Dihydrogen transfer

Dihydrogen Transfer and Symmetry The Role of Symmetry in the Chemistry of Dihydrogen Transfer in the Light of NMR Spectroscopy... 

Fig. 6.15 An ene reaction drawn as a [a-2s+n2s+n2s] process and a dihydrogen transfer drawn as a [tT2s+(T2s+ n 2s]...

Other pericyclic reactions of alkynes that have been studied computationally include the addition of singlet methylene to acetylene [109], the addition of carbon monosulfide to acetylene [110], the [2 + 2] dimerization [100, 111], and the dihydrogen transfer reaction between acetylene and ethylene [112, 113]. 

Figure 1-4 Transition structures of dihydrogen transfer reactions (MP2/6-31G, McKee and Stanbury [112,113]).

In two theoretical papers, McKee treated the electronic structure and the N2 reactivity of the FeMoco. In a first study, the evolution of H2 under turnover conditions was analyzed in the second paper, the bonding of N2, acetylene and CO to the FeMoco, and a possible concerted dihydrogen transfer to bound N2, were addressed. The calculations are based on a simplified... 

There have already been several theoretical investigations, using mainly nonempirical methods, into intermolecular concerted dihydrogen transfer concerned, for example, with hydrogenation of ethylene by ethane [92] or with reactions between hydroxymethylene and ethylene [93], acetic acid and methanol [94, 95], methanol and formaldehyde [96]. 

The reaction of C/S-N2H2 with unsaturates, mainly ethylene, via a six-membered cyclic activated complex was treated theoretically assuming that the dihydrogen transfer proceeds in a concerted way [9 to 15]. Two recent semiempirical SCF MO studies (AMI and MINDO) took a look at the hydrogenation not only via the concerted, but also examined a stepwise mechanism. Whereas the AMI method favors the concerted hydrogen transfer, the MINDO method favors the stepwise pathway [16, 17]. 

Nj. Ab initio SCF calculations at various levels were performed on the symmetric dihydrogen transfer reaction c/s-N2H2 N2 a pericyclic transition structure with synchronous motion of the transferring hydrogen atoms was derived [9]. 

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