ERA-Chemistry (administered by OTKA, the Scientific Research Fund of Hungary)
Title of the proposal:
Tunneling in novel hydroxycarbenes
Three years (2009–2012)
Attila G. Császár and Peter R. Schreiner (Giessen, Germany)
Building on the complementary backgrounds and expertise of the Giessen (experimental organic chemists and spectroscopists) and the Budapest (computational quantum chemists) groups, a joint program is proposed that uniquely combines the preparation, detection, and spectroscopic as well as computational characterization of designed novel carbenes exhibiting enhanced hydrogen and possibly heavy-atom tunnelling under large barriers at low cryogenic temperatures (down to 6 K). The very low temperatures and the noble gas environment of cryogenic matrices are ideally suited for quantum chemical reaction rate and tunnelling (quantum reaction dynamics) studies on single ground-state surfaces. The proposed full- and reduced-dimensionality reaction dynamics computations are expected to guide new experiments and, when augmented with sophisticated electronic structure computations, should shed light on the factors that govern enhanced quantum mechanical tunnelling under large barriers near 0 K on timescales of minutes to days.
Questions the proposed research aims to answer include:
(a) how do electronic substituent effects alter the rates of H-tunnelling in novel unsaturated hydroxycarbenes;
(b) how large a barrier can be afforded for observable H-tunnelling;
(c) can hydrogen bonding be used to tune the rate of H-tunneling?
Novel aspects of the proposed research program include:
(a) systematic preparation of a series of electronically related substituted, currently unknown hydroxycarbenes;
(b) development of synthetic routes to substituted hydroxycarbenes;
(c) studying the electronic effects on tunnelling, utilizing the most advanced levels of quantum chemistry (including ground-breaking electronic structure, nuclear motion, and reaction dynamics computations);
(d) variational determination of rovibrational spectra of carbenes containing five or more atoms and/or multiple minima on their PES;
(e) quantum chemical computation of microcanonical rate constants based on the availability of a time-independent machinery similar to that which allows determination of a nearly complete set of stationary rotational-vibrational wave functions and energy levels.