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Investigating Mechanism, Transition State, and Products Distribution of Catalys-Free Hydrothiolation Reactions of Unactivated Terminal Alkynes by Dithiocarbamic Acids

Kolivand, Mohammad | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57562 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Ziyaei Halimehjani, Azim
  7. Abstract:
  8. In this study, catalyst-free hydrothiolation reactions of unactivated terminal alkynes by dithiocarbamic acids have been investigated via computational chemistry approach and by Gaussian 09, GaussVeiw 5.0, and Spartan '14 V1.1.4 software from the perspective of the reaction mechanism, transition state, and the distribution of products. The calculation results have shown that the various in situ produced dithiocarbamic acids addition to unactivated terminal alkynes in which the alkyl group attached to the carbon 2 is an aliphatic hydrocarbon alkyl is through Markovnikov type path and this product is thermodynamically more stable which is in agreement with the experimental results. The NBO analysis also showed a more positive relative charge on carbon 2 indicating that the addition should be carried out as a Markovnikov addition. Also, the results of this research have shown that the phenylacetylene hydrothiolation products (Z isomer of S-vinyl dithiocarbamates in the anti-Markovnikov addition type) were under kinetic control. It is expected that with increasing temperature and reaction time this product will mainly change to its more stable isomer, E. By changing the alkyl group to trimethylsilyl, the reaction path has been switched into an anti-Markovnikov addition and the product was mainly E. In this regard, the calculations also show that the mentioned product is more stable than the Markovnikov addition product and the Z isomer from the thermodynamics point of view. Also, the NBO analysis has shown that the positive relative charge on carbon 1 is more than the one on the adjacent carbon atom and the attack on carbon 1 takes place which is the confirmation of the regioselectivity in this reaction. Regarding the evidence, the concerted mechanism is proposed for this reaction. In the concerted mechanism, the calculations have shown that the proposed transition state for this reaction in the Markovnikov addition type requires less activation energy and the formation of the resulting product from this pathway is more favorable
  9. Keywords:
  10. Markovnikov Addition ; Stereoselective Synthesis ; Theoretical Calculations ; Anti-Markovnikov Addition ; Regioselective Synthesis ; Terminal Alkynes ; Vinyl Dithiocarbamate

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