHEM A; PG: 6; GA: 311EYSource 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
Study of 1, 2-chlorine migration in (Alpha,alpha-dichlorobenzyl) chlorocarbene generated by laser flash photolysis of 3-chloro-3-(Alpha,alpha-dichlorobenzyl) diazirine
No full textPT: J; CR: BONNEAU R, 1989, J AM CHEM SOC, V111, P5973 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 JONES M, 1973, CARBENES, V1 JONES M, 1975, CARBENES, V2 JONES WM, 1980, REARRANGEMENTS GROUN, V1 KIRMSE W, 1971, CARBENE CHEM LAVILLA JA, 1989, J AM CHEM SOC, V111, P6877 LIU MTH, IN PRESS J PHOTOCHEM LIU MTH, IN PRESS J PHYS ORG LIU MTH, 1987, CHEM DIAZIRINES LIU MTH, 1989, J AM CHEM SOC, V111, P6873 LIU MTH, 1990, J AM CHEM SOC, V112, P3915 LIU MTH, 1990, J CHEM SOC CHEM COMM, P1650 MORGAN S, 1991, J AM CHEM SOC, V113, P2782 MOSS RA, 1990, J AM CHEM SOC, V112, P5642 REGITZ M, 1989, METHODEN ORGANISCH E, V19 SCHAEFER HF, 1979, ACCOUNTS CHEM RES, V12, P288; NR: 17; TC: 4; J9: J ORG CHEM; PG: 3; GA: HN858Source type: Electronic(1
A Subband-Selective Broadband GSC with Cosine-Modulated Blocking Matrix
Full text linkIn this paper, a novel subband-selective generalized sidelobe canceller (GSC) for partially adaptive broadband beamforming is proposed. The columns of the blocking matrix are derived from a prototype vector by cosine-modulation, and the broadside constraint is incorporated by imposing zeros on the prototype vector appropriately. These columns constitute a series of bandpass filters, which select signals with specific angles of arrival and frequencies. This results in highpass-type bandlimited spectra of the blocking matrix outputs, which is further exploited by subbands decomposition and suitably discarding the low-pass subbands prior to running independent unconstrained adaptive filters in each non-redundant subband. By these steps, the computational complexity of a GSC implementation is greatly reduced compared to fully adaptive GSC schemes, while performance is comparable or even enhanced due to subband decorrelation in both spatial and temporal domains
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
Energy barrier for 1,2-chlorine migration in α-methyl-αlpha-chlorobenzyl(chloro)carbene
No full textPT: J; CR: BONNEAU R, 1989, J AM CHEM SOC, V111, P5973 BONNEAU R, 1989, J PHYS CHEM-US, V93, P4802 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 LIU MT, UNPUB LIU MTH, 1985, J CHEM SOC CHEM COMM, P982 LIU MTH, 1990, J AM CHEM SOC, V112, P3915 PLATZ MS, 1989, J AM CHEM SOC, V111, P6874 WARNER PM, 1984, TETRAHEDRON LETT, P4211; NR: 8; TC: 5; J9: J CHEM SOC CHEM COMMUN; PG: 3; GA: EL425Source type: Electronic(1
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
Synthesis of 3-substituted indolizines from the reaction of chlorocarbenes with 2-vinylpyridine
No full text3-Substituted indolizines have been obtained in a one-step procedure from the reaction of chlorocarbenes with 2-vinylpyridine.PT: J; CR: BERGNIELSEN K, 1977, ACTA CHEM SCAND B, V21, P224 BONNEAU R, 1989, J CHEM SOC P1, P1547 GRAHAM WH, 1965, J AM CHEM SOC, V87, P4396 JACKSON JE, 1988, J AM CHEM SOC, V110, P5595 LAWS AP, 1987, J CHEM SOC PERK T 2, P591 LIU MTH, 1984, TETRAHEDRON, V40, P887 LIU MTH, 1992, J AM CHEM SOC, V114, P3604 MODARELLI DA, 1991, J AM CHEM SOC, V113, P8985 OHSAWA A, 1979, CHEM LETT, P241 REGEN SL, 1982, J ORG CHEM, V47, P1587 SWINBOURNE FJ, 1978, ADV HETEROCYCL CHEM, V23, P103 UCHIDA T, 1976, SYNTHESIS-STUTTGART, P209; NR: 12; TC: 12; J9: J CHEM SOC CHEM COMMUN; PG: 2; GA: MY782Source type: Electronic(1
Quantum yield of formation of diazo compounds from the photolysis of diazirines
No full textPT: J; CR: BALLY T, 1994, ANGEW CHEM INT EDIT, V33, P1964 BAYLEY H, 1978, BIOCHEMISTRY-US, V17, P2420 BONNEAU R, 1991, PURE APPL CHEM, V63, P289 BONNEAU R, 1996, J AM CHEM SOC, V118, P3829 BRADLEY GF, 1977, J CHEM SOC P2, P1214 BRINTON RK, 1951, J CHEM PHYS, V20, P1394 CLOSS GL, 1962, J AM CHEM SOC, V84, P4350 FREY HM, 1965, J CHEM SOC, P1700 GANZER GA, 1986, J AM CHEM SOC, V108, P1517 JACKSON JE, 1989, J AM CHEM SOC, V111, P6874 KUPFER R, 1994, J AM CHEM SOC, V116, P7393 LIU MTH, IN PRESS J AM CHEM S LIU MTH, 1987, J ORG CHEM, V52, P4223 MODARELLI DA, 1992, J AM CHEM SOC, V114, P7034 MOSS RA, 1981, TETRAHEDRON LETT, V22, P3749 MOSS RA, 1994, ADV CARBENE CHEM, V1 MULLER E, 1960, CHEM BER, V93, P1541 ROSENBERG MG, 1996, TETRAHEDRON LETT, V37, P3235 SMITH RAG, 1975, J CHEM SOC P2, P686 WHITE WR, 1992, J ORG CHEM, V57, P2841 YAMAMOTO N, 1994, J AM CHEM SOC, V116, P2064; NR: 21; TC: 17; J9: J AMER CHEM SOC; PG: 2; GA: VA026Source type: Electronic(1
Adamantylidene revisited: flash photolysis of adamantanediazirine
No full textIrradiation of 2-adamantane-2,3'-[3H]-diazirine (1) in isooctane at room temperature gives two primary photoproducts, 2-diazoadamantane and 2-adamantylidene (Ad:), with quantum yields of about 0.5 each. The fluorescence quantum yield of 1 is small, phi(f) approximate to 10(-4). The reactivity of Ad: was studied by nanosecond laser flash photolysis; it is best described as that of a carbene equilibrating between the singlet ground state and a low-lying triplet state. Ad: reacts with the precursor diazirine 1, pyridine, acetonitrile, tetramethylethylene, amines, water, and acetic acid with rate constants approaching the diffusion-controlled limit, as well as with molecular oxygen (k(O2) = 2.3 x 10(9) M-1 s(-t)). Reaction of Ad: with 1 (k(X) = 3.6 x 10(9) M-1 s(-1)) gives an ylide, lambda(max) = 290 nm, which forms adamantanone azine as a stable product by a reaction having activation parameters E-a = 15.5 kcal mol(-1) and A = 2 x 10(12) s(-t). At low concentrations of 1 in thoroughly dry, degassed solvents, the lifetime of Ad: reaches ca. 225 ns in isooctane, 500 ns in perfluorodecalin, and 700 ns in benzene. Diazoadamantane forms azine by a second-order reaction with a half-life of several hours at 10(-4) concentration. (C) 1998 Elsevier Science S.A. All rights reserved.PT: J; CR: BALLY T, 1994, ANGEW CHEM INT EDIT, V33, P1964 BATTINO R, 1983, J PHYS CHEM REF DATA, V12, P163 BERLMAN IB, 1971, HDB FLUORESCENCE SPE BETHELL D, 1966, J CHEM SOC B, P778 BETHELL D, 1969, J CHEM SOC B, P749 BONNEAU R, 1989, J AM CHEM SOC, V111, P5973 BONNEAU R, 1991, J AM CHEM SOC, V113, P9872 BONNEAU R, 1994, J AM CHEM SOC, V116, P3145 BONNEAU R, 1996, J AM CHEM SOC, V118, P7229 BONNEAU R, 1997, PURE APPL CHEM, V69, P979 BRINKER UH, 1993, ANGEW CHEM INT EDIT, V32, P1344 BUTERBAUGH JS, 1997, J AM CHEM SOC, V119, P3580 DIX EJ, 1993, J AM CHEM SOC, V115, P10424 GAUGLITZ G, 1984, Z PHYS CHEM NEUE FOL, V139, P237 GAUGLITZ G, 1985, J PHOTOCHEM, V30, P121 GE CS, 1994, J CHEM SOC CHEM COMM, P1479 GRILLER D, 1984, J AM CHEM SOC, V106, P2227 HELLER HG, 1981, J CHEM SOC P2, V2, P341 HO GJ, 1989, J AM CHEM SOC, V111, P6875 ISAEV SD, 1973, ZH ORG KHIM+, V9, P724 KUPFER R, 1994, J AM CHEM SOC, V116, P7393 LAVILLA JA, 1989, J AM CHEM SOC, V111, P6877 LIU MTH, 1977, TETRAHEDRON LETT, P3139 LIU MTH, 1989, J AM CHEM SOC, V111, P6873 LIU MTH, 1990, J CHEM SOC CHEM COMM, P1482 LIU MTH, 1994, J PHOTOCH PHOTOBIO A, V84, P133 MODARELLI DA, 1992, J AM CHEM SOC, V114, P7034 MORGAN S, 1991, J AM CHEM SOC, V113, P2782 MOSS RA, 1981, TETRAHEDRON LETT, V22, P3749 MOSS RA, 1990, J AM CHEM SOC, V112, P1638 MOSS RA, 1990, J AM CHEM SOC, V112, P5642 MOSS RA, 1997, CHEM COMMUN 0321, P617 OVERBERGER CG, 1964, J ORG CHEM, V29, P1188 PADWA A, 1991, CHEM REV, V91, P263 PARKER CA, 1968, PHOTOLUMINESCENCE SO PERSY G, 1987, EPA NEWSLETTER, V29, P45 SCAIANO JC, 1989, J ORG CHEM, V54, P1612 SHUSTOV GV, IN RPESS TOSCANO JP, 1994, J AM CHEM SOC, V116, P8146 UHLMANN E, 1996, J PHOTOCH PHOTOBIO A, V98, P45 WERSTIUK NH, 1984, CAN J CHEM, V62, P2391 YATES P, 1962, TETRAHEDRON, V18, P881; NR: 42; TC: 11; J9: J PHOTOCHEM PHOTOBIOL A-CHEM; PG: 11; GA: 108KVSource type: Electronic(1
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