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41.
Insights into unusual stability of 5‐membered‐ring endocyclic benzyl carbocations in aqueous solution 下载免费PDF全文
The acyclic o‐oxygen benzyl carbocation 1 , the 6‐membered‐ring endocyclic o‐oxygen benzyl carbocation 2 , and the 5‐membered‐ring endocyclic o‐oxygen benzyl carbocation 3 were used as model compounds to get insights into the general phenomenon for the unusual stability of the 5‐membered‐ring endocyclic benzyl carbocations in aqueous solution. The hydride‐ion affinities of 1 , 2 , and 3 in gas phase, acetonitrile, and DMSO were calculated and compared by the density functional theory method, and 3 isodesmic reactions were designed to confirm their thermodynamic stability. What we found is that the 5‐membered‐ring endocyclic o‐oxygen stabilizes the benzyl carbocation 3 less than the acyclic o‐oxygen stabilizes the benzyl carbocation 1 in gas phase because of ring strain and through‐bond induction. However, the high solvation energies of the 5‐membered‐ring endocyclic o‐oxygen benzyl carbocation 3 not only offset the destabilizing effects of ring strain and through‐bond induction but also make it even more stable than the acyclic o‐oxygen benzyl carbocation 1 in polar solvents like acetonitrile, DMSO, and water. 相似文献
42.
E. Brambilla A. Gatti L.A. Lugiato M.I. Kolobov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):127-135
We analyze theoretically spatial structures appearing in the far diffraction zone of the electromagnetic field emitted in
the cavityless parametric down-conversion. We investigate in detail the spatial correlation functions of intensity and demonstrate
the existence of strong quantum correlations between the regions of the far field symmetrical with respect to the optical
axis. Our simplified model allows us to obtain analytical results for some limiting cases. We demonstrate that in the limit
of small diffraction and ideal quantum efficiency of photodetection the noise reduction in the photocurrent difference between
symmetrical regions in the far diffraction field becomes complete at zero frequency of photocurrent fluctuations.
Received 5 February 2001 and Received in final form 11 April 2001 相似文献
43.
H.-y. Fan A. Wünsche 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(3):405-412
We examine the existence of right-hand eigenstates (or eigenkets) of the boson creation operator a
and determine their coordinate and their Bargmann representation. The eigenkets of the creation operator are ultrasingular
and cannot be considered as a limiting case of normalizable states. Applications of these eigenstates as auxiliary states
for purposes of representation of states by path integrals over coherent states are discussed. A completeness relation for
coherent states on paths through the complex plane is derived and special examples of its application are considered.
Received 9 March 2001 and Received in final form 13 June 2001 相似文献
44.
Quantum controlled phase gate and cluster states
generation via two superconducting quantum interference devices in a
cavity 总被引:3,自引:0,他引:3
Z.-Y. Xue G. Zhang P. Dong Y.-M. Yi Z.-L. Cao 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):333-336
A scheme for implementing 2-qubit quantum controlled phase gate (QCPG) is proposed with two superconducting quantum interference
devices (SQUIDs) in a cavity. The gate operations are
realized within the two lower flux states of the SQUIDs by using a quantized cavity field and classical microwave pulses.
Our scheme is achieved without any type of measurement, does not use the cavity mode as the data bus and only requires a very
short resonant interaction of the SQUID-cavity system. As an application of the QCPG operation, we also propose a scheme for
generating the cluster
states of many SQUIDs. 相似文献
45.
P. Lougovski H. Walther E. Solano 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,37(3):423-426
We present a method of measuring expectation values of quadrature
moments of a multimode field through two-level probe
“homodyning”. Our approach is based on an integral transform
formalism of measurable probe observables, where analytically
derived kernels unravel efficiently the required field information
at zero interaction time, minimizing decoherence effects. The
proposed scheme is suitable for fields that, while inaccessible to
a direct measurement, enjoy one and two-photon Jaynes-Cummings
interactions with a two-level probe, like spin, phonon, or cavity
fields. Available data from previous experiments are used to
confirm our predictions. 相似文献
46.
Resin-bound α-keto mesylates were cleaved under acidic conditions (TFA/CH2Cl2) in the presence of a variety of aryl or alkyl thiols to give the corresponding thioethers. Access to the target compounds via standard nucleophilic displacement proved to be much less efficient. The stereochemical outcome of the reaction suggested formation of a highly reactive α-keto carbocation trapped in situ by the thiol acting as a scavenger. 相似文献
47.
48.
A. Waleh M. L. Cher G. H. Loew U. T. Mueller-Westerhoff 《Theoretical chemistry accounts》1984,65(3):167-177
INDO-SCF calculations with constrained geometry optimization have been performed to determine the bridge geometries in [1.1]ferrocenophane and its carbocation and carbanion to address the question of possible C-H-C hydrogen bonding in the carbanion derivative. In the equilibrium geometry of the carbanion, the endo-hydrogen is bonded to one of the bridge carbon atoms and the calculated distance between the two bridge carbons seems too large to accommodate a stable C-H-C hydrogen bond. The results indicate that the observed proton NMR spectrum of carbanion should be interpreted in terms of rapid proton exchange between two bridge carbon atoms rather than a symmetric hydrogen bond. The ground state charge distributions show that the ionic bridges in both carbanion and carbocation are highly conjugated and most of the ionic charge in both molecules is distributed over the ferrocene ring system. The charge on the iron varies only slightly among the three molecules and the formal oxidation state of iron remains +2. The role of the iron seems to be that of a conduit for charge transfer between ferrocene rings upon conjugation. 相似文献
49.
Photolysis of 2,2,4,6-tetramethyl- (1) and 1,2,2,4,6-pentamethyl-1,2-dihydroquinoline (2) in methanolic alkali yields only 4-methoxy-2,2,4,6-tetramethyl-1,2,3,4-tetrahydroquinoline in the former case and a mixture of 4-methoxy- and 4-hydroxy-1,2,2,4,6-pentamethyl-1,2,3,4-tetrahydroquinoline in the latter case. This result was rationalized by the existence of two resonance structures of an intermediate cation, viz., carbocationic and ortho-quinomethaneiminium species. The cation from 1 reacts with an alkali in the ortho-quinomethaneiminium form, and the cation generated from 2 reacts in the carbocationic form. 相似文献
50.
Nanosecond time-resolved UV/vis absorption spectroscopy on laser flash photolysis was conducted for photoinduced electron-transfer reactions of 7-benzhydrylidenenorbornene (1) and 7-benzhydrylidenenorbornane (5). The differences in the observed absorption bands and the structures of 1+ and 5+ were evaluated successfully using calculations based on (time dependent) density functional theory, confirming the nonclassical nature of 1+. 相似文献