Theoretical Computations on the Pyrolysis of Alkyl (dithio)acetates

2020 ◽  
Vol 17 (3) ◽  
pp. 224-233
Author(s):  
Xun Zhu ◽  
Chen Jian ◽  
Xiuqin Zhou ◽  
Abdullah M. Asiri ◽  
Khalid A. Alamry ◽  
...  
Keyword(s):  
Transition States ◽  
Membered Ring ◽  
Pyrolysis Process ◽  
Alkyl Esters ◽  
Charge Distributions ◽  
Theoretical Analyses

The pyrolysis of methyl alkyl esters I to III and dithioesters IV to VI were theoretically calculated. All possible pyrolysis paths were considered. Both esters and dithioesters presented three potential paths via six-, four- and five-membered ring transition states, respectively. The calculation processes were calculated using MP2/6-31G(d) set. In-depth theoretical analyses were also presented, including NBO related analyses, synchronicities, and charge distributions, to reveal the detailed pyrolysis process.

Understanding difficulties of irregular number-membered ring transition states for intramolecular proton transfer in excited state

Tetrahedron ◽  
2017 ◽  
Vol 73 (4) ◽  
pp. 403-410 ◽  
Author(s):  
Xiaozhuan Qin ◽  
Ge Ding ◽  
Zhenqiang Wang ◽  
Yulong Gong ◽  
Fang Gao ◽  
...  
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Transition States ◽  
Intramolecular Proton Transfer ◽  
Membered Ring

The effect of pressure on cyclic reactions

1967 ◽  
Vol 20 (7) ◽  
pp. 1335 ◽  
Author(s):  
AH Ewald ◽  
DJ Ottley
Keyword(s):  
Transition States ◽  
Membered Ring ◽  
Aqueous Acetone ◽  
Effect Of Pressure ◽  
Cyclic Reaction

Rates of the cyclization of 4-chlorobutanol and of some analogous non- cyclic solvolysis reactions have been measured in water, methanol, and aqueous acetone at pressures up to 3000 atm. The volume of activation of the cyclic reaction is less negative than those of the linear reactions, in each solvent, but it is suggested that the transition states of both types of reaction may be solvated to about the same extent. The volume of activation for the formation of an eight-membered ring in the cyclization of 4-bromobutylcatechol monoether was also determined.

scholarly journals What Differs on the Enzymatic Acetylation Mechanisms for Arylamines and Arylhydrazines Substrates? A Theoretical Study

2009 ◽  
Vol 2009 ◽  
pp. 1-5
Author(s):  
Qing-An Qiao ◽  
Xiao-Min Sun ◽  
Jie Jing ◽  
Xin Chen ◽  
Hua-Yang Wang ◽  
...  
Keyword(s):  
Experimental Data ◽  
Density Functional Theory ◽  
Density Functional ◽  
Theoretical Study ◽  
Transition States ◽  
Ring Structure ◽  
Membered Ring ◽  
Functional Theory ◽  
Lone Pairs ◽  
The Density Functional Theory

The acetylation mechanisms of several selected typical substrates from experiments, including arylamines and arylhydrazines, are investigated with the density functional theory in this paper. The results indicate that all the transition states are characterized by a four-membered ring structure, and hydralazine (HDZ) is the most potent substrate. The bioactivity for all the compounds is increased in a sequence ofPABA≈4-AS<4-MA<5-AS≈INH<HDZ. The conjunction effect and the delocalization of the lone pairs of N atom play a key role in the reaction. All the results are consistent with the experimental data.

Synthesis, structure, and hydrolysis of esters of strained and unstrained N-phosphonylureas

1987 ◽  
Vol 65 (8) ◽  
pp. 1838-1844 ◽  
Author(s):  
Ronald Kluger ◽  
Gregory R. J. Thatcher ◽  
William C. Stallings
Keyword(s):  
Membered Ring ◽  
Equatorial Position ◽  
Alkyl Esters ◽  
Aqueous Acetonitrile ◽  
Phenoxy Group ◽  
X Ray Crystallography ◽  
Urea Group ◽  
Leaving Groups ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

Compounds 1–5 were prepared to compare reactivity patterns of cyclic and acyclic phosphonylurea esters. The rates and products of reactions of phosphonylurea esters (1–3) with hydroxide in aqueous acetonitrile were analyzed. In these compounds the phosphonate moiety is in a strained five-membered ring, which also contains the ureido group. Structural determination of 1 by X-ray crystallography indicates that the five-membered ring is planar and the internal ring angle at phosphorus is 93.1°. The endocyclic N—C—N angle of the ureido group is 111°. The compounds undergo hydrolysis in alkaline aqueous acetonitrile at 35 °C with a rate about 106 times that of analogues (4, 5) in which the phosphonate group is exocyclic to the ureido ring. Compound 1 undergoes alkaline hydrolysis (k = 9.0 × 103 M−1 s−1) to release the phenoxy group to give 6. The hydrolysis of alkyl esters 2 (k = 2.4 × 104 M−1 s−1)and 3(k = 1.3 × 103 M−1 s−1) leads to cleavage of the endocyclic P—N bond, producing 7 and 8 respectively. The exocyclic alkyl esters (4 and 5) also cleave at the P—N bond with respective rate constants of 6.5 × 10−3 M−1 s−1 and 4.4 × 10−2 M−1 s−1. The data are consistent with a mechanism in which hydroxide adds to 1 to form a pentacoordinate phosphorus intermediate with the phenoxy group in an equatorial position and the ureido ring in apical and equatorial positions (with nitrogen apical). The departure of the urea group is slower than pseudorotation of the intermediate and expulsion of phenoxide. In the isomerized intermediate, phenoxy is apical but the methylene group of the ring, which has low apicophilicity, must also be apical. Reactions of 2 and 3, which have more basic oxygen leaving groups, occur with P—N cleavage because expulsion from the isomerized intermediate in those cases is not sufficiently fast. These results fit reaction patterns at phosphorus that are determined by ring strain and electronegativity of ligands. Contributions from effects due to antiperiplanar interactions between bonding and nonbonding electrons are not detected.

Pyrolysis of (thio)carbonates via computation analysis

2018 ◽  
Vol 17 (06) ◽  
pp. 1850041
Author(s):  
Jingjing Xia ◽  
Abdullah M. Asiri ◽  
Khalid A. Alamry ◽  
Ping Wu ◽  
Zhihao Huang
Keyword(s):  
Transition States ◽  
Membered Ring ◽  
The Other ◽  
Energy Barriers ◽  
Calculation Results ◽  
Computation Analysis ◽  
Step Mechanism ◽  
Pyrolysis Processes

The regioselective production of alkenes from (thio)carbonates was calculated by MP2/6-31G(d) method via pyrolysis processes. Four (thio)carbonates were calculated in this paper. They are S-sec-butyl O-methyl thiocarbonate (I), O-sec-butyl S-methyl thiocarbonate (II), sec-butyl methyl thioncarbonate (III), and sec-butyl methyl dithiocarbonate (IV). Thirteen potential thermolysis routes were revealed for the pyrolysis of each substance, including nine routes to produce regioselective alkenes and four rearrangement/decompose alternatives. Among nine alkene generation routes, six-membered ring transition states via a two-step mechanism required the lowest energy, while the other routes exhibited higher energy barriers. The calculation results demonstrated an alkene distribution hierarchy of 1-butene [Formula: see text] E-butene [Formula: see text] Z-butene for substances I and II, and an order of E-butene [Formula: see text] 1-butene [Formula: see text] Z-butene for substances III and IV.

REGIOSELECTIVITY INVESTIGATION FOR THE PYROLYSIS OF XANTHATES: A COMPUTATIONAL STUDY

2013 ◽  
Vol 12 (07) ◽  
pp. 1350064 ◽  
Author(s):  
PING WU ◽  
JOHNNY TRUONG ◽  
YONGSHUN HUANG ◽  
JIAXING LI
Keyword(s):  
Oxygen Atom ◽  
Computational Study ◽  
Transition States ◽  
Major Product ◽  
Membered Ring ◽  
Computational Results ◽  
Atomic Size ◽  
Rate Determining Step ◽  
Ring Transition State ◽  
Step Mechanism

MP2/6-31+G(d,p)//MP2/6-31G(d) method was employed to investigate the pyrolyses of O -sec-butyl S -methyl xanthate (Chugeav reaction) and S -sec-butyl O -methyl xanthate, which gave regioselective products of E-butene, Z-butene and 1-butene. Both procedures were found to have 13 possible pathways, of which nine pathways would generate the alkene products. For O -sec-butyl S -methyl xanthate, the computational results indicated that the most favorable three pathways corresponded to a two-step mechanism, with the rate-determining step to be a thion sulfur atom involved six-membered ring transition states. The calculated products distribution was consistent with the experimental observations. However, for S -sec-butyl O -methyl xanthate, thiol-participated four-membered ring transition states were found to be more energetically favored than the six-membered ring transition state to produce 1-butene, which can be attributed to a larger sulfur atomic size than an oxygen atom. As the calculation result, only trace amount of 1-butene could be obtained with a major product being E-butene and Z-butene as a minority.

Studies on the transannular Diels–Alder reaction of 15-membered macrocyclic trienes containing a trans-trans diene. Part II: Evidence for unsymmetrical transition states in the formation of A.B.C.[6.6.7] tricyclic products

1995 ◽  
Vol 73 (10) ◽  
pp. 1695-1710 ◽  
Author(s):  
Dennis G. Hall ◽  
Renate Müller ◽  
Pierre Deslongchamps
Keyword(s):  
Lewis Acids ◽  
Transition States ◽  
Preceding Paper ◽  
Alder Reaction ◽  
Membered Ring ◽  
Diels Alder ◽  
Proximity Effects ◽  
Diels Alder Reaction ◽  
Stereocontrolled Synthesis ◽  
First Time

In the preceding paper (Part I) we described the preparation of 10 model TTT and TTC cyclopentadecatrienes. Their conversion to A.B.C.[6.6.7] tricyclic products via a transannular Diels–Alder (TADA) reaction and the analysis of the resulting diastereoselection along with proofs of structures are described in the present article (Part II). The required temperature of reaction was significantly higher (~100 °C) in comparison to that required for the 14-membered lower homologs, indicating that proximity effects are playing a key role in the TADA reaction. The presence of ester groups in the chain was found to favor either of the two possible transition states (endo or exo) on the basis of steric effects, thus controlling the TST/CSC ratio of tricycles from TTC macrocycles, and the TAC/CAT ratio from TTT macrocycles. A formyl substituent on the dienophile can further influence the diastereoselection through the hypothesis of unsymmetrical transition states and allowed, for the first time, the use of Lewis acids as catalysts in the TADA reaction. This investigation demonstrates a general methodology for the stereocontrolled synthesis of A.B.C.[6.6.7] tricycle structures related to several polycyclic natural products. Keywords: transannular, Diels–Alder, 15-membered ring, A.B.C.[6.6.7] tricycles, diterpene.

A theoretical study towards thermolysis process of thionesters and thiolesters

2018 ◽  
Vol 17 (02) ◽  
pp. 1850014 ◽  
Author(s):  
Xun Zhu ◽  
Xiuqin Zhou ◽  
Dongsheng Xiang ◽  
Ping Wu
Keyword(s):  
Theoretical Study ◽  
Theoretical Calculations ◽  
Transition States ◽  
Membered Ring ◽  
Basis Set ◽  
Reaction Progress ◽  
Alkyl Groups ◽  
Thermal Elimination ◽  
Bond Indices ◽  
Wiberg Bond Indices

This paper focuses on the thermal elimination of alkenes from methyl alkyl thionacetates and thiolacetates. Three alkyl groups are calculated: ethyl, isopropyl and tert-butyl. Possible elimination mechanisms are considered, including six- and four-membered ring transition states for alkene elimination, four-membered ring isomerization and a possible five-membered ring decomposition. Theoretical calculations are performed with the MP2 method and the 6-31G* basis set. Wiberg bond indices are also summarized to monitor the reaction progress.

Resolution in the scanning tunneling microscope

1991 ◽  
Vol 49 ◽  
pp. 488-489
Author(s):  
R. J. Wilson ◽  
D. D. Chambliss ◽  
S. Chiang ◽  
V. M. Hallmark
Keyword(s):  
Scanning Tunneling Microscope ◽  
Fundamental Principle ◽  
Atomic Scale ◽  
Lateral Resolution ◽  
Scanning Tunneling ◽  
Electronic Noise ◽  
Vertical Resolution ◽  
Tunneling Microscopy ◽  
Spatial Profile ◽  
Theoretical Analyses

Scanning tunneling microscopy (STM) has been used for many atomic scale observations of metal and semiconductor surfaces. The fundamental principle of the microscope involves the tunneling of evanescent electrons through a 10Å gap between a sharp tip and a reasonably conductive sample at energies in the eV range. Lateral and vertical resolution are used to define the minimum detectable width and height of observed features. Theoretical analyses first discussed lateral resolution in idealized cases, and recent work includes more general considerations. In all cases it is concluded that lateral resolution in STM depends upon the spatial profile of electronic states of both the sample and tip at energies near the Fermi level. Vertical resolution is typically limited by mechanical and electronic noise.

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