Intramolecular 1,5-hydrogen transfer, computational

In the meantime, the computational contribution became a versatile and relatively easy to use instrument. An example is shown in Fig. 4.5b, where the potential energy surfaces for the intramolecular hydrogen transfer reaction of o-nitroben-zaldehyde in ground and singlet excited state are reported [86]. Calculations by the more reliable MS-CASPT2//CASSCF approach have been likewise carried out [87] as well as molecular dynamics simulations [85] (Fig. 4.6). 

In contrast, there are some examples in which parent pyridylidenes have been implicated in the functionalization of pyridines. In this context Bergman and coworkers found that the formation of the Rh—NHC complex 18 via C-H bond activation of the heterocycle 17 (see Scheme 28) was the key step in the Rh-catalyzed coupling of N-heterocycles and olefins.The 1,2-hydrogen shift involved in this process was studied in detail, using experimental and computational methods, and an intramolecular hydrogen transfer pathway through Rh—H intermediates was found to be the more plausible mechanism. 

Computer simulation of intramolecular hydrogen atom transfer to carbonyl oxygen has been achieved by a Monte Carlo method. In particular, the model has been found to give good agreement when applied to intramolecular P-, y-, 6-, -, and ( -hydrogen atom abstraction in ketones as well as q- and 0-proton transfer in oxoesters, and it has also been used to predict the reactivities of... 

The previous studies of concerted hydrogen atom and proton transfer in hydrogen-bonded systems have been limited to studies of reaction pathways for simple model systems [4-8] with simple, reduced dimensionality methods for including quantum tunneling [13,14,34,35]. The applicability of modem computational methods to such systems is exemplified by more recent studies of the energetics of intramolecular hydrogen atom transfer in molecules such as malonaldehyde [36-39] and models of... 

Formal intramolecular hydrogen abstraction (proceeding through coupled electron and proton transfer) occurs in the titi triplet excited state of furanone derivatives, upon acetone photosensitization. After hydrogen transfer from the tetrahydropyran to the (I position of the furanone moiety, radical recombination leads to the final products (18). The results of computational studies on model structures are in accordance with experimental observations and reveal that the reactivity and selectivity are mainly determined by the hydrogen-abstraction step. ... 

Further, computational study of the possible binding modes between 14 and enolic form of 11 revealed the most facile route for the proton transfer (Scheme 3.23). Initial formation of the adduct 16 is followed by a barrierless proton transfer resulting in the ion pair 16 in which all three NH protons are involved in multiple intramolecular hydrogen bonds. 

Eq. (3.8) assumes harmonic vibrational motion, a satisfactory approximation for the range of momentum transfers covered by the neutron data. NVR adjusted the OD distance, its rms-variation, and the rms-variation in the intramolecular DD distance by least-squares. The DD distance itself was computed from the OD distance and an assumed DOD angle of 104.5°, because its value, 1.58 A, is too close to the hydrogen-bonded D2O...D distance expected near 1.8 A. The molecular structure function 5m(s) calculated from these parameters is compared with the total structure function BN(s) in Fig. 7d. 

An experimental and computational study describing a cascade transformation that breaks all three C-C bonds in a polarized alkyne moiety has been reported (Scheme 5)." Facile intermolecular Michael addition is followed by the relatively slow intramolecular steps. The slowest step corresponds to the 5-exo trig closure at the carbonyl-substituted alkene. This process is facilitated by the coupling of the intramolecular Michael addition with a concerted proton transfer along a resonance-assisted hydrogen bond path, which avoids the formation of an unfavourable zwitterionic intermediate. 

Another relevant experimental measurement is the kinetic isotope effect (KIE). The KIE for intramolecular or intermolecular HT is defined as the ratio between the rate constants for hydrogen and deuterium transfer (KIE = k /k ). Experimentally, it is usually determined with NMR spectroscopy [103, 104], while computationally quantum simulations are required since the major factors that affect it are the zero-point energy and QM tunneling [105]. 

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