Microwave Spectrum, Dipole Moment, and Intramolecular Hydrogen Bond of 2-Methoxyethanol

1972 ◽  
Vol 50 (8) ◽  
pp. 1149-1156 ◽  
Author(s):  
Paul Buckley ◽  
Mireille Brochu
Keyword(s):  
Dipole Moment ◽  
Minimum Energy ◽  
Lone Pair ◽  
Microwave Spectrum ◽  
Rotational Isomer ◽  
Ether Oxygen ◽  
Intramolecular Hydrogen ◽  
Lone Pair Electrons ◽  
Hydroxyl Hydrogen Atom ◽  
Hydroxyl Hydrogen

The minimum energy conformation of 2-methoxyethanol (CH3OCH2CH2OH) has been determined from an analysis of its microwave spectrum. The rotational constants of the normal species are: A = 12982.35, B = 2742.48, and C = 2468.10 MHz; the dipole moment components are μa = 2.03, μb = 1.15, [Formula: see text] and μ = 2.36 ± 0.03 D. For the CH3OCH2CH2OD species: A = 12385.71, B = 2724.74, and C = 2431.42 MHz. The conformation consistent with this data is gauche about each of the C—C, C—O(H) and C—O(ether) bonds, having dihedral angles of 57 ± 3°, 45 ± 5°, and 8 ± 3°, respectively. This distorted conformation is one in which the hydroxyl hydrogen atom is approximately aligned with the nearest sp3 lone pair electrons of the ether oxygen atom. Transitions in three excited torsional states have also been observed but no other rotational isomer was detected.

Dipole Moment as a Possible Diagnostic Descriptor of the Conformational Isomerism of the Ammonia Molecule

2012 ◽  
pp. 58-75
Author(s):  
Dulal C. Ghosh ◽  
Sandip Kumar Rajak
Keyword(s):  
Dipole Moment ◽  
Equilibrium Shape ◽  
Lone Pair ◽  
Molecular Orbitals ◽  
Energy Curve ◽  
Conformational Isomerism ◽  
Localized Molecular Orbitals ◽  
Time Symmetry ◽  
Quantum Mechanical Study ◽  
Lone Pair Electrons

In this report, Ghosh and Rajak have made a detailed quantum mechanical study of the variation of the dipole moment of ammonia as a function of its conformations evolving during the process of its umbrella inversion by invoking their method of dipole correlation of electronic structure as basis. Ghosh et al discover a surprising result that the variation of dipole moment mimics the total energy curve as a function of reaction coordinates revealing the fact that the dipole moment is one possible diagnostic descriptor of the conformational isomerism of molecules containing lone pair electrons. The dipole is calculated and partitioned into bond and lone pair components for a large number of conformations between the equilibrium shape and the transition state of inversion and the results are interpreted and correlated in terms of the localized molecular orbitals, LMOs generated from the canonical molecular orbitals, CMO’s of each conformation. Anderson, from the concept of space time symmetry, postulated that ammonia has zero dipole moment. Present study reveals that Anderson’s correlation relied upon the bond moment only while the major component of dipole of ammonia originates from the lone pair of nitrogen.

scholarly journals Microwave Spectrum, Conformation, Intramolecular Hydrogen Bond and Dipole Moment of 2,3-Butadien-1-ol.

1983 ◽  
Vol 37a ◽  
pp. 679-684 ◽  
Author(s):  
Anne Horn ◽  
K.-M. Marstokk ◽  
Harald Møllendal ◽  
Hanno Priebe ◽  
Ole Faurskov Nielsen
Keyword(s):  
Hydrogen Bond ◽  
Dipole Moment ◽  
Intramolecular Hydrogen Bond ◽  
Microwave Spectrum ◽  
Intramolecular Hydrogen

Critical Survey of the method of ionic-homopolar resonance

1951 ◽  
Vol 207 (1088) ◽  
pp. 63-73 ◽  
Keyword(s):  
Dipole Moment ◽  
Lone Pair ◽  
Atomic Radius ◽  
Substantial Part ◽  
Critical Survey ◽  
Conventional Theory ◽  
Total Dipole Moment ◽  
Atomic Orbitals ◽  
Individual Bond ◽  
Lone Pair Electrons

Some of the theoretical difficulties in the method of ionic-covalent resonance are discussed. They include our ignorance of the fundamental energies, and also of the orbitals used. If these are hybrids, as usually occurs, considerable care is required in using the conventional theory because: (1) the atomic radius, and (2) the effective electronegativity of a hybrid depend on the degree of mixing of the basic atomic orbitals. In polyatomic molecules the lone-pair electrons play a substantial part in determining the total dipole moment, and there are further difficulties associated with (1) independence, (2) partial delocalization, and (3) possible 'bent’ character of the bonds. As a result many bonds (e.g. CH, NH, OH) are intrinsically much less ionic than is usually supposed. In addition the dipole moment of a molecule does not depend in any simple way upon the formal charges associated with the atoms; nor does it provide a completely satisfactory basis for assigning individual bond moments. The paper concludes with an outline of some possible improvements which merit further research.

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