Gaussian molecular orbital calculations of the barrier to internal rotation in the ethyl cation

1970 ◽  
Vol 4 (6) ◽  
pp. 625-630 ◽  
Author(s):  
L. J. Massa ◽  
S. Ehrenson ◽  
M. Wolfsberg
Keyword(s):  
Internal Rotation ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Ethyl Cation

The thioformamidyl group as an α-substituent in carbocations

1995 ◽  
Vol 73 (9) ◽  
pp. 1468-1477 ◽  
Author(s):  
M. Bertone ◽  
D.L.J. Vucković ◽  
A. Cunje ◽  
C.F. Rodriquez ◽  
E. Lee-Ruff ◽  
...  
Keyword(s):  
Molecular Orbital ◽  
Ring Opening ◽  
Molecular Orbital Calculations ◽  
Transition Structure ◽  
Isodesmic Reactions ◽  
Open Structure ◽  
Methyl Group ◽  
Benzyl Cation ◽  
Stabilizing Effect ◽  
Ethyl Cation

Abinitio: molecular orbital calculations at MP2(FULL)/6-311G(d,p) or MP2(FULL)/6-31G(d,p) are reported for carbocations RR′CCHO+, RR′CCHS+, RR′CCONH2+, and RR′CCSNH2+where R and R′ are H, CH3, C-C3H5, and C6H5. Primary (R=R′=H), secondary (R=H, R′=alkyl or phenyl), and tertiary (R′=R′=CH3) ions prefer the cyclic oxiranyl or thiiranyl structure 9, with the open structure 8 being a transition structure for ring opening. Tertiary carbocations with R=R′=phenyl or cyclopropyl and the 9-thioformamidyl-9-fluorenyl cation have the open structure. Isodesmic reactions show CONH2 to be weakly stabilizing in the methyl cation, and CSNH2 has a larger stabilizing effect, roughly equivalent to that of a methyl group. An α-thioamide substituent is less stabilizing in the ethyl cation and even less stabilizing in the isopropyl cation. In C6H5CHCSNH2+ the CSNH2 group is slightly destabilizing and, by extrapolation, is more destabilizing in Ar2CCSNH2+. The rearrangement of the α-thioformamidyl-benzyl cation to benzothiophene is calculated to have a low barrier, 15.4 kcal/mol at HF/6-31G(d,p). Keywords: molecular orbitals, destabilized carbocations, rearrangement.

scholarly journals The para substituent dependence of the internal rotational barrier in benzenethiol

1977 ◽  
Vol 55 (3) ◽  
pp. 552-556 ◽  
Author(s):  
Ted Schaefer ◽  
William J. E. Parr
Keyword(s):  
Ab Initio ◽  
Internal Rotation ◽  
Molecular Orbital ◽  
Rotational Barrier ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Fluorine Nucleus ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

On the basis of the observed spin–spin coupling constants between the sulfhydryl and ring protons and a hindered rotor treatment of the twofold barrier to internal rotation in a series of para substituted benzenethiol derivatives, it is argued that V2 is essentially zero in p-amino-benzenethiol and is 2.5 ± 0.2 kcal/mol in p-nitrobenzenethiol; having intermediate values for the methoxy, fluoro, methyl, and bromo derivatives in solution. The results are based on an assumed relationship between the four-bond and the fictitious six-bond couplings to the sulfhydryl proton. The conclusions are consistent with the observed magnitudes of the couplings over six and seven bonds, respectively, between the sulfhydryl proton and the fluorine nucleus and the methyl protons in the appropriate derivatives; as well as with the coupling between the sulfhydryl and methyl protons in 4-bromo-3-methylbenzenethiol. The experimental barriers are compared with ab initio molecular orbital calculations of their substituent dependence.

Gaussian molecular orbital calculations of hyperconjugation in the ethyl cation

1971 ◽  
Vol 11 (2) ◽  
pp. 196-197 ◽  
Author(s):  
L.J. Massa ◽  
S. Ehrenson ◽  
M. Wolfsberg ◽  
C.A. Frishberg
Keyword(s):  
Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Ethyl Cation

Conformational preferences and barriers to internal rotation in fluorothioanisoles from long-range spin–spin couplings, photoelectron spectroscopy, and semiempirical molecular orbital calculations

1993 ◽  
Vol 71 (10) ◽  
pp. 1741-1750 ◽  
Author(s):  
Dietmar Chmielewski ◽  
Nick Henry Werstiuk ◽  
Timothy A. Wildman
Keyword(s):  
Internal Rotation ◽  
Molecular Orbital ◽  
Long Range ◽  
Photoelectron Spectra ◽  
Semiempirical Methods ◽  
Molecular Orbital Calculations ◽  
Methyl Carbon ◽  
Conformational Preferences ◽  
Barriers To Internal Rotation ◽  
Semiempirical Molecular Orbital

The conformational preferences and barriers to internal rotation about the S—C(phenyl) bond have been investigated for thioanisole and its 2-fluoro, 2,6- and 3,5-difluoro, and 2,3,5,6-tetrafluoro derivatives. Measurements of long-range spin–spin couplings between the methyl carbon and the para ring proton indicate that the 2-fluoro and 3,5-difluoro compounds prefer conformations with all heavy atoms coplanar. The 2,6-difluoro and 2,3,5,6-tetrafluoro compounds prefer conformations in which the methyl carbon lies in or near the plane perpendicular to the aromatic ring. Semiempirical molecular orbital calculations with the MNDO method indicate that all of the molecules prefer perpendicular conformations while similar calculations with AM1 indicate that all prefer planar conformations. Apparently the conformational behaviour can be quite sensitive to subtle changes in intramolecular interactions, which may indicate improvements to these semiempirical methods. The NMR results have been used to derive an internally consistent set of rotational potentials. Synthetic photoelectron spectra derived from these potentials and the AM1 orbital energies are in good agreement with the experimental spectra.

Interactions between Methylene Blue and Pullulan According to Molecular Orbital Calculations

2020 ◽  
Vol 140 (11) ◽  
pp. 529-533
Author(s):  
Pasika Temeepresertkij ◽  
Saranya Yenchit ◽  
Michio Iwaoka ◽  
Satoru Iwamori
Keyword(s):  
Methylene Blue ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations
Sign in / Sign up

Export Citation Format

Share Document