A DFT Study of NBO and NICS Analysis of the Allylic Rearrangements (the Claisen and Thio-Claisen Rearrangements) of 3-(Vinyloxy)prop-1-ene and Allyl Vinyl Sulfide

Zahedi, Ehsan; Shiroudi, Abolfazl; Ali‐Asgari, Safa; Keley, Vahid

doi:10.1080/10426507.2010.492364

Cited by 10 publications

(5 citation statements)

References 26 publications

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“…The triple-ζ basis set adds three sizes of s and p functions to the atoms and adds a d function to heavy atoms and a p function to hydrogen atoms, respectively. 20 In order to confirm the nature of the stationary species and evaluate the thermodynamics and kinetics parameters, we carried out calculations at the same level of theory. Initial estimates of the geometries of compounds 1-3 (see Figure 1) and related products were obtained by a molecular-mechanics program PC-MODEL (88.0) 21 followed by full minimization using semiempirical PM3 in the MOPAC 6.0 computer program.…”

Section: Computational Detailsmentioning

confidence: 99%

DFT Calculations of the Elimination Kinetics of Silacyclobutanes and its Methyl Derivatives in the Gas-Phase

Shiroudi¹,

Zahedi²

2012

Phosphorus, Sulfur, and Silicon and the Related Elements

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The gas-phase thermal decomposition kinetics of silacyclobutane (1), 1-methylsilacyclobutane (2), and 1,1-dimethyl-1-silacyclobutane (3) has been theoretically studied at the B3LYP/6-311G * * , B3PW91/6-311G * * , and MPW1PW91/6-311G * * levels. The B3LYP/6-311G * * method was found to give a reasonable good agreement with the experimental kinetics and thermodynamic parameters. The decomposition reaction of compounds 1-3 yields ethylene and the corresponding silene. Based on the optimized ground state geometries using B3LYP/6-311G * * method, the natural bond orbital (NBO) analysis of donor-acceptor (bonding-antibonding) interactions revealed that the perturbation energies (E 2 ) associated with the electronic delocalization from σ Si1-C2 to σ * C4-Si1 orbitals increase from compounds 1 to 3. The σ Si1-C2 →σ * C4-Si1 resonance energies for compounds 1-3 are 1.17, 1.26, and 1.43 kcal/mol, respectively. Also, the decomposition process in these compounds is controlled by σ →σ * resonance energies. Moreover, the obtained order of energy barriers could be explained by the number of electron-releasing methyl groups substituted to the Si sp2 atom. NBO analysis shows that the occupancies of σ Si1-C2 bonds decrease for compounds 1-3 as 3 < 2 < 1, and the occupancies of σ * Si1-C2 bonds increase in the opposite order (3 > 2 > 1). Moreover, these results can fairly explain the decrease of the energy barriers ( E o ) of the decomposition reaction of compounds 1 to 3. The calculated data demonstrate that in the decomposition process 619 Downloaded by [McMaster University] at 07:15 17 March 2015 620 A. SHIROUDI AND E. ZAHEDI of the studied compounds, the polarization of the C 3 -C 4 bond is the rate determining factor. Analysis of bond orders, NBO charges, bond indexes, synchronicity parameters, and IRC calculations indicate that these reactions are occurring through a concerted and asynchronous four-membered cyclic transition state type of mechanism.

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Section: Computational Detailsmentioning

confidence: 99%

DFT Calculations of the Elimination Kinetics of Silacyclobutanes and its Methyl Derivatives in the Gas-Phase

Shiroudi¹,

Zahedi²

2012

Phosphorus, Sulfur, and Silicon and the Related Elements

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“…Our previous studies on the transition states of Claisen, thio-Claisen, Cope and aza-Cope rearrangements [6,7] show that the maximum current occurred in the centre of the ring. Thus, in the present study the NICS calculations have been performed at this location.…”

Section: The Nucleus-independent Chemical Shift (Nics) Studymentioning

confidence: 97%

“…The single Slater determinant (wave function) for the boat-like transition state is 1 C boat ¼j : : :7b 2 2 5b 2 1 7b 2 2 j [5,6]. Recently, Zahedi et al studied and compared Claisen, thio-Claisen [7], Cope and aza-Cope [6] allylic rearrangements to take into consideration the substituent (steric) effect. However, in this study, we have calculated and compared kinetic and thermochemical parameters for the Cope rearrangement of substituted hexa-1,5-dienes in the gas phase ( Figure 1).…”

Section: Introductionmentioning

confidence: 97%

Dft Study of Allylic Rearrangements (Cope Rearrangements) of Substituted Hexa-L,5-Dienes: Nbo and Nics Analysis

Aghaie

Zahedi

Mohammadkhani

et al. 2011

Progress in Reaction Kinetics and Mechanism

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Ab initio density functional theory (DFT) calculations have been performed on the [3,3] sigmatropic rearrangement of substituted hexa-1,5-dienes (the Cope rearrangement) in the gas phase. The barrier heights calculated at the B3LYP=6-311G** level of theory were in a good agreement with experimental data. Optimized transition states at the B3LYP=6-311G** level were used to calculate nucleus-independent chemical shifts (NICS) and also natural bond orbital analysis (NBO) at the same level. Our results indicate that the aromaticities of the transition states are controlled by the out-of-plane component and these reactions are controlled kinetically by the aromaticity of the transition states. Based on the NBO analysis, the greater resonance energy for s ?p* and s ?s* delocalization in R2 (compared to R1 and R3) could facilitate the Cope rearrangement of R2. The greater s * 3À4 anti-bonding orbital occupancy and the lower s 3À4 bonding orbital occupancy in R1 could facilitate the Cope rearrangement of R1 compared to R3. Comparative examination between substituted and un-substituted hexa-1,5dienes show that in these reactions, steric parameters play no significant rule in the general mechanism of the Cope rearrangement. Figure 1 [3,3] sigmatropic rearrangement of substituted hexa-1,5-dienes (the Cope rearrangement) via two pathways (chair-like and boat-like).

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“…The NICS values are the isotropic chemical shifts of the respective bqs, and the eigenvalues of the chemical shift tensors were used to separate the isotropic NICS values into their in-plane and out-of-plane components. Since the NICS values are distance-dependent, the N@r symbol will be used in this article to denote the NICS value (ppm) at distance r(Å) from the molecular plane [41].…”

Section: The Nucleus-independent Chemical Shift (Nics) Studymentioning

confidence: 99%

Isomerisation Reactions of α-Methyl Allyl [Acetate, Trifluoroacetate]: Theoretical Study

Shiroudi

Zahedi

2013

Progress in Reaction Kinetics and Mechanism

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The [3,3]-sigmatropic rearrangement reactions of α-methyl allyl acetate (1), and α-methyl allyl trifluoroacetate (2) have been studied using ab initio molecular orbital (MO) methods at the HF, B3LYP, B3PW91, and BHandHLYP levels with a 6-31++G ** basis set. Among the methods used in this study, the values for activation parameters obtained with the BHandHLYP/6-31++G ** method are in good agreement with experimental values. The calculated data demonstrate that in the rearrangement reactions of the compounds studied, the polarisation of the O 3 -C 4 bond is rate determining. Optimised transition states at the BHandHLYP/6-31++G ** level were used for calculating the nucleusindependent chemical shift (NICS) and also a natural bond orbital (NBO) analysis was carried out at the same level. Based on the optimised ground state geometries using the BHandHLYP/6-31++G ** method, the NBO analysis of donor -acceptor (bonding -antibonding) interactions revealed that the stabilisation energies associated with electronic delocalisation from the σ O(3) -C(4) bonding orbital to the π * C(5) = C(6) antibonding orbital, increase from compounds 1 to 2. The σ O(3) -C(4) →π * C(5) = C(6) resonance energies for compounds 1 and 2 are 1.59 and 1.62 kcal mol -1 , respectively. Also, analysis of the donor -acceptor interactions σ O(3) -C(4) →π * C(5) = C(6) suggests that in these rearrangements, the TS structure in compound 2 has more aromatic character than for compound 1. The NBO results revealed that in these rearrangements, activation energies are not controlled by the σ O(3) -C(4) →π * C(5) = C(6) resonance energy. NICS results indicate that the aromaticities of the transition states are controlled by the out-of-plane component. The predicted high-pressure-limit rate constants for the rearrangement reactions of compounds 1 and 2 are represented as 6.12 × 10 12 exp(-21604 / T), and 1.04 × 10 13 exp(-17846 / T) s -1 , respectively. The fall-off pressures for the rearrangement reactions 1 and 2 are found to be 9.56 × 10 -5 and 1.09 × 10 -3 mmHg, respectively. The fall-off pressures of compounds 1 and 2 in both reactions are PRK1200146_FINAL.indd 249 21/08/2013 12:09:07 Abolfazl Shiroudi and Ehsan Zahedi www.prkm.co.uk 250in the following order: P 1/2 (2) > P 1/2 (1) and the rates follow as: rate (2) > rate (1). Analysis of bond order, NBO charges, bond indices and synchronicity parameters suggest the Claisen rearrangement reactions of 1 and 2 occur through a concerted and slightly asynchronous six-membered cyclic transition state type of mechanism.

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A DFT Study of NBO and NICS Analysis of the Allylic Rearrangements (the Claisen and Thio-Claisen Rearrangements) of 3-(Vinyloxy)prop-1-ene and Allyl Vinyl Sulfide

Cited by 10 publications

References 26 publications

DFT Calculations of the Elimination Kinetics of Silacyclobutanes and its Methyl Derivatives in the Gas-Phase

DFT Calculations of the Elimination Kinetics of Silacyclobutanes and its Methyl Derivatives in the Gas-Phase

Dft Study of Allylic Rearrangements (Cope Rearrangements) of Substituted Hexa-L,5-Dienes: Nbo and Nics Analysis

Isomerisation Reactions of α-Methyl Allyl [Acetate, Trifluoroacetate]: Theoretical Study

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