An ab initio molecular orbital study of the structure and properties of propadienone (methyleneketene)

1978 ◽  
Vol 31 (1) ◽  
pp. 1 ◽  
Author(s):  
L Radom
Keyword(s):  
Carbon Monoxide ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Heat Of Formation ◽  
Basis Sets ◽  
Orbital Theory ◽  
Orbital Interactions ◽  
Planar Molecule ◽  
Split Valence ◽  
Acetylene Carbon

Ab initio molecular orbital theory with minimal (STO-3G) and split- valence (4-31G) basis sets has been used to obtain fully optimized structures for propadienone, allene, butatriene, carbon dioxide, ketene and vinylidene. Propadienone is predicted to be a planar molecule with C2V symmetry. The systematic deficiencies of the STO-3G and 4-31G basis sets have been taken into account in deriving a complete ro structure for propadienone. A striking feature of this structure is the HCH angle (117.°) which is about 5° smaller than the corresponding angle (122.3°) in ketene. An estimate (125 kJ mol-1) of the heat of formation of propadienone is reported. The alternating dipole moment magnitudes in the series H2CO, H2CCO and H2CCCO are explained in terms of orbital interactions. Propadienone is predicted to be considerably (about 135 kJ mol-1) more stable than vinylidene+carbon monoxide but slightly (about 10-20 kJ mol-1) less stable than acetylene+carbon monoxide.

Structures of simple anions from ab initio molecular orbital calculations

1976 ◽  
Vol 29 (8) ◽  
pp. 1635 ◽  
Author(s):  
L Radom
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Basis Set ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Limited Information ◽  
Orbital Theory ◽  
Comparable Quality ◽  
Split Valence ◽  
Theoretical Results

Ab initio molecular orbital theory with the minimal STO-3G and split-valence 4-31G basis sets is used to obtain geometries of 18 anions:OH-, NH2-, HF2-, BH4-, BF4-, C22-, CN-, NCN2-, N3-, NO2-, NO3-, 0CCO2-, CO32-, HCOO-, CH3COO-, C2O42-, C4O42- and C(CN)3-. The theoretical results are compared with experimental results from the literature. The STO-3G basis set performs somewhat worse for anions than for neutral molecules. On the other hand, the 4-31G basis set gives good results and predicts bond lengths to within 0.02� for all the molecules considered. Limited information on bond angle predictions suggests that these are of comparable quality to those for neutral molecules. The tricyanomethanide ion is predicted to be planar.

The Heat of Formation of Formaldimine

1992 ◽  
Vol 45 (1) ◽  
pp. 285 ◽  
Author(s):  
BJ Smith ◽  
JA Pople ◽  
LA Curtiss ◽  
L Radom
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Heat Of Formation ◽  
Molecular Orbital Theory ◽  
Orbital Theory

Ab initio molecular orbital theory at the G 2 level has been used to predict new values for the heat of formation of formaldimine (CH2=NH): ?Hfº0 = 94 ±10 kJ mol-1 and ?Hfº298 = 86 ±10 kJ mol-1.

Nitrosyl cyanide and related aspects of the ONCN potential surface

1978 ◽  
Vol 31 (11) ◽  
pp. 2349 ◽  
Author(s):  
BG Gowenlock ◽  
L Radom
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Related Species ◽  
Potential Surface ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Hartree Fock ◽  
Split Valence ◽  
Good Agreement

Ab initio molecular orbital calculations using the restricted Hartree-Fock approach have been carried out for nitrosyl cyanide and related species on the ONCN potential surface. Full geometry optimizations have been performed with the minimal STO-3G and split-valence 4-31G basis sets. Calculated (4-31G) geometries are in good agreement with available experimental data as are the energy changes in the reactions ONCN → NO + CN and NO + CN → N2 + CO. Possible mechanisms are discussed.

Ab initio studies on amides: acetamide, N-methylformamide and N-methylacetamide

1982 ◽  
Vol 35 (6) ◽  
pp. 1071 ◽  
Author(s):  
L Radom ◽  
NV Riggs
Keyword(s):  
Ab Initio ◽  
Internal Rotation ◽  
Molecular Orbital ◽  
Basis Sets ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Methyl Group ◽  
Barriers To Internal Rotation ◽  
Reported Data

Ab initio molecular orbital theory with the STO-3G and 4-31G basis sets has been used to investigate the geometries, preferred conformations, and barriers to internal rotation for acetamide, N-methylformamide and N-methylacetamide. Results are compared with corresponding previously reported data for formamide. For acetamide, the preferred conformation has the methyl group staggered with respect to the N-C bond whereas for N-methylformamide the methyl group is eclipsed with respect to this bond. Both N-methylformamide and N-methylacetamide prefer a Z-arrangement, i.e. methyl cis to C=O about the N-C bond. Experimentally determined barriers to internal rotation about the N-C bond generally lie within the range spanned by the STO-3G and 4-31G estimates.

The molecular structure of ammonia oxide (NH3O). An ab initio study

1977 ◽  
Vol 30 (4) ◽  
pp. 699 ◽  
Author(s):  
L Radom ◽  
JS Binkley ◽  
JA Pople
Keyword(s):  
Molecular Structure ◽  
Ab Initio ◽  
Bond Length ◽  
Basis Sets ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Trimethylamine Oxide ◽  
Polarization Functions ◽  
Split Valence ◽  
Calculated Bond Length

Ab initio molecular orbital theory is used to determine the molecular structure of ammonia oxide (NH3O). It is found that the N-O bond length is considerably overestimated by minimal (STO-3G), split-valence (4-31G and 6-31G) and large sp basis sets. This fault is rectified when polarization functions on nitrogen and oxygen are included in the basis (6-31G*) leading to the best theoretical value for the N-O length of 1.377 A. Electron correlation has little effect on the calculated bond length. Calculations (STO-3G and 4-31G) are also reported for trimethylamine oxide.

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