ChemInform Abstract: MOLECULAR ORBITALS FROM GROUP ORBITALS. 6. QUANTITATIVE EVALUATION AND NATURE E OF THE STABILIZING AND DESTABILIZING ORBITAL INTERACTIONS IN DIFLUOROETHYLENES AND FLUOROPROPENES

1978 ◽  
Vol 9 (37) ◽  
Author(s):  
M.-H. WHANGBO ◽  
D. J. MITCHELL ◽  
S. WOLFE
Keyword(s):  
Quantitative Evaluation ◽  
Molecular Orbitals ◽  
Orbital Interactions ◽  
Group Orbitals

Molecular orbitals from group orbitals. IX. The problem of hybrid lone pairs

1979 ◽  
Vol 57 (7) ◽  
pp. 729-732 ◽  
Author(s):  
Daniel Kost ◽  
H. Bernhard Schlegel ◽  
David John Mitchell ◽  
Saul Wolfe
Keyword(s):  
Ab Initio ◽  
Molecular Orbitals ◽  
Congeneric Species ◽  
Matrix Elements ◽  
Orbital Interactions ◽  
Lone Pairs ◽  
Conformational Properties ◽  
Group Orbitals

The quantitative PMO analysis of the ab initio wavefunction of a molecule A—B is based upon a partitioning of the Fock matrix elements of this wavefunction to obtain the fragments A and B, followed by computation of the stabilizing and destabilizing orbital interactions between the orbitals of these fragments that contribute to the HOMO of A—B. However, when one or both of the fragments is NH2 or a congeneric species, neither the 3a1 nor the 1b1 orbital of this fragment is appropriate for overlap with the second fragment, and the PMO analysis cannot be performed. A solution to this problem is proposed, and has been tested by application to various conformational properties of methylamine.

Orbital interactions. IX. The effect of remote substituents on the electrophilic nitration of a series of 11-substituted exo-hexahydro-7,10-methanofluoranthenes

1980 ◽  
Vol 33 (4) ◽  
pp. 795 ◽  
Author(s):  
MJ Oliver ◽  
HK Patney ◽  
MN Paddon-Row
Keyword(s):  
Product Distribution ◽  
Molecular Orbitals ◽  
Orbital Interactions ◽  
Opposite Result ◽  
Field Effects ◽  
Methoxy Substituent ◽  
Salient Features ◽  
Scf Calculations

Product distribution and the relative rates of nitration (Cu(NO3)2,3H2O/Ac2O) of a series of 11-substituted exo-hexahydro-7,10- methanofluoranthenes, (8), (9b), (10) and (11b), and acenaphthene, (12), have been determined. It was observed that a syn-methoxy substituent, as in (11b), greatly enhanced the reactivity of the acenaphthene ring towards nitration compared with unsubstituted (8), the α position being activated more than the γ position. Precisely the opposite result was obtained for the nitration of the ketone (10). These results are explained in terms of the consequences of through- space orbital interactions (OITS), operating between the molecular orbitals of the 11-substituent and those of the acenaphthene ring; a PMO model is used for the nitration reaction. The results of INDO MO SCF calculations on the water-acenaphthene complex (22) and the formaldehyde-acenaphthene complex (23), which are intended to mimic the salient features of (11b) and (10) respectively, lend support to the OITS proposal. However, alternative proposals, based on field effects (in the case of (10)) and on the formation of a complex (24) for the nitration of (11b), are also discussed.

Molecular orbitals from group orbitals. I. A perturbational molecular orbital treatment of the electronic structures, shapes and conformations of AHmBHn Systems

1976 ◽  
Vol 54 (6) ◽  
pp. 949-962 ◽  
Author(s):  
Myung-Hwan Whangbo ◽  
Saul Wolfe
Keyword(s):  
Molecular Orbital ◽  
Electronic Structures ◽  
Molecular Orbitals ◽  
Orbital Interaction ◽  
Molecular Systems ◽  
Group Orbitals

A procedure is proposed which allows the group orbitals of a fragment AHm—to be obtained from the molecular orbitals of the molecule AHm—H. Orbital interaction diagrams constructed from these group orbitals have been found useful in the description of the electronic structures and conformations of a variety of molecular systems of the type AHmBHn. The molecules that have been treated by this procedure include ethane, hydrazine, diphosphine, aminophosphine, aminoborane, and sulfonium and phosphonium ylids.

Quantitative Evaluation of Weak Nonbonded Se···F Interactions and Their Remarkable Nature as Orbital Interactions

2002 ◽  
Vol 124 (9) ◽  
pp. 1902-1909 ◽  
Author(s):  
Michio Iwaoka ◽  
Hiroto Komatsu ◽  
Takayuki Katsuda ◽  
Shuji Tomoda
Keyword(s):  
Quantitative Evaluation ◽  
Orbital Interactions

A Photoelectron Investigation of the Peroxide Bond

1975 ◽  
Vol 53 (22) ◽  
pp. 3439-3447 ◽  
Author(s):  
R. S. Brown
Keyword(s):  
Dihedral Angle ◽  
Ground State ◽  
Vibrational Frequencies ◽  
Molecular Orbitals ◽  
Photoelectron Spectra ◽  
Raman Spectroscopic ◽  
Orbital Interactions ◽  
Highest Occupied Molecular Orbitals ◽  
Peroxide Bond

The photoelectron spectra of several peroxides and their interpretation is presented. The effects of substituents is separated from vicinal orbital interactions using as a guideline the effect of similar substitution on the ether analogues. It is found that by comparison of Raman spectroscopic frequencies of the peroxide ground state, and vibrational frequencies for the ion (via pes), that the HOMO of peroxides is antibonding with respect to the O—O linkage. Additionally, the dependence of the splitting of the two highest occupied molecular orbitals on dihedral angle is verified by the pe spectra of several well-defined cyclic peroxides. Finally, the pe spectrum of tetramethyl-1,2-dioxacyclobutane (tetramethyl dioxetane) is presented indicating that it is not unlike other cyclic peroxides.

Molecular orbitals from group orbitals. IV. Quantitative perturbational molecular orbital analysis of the methyl rotational barriers in (CH3)2X molecules. Effect of the fragmentation mode upon the results of the analysis

1977 ◽  
Vol 55 (15) ◽  
pp. 2778-2787 ◽  
Author(s):  
Myung-Hwan Whangbo ◽  
Saul Wolfe
Keyword(s):  
Molecular Orbital ◽  
Qualitative Description ◽  
Orbital Energy ◽  
Orbital Interactions ◽  
Group Orbitals ◽  
Principal Property ◽  
Quantitative Results ◽  
Molecular Orbital Analysis ◽  
Orbital Analysis ◽  
Qualitative Discussion

A quantitative perturbational molecular orbital (PMO) analysis has been performed on ab initio SCF-MO wavefunctions associated with the rotation of the methyl groups in a series of (CH3)2X molecules (X = CH2, O, S, C=O, C=CH2). Two fragmentation modes have been investigated: Method a, in which the system is dissected into X and (CH3)2; and Method b, in which the system is dissected into CH3X and CH3. Both fragmentation modes reproduce the principal property of these molecules, viz., that the more crowded SS conformation is preferred. However, whether this conformational preference is controlled by two-electron stabilizing effects or four-electron destabilizing effects is found to depend upon both the mode of fragmentation and the nature of the substituent X. The quantitative results are supplemented by a detailed qualitative description of the nature of the group orbitals associated with the two fragmentation modes and the various types of orbital interactions. It is shown that orbital energy differences control the qualitative discussion of Method a, and overlap effects control that of Method b. Although the final result, i.e., the preference for the SS conformation, and the behaviour of individual orbital interactions are anticipated correctly by the qualitative arguments, these are unable to assess the relative contributions of the stabilizing and destabilizing interactions.

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