The vibrational spectrum, barrier to internal rotation, and ab initio calculations of 2-chloropropane

1991 ◽  
Vol 69 (11) ◽  
pp. 1845-1856 ◽  
Author(s):  
J. F. Sullivan ◽  
Aiying Wang ◽  
Mei-Shiow Cheng ◽  
J. R. Durig
Keyword(s):  
Vibrational Spectrum ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Internal Rotation ◽  
Far Infrared ◽  
Basis Sets ◽  
Equilibrium Geometry ◽  
Coupling Term ◽  
Hartree Fock ◽  
Experimental Values

The Raman spectra (3200–50 cm−1) of gaseous, liquid, and solid 2-chloropropane-d3 (isopropyl-d3 chloride), CH3(CD3)CHCl, and the infrared spectra (3200–50 cm−1) of the gas and solid have been recorded. The torsional transitions observed in the far infrared spectrum of the gaseous sample recorded at a resolution of 0.10 cm−1 between 265 and 135 cm−1 were analyzed in terms of the semirigid rotor model. An effective barrier of 1378 ± 4 cm−1 (3.94 ± 0.01 kcal/mol), cosine–cosine coupling term of 166 ± 10 cm−1 (0.47 ± 0.03 kcal/mol), and sine–sine coupling term of −173 ± 1 cm−1 (−0.49 ± 0.01 kcal/mol) were determined by fitting ten observed frequencies arising from the CH3 and CD3 torsions. The assignment of the 27 fundamentals is given and discussed. A complete equilibrium geometry, barrier to internal rotation, and vibrational frequencies have been determined by ab initio Hartree–Fock gradient calculations employing either 3-21G* or 6-31G* basis sets for both the d0 and d3 species. These calculated results are compared to the experimental values as well as to the corresponding quantities for some similar molecules. Key words: 2-chloropropane, vibrational spectrum; ab initio calculations; barrier to internal rotation.

The simplified ab initio method calculation of linear polarizability

1973 ◽  
Vol 26 (5) ◽  
pp. 921 ◽  
Author(s):  
RD Brown ◽  
GR Williams
Keyword(s):  
Ab Initio ◽  
Small Molecules ◽  
Basis Set ◽  
Basis Sets ◽  
Orbital Method ◽  
Polarizability Anisotropy ◽  
Minimal Basis ◽  
Hartree Fock ◽  
Numerical Performance ◽  
Experimental Values

The simplified ab-initio molecular-orbital method described previously is particularly suited to the calculation of polarizabilities by the non-perturbative coupled Hartree-Fock technique. Trial calculations on CO and HF, for which comparison with corresponding ab-initio calculations is possible, show that the method gives an adequate numerical performance. Minimal basis set calculations in general tend to give values that are considerably too low because of inadequate flexibility of the basis and this is the origin of the large discrepancy between theory and experiment, especially for small molecules. ��� Results are also reported for N2O and O3. For these larger systems the SAI results with minimal basis sets are noticeably nearer experimental values. The polarizability anisotropy for N2O is particularly well reproduced by the SAI method. �

scholarly journals Isolation of a Halogen-Bonded Complex Formed between Methane and Chlorine Monofluoride and Characterisation by Rotational Spectroscopy and Ab Initio Calculations

Molecules ◽  
2019 ◽  
Vol 24 (23) ◽  
pp. 4257 ◽  
Author(s):  
Anthony C. Legon ◽  
David G. Lister ◽  
John H. Holloway ◽  
Devendra Mani ◽  
Elangannan Arunan
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Internal Rotation ◽  
Halogen Bond ◽  
Spectroscopic Constants ◽  
Bond Critical Point ◽  
Equilibrium Geometry ◽  
Rotational Spectrum ◽  
Pulsed Jet ◽  
Explicitly Correlated

A halogen-bonded complex formed between methane and chlorine monofluoride has been isolated in the gas phase before the reaction between the components and has been characterised through its rotational spectrum, which is of the symmetric-top type but only exhibits K = 0 type transitions at the low effective temperature of the pulsed-jet experiment. Spectroscopic constants for two low-lying states that result from internal rotation of the CH4 subunit were detected for each of the two isotopic varieties H4C···35ClF and H4C···37ClF and were analysed to show that ClF lies on the symmetry axis with Cl located closer than F to the C atom, at the distance r0(C···Cl) ≅ 3.28 Å and with an intermolecular stretching force constant kσ ≅ 4 N m−1. Ab initio calculations at the explicitly correlated level CCSD(T)(F12c)/cc-pVTZ-F12 show that in the equilibrium geometry, the ClF molecule lies along a C3 axis of CH4 and Cl is involved in a halogen bond. The Cl atom points at the nucleophilic region identified on the C3 axis, opposite the unique C–H bond and somewhere near the C atom and the tetrahedron face centre, with re(C···Cl) = 3.191 Å. Atoms-in-molecules (AIM) theory shows a bond critical point between Cl and C, confirming the presence of a halogen bond. The energy that is required to dissociate the complex from the equilibrium conformation into its CH4 and ClF components is only De ≅ 5 kJ mol−1. A likely path for the internal rotation of the CH4 subunit is identified by calculations at the same level of theory, which also provide the variation of the energy of the system as a function of the motion along that path. The barrier to the motion along the path is only ≅ 20 cm−1.

Ab initio studies of isocyanatoborane and difluoroisocyanatoborane; bent or linear BNCO chains?

1991 ◽  
Vol 69 (6) ◽  
pp. 1000-1005 ◽  
Author(s):  
Susan Ellis ◽  
Edward G. Livingstone ◽  
Nicholas P. C. Westwood
Keyword(s):  
Carbon Atom ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Potential Surface ◽  
Energy Difference ◽  
Basis Set ◽  
Basis Sets ◽  
Hartree Fock ◽  
Split Valence ◽  
Valence Basis Set

Ab initio calculating at the 3-21G, 6-31G*, 6-31G**, 6-311G*, and 6-311G** Hartree–Fock levels, have been performed on the unknown H2BNCO and F2BNCO molecules in order to establish the geometries of these isoelectronic propadienone analogues. For H2BNCO the double split valence basis sets lead to linear BNCO chains, whereas either a triple split valence basis set, or the inclusion of correlation to second order (MP2/6-31G*) gives trans-bent structures. These have angles at nitrogen of 153.6° (6-311G*) or 149.9° (MP2/6-31G*), with the potential surface for angle bending extremely flat, and 0.5 kJ mol−1 (6-311 G*) or 1.12 kJ mol−1 (MP2/6-31 G*) separating the C2v and Cs structures. For the bent structures there is a small trans-bend (4–6°) at the carbon atom. The F2BNCO molecule is also linear at the 3-21G level, but is, however, already trans-bent (145.6° at nitrogen, 175.9° at carbon) at the 6-31G* Hartree–Fock level; 1.47 kJ mol−1 separates the bent and linear structures. The triple split valence basis set 6-311G* leads to a further decrease in the angle at nitrogen (141.0°), and a similar NCO angle (175.9°), with the bent structure favoured by 3.85 kJ mol−1. MP2/6-31G* calculations give a minimum with an angle at nitrogen of 140.2°, and a bent-linear energy difference of 3.58 kJ mol−1. Key words: ab initio calculations, isocyanatoboranes, structures, quasilinearity, propadienone analogues.

Far infrared spectrum, barrier to internal rotation, and ab initio calculations for 3,3,3-trifluoropropene

2000 ◽  
Vol 23 (2) ◽  
pp. 137-150 ◽  
Author(s):  
Gamil A Guirgis ◽  
Huimin Zhen ◽  
James B Robb ◽  
James R Durig
Keyword(s):  
Infrared Spectrum ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Internal Rotation ◽  
Far Infrared
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