Bulletin of the Korean Chemical Society

  • 제7권5호
  • /
  • Pages.395-399
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  • 1986
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  • 0253-2964(pISSN)
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  • 1229-5949(eISSN)
대한화학회 (Korean Chemical Society)
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MNDO Studies on Intramolecular Proton Transfer Equilibria of Acetamide and Methyl Carbamate$^1$

  • 발행 : 1986.10.20
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초록

Intramolecular proton transfer equilibria of acetamide and methyl carbamate have been studied theoretically by MNDO MO method. For both substrates, carbonyl-O protonated tautomer was found to be the most stable form, the next most stable one being N-protonated form. Gas phase proton transfers take place by the 1,3-proton rearrangement process and in all cases have prohibitively high activation barriers. When however one solvate water molecule participates in the process, the barriers are lowered substantially and the process proceeds in an intermolecular manner through the intermediacy of the water molecule via a triple-well type potential energy surface; three wells correspond to reactant(RC), intermediate(IC) and product complex(PC) of proton donor-acceptor pairs whereas two transition states(TS) have proton-bridge structure. General scheme of the process can be represented for a substrate with two basic centers(heteroatoms) of A and B as, $$ABH\limits^+\;+\;H_2O\;{\to}\;ABH\limits^+{\cdots}{\limits_{RC}}OH_2\;{\to}\;AB{\cdots}H\limits_{TS}^+{\cdots}{\limits_{1}}OH_2\;{\to}\;AB{\cdots}{\limits_{IC}}H\limits^+OH_2\;{\to}\;BA{\cdots}H\limits_{TS}^+{\cdots}{\limits_{2}}OH_2\;{\to}\;BA H\limits^+{\cdots}{\limits_{PC}}OH_2\;{\to}\;BAH\limits^+\;+\;H_2O$$ Involvement of a second solvate water had negligible effect on the relative stabilities of the tautomers but lowered barrier heights by 5∼6 Kcal/mol. It was calculated that the abundance of the methoxy-O protonated tautomer of the methyl carbamate will be negligible, since the tautomer is unfavorable thermodynamically as well as kinetically. Fully optimized stationary points are reported.

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참고문헌

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피인용 문헌

  1. Theoretical studies on the acid hydrolysis of methyl carbamate vol.8, pp.6, 1987, https://doi.org/10.1002/jcc.540080607
  2. Theoretical studies on the hydrolysis of urea in acid solution vol.2, pp.4, 1986, https://doi.org/10.1002/poc.610020402
  3. AM1 studies on the acid hydrolysis of acetamide vol.3, pp.6, 1986, https://doi.org/10.1002/poc.610030608
  4. Photosensitized Reactions of Oxime Ethers: A Steady-State and Laser Flash Photolysis Study vol.69, pp.9, 1986, https://doi.org/10.1021/jo049941a