Harmonic Force Fields from Scaled SCF Calculations: Program ASYM40

Hedberg, Lise; Mills, Ian

doi:10.1006/jmsp.2000.8168

Cited by 119 publications

(104 citation statements)

References 18 publications

(26 reference statements)

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“…[39][40][41][42] This procedure has been investigated extensively in systematic ab initio studies of vibrational anharmonicity in our laboratories. [43][44][45][46][47][48] The computation of spectroscopic constants from input force fields was performed by employing both the ANHARM [49,50] and ASYM40 [51] programs. In determining the total vibrational contributions to ground-state rotational constants, Coriolis resonances need not be considered because all resonance denominators cancel in the summation over normal modes.…”

Section: Methodsmentioning

confidence: 99%

Molecular Structure of Proline

Allen

Czinki

Császár

2004

Chemistry A European J

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The molecular structures of the two lowest-energy conformers of proline, Pro-I and Pro-II, have been characterized by ab initio electronic structure computations. An extensive MP2/6-31G* quartic force field for Pro-I, containing 62,835 unique elements in the internal coordinate space, was computed to account for anharmonic vibrational effects, including total zero-point contributions to isotopomeric rotational constants. New re and improved r0 least-squares structural refinements were performed to determine the heavy-atom framework of Pro-I, based on experimentally measured (A. Lesarri, S. Mata, E. J. Cocinero, S. Blanco, J. C. Lopez, J. L. Alonso, Angew. Chem. 2002, 114, 4867; Angew. Chem. Int. Ed. 2002, 41, 4673) rotational constant sets of nine isotopomers and our ab initio data for structural constraints and zero-point vibrational (ZPV) shifts. Without the ab initio constraints, even the extensive set of empirical rotational constants cannot satisfactorily fix the molecular structure of the most stable conformer of proline, a 17-atom molecule with no symmetry. After imposing the ab initio constraints, excellent agreement between theory and experiment is found for the heavy-atom geometric framework, the root-mean-square (rms) residual of the empirical rotational constant fit being cut in half by adding ZPV corrections. The most significant disparity, about 0.07 A, between the empirical and the best ab initio structures, concerns the r(N...H) distance of the intramolecular hydrogen bond. Some of the experimental quartic centrifugal distortion constants assigned to Pro-II have been corrected based on data obtained from a theoretical force field.

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Section: Methodsmentioning

confidence: 99%

Molecular Structure of Proline

Allen

Czinki

Császár

2004

Chemistry A European J

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“…There are a number of approaches for the computation of these corrections. These include the "rectilinear harmonic approximation" [23,24] (implemented, for example, in the programs ASYM40 [23,24] and SHRINK; [25][26][27][28] first approximation: k h0 ), the improved "curvilinear harmonic approximation" [26,28] (implemented in SHRINK; second approximation: k h1 ) and the more realistic "anharmonic approximation" (also implemented in SHRINK; k 3 , calculated at the first-order perturbation theory level by using third derivatives of the potential energy [28] ). A novel approach involves calculating vibrational corrections by using molecular dynamics (MD).…”

Section: Gas-phase Structuresmentioning

confidence: 99%

Functionalized Bis(pentafluoroethyl)phosphanes: Improved Syntheses and Molecular Structures in the Gas Phase

et al. 2013

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(C2F5)2PNEt2 represents an excellent starting material for the selective synthesis of bis(pentafluoroethyl)phosphane derivatives. The moderately air‐sensitive aminophosphane is accessible on a multi‐gram scale by treating Cl2PNEt2 with C2F5Li. Treatment with gaseous HCl or HBr yielded the corresponding phosphane halides (C2F5)2PCl and the so far unknown (C2F5)2PBr in good yields. The hitherto unknown (C2F5)2PF was obtained by treating (C2F5)2PBr with excess antimony trifluoride. Treatment of (C2F5)2PCl with Bu3SnH led to the quantitative formation of (C2F5)2PH. Deprotonation formally yielded the (C2F5)2P– anion in a form that was stabilized by coordination to mercury ions to form the complex [Hg{P(C2F5)2}2(dppe)]. An improved high‐yielding synthesis of (C2F5)2POH was achieved by treating (C2F5)2PNEt2 with p‐toluenesulfonic acid. The gas‐phase structures of (C2F5)2PH and (C2F5)2POH were determined by electron diffraction. The vibrational corrections employed in the data analysis of the diffraction data were derived from molecular dynamics calculations. Both compounds exist in the gas phase mostly as C1‐symmetric cis,cis conformers with regard the orientation of the C2F5 groups relative to the functional groups H and OH. The presence of a second conformer at ambient temperature is likely in both cases. The refined amounts of dominant conformers are 94(6) and 85(6) % for (C2F5)2PH and (C2F5)2POH, respectively. The conformational behaviour was further explored by potential energy surface scans based on DFT calculations. Important experimental structural parameters for the most stable conformers are re(P–C)average = 1.884(3) Å for (C2F5)2PH and re(P–C)average = 1.894(4) Å and re(P–O) = 1.582(3) Å for (C2F5)2POH. The different coordination properties of (C2F5)3P, (C2F5)2POH, (CF3)3P and (CF3)2POH were evaluated by complex formation with [Ni(CO)4]: the maximum achievable number of CO ligands substituted by (C2F5)3P is 1, by (C2F5)2POH is 2, by (CF3)3P is 3 and by the smallest ligand (CF3)2POH is 4.

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“…[48] For calculation of the quartic centrifugal distortion constants from quadratic force fields the package ASYM40 [49] was employed.…”

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confidence: 99%

Conformers of Gaseous Proline

Czinki

Császár

2003

Chemistry A European J

106

100

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Accurate geometries, relative energies, rotational and quartic centrifugal distortion constants, dipole moments, harmonic vibrational frequencies, and infrared intensities were determined from ab initio electronic structure calculations for eighteen conformers of the neutral form of the amino acid L-proline. Only four conformers have notable population at low and moderate temperature. The second most stable conformer is only 2+/-2 kJ mol(-1) above the global minimum, while the third and fourth conformers are nearly degenerate and have an excess energy of 7+/-2 kJ mol(-1) relative to the global minimum. All four conformers have one hydrogen bond: N.HO in the lower energy pair of conformers, and NH.O in the higher energy pair of conformers. The conformer pairs differ only in their ring puckering. The relative energies of the conformers include corrections for valence electron correlation, extrapolated to the complete basis set limit, as well as core correlation and relativistic effects. Structural features of the pyrrolidine ring of proline are discussed by using the concept of pseudorotation. The accurate rotational and quartic centrifugal distortion constants as well as the vibrational frequencies and infrared intensities should aid identification and characterization of the conformers of L-proline by rotational and vibrational spectroscopy, respectively. Bonding features of L-proline, especially intramolecular hydrogen bonds, were investigated by the atoms-in-molecules (AIM) technique.

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Harmonic Force Fields from Scaled SCF Calculations: Program ASYM40

Cited by 119 publications

References 18 publications

Molecular Structure of Proline

Molecular Structure of Proline

Functionalized Bis(pentafluoroethyl)phosphanes: Improved Syntheses and Molecular Structures in the Gas Phase

Conformers of Gaseous Proline

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