Theoretical study on some inter- and intra-molecular interactions [Elektronische Ressource] / vorgelegt von Hongjun Fan

Fan Gang, Hongjun

Informations

• Publié par: universitat_siegen
• Publié le: 01 janvier 2004
• Nombre de lectures: 17
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Theoretical Study on
Some Inter- and Intra-Molecular Interactions





Dissertation
zur Erlangung des Grades eines Doktors
der Naturwissenschaften,



vorgelegt von
Hongjun Fan, M. Sc.
geb. am 21. Juli 1972 in Jiajiang, Sichuan, V. R. China,




eingereicht beim Fachbereich 8
der Universität Siegen,
Siegen 2004

















Erster Gutachter: Prof. Dr. W.H.E. Schwarz

Zweiter Gutachter: Prof. Dr. M. Albrecht

Tag der mündlichen Prüfung: September 15, 2004


urn:nbn:de:hbz:467-815 Abstract:
Theoretical studies on some intra- and inter-molecular weak interactions
Ab-initio MP2&CI and DF calculations were used to study some chemical topics that involve
inter- and intra-molecular so-called weak interactions. These topics include: i) What is the
physical origin of the single bond rotational barrier, e.g. of ethane? Our answer is that the
kinetic Pauli repulsion between CH bond pairs is much more important than hyperconjugative
attraction of CH bond pairs through virtual CH σ* orbitals. ii) What is the physical origin of the
bond length expansion of electron-rich main-group molecules, e.g. F etc.? It is here dominantly 2
explained by inter-atomic lone pair repulsion, with possible contributions also from atomic
hybridization effects of the bonding AOs. The importance of the tails of the lone pairs is stressed.
iii) What is the physical origin of reduced nonbonded interatomic separations? We found that
most so-called reduced distances in the literature are simply due to the contraction of positively
charged atoms. If the ubiquitous charge dependence of effective atomic radii is accounted for, a
few really reduced distances survive. They are caused by specific orbital interactions of heavy
nonmetal atoms, by specific charge attractions or by clamping bridges. iiii) What is the origin of
the different orientations of fluorescence of dye molecules in zeolite channels? Oxonine was
studied. We can explain the results of single molecule fluorescence microscopy. Correct van der
Waals radii, silica - dye molecule - attractions and rotation of the optical transition moment due
to orbital interactions are more important than the electrostatic Stark effect.

Zusammenfassung:
Theoretische Studien an intra- und inter-molekularen Schwachen
Wechselwirkungen
Ab-initio-MP2&CI- und DF-Rechnungen wurden zur Untersuchung einiger chemischer Problem benutzt, die
mit den sogenannten inter- and intra-molekularen Schwachen Wechselwirkungen zusammenhängen. i) Was ist
die physikalische Ursache der Einfachbindungs-Rotationsbarriere, z.B. von Ethan? Unsere Antwort ist, dass
die kinetische Pauli-Abstoßung zwischen CH-Bindungspaaren viel wichtiger ist als die hyperkonjugative
Anziehung von CH-Bindungspaaren über virtuelle CH- σ*-Orbitale. ii) Was ist die physikalische Ursache der
Bindungslängen-Dehnung bei elektronenreichen Hauptgruppen-Molekülen wie z.B. F usw.? Wir geben eine 2
begründete Erklärung durch interatomare Abstoßung von Einsamen Paaren, möglicherweise verstärkt durch
Hybridisierungseffekte der Bindungs-AOs. Die rückwärtigen Schwänze der Einsamen Paare sind besonders
relevant. iii) Was ist die physikalische Ursache der verkürzten nichtbindenden Atomabstände? Wir fanden,
dass die meisten sogenannten verkürzten Abstände in der Literatur auf Vernachlässigung der Verkleinerung der
Radien von positiv geladenen Atomen beruhen. Wenn die generelle Ladungsabhängigkeit der effektiven
Atomradien mitberücksichtigt wird, bleiben einige wenige echt verkürzte Abstände übrig. Sie sind durch
spezifische Orbitalwechselwirkungen schwerer Nichtmetallatome, durch starke Ladungs-Anziehungen oder
durch klammernde Brücken verursacht. iiii) Was bedingt die unterschiedlichen Fluoreszenz-Orientierungen
von Farbstoffmolekülen in Zeolith-Kanälen? Oxonin wurde studiert. Wir erklären die Ergebnisse der
Einzelmolekül-Fluoreszenzmikroskopie durch Verwendung korrekter van der Waals-Radien, durch
Silikat-Farbstoff-Anziehungen und durch die Drehung des optischen Übergangsmoments wegen
Orbitalwechselwirkungen. Der Starkeffekt in den Kanälen spielt keine Rolle. Acknowledgements

First, I want to express my deep gratitude to Prof. Dr. W. H. Eugen Schwarz, my doctor
supervisor, for his excellent guidance of my PhD work and his kind help of my life in Siegen.

I am very grateful to Prof. Dr. Shuguang Wang for the very helpful discussions and some
collaboration in Shanghai.
I would like to thank Prof. Dr. G. Calzaferri, Prof. Dr. A. J. Meixner, and Dr. C. Debus for the
constructive discussions and for the additional experimental and numerical details on the topic
of dye molecules in zeolite; I also thank Dr. Jier Schwarz-Niu for the preliminary works on
the transition dipole moment of oxonine.
I thank Prof. Dr. B. Engelen and Dr. M. Panthöfer for the helpful discussions and on the
experimental details, in particular those prior to publication, on the topic of reduced
nonbonded distances.
And I thank Prof. Dr. A. Maercker for the constructive suggestions drawing our attention to
the hot topic of the rotational barrier of ethane.

I would like to thank Dr. Holger Poggel for his assistance with the computers and software,
and Mrs. Petra Schöppner, Mrs. Doris Spiller and Mrs. Erika Stei for their assistance
concerning administrative and bureaucratic affairs.

I gratefully acknowledge financial supports by Universität Siegen and by Deutsche
Forschungs-Gemeischaft.

At last I would like to thank my wife, my parents and all the friends I met in Siegen.
Contents
Acknowledgement
Abstract, Zusammenfassung
Contents
1. Introduction: On Weak Interactions ······························································· 1
References ············································································································ 4
2. The Rotational Barrier of Ethane ····································································· 5
2.1. Facts and Interpretations ··············································································· 5
2.2. The Partitioning Strategy ·············································································· 5
2.3. Electronic Relaxation and Nuclear Flexing ·················································· 6
2.4. The Generally Paradoxical Role of Relaxation ············································· 7
2.5. A Simple Formal Model of Relaxation ·········································