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Project
Descriptions: Temperature
Effects on Structure |
Hydrogen Bonding
(with Prof Janet Del Bene, Ohio) Our research investigates
environmental effects on the structures and spectroscopic properties of
hydrogen-bonded complexes. In
particular, we are interested in NMR spin-spin coupling constants across
hydrogen bonds. Our quest has been to better understand these properties, to
elucidate relationships among structures, IR and NMR properties, and to
provide a firm theoretical basis for the interpretation of relevant
experimental data. We have completed studies
of environmental effects on the structures and IR and NMR properties of the
hydrogen-bonded ClH:pyridine and ClH: and BrH:trimethylammonia
complexes. These studies support the
use of NMR spin-spin coupling constants as a fingerprint of hydrogen-bond
structure. We have initiated
systematic studies of spin-spin coupling constants across hydrogen bonds in
an effort to assess the factors that are important in determining the
magnitude of such coupling constants, and the relationships between coupling
constant and structure. For example,
it is well known that vibrational averaging can influence spin-spin coupling
constants. We have generated potential energy surfaces and coupling constant
surfaces in order to estimate the effects of zero-point motion and thermal
vibrational averaging on coupling constants in the CNH:NCH hydrogen bonded
complex and the FHF— ion.
To our knowledge, this is the first time such studies have ever been
performed. The FHF— ion
has, for many years, presented a major theoretical challenge, and these
studies are the first to accurately predict FF spin-spin coupling constants
in this system. We have seen further
evidence of correlation between NMR parameters and hydrogen bond type in more
detailed investigations of coupling across N-H-N hydrogen bonds. These investigations have also allowed us
to determine the conditions under which a ‘proton-shared’ hydrogen bond can
form. Specifically we have shown that
such a hydrogen bond is unlikely to form in neutral species. Our contributions to the
field include: 1. A rigorous and robust
method for computing vibrational frequencies in ‘floppy’ hydrogen-bonded
complexes. 2. Use of electric fields
to model the environment of hydrogen bonded complexes and to show the
influence of the environment on the structures and spectra of such complexes. 3. Evaluation of NMR XY
spin-spin coupling constants across X-H-Y hydrogen bonds and identification
of the factors that determine the magnitude of these coupling constants. 4. Elucidation of the
relationships among hydrogen bond types, structures, the IR proton-stretching
frequency and the NMR properties of chemical shift and XY spin-spin coupling
constant across the hydrogen bond. We are the first to make the connection
between IR and NMR properties and to show how the XY spin-spin coupling
constant may be used to determine hydrogen bond type and intermolecular
distance. 5. Evaluation of the
effects of zero-point motion and thermal vibrational averaging on spin-spin
coupling constants and the isotropic chemical shielding constant for the
hydrogen-bonded proton. Although this work is still
in its infancy it has already provided insight into the interpretation of
relevant experimental data. The
findings of this research have already led to a better understanding of the
structures and vibrational spectroscopy of the hydrogen bond, and how these
properties may be influenced by the environment. Given the ubiquitousness of the hydrogen bond, this work has
far-reaching consequences in many areas.
The demonstration that the XY spin-spin coupling constant across an
X-H-Y hydrogen bond is dominated by the distance dependent Fermi contact term
will have an impact on the interpretation of NMR data obtained in a wide
range of disciplines. This work will
provide sound theoretical foundation for the interpretation of NMR and IR
data, and structure determination from these data. Publications M. J. T. Jordan and K. C.
Thompson “The Response of a Molecule to an External Electric Field:
Predicting Structural and Spectroscopic Change”, Chem. Phys. Lett. 370, 14-20
(2003). J. E. Del Bene and M. J. T.
Jordan “ To What Extent Do External
Fields and Vibrational and Isotopic Effects Influence NMR Coupling
Constants? Two-Bond Cl-N Spin-Spin
Coupling Constants (2hJCl-N) in Model ClH:NH3
Complexes” J. Phys. Chem. A 106, 5385-5392 (2002). J. S.-S. Toh, M. J. T.
Jordan, B. Husowitz and J. E. Del Bene “Can proton-shared or ion-pair
hydrogen bonds be produced in uncharged complexes? A systematic ab initio
study of the structures and selected NMR and IR properties of complexes with
N-H-N hydrogen bonds” J. Phys. Chem. A. 105, 10906-10914 (2001). M. J. T. Jordan, J. S.-S.
Toh and J. E. Del Bene, “Vibrational averaging of NMR properties for an N-H-N
hydrogen bond” Chem Phys Lett. 346 288-192 (2001). J. E. Del Bene, M. J. T.
Jordan, S. A. Perera and R. J. Bartlett, “Vibrational effects on the F-F
spin-spin coupling constant (2hJFF) in FHF-
and FDF-”, J. Phys. Chem A, 105, 8399-8402 (2001). J. E. Del Bene and M. J. T.
Jordan, “What a difference a decade makes: progress in ab initio studies of
the hydrogen bond”, invited paper for a special issue of Theochem to
celebrate the 10th CCTCC, Theochem, 573, 11-23 (2001). K. Chapman, D. Crittenden,
J. Bevitt, M. J. T. Jordan and J. E. Del Bene, “Relating environmental
effects and structures, IR and NMR properties of hydrogen-bonded complexes:
ClH:pyridine”, J. Phys. Chem. A., 105, 5442-5449 (2001). J. E. Del Bene and M. J. T.
Jordan, “Vibrational spectroscopic and NMR properties of hydrogen-bonded
complexes: do they tell us the same thing?”, J. Am. Chem. Soc., 122,
4794-4797 (2000). M. J. T. Jordan and J. E.
Del Bene, “Unravelling environmental effects on hydrogen-bonded complexes:
matrix effects on the structures and proton stretching frequencies of
hydrogen-halide complexes with ammonia and trimethylamine”, J. Am. Chem.
Soc., 122, 2101-2115 (2000). J. E. Del Bene and M. J. T.
Jordan, “Vibrational Spectroscopy of the Hydrogen Bond: An Ab Initio Chemical
Perspective”, Int. Rev. in Phys. Chem., Vol. 18, no. 1, 119-162 (1999).
Invited review article, edited by D.C. Clary. J. E. Del Bene and M. J. T.
Jordan, “A comparative study of vibrational anharmonicity in the bihalide
anions XHX–: X=F, Cl and Br”, Spectrochimica Acta, Part A, 55,
719-729 (1999). An invited paper in a special issue entitled “Theoretical
Spectroscopy: State of the Science” edited by T.J. Lee and M. Head-Gordon. J. E. Del Bene and M. J. T.
Jordan, “A comparative study of anharmonicity and matrix effects on the
complexes XH:NH3, X=F, Cl and Br”, J. Chem. Phys., 108, 3205-3212
(1998). J. E. Del Bene, M. J. T.
Jordan, P. M. W. Gill and A. D. Buckingham, “An ab initio study of
anharmonicity and matrix effects on the hydrogen-bonded BrH:NH3
complex”, Mol. Phys., 92, 429-439 (1997). Invited contribution to a special
issue of Molecular Physics in honour of Professor John Pople, Nobel Laureate
in Chemistry, ed N. C. Handy. |