Are Polarized Cyclobutadienes Non-Aromatic?

2000 ◽  
Vol 53 (6) ◽  
pp. 443 ◽  
Author(s):  
Mathias Ugelstad Frederiksen ◽  
Richard Francis Langler ◽  
Keith Jeffery Watson ◽  
Andrea Penwell ◽  
Katherine Valenta Darvesh
Keyword(s):  
Molecular Orbital ◽  
Energy Gap ◽  
Molecular Orbital Calculations ◽  
Triplet Energy ◽  
Mp2 Calculations ◽  
Antiaromatic Character ◽  
Semiempirical Molecular Orbital

A series of non-alternant cyclobutadienes, both hydrocarbon and heteroatom-substituted, are examined by means of PM3 semiempirical molecular orbital calculations. The results show that even very substantial polarization has no simply predictable effect on antiaromatic character as measured by the singlet–triplet energy gap. MP2 calculations on selected hydrocarbons lead to the same conclusion.

Use of semiempirical molecular orbital calculations for the evaluation of force fields

1984 ◽  
Vol 93 (6) ◽  
pp. 917-926
Author(s):  
A. Annamalai ◽  
M. Kanakavel ◽  
Surjit Singh
Keyword(s):  
Molecular Orbital ◽  
Force Fields ◽  
Molecular Orbital Calculations ◽  
Semiempirical Molecular Orbital

Substituent effects in carbocations CX+, CHX+•, and CH2X+, and in singlet and triplet carbenes CHX. Proton affinities of singlet carbenes

1985 ◽  
Vol 63 (12) ◽  
pp. 3582-3586 ◽  
Author(s):  
A. C. Hopkinson ◽  
M. H. Lien
Keyword(s):  
Energy Gap ◽  
Single Point ◽  
Substituent Effects ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Proton Affinities ◽  
Interaction Method ◽  
Triplet Energy ◽  
Configuration Interaction Method ◽  
Singlet Carbenes

Abinitio molecular orbital calculations with a 6-31G* basis set have been used to optimise structures for CX+, CHX+•, CHX (both singlets and triplets), H2CX+ and H3CX (X = H, CH3, NH2, OH, F, CN, and NC). Single point calculations were then performed on the 6-31G* optimised structures using a configuration interaction method involving all single and double excitations from the valence shell. Stabilisation energies for the carbocations are compared with those already reported for H2CX+. For the carbenes the single-triplet energy gap is examined as a function of substituent and the stabilisation energies of the singlet carbenes are compared with those of the isoelectronic carbocations H2CX+. Proton affinities are reported for the singlet carbenes and are compared with the proton affinities of similarly substituted ethylenes, H2C=CHX.

He(I) photoelectron spectra and semiempirical molecular-orbital calculations on methylmetal halides of Group 4A elements

1976 ◽  
pp. 731 ◽  
Author(s):  
Alberto Flamini ◽  
Elvio Semprini ◽  
Ferdinanda Stefani ◽  
Salvatore Sorriso ◽  
Giuseppe Cardaci
Keyword(s):  
Molecular Orbital ◽  
Photoelectron Spectra ◽  
Molecular Orbital Calculations ◽  
Semiempirical Molecular Orbital

Conformational analysis of aminovinylpyrazine by semiempirical molecular orbital calculations

1997 ◽  
Vol 33 (1) ◽  
pp. 33-39 ◽  
Author(s):  
Hisayoshi Shiozaki ◽  
Atsushi Oshida ◽  
Dongfeng Hou ◽  
Masaru Matsuoka
Keyword(s):  
Conformational Analysis ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Semiempirical Molecular Orbital

Semiempirical molecular orbital calculations on the prototropic tautomerism of 2-thiocytosine

1991 ◽  
Vol 251 ◽  
pp. 195-204 ◽  
Author(s):  
J.Guillermo Contreras ◽  
Joel B. Alderete ◽  
Juan A. Gnecco
Keyword(s):  
Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Prototropic Tautomerism ◽  
Semiempirical Molecular Orbital
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