Intramolecular rotation process

The nucleophilicity of the sulphur in (toluene)Ct(CO)2(CS) has allowed adduction by Cr(CO)s. The oxidation of (hmb)M(CO)3 (M= Mo or W) by I2 has allowed the isolation of the complex ((hmb)H(CO)3l] and a series of polyhalometallate anions.The interaction of (arene)Cr(CO)3 with solvents has been examined using nmr spectroscopy. Particularly large upfield shifts are found for the aromatic hydrogens in aromatic solvents.Other nmr spectroscopic studies include the investigation of relaxation times for Mo, and O in (arene)Mo(CO)3 complexes and a nmr study of cyclophaneMo(CO)3 complexes.Intramolecular rotational processes have been examined by nmr in the (C5Et5 )M(CO) 2l< (I = CS or PR3) complexes. 

Through this study, we have shown that the excimer fluorescence technique of a probe simply dispersed in a macromolecular medium provides detailed information about the molecular motions of the polymer. Although the intramolecular rotational process reflects the glass transition of the host medium, within the same matrix, the absolute values of the experimental correlation times, differ for each probe. In Table 3... 

C. Pseudorotation.—An alternative intramolecular exchange process to Berry pseudorotation has been suggested, which also occurs with conservation of angular momentum. It has been called a turnstile-rotation process because it involves the rotation of an apical-radial pair of ligands... 

These experiments while moving beyond simple structure determination, still depend primarily on structure determination as their primary tool. A number of experiments have moved beyond this to exploit other characteristics of NMR. For example, spin saturation transfer can be used to study internal rotation of molecules (59, 60), and line shape analyses can be used to study intramolecular exchange processes (61), conformational interchange (62) and... 

Figure 1. Linewidlhs of different rotational transitions in the 14q1q vibronic band of benzene measured with Doppler-free two-photon absorption. The observed strong dependence on the quantum number J of the rotational angular momentum is evidence for a rotationally dependent intramolecular coupling process. (Taken from Ref. 3.)...

F and NMF are also highly structured solvents as a result of hydrogen bonding. The low-frequency relaxation process in these systems can be attributed to the cooperative motion of hydrogen-bonded clusters. The process at the highest frequencies has a similar relaxation time to those observed in DMF and DMA. Thus, it is probably due to intramolecular rotation about the C-N bond in the monomer. The intermediate relaxation observed in NMF is attributed to rotational diffusion of a monomer. Relaxation parameters for F and NMF are also summarized in table 4.5. 

The divergent outcome between the reactions of diaryliodonium salts with charged nucleophiles and with neutral nucleophiles was also explained by this model. In principle, the 10-1-3 intermediate, which is formed in the first step of the overall process, can decompose by two routes. When intramolecular rotation is possible, ligand coupling takes place easily. The second possibility is the homolytic cleavage of the iodine-nucleophile bond, leading to a pair of radicals formed by one electron reduction of the iodonium cation. 

In addition, to a very fast intramolecular rotation/flip (process A) of the... 

The lack of fluorescence of TAM dyes in solution is attributed to an extremely rapid, nomadiative deactivation process brought about by intramolecular rotation of the flexible aryl groups. Suppression of molecular rotation, by increasing the viscosity of the medium, by binding of the dye to a polymer or protein, or by selfassociation, diminishes this radiationless process. Coincident with this change in photophysical properties is often a dramatic increase in sensitivity toward photofading due to an increase in the quantum yield of the relatively long-lived and photochemically active triplet state [139-143]. The triplet state of the dye cation... 

The final intramolecular process which has been examined is illustrated in 20, Eq. (10), and in 21a and 21b (36, 47). This process has been represented as a rotational process taking the bridging cyclopropyl... 

---