62nd Annual Report on Research 2017

Specific Aims

Our goal in the original application is to determine the role of thermally-activated heavy-atom tunneling (TAHAT) in the cycloaromatization reactions of hydrocarbons yielding diradicals, namely (1) a,3-didehydrotoluene, (2) fulvenyl diradical, and (3) 1,5-didehydroindene. The aims remain the same and have not been modified.  Thus far, we have successfully obtained quantitatively and qualitatively accurate descriptions of the cycloaromatization of (1) and (2). Progress has been made toward determining of the contribution of tunneling in cycloaromatizations leading to (3) 1,5-didehydroindene.

Studies and Results

Our methodology has enabled the determination of thermally activated heavy-atom tunneling in reactions leading to a,3-didehydrotoluene. In collaboration with Dr. Charles Doubleday (Columbia University) a manuscript on contribution of carbon atom tunneling in cycloaromatization leading to a,3-didehydrotoluene and twelve other organic reactions was recently published in Angewandte Chemie International Edition in English. The primary goal was to test the scope of heavy-atom tunneling in organic chemistry, and to check the accuracy of one-dimensional tunneling models. The reactions included pericyclic, cycloaromatization, radical cyclization and ring opening, and S_N2. When compared at the temperatures that give the same effective rate constant of 3 x 10^-5 s^-1, tunneling accounted for 25 – 95% of the rate in 8 of the 13 reactions. Values of transmission coefficients predicted by Bell's formula, k_Bell, agreed well with multidimensional tunneling (canonical variational transition state theory with small curvature tunneling), k_SCT. This study suggests that k_Bell could be used as a useful first choice for predicting transmission coefficients in heavy-atom tunnelling.

During the third year of the ACS PRF UR4 grant, a total of 3 papers have been published. In addition to the manuscript published in Angewandte, one of the two papers has appeared in the Journal of Physical Chemistry A in 2017 and described a nitrosamine photooxidation reaction producing unstable peroxy intermediate, the nature of which was studied using DFT methods. Also in 2017, a manuscript that described the synthesis of substituted pyrroles via Cadogan-Sundberg method was published in Tetrahedron Letters, where calculations helped to determine that the reaction favors the path through the nitrene intermediate.

In summary, the above papers published describe tunneling, and chemistry of reactive intermediates including diradicals, nitrenes, and peroxy nitrosamines.

Significance

In addition to the impact on fundamental understanding of chemical reactivity and C-C bond formation, this research grant has had a significant effect on my career. Importantly, the PRF grant support has allowed my research group to collect data used in the presentations of an invited talk entitled Heavy-atom Tunneling in thirteen Organic Reactions: Bell's Formula Matches Multidimensional Tunneling a ³ 250 K at the Quantum Atomic & Molecular Tunneling in Solids and Other Condensed Phases QAMTS 2017, Madison, Wisconsin, on May 23, 2017. In addition, I was delighted to give the shorter version of the tunneling talk at the Roald Hoffmann Special Symposium honoring Prof. Roald Hoffmann's 80^th Birthday at the 254th ACS National Meeting in Washington, DC, on August 20, 2017.

Furthermore, this research grant has had a significant impact on students in my group at Baruch College. It has provided my students with the opportunity to carry out computational research and collect results that earned them the first at the Creative Inquiry Day at Baruch College on May 19, 2017. Two students, Thuong Tran and Frankie Benavides, had delivered oral presentations at the 65^rd Annual Undergraduate Research Symposium of the American Chemical Society, Fordham University, New York on May 6, 2017. In Fall 2017, one of the students supported by the ACS PRF grant, Kitae (Mikey) Kwon, has joined a Ph.D. program in chemistry at Duke University.

Plans

We will continue to address the Specific Aims in the next year of support, and will utilize our developed methodology to address contributions of tunneling in cycloaromatization reactions leading to 1,5-didehydroindene.