The chemistry of the electrocatalytic reduction of CO 2 using nitrogen containing heteroaromatics is further explored by the direct comparison of imidazole and pyridine catalyzed CO 2 reduction at illuminated iron pyrite electrodes. The mechanism of imidazole based catalysis of CO 2 reduction is investigated by analyzing the catalytic activity of a series of imidazole derivatives using cyclic voltammetry. While similar product distributions are obtained for both imidazole and pyridine, the imidazole catalyzed reduction of CO 2 likely proceeds via a very different mechanism involving the C2 carbon of the imidazole ring.

The high resolution spectra of the fundamental and first overtone of the acetylenic C-H stretch in tert.-butylacetylene-d 9 and (trimethylsilyl)acetylene-d 9 have been measured using optothermal detection of a collimated molecular beam. IVR lifetimes determined from the homogeneously broadened Iineshapes are compared to those of their undeuterated analogues. It is found that for both molecules, at both levels of excitation, deuterating the methyl rotors results in an increased rate of IVR. The results indicate that the previously suggested methyl rotor effect, as an enhancer for IVR, plays a secondary role to increasing the number of low order resonances to which the C-H stretch can couple. Although the torsional modes are important for the molecules to exhibit statistical case IVR and contribute to the filled-in homogeneous Iineshapes, the rate of energy relaxation seems to be dominated by the number of low order resonances.

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3,7-Bis(butylmethylamino)-1,5,2,4,6,8-dithiatetrazocine (3) was prepared in two steps from N-methylbutylamine in 14% overall yield. At room temperature the I H N M R spectrum of 3 shows two methyl resonances (in a roughly 1:l ratio) and four resonances for the Ca methylene protons of the butyl groups (roughly 1:l:l:l). These data indicate that compound 3 displays both cis/trans isomerism and a bent heterocyclic ring in solution. Heating of compound 3 in a variable-temperature N M R experiment results in coalescence of the two methyl and four Ca resonances to a singlet and a triplet, respectively, at temperatures corresponding to an activation energy (AG,*) of approximately 17 kcal/mol for the exchange process. This value is the free energy of activation for rotation of the dialkylamino groups and also represents a lower limit for the activation energy for inversion of the bent dithiatetrazocine ring. Ab initio calculations on the 3,7-diamino-l,5,2,4,6,8-dithiatetrazocine system suggest that the activation energies for amine rotation and ring inversion are very similar: 17.1 and 17.3 kcal/mol, respectively. Spectral simulations of the N M R data for 3 support this conclusion, with the best experimental estimates of the free energies of activation for the two processes being 17.3 f 0.1 and 17.7 i 0.5 kcal/mol, respectively. Notably, the calculations indicate that the ring inversion procedes asymmetrically-in the transition state one side of the ring is more highly bent than the other-and there is a nearly planar intermediate along the pathway.