Approaching Aromatic Interactions with Small Molecule Model Systems

220 Pages·2016·7.72 MB·English

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Theses and Dissertations
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Ping Li
University of South Carolina - Columbia
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Li, P.(2015). Approaching Aromatic Interactions with Small Molecule Model Systems: Assessing N-
Heteroarene in ∏ -Stacking and CH-∏ Interactions, Crystal Engineering of Atropisomeric Rotors, and
Developing Responsive Organic Charge-Transfer Complex. (Doctoral dissertation). Retrieved from
https://scholarcommons.sc.edu/etd/3233
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APPROACHING AROMATIC INTERACTIONS WITH SMALL MOLECULE MODEL
SYSTEMS: ASSESSING N-HETEROARENE IN Π-STACKING AND CH-Π
INTERACTIONS, CRYSTAL ENGINEERING OF ATROPISOMERIC ROTORS, AND
DEVELOPING RESPONSIVE ORGANIC CHARGE-TRANSFER COMPLEX

Ping Li

Bachelor of Science
East China University of Science and Technology, 2006

Submitted in Partial Fulfillment of the Requirements

For the Degree of Doctor of Philosophy in

Chemistry

College of Arts and Sciences

University of South Carolina

2015

Accepted by:

Ken D. Shimizu, Major Professor

Linda S. Shimizu, Committee Member

Daniel L. Reger, Committee Member

Andreas Heyden, Committee Member

Lacy Ford, Senior Vice Provost and Dean of Graduate Studies
© Copyright by Ping Li, 2015
All Rights Reserved.
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DEDICATION
To my dad, Zhongyuan Li

iii
ACKNOWLEDGEMENTS
First and foremost, I would like to thank my advisor Dr. Ken D. Shimizu for his
years of guidance and support. I am truly grateful not only for the knowledge and skills he
passed on to me but, more importantly, the habit of thinking critically and the rigorous and
meticulous professionalism. All of these will surely benefit my career and life in future.
Next, I would like express me wholehearted appreciation to the Shimizu group members,
both current and former. Without the help and encouragements from theirs, I perhaps could
not have accomplished even half what I have now. I am also so honored to meet and work
with a highly talented group of fellow students, postdoc researchers, faculty, and staffs at
the chemistry department. I shall give special thanks to our personnel at the NMR, X-ray
crystallography, and MS facilities for their kind and patient help on various research
problems.
At last, I would like express my deepest gratitude to my dad, Zhongyuan Li, my
cousin Amanda Ling, my mentor Dr. Wei Wang, my best buddies Xinyue Wei and Zimu
Liu, and countless friends who have helped and supported me along the way. My pursuit
in chemistry took some unexpected turns at the beginning. Without their caring and help,
I would have never come out that miserable period of life. I owe this dissertation to them
much more than to myself. In the end, I want to close with a dedication to my dad: “Dad,
thank you for being so supportive over these years! I hope what I have accomplished make
you proud. I love you!”
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ABSTRACT
Non-covalent interactions involving aromatic species are important in many areas
in chemistry, biochemistry, and materials sciences. During the past two decades, small
molecule model systems have emerged as a powerful tool to advance our knowledge of the
stability trends for aromatic interactions in the condensed phase. Among these, the C-
shape N-arylimide molecular balances developed by our laboratory have proven to be one
most successful and versatile model systems that can be readily adapted to investigate
various types of aromatic interactions. These molecular balances are particularly apt at
isolating and accurately measuring the targeted weak aromatic interaction energies for
different geometries. In this dissertation, our experimental efforts in utilizing the N-
arylimide molecular balance to examine the impacts of nitrogen-containing aromatic
surfaces (N-heteroarenes) on π-stacking and CH-π interactions are detailed. Polar N-
heteroarenes displayed pronounced electrostatic character in these interactions which
influenced both their stability trends and geometric preferences. Introducing a formal
positive charge at the heterocyclic nitrogen greatly enhanced these electrostatic effects.
Next, this versatile molecular model system was applied to the study of the relationship
between the solution and solid-state conformational preferences for rapid interconverting
conformers. Close examination of a library of atropisomeric O-tolyl succinimide rotors
revealed that the solution conformational preferences were generally excellent predictors
of the conformational preferences in crystal structures. Interestingly, the correlation
function between the solid-state and solution mole fraction of syn- conformer (χ ) were
syn
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not linear but fit to a step-function trend where the solid-state χ was either 0 or 1 for most
syn
rotors except for those with a solution χ of 0.50 ± 0.06. Finally, we examined the
syn
behavior of a dynamic intramolecular aromatic stacking donor-acceptor-donor complex.
This system displayed interesting reversible color changes in the solid-state when treated
with different organic solvents. The unique responsive behavior was attributed to solvent-
induced changes in the intramolecular stacking geometry of the D-A-D complex.
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TABLE OF CONTENTS
DEDICATION ....................................................................................................................... iii
ACKNOWLEDGEMENTS ........................................................................................................ iv
ABSTRACT ............................................................................................................................v
LIST OF TABLES ................................................................................................................ viii
LIST OF FIGURES ...................................................................................................................x
CHAPTER 1: MOLECULAR BALANCES AND THEIR APPLICATIONS IN
EXPERIMENTAL STUDIES OF NON-COVALENT AROMATIC INTERACTIONS ..................1
CHAPTER 2: A COMPREHENSIVE EXPERIMENTAL STUDY OF N-HETEROCYCLIC
Π-STACKING INTERACTIONS OF NEUTRAL AND CATIONIC PYRIDINES .......................37
CHAPTER 3: THE CH-Π INTERACTION OF METHYL ETHERS AS A MODEL
FOR CARBOHYDRATE-N-HETEROARENE INTERACTIONS ...........................................82
CHAPTER 4: CORRELATION BETWEEN SOLID-STATE AND SOLUTION
CONFORMATIONAL RATIOS IN A SERIES OF
N-(O-TOLYL)SUCCINIMIDE MOLECULAR ROTORS. .................................................123
CHAPTER 5: SOLVENT-INDUCED REVERSIBLE SOLID-STATE COLOR
CHANGE OF AN INTRAMOLECULAR CHARGE-TRANSFER COMPLEX. ........................165
CHAPTER 6: FUTURE WORK. .............................................................................................189
APPENDIX A− COPYRIGHT PERMISSIONS. .........................................................................195

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LIST OF TABLES
Table 2.1 Measured plane-to-plane angle (α), centroid-to-plane distance (D) and horizontal
centroid-to-centroid off-set (H) between the two π-stacking six-membered rings in
the crystal structures of balances 1’, 2, 3’, 4, 6, and 7. ............................................48
Table 2.2 Measured conformational equilibrium energies (ΔG, kcal/mol) for balances 1-7
in DMSO-d at 23 °C and relative energies (ΔΔG, kcal/mol) of the N-heterocyclic
6
balances 2-7 relative to the non-heterocyclic balance 1 ...........................................53
Table 2.3 Measured relative energies (ΔΔG, kcal/mol) of the N-heterocyclic balances 2-7
relative to the non-heterocyclic balance 1 ................................................................58
Table 2.4 The measured ΔG’s [kcal/mol] in deutrated solvents at rt. ...............................74
Table 2.5 Tabulated data for the correlation plot in the text ..............................................74
Table 2.6 Measured geometric parameters (r and h) defined for characterizing the O-π
interactions in crystal structure 1’, 2, 3’, 4, 6 and 7. ................................................75
Table 2.7 The measured relative amounts of added MsOH, folded/unfolded ratios and
calculated ΔG’s in the titration experiment of |2 + MsOH → 4| in DMSO-d . .......77
6
Table 2.8 The measured relative amounts of added MsOH, folded/unfolded ratios and
calculated ΔG’s in the titration experiment of |3 + MsOH → 5|in DMSO-d .........77
6
Table 2.9 The measured relative amounts of added MsOH, folded/unfolded ratios and
calculated ΔG’s in the titration experiment of |2 + MsOH → 4|in CD CN .............78
3
Table 2.10 The measured relative amounts of added MsOH, folded/unfolded ratios and
calculated ΔG’s in the titration experiment of |3 + MsOH → 5|in CD CN .............78
3
Table 2.11 The measured relative amounts of added MsOH, folded/unfolded ratios and
calculated ΔG’s in the titration experiment of |2 + MsOH → 4| in CDCl ..............79
3
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Table 2.12 The measured relative amounts of added MsOH, folded/unfolded ratios and
calculated ΔG’s in the titration experiment of |3 + MsOH → 5| in CDCl ..............79
3
Table 3.1 1H NMR solution measurements of balances 1-6 in CD Cl at 25 °C ...............86
2 2
Table 3.2 Measured geometric parameters for characterizing CH-π interactions in crystal
structures 1’-3’ and 6’: the atom-to-plane distance (D), CH-to-plane accessing angle
(α) and the hydrogen projection-to-centroid displacement (d ), the closest annular
1
sp2 atom (X), and the hydrogen projection-to-X displacement (d ). ......................110
2
Table 3.3 Measured folding energies (∆G, kcal/mol) for balances 1, 2, 3 and 6 in six
common organic solvents at 25 ˚C .........................................................................121
Table 3.4 Measured [folded]/[unfolded] ratios using two different sets of peaks, i.e., the
arm OCH protons (H ) and the succinimide methide protons (H ) in six solvents
3 arm S
at 25 ˚C. ..................................................................................................................122
Table 3.5 Measured ∆G’s (kcal/mol)a for balances 4 and 5 in C D , CD Cl and DMSO-d
6 6 2 2 6
at 25 ˚C. ..................................................................................................................122
Table 4.1 Measured mole fraction of syn-conformer (𝜒 ) in solution and in solid-state
syn
crystals and relevant information of crystal structure. ...........................................135
Table 4.2 Measured bite angle (θ) for 30 rotors in their crystal structures ......................137
Table 4.3 The measured in-solution χ for 30 rotors in this study.................................139
syn
Table 5.1 Measured geometric parameters in crystal structures of 1 and 2 .....................187
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