HIGH-LEVEL AB INITIO QUANTUM CHEMICAL STUDIES OF THE COMPETITION BETWEEN ...

168 Pages·2014·3.83 MB·English

HIGH-LEVEL AB INITIO QUANTUM CHEMICAL STUDIES OF THE COMPETITION
BETWEEN CUMULENES, CARBENES, AND CARBONES
by
SHIBLEE RATAN BARUA
(Under the Direction of WESLEY D. ALLEN)
ABSTRACT
High-accuracy computations involving coupled-cluster methods in concert with series of
correlation-consistent basis sets are utilized to explore the geometric structures, relative
energetics, and vibrational spectra of some molecular systems with unusual properties, namely
C(BH) , C(AlH) and HCNO. Reliable focal point analyses (FPA) targeting the CCSDT(Q)/CBS
2 2
limit for the ground electronic state of C(BH) reveals a relative energy difference of only 0.02
2
kcal mol−1 between a linear and a bent (∠BCB ≈ 90°) structure, thus identifying an unusual case
of an “angle-deformation” isomer. Highly accurate CCSD(T)/cc-pVTZ and composite
c~CCSDT(Q)/cc-pCVQZ anahrmonic vibrational frequency computations precisely reproduced
the experimental IR spectra for linear C(BH) , and made excellent predictions for the hitherto
2
unobserved bent isomer. With the aid of elaborate bonding analyses, linear C(BH) is described
2
as a cumulene, while bent C(BH) can be best characterized as a carbene with a little carbone
2
character. A similar FPA treatment yields bent C(AlH) (∠AlCAl ≈ 98°) as the ground electronic
2
structure, comfortably placing it 9.60 kcal mol−1 below its linear counterpart, thus confirming the
dominance of a carbene/carbone model for the Al analogue of C(BH) . Confident predictions for
2
the heretofore undetected bent C(AlH) are made through anharmonic frequency computations
2
at the CCSD(T)/cc-pV(T+d)Z level. Next, a highly accurate and computationally demanding
AE-CCSDT(Q)/CBS treatment predicts a bent ground electronic structure for the classic
quasilinear HCNO molecule (∠HCN ≈ 174°), lying a miniscule 0.22 cm−1 below the
corresponding linear geometry, thus indicating an intermediate between a cumulene and a
carbene model. Exhaustive investigation is carried out on the geometric structures and for the
harmonic vibrational frequencies for both linear and bent HCNO, and a similarly elaborate
benchmarking is pursued for the HCN molecule. Finally, a rigorous theoretical analysis of the
topology of polytwistane is performed to reveal a non-repeating, helical, carbon nanotube.
Utilizing homodesmotic equations and including explicit computations as high as CCSD(T)/cc-
pVQZ, the FPA treatment of the enthalpy of formation ultimately yields (polytwistane) =
°
∆(cid:2)(cid:3)(cid:4)
+1.28 kcal (mol CH)−1, thus demonstrating the thermodynamic and synthetic viability of this
polymer when compared to acetylene.

INDEX WORDS: Cumulene; Carbene; Carbone; Coupled-cluster theory; Correlation-
consistent basis sets; Basis-set extrapolation; Focal point analysis; Angle-
deformation isomer; Vibrational perturbation theory; Isotopic shifts;
Intrinsic reaction path; Quantum tunneling; Quasilinear; Homodesmotic
equations; Carbon nanotube; Saturated polymer; Double helix; Irrational
periodicity.
HIGH-LEVEL AB INITIO QUANTUM CHEMICAL STUDIES OF THE COMPETITION
BETWEEN CUMULENES, CARBENES, AND CARBONES

by

SHIBLEE RATAN BARUA
B.A., Berea College, Berea, KY, 2008

A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial
Fulfillment of the Requirements for the Degree

DOCTOR OF PHILOSOPHY

ATHENS, GEORGIA
2014
© 2014
Shiblee Ratan Barua
All Rights Reserved
HIGH-LEVEL AB INITIO QUANTUM CHEMICAL STUDIES OF THE COMPETITION
BETWEEN CUMULENES, CARBENES, AND CARBONES

by

SHIBLEE RATAN BARUA

Major Professor: Wesley D. Allen
Committee: Henry F. Schaefer III
Gary E. Douberly

Electronic Version Approved:

Maureen Grasso
Dean of the Graduate School
The University of Georgia
May 2014
DEDICATION

To my Dad, Mr. Mukul Ratan Barua, whose constant encouragement and support have brought
me this far.
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ACKNOWLEDGEMENTS
A lot of people have influenced me in positive ways, but the one person who stood a mile
ahead of everyone else was my Dad. His constant encouragement, his support, and his
compassion for the growth and success of his two children were unparalleled in my opinion. He
was not only my father, but a great friend as well. Despite his limited income as a government
official, he provided the best education available out there in Bangladesh for his two children,
and I am ever so grateful to him for that. From thousands of miles away during our phone
conversations, however brief they might be, he always mentioned how happy he would be to see
me get my Doctorate. I could not fulfill his wish during his lifetime, nor could I be there when he
breathed his last on May 3rd 2013. As I inch closer to my degree, I realize that he would be the
happiest person in the world right now; happier than me would probably not be an exaggeration.
I would like to take this opportunity to show my utmost gratefulness to the best Dad in the world
for always being there for me and believing in me. Thank You. Thank You from the depth of my
heart.
My family members have always played a huge supporting role in my life. My elder
brother Parag and my mom have backed me up and urged me forward. It’s sad how the three of
us are so far apart from each other right now; my mom in Bangladesh, my brother in Sydney, and
me being here in the States. Hopefully some day we could all live close together as a family once
again. Special thanks to all my cousins (Muna, Nina, Turna, Upama, Pallab, Kallol, Hillol), who
still remain the closest people in my life no matter how much time passes between our phone
conversations. I have a lot of friends here in the States and back in Bangladesh that I need to
v
mention right now, but would soon run out of pages if I do so. However, I would especially like
to thank my friend Kelsey Turner for providing me the support that I needed during my father’s
death, and for always being there for me when I needed somebody to rely on.
I often jokingly call my group-mate Jowa as my “semi-mentor”, and rightly so. He has
helped me enormously throughout my research work. Being completely unaware of how
computational quantum chemistry actually works, I had to learn everything from scratch. Jowa
was patient with me and taught me well. I was very lucky to have someone like him to guide me
through. He is an excellent co-worker and a very good friend, and I am still trying to find a way
to beat him in badminton. I would also like to thank my friend Kedan for keeping me entertained
with her lively smile in the office; I’ll definitely miss our fun and random conversations.
Last, but not least, I would like to show my sincere gratefulness to the faculty members at
the CCQC, Dr. Schaefer and Dr. Allen. Dr. Schaefer has provided us with a wonderful facility
conducive for state-of-the-art research work. I admire his friendly personality and great stories
during his lectures. My mentor, Dr. Allen, has been very supportive, caring, and accommodating
towards all his students. Our group has a good number of international students, and he has never
said no to any of our requests for visiting our respective homelands. The only thing he would ask
for is whether we have internet access back home so that we could continue our research work
away from the office. His Advanced Quantum course gifted me many sleepless nights and
hundreds of pages of homework assignments. In hindsight, the struggle was totally worth it since
I learned an outrageous amount in that class. It has surely been a pleasure working under Dr.
Allen for the last six years or so.
Now, off to some quantum chemistry...

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TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS .............................................................................................................v
CHAPTER
1 HIGH-LEVEL AB INITIO QUANTUM CHEMICAL THEORY AND ITS
APPLICATION IN CARBON CHEMISTRY 1
1.1 INTRODUCTION .............................................................................................1
1.2 THEORETICAL METHODS ............................................................................3
1.3 BASIS-SET EXTRAPOLATION ...................................................................10
1.4 FOCAL POINT ANALYSIS ...........................................................................11
1.5 AUXILIARY CORRECTIONS.......................................................................15
1.6 ANHARMONIC VIBRATIONAL FREQUENCIES .....................................16
1.7 RESEARCH OVERVIEW ..............................................................................19
REFERENCES ......................................................................................................20
2 NEARLY DEGENERATE ISOMERS OF C(BH) : CUMULENE, CARBENE,
2
OR CARBONE? 24
2.1 ABSTRACT .....................................................................................................25
2.2 INTRODUCTION ...........................................................................................26
2.3 COMPUTATIONAL METHODS ...................................................................28
2.4 RESULTS AND DISCUSSION ......................................................................31
2.5 THE ALUMINUM ANALOGUE, C(AlH) ....................................................59
2
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2.6 CONCLUSIONS..............................................................................................71
2.7 ACKNOWLEDGEMENTS .............................................................................73
REFERENCES ......................................................................................................74
3 QUASILINEARITY IN FULMINIC ACID (HCNO) MOLECULE 84
3.1 ABSTRACT .....................................................................................................84
3.2 INTRODUCTION ...........................................................................................85
3.3 THEORETICAL METHODS ..........................................................................87
3.4 RESULTS AND DISCUSSION ......................................................................89
3.5 CONCLUSIONS..............................................................................................95
REFERENCES ......................................................................................................96
4 POLYTWISTANE 101
4.1 ABSTRACT ...................................................................................................102
4.2 INTRODUCTION .........................................................................................102
4.3 TOPOLOGY AND COMPUTATIONAL ANALYSIS ................................105
4.4 POLYTWISTANE THERMOCHEMISTRY ................................................117
4.5 CONCLUSIONS............................................................................................121
4.6 ACKNOWLEDGEMENTS ...........................................................................122
REFERENCES ....................................................................................................122
5 SUMMARY AND CONCLUSIONS 127
APPENDIX
A SUPPORTING INFORMATION FOR CHAPTER 2 ...............................................129
B SUPPORTING INFORMATION FOR CHAPTER 4 ...............................................145
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