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The gas-phase electronic absorption spectra of triethylenediamine and quinuclidine have been measured. Each compound shows two strong bands in the regions 1650–2500 Å and 1650–2300 Å, respectively, which have well-resolved vibrational structure, as well as very weak, structured absorption at longer wavelengths (2560–2700 Å for triethylenediamine and 2300–2500 Å for quinuclidine). An essentially complete vibrational analysis of all but one of these bands has been accomplished. The results indicate a substantial change in the equilibrium positions of the nuclei in the excited states relative to the positions in the ground state. For quinuclidine, the most prominent excited state vibrational mode can be correlated with the ground-state mode which corresponds to an approach to planarity of the nitrogen-bearing end of the molecule. For triethylenediamine, ambiguities in the ground-state assignments preclude conclusions about the upper state geometry. By comparisons with the spectra of other amines, the strong electronic bands of triethylenediamine and quinuclidine are assigned as n → p Rydberg transitions. Exciton model calculations of the shift of the first strong band of triethylenediamine relative to the corresponding band in quinculidine predict changes of about 3000 cm−1 to lower energy for an n → 3pz transition and about 1500 cm−1 to higher energy for an n → px y transition. The observed shift of the 0–0 band is 3920 cm−1 to lower energy, which is clearly in accord with z polarization. The weak, longer-wavelength absorption of the cage amines is tentatively considered to arise from sub-Rydberg transitions.

J . Am. Chem. 0.6 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 / lO-'mol' dm4 az 1 + Ga' Figure 7. J vs. a 2 / ( 1 + &'a2) plot for the polynactin-KSCN system.[PN] = 0.1 mol d d .discrepancy may be due to a difference in the stirring conditions between the ion-transfer and ion-transport experiments. If the two experiments could be carried out under the same stirring conditions, a theoretical curve for ion transport might be drawn by use of the apparent rate constant derived from ion-transfer experiments.For all the carriers studied here, the value of k, is comparable to that of k,, so that the rate of release does not control the overall rate of transport. When log K, is higher than 4-6 for a monovalent cation, the rate of transport decreases with an increase in K, as SOC. 1986, 108, 3907-3912 3907 demonstrated by Behr and co-workers.' The rate of release decreases with an increase in the stability constant of the complex and controls the rate of transport in the region of high stability.I6 When K, is very high, the concentration of the complex at the interface on the release side (EM*) is not longer negligible in comparison with the concentration in the bulk solution (EM).Under these circumstances, we have to use eq 12, or J , = k,'rM where k,' = k,( 1 -E M * / E M ) ; the k,' apparently decreases with an increase in EM*. The k,' values, calculated from J , values previously determined for potassium pi~rate,'~.'' were 0.27 X loW4 and 0.82 X cm s-' for cryptand 2.2.2 and dibenzocryptand 2.2.2, respectively. These values are 1-2 orders of magnitude lower than those for crown ethers. In such a case, the transport of the ion does not proceed so fast as would be expected from its high affinity to the carrier. However, most of the metal complexes with macrocyclic ligands exhibit log K, of 4-6 or so that the rate of transport is predictable from the extractability of the metal ion. (16) Yoshida, S.; Hayano, S. J. Membr. Sei. 1986, 26, 99-106. (17) When CM was 1 X mol dm'j, the J, values were 1.6 X and mol min-' cm-* for cryptand 2.2.2 and dibenzocryptand 2.2.2, 4.9 X reswctivelv. 118) Sh'chori, E.; Nae, N.; Grcdzinski, J. J. J. Chem. SOC., Dalfon Trans. (19) Izatt, R. M.; Nelson, D. P.; Rytting, J. H.; Haymore, B. L.; Chris-1975, 2381-2386. tensen, J. J.Abstract: The second derivative of th_e gas-phase absorption spectrum of trimethylamine (TMA) is used to assign the po_sitions of many vibrational features in the A -X transition. Considerable regularity in these positions indicates that the A state potential is harmonic in the out-of-planepending coordinate, and a frequency of 375 cm-' is assigned. Calculations based on the finite difference method using an X-state inversion potential of local harmonic wells joined by a parabolic or quartic cap and a harmonic A state are successfully used to fit the shapes of both the absorption and fluorescence spectra. Most of the Franck-Condon activity in fluorescence involves transitions to the u" = 14-18 states, explaining the large Stokes' shift as well as the vertical shape. The origin of the ...

A series of computational chemistry projects is described that focuses on the isomerization reactions, HNC–HCN and CH3NC–CH3CN. These projects guide students through several applications involving transition state location and optimization, intrinsic reaction coordinate potential energy surface construction, and the calculation of reaction rate constants. The calculations are at a high enough level of theory to allow them to obtain good results, while not demanding unrealistic computing resources or computational sophistication.