The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Jay S Siegel - One of the best experts on this subject based on the ideXlab platform.
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steric isotope effects gauged by the bowl Inversion Barrier in selectively deuterated pentaarylcorannulenes
Journal of the American Chemical Society, 2008Co-Authors: Tomoharu Hayama, Kim K Baldridge, And Anthony Linden, Jay S SiegelAbstract:Motivated by a greater bowl depth and Barrier to bowl Inversion in sym-1,3,5,7,9-pentamanisylcorannulene compared to corannulene, an experimental plan is developed to measure the effective hydrogen/deuterium steric kinetic isotope effect (KIE). Symmetry arguments are used to design orthogonal isotope labeling patterns so that the Barrier for the CD3 compound can be measured in the presence of the CH3 compound. This scheme eliminates the differential uncertainty in the temperature measurement by allowing both Barriers to be measure in the same sample, which in turn reduces the error in determining the differential Barrier. Ab initio computations corroborate the structure and isotope effect found experimentally. The predicted and determined steric KIE at 250 K is 1.08 (modified QUIVER at M06-2X/cc-pVDZ) and 1.22 ± 0.06 (VT-NMR), respectively. The results stem from differences in zero-point energy of the CH and CD motions; however, the phenomenology makes the CD3 group appear effectively “stickier” than CH3....
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Structure/energy correlation of bowl depth and Inversion Barrier in corannulene derivatives: combined experimental and quantum mechanical analysis.
Journal of the American Chemical Society, 2001Co-Authors: T. Jon Seiders, Kim K Baldridge, Gunther H Grube, Jay S SiegelAbstract:Synthesis of a series of corannulene derivatives with varying bowl depths has allowed for a study correlating the structure (bowl depth) and the energy of bowl Inversion. Substituents placed in the peri positions are repulsive and flatten the bowl, thus causing a decrease in the bowl Inversion Barrier. Conversely, annelation across the peri positions causes a deepening of the bowl, thus an increase in the bowl Inversion Barrier. Barriers between 8.7 and 17.3 kcal/mol have been measured, and their structures have been calculated using a variety of ab initio methods. The energy profile of an individual corannulene derivative is assumed to fit a mixed quartic/quadratic function from which an empirical correlation of bowl depth and Inversion Barrier that follows a quartic function is derived. Structure/energy correlations of this type speak broadly of the nature of enzymatic and catalytic activation of substrates.
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structure energy correlation of bowl depth and Inversion Barrier in corannulene derivatives combined experimental and quantum mechanical analysis
Journal of the American Chemical Society, 2001Co-Authors: Jon T Seiders, Kim K Baldridge, Gunther H Grube, Jay S SiegelAbstract:Synthesis of a series of corannulene derivatives with varying bowl depths has allowed for a study correlating the structure (bowl depth) and the energy of bowl Inversion. Substituents placed in the peri positions are repulsive and flatten the bowl, thus causing a decrease in the bowl Inversion Barrier. Conversely, annelation across the peri positions causes a deepening of the bowl, thus an increase in the bowl Inversion Barrier. Barriers between 8.7 and 17.3 kcal/mol have been measured, and their structures have been calculated using a variety of ab initio methods. The energy profile of an individual corannulene derivative is assumed to fit a mixed quartic/quadratic function from which an empirical correlation of bowl depth and Inversion Barrier that follows a quartic function is derived. Structure/energy correlations of this type speak broadly of the nature of enzymatic and catalytic activation of substrates.
Arthur M Halpern - One of the best experts on this subject based on the ideXlab platform.
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Ab initio study of cyclobutane: molecular structure, ring-puckering potential, and origin of the Inversion Barrier.
The journal of physical chemistry. A, 2005Co-Authors: Eric D Glendening, Arthur M HalpernAbstract:The structure and ring-puckering properties of cyclobutane and its perdeuterated isotopomer are studied using high-level ab initio methods and complete basis set extrapolations. Calculations reveal significant coupling between the ring-puckering (theta) and CH(2)-rocking (alpha) motions, with equilibrium angles (theta(eq) = 29.59 degrees and alpha(eq) = 5.67 degrees) that are within the range of experimentally determined values. Our best estimate of the Inversion Barrier is 482 cm(-1), in excellent agreement with recent experimental determinations. Ring-Inversion transition frequencies are evaluated from the eigenstates of the intrinsic reaction coordinate potentials for cyclobutane and cyclobutane-d(8). Natural bond orbital analysis shows that sigma(CC) --> sigma(CH)* and sigma(CH) --> sigma(CH)* hyperconjugative interactions are strengthened as cyclobutane puckers, thereby suggesting that Inversion Barriers in four-membered ring systems are a consequence of electronic delocalization rather than torsional strain.
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ab initio study of cyclobutane molecular structure ring puckering potential and origin of the Inversion Barrier
Journal of Physical Chemistry A, 2005Co-Authors: Eric D Glendening, Arthur M HalpernAbstract:The structure and ring-puckering properties of cyclobutane and its perdeuterated isotopomer are studied using high-level ab initio methods and complete basis set extrapolations. Calculations reveal significant coupling between the ring-puckering (θ) and CH2-rocking (α) motions, with equilibrium angles (θeq = 29.59° and αeq = 5.67°) that are within the range of experimentally determined values. Our best estimate of the Inversion Barrier is 482 cm-1, in excellent agreement with recent experimental determinations. Ring-Inversion transition frequencies are evaluated from the eigenstates of the intrinsic reaction coordinate potentials for cyclobutane and cyclobutane-d8. Natural bond orbital analysis shows that σCC → σCH* and σCH → σCH* hyperconjugative interactions are strengthened as cyclobutane puckers, thereby suggesting that Inversion Barriers in four-membered ring systems are a consequence of electronic delocalization rather than torsional strain.
Kim K Baldridge - One of the best experts on this subject based on the ideXlab platform.
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steric isotope effects gauged by the bowl Inversion Barrier in selectively deuterated pentaarylcorannulenes
Journal of the American Chemical Society, 2008Co-Authors: Tomoharu Hayama, Kim K Baldridge, And Anthony Linden, Jay S SiegelAbstract:Motivated by a greater bowl depth and Barrier to bowl Inversion in sym-1,3,5,7,9-pentamanisylcorannulene compared to corannulene, an experimental plan is developed to measure the effective hydrogen/deuterium steric kinetic isotope effect (KIE). Symmetry arguments are used to design orthogonal isotope labeling patterns so that the Barrier for the CD3 compound can be measured in the presence of the CH3 compound. This scheme eliminates the differential uncertainty in the temperature measurement by allowing both Barriers to be measure in the same sample, which in turn reduces the error in determining the differential Barrier. Ab initio computations corroborate the structure and isotope effect found experimentally. The predicted and determined steric KIE at 250 K is 1.08 (modified QUIVER at M06-2X/cc-pVDZ) and 1.22 ± 0.06 (VT-NMR), respectively. The results stem from differences in zero-point energy of the CH and CD motions; however, the phenomenology makes the CD3 group appear effectively “stickier” than CH3....
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Structure/energy correlation of bowl depth and Inversion Barrier in corannulene derivatives: combined experimental and quantum mechanical analysis.
Journal of the American Chemical Society, 2001Co-Authors: T. Jon Seiders, Kim K Baldridge, Gunther H Grube, Jay S SiegelAbstract:Synthesis of a series of corannulene derivatives with varying bowl depths has allowed for a study correlating the structure (bowl depth) and the energy of bowl Inversion. Substituents placed in the peri positions are repulsive and flatten the bowl, thus causing a decrease in the bowl Inversion Barrier. Conversely, annelation across the peri positions causes a deepening of the bowl, thus an increase in the bowl Inversion Barrier. Barriers between 8.7 and 17.3 kcal/mol have been measured, and their structures have been calculated using a variety of ab initio methods. The energy profile of an individual corannulene derivative is assumed to fit a mixed quartic/quadratic function from which an empirical correlation of bowl depth and Inversion Barrier that follows a quartic function is derived. Structure/energy correlations of this type speak broadly of the nature of enzymatic and catalytic activation of substrates.
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structure energy correlation of bowl depth and Inversion Barrier in corannulene derivatives combined experimental and quantum mechanical analysis
Journal of the American Chemical Society, 2001Co-Authors: Jon T Seiders, Kim K Baldridge, Gunther H Grube, Jay S SiegelAbstract:Synthesis of a series of corannulene derivatives with varying bowl depths has allowed for a study correlating the structure (bowl depth) and the energy of bowl Inversion. Substituents placed in the peri positions are repulsive and flatten the bowl, thus causing a decrease in the bowl Inversion Barrier. Conversely, annelation across the peri positions causes a deepening of the bowl, thus an increase in the bowl Inversion Barrier. Barriers between 8.7 and 17.3 kcal/mol have been measured, and their structures have been calculated using a variety of ab initio methods. The energy profile of an individual corannulene derivative is assumed to fit a mixed quartic/quadratic function from which an empirical correlation of bowl depth and Inversion Barrier that follows a quartic function is derived. Structure/energy correlations of this type speak broadly of the nature of enzymatic and catalytic activation of substrates.
Steven M Bachrach - One of the best experts on this subject based on the ideXlab platform.
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Ring strain energy and Inversion Barrier of phospha[3]radialene and aza[3]radialene
The Journal of Physical Chemistry, 1993Co-Authors: Steven M BachrachAbstract:The geometries of [3]radialene, aza[3]radialene, and phospha[3]radialene were completely optimized at the HF/6-31G * level. The ring strain energies of these species were evaluated using group equivalent reactions and found to be 52.86, 49.96, and 35.84 kcal mol -1 , respectively. The heteroatomic radialenes both have nonplanar heteroatoms. The Inversion Barriers (at MP2/6-31G * ) for aza[3]radialene and phospha[3]radialene are 7.96 and 54.10 kcal mol -1 , respectively. The geometries, ring strain energies, and Inversion Barriers are discussed in terms of relative electron delocalization between the exocyclic π-bonds and the lone pair
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STRUCTURE AND Inversion Barrier OF PHOSPHIRENE AND 1,2-DIHYDROPHOSPHETE. AN AB INITIO STUDY
The Journal of Organic Chemistry, 1991Co-Authors: Steven M BachrachAbstract:The geometry of 1H-phosphirene (1), 2H-phosphirene (2), and 1,2-dihydrophosphete (3) were optimized at HF/6-31G*, and single-point calculations at MP2 were performed. The transition structure for Inversion at P of 1 and 3 were also optimized (1 pl and 3 pl). The Inversion Barrier of 1 and 3 is determined. 1 is not antiaromatic based on the highly pyramidal P atom and no energetic destabilization. Analysis of the electron density distribution and comparison with the Inversion Barriers of N analogues indicate that the antiaromatic contribution in 1 pl is small
Eric D Glendening - One of the best experts on this subject based on the ideXlab platform.
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Ab initio study of cyclobutane: molecular structure, ring-puckering potential, and origin of the Inversion Barrier.
The journal of physical chemistry. A, 2005Co-Authors: Eric D Glendening, Arthur M HalpernAbstract:The structure and ring-puckering properties of cyclobutane and its perdeuterated isotopomer are studied using high-level ab initio methods and complete basis set extrapolations. Calculations reveal significant coupling between the ring-puckering (theta) and CH(2)-rocking (alpha) motions, with equilibrium angles (theta(eq) = 29.59 degrees and alpha(eq) = 5.67 degrees) that are within the range of experimentally determined values. Our best estimate of the Inversion Barrier is 482 cm(-1), in excellent agreement with recent experimental determinations. Ring-Inversion transition frequencies are evaluated from the eigenstates of the intrinsic reaction coordinate potentials for cyclobutane and cyclobutane-d(8). Natural bond orbital analysis shows that sigma(CC) --> sigma(CH)* and sigma(CH) --> sigma(CH)* hyperconjugative interactions are strengthened as cyclobutane puckers, thereby suggesting that Inversion Barriers in four-membered ring systems are a consequence of electronic delocalization rather than torsional strain.
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ab initio study of cyclobutane molecular structure ring puckering potential and origin of the Inversion Barrier
Journal of Physical Chemistry A, 2005Co-Authors: Eric D Glendening, Arthur M HalpernAbstract:The structure and ring-puckering properties of cyclobutane and its perdeuterated isotopomer are studied using high-level ab initio methods and complete basis set extrapolations. Calculations reveal significant coupling between the ring-puckering (θ) and CH2-rocking (α) motions, with equilibrium angles (θeq = 29.59° and αeq = 5.67°) that are within the range of experimentally determined values. Our best estimate of the Inversion Barrier is 482 cm-1, in excellent agreement with recent experimental determinations. Ring-Inversion transition frequencies are evaluated from the eigenstates of the intrinsic reaction coordinate potentials for cyclobutane and cyclobutane-d8. Natural bond orbital analysis shows that σCC → σCH* and σCH → σCH* hyperconjugative interactions are strengthened as cyclobutane puckers, thereby suggesting that Inversion Barriers in four-membered ring systems are a consequence of electronic delocalization rather than torsional strain.
