An AM1 calculational study of the Diels–Alder addition of maleic anhydride to C5-substituted pentamethylcyclopentadienes and 2,5-dimethylthiophene oxide. An attempt to ascertain the factors controlling the π-facial selectivities and relative reactivities

1994 ◽  
Vol 72 (12) ◽  
pp. 2493-2505 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
Jiangong Ma
Keyword(s):  
Maleic Anhydride ◽  
Transition State ◽  
Empirical Method ◽  
Diels Alder ◽  
Facial Selectivity ◽  
Semi Empirical

The Diels–Alder reactions of maleic anhydride (1) with a group of C5-substituted cyclopentadienes and 2,5-dimethylthiophene oxide (5) have been studied with the semi-empirical method AM1. We find that the facial selectivities and relative reactivities found experimentally for six dienes (2a–2f) are accurately reproduced at this level of theory. The results of the calculational study provide no concrete support for the proposal that σ–σ* hyperconjugation in the transition state – an interaction between a σ bond at C5 of the cyclopentadiene and the incipient σ bonds anti to it (the Cieplak effect) – is the major source of the syn facial selectivity observed for 2a–2d. In addition, the relative reactivities and facial selectivities are predicted for a number of cyclopentadienes which will be synthesized and studied experimentally.

Synthesis of functionalized hexahydro-, octahydro-, and decahydro-1H-phenalenes via Diels–Alder reactions of 1-methylene-4a-methoxycarbonyl-1,2,3,4,4a,5,6,7-octahydronaphthalene and related dienes

1993 ◽  
Vol 71 (9) ◽  
pp. 1463-1483 ◽  
Author(s):  
Edward Piers ◽  
Richard W. Friesen ◽  
Paul Kao ◽  
Steven J. Rettig ◽  
James Trotter
Keyword(s):  
Maleic Anhydride ◽  
Transition State ◽  
Methyl Acrylate ◽  
Diels Alder ◽  
Cycloaddition Reactions ◽  
Methoxycarbonyl Group ◽  
The Face ◽  
Group Reaction ◽  
Bicyclic Dienes

The results of a study of Diels–Alder reactions of the bicyclic dienes 6–8 with a variety of dienophiles are reported. Although 6 and 7 undergo cycloaddition reactions smoothly and efficiently, thermal Diels–Alder reactions of 8 are generally sluggish or, under the conditions investigated, do not proceed at all. Additions of tetracyanoethylene (TCNE) to 6–8 are highly face-selective, with preferential attack of the dienophile on the side of the dienes opposite to the angular methoxycarbonyl group. Reaction of 7 with maleic anhydride (MAN) is completely face-selective and proceeds preferentially via an endo transition state. Diels–Alder reactions of 6 and 7 with methyl acrylate (MAC) and nitroethylene (NE) are entirely regioselective, but the face-selectivities, which vary from ~2:1 to ~3:1, are rather low. The use of this chemistry as a method for the synthesis of functionalized, stereochemically defined, perhydro-1H-phenalenes is demonstrated.

Modeling the Effects of O-sulfonation on the CID of Serine

2020 ◽  
Author(s):  
Kenneth Lucas ◽  
George Barnes
Keyword(s):  
Sulfo Group ◽  
High Energy ◽  
Empirical Method ◽  
Side Chain ◽  
Energy Structure ◽  
Direct Dynamics ◽  
Theoretical Mass ◽  
Intermolecular Proton Transfer ◽  
Dynamics Simulations ◽  
Semi Empirical

We present the results of direct dynamics simulations and DFT calculations aimed at elucidating the effect of \textit{O}-sulfonation on the collision induced dissociation for serine. Towards this end, direct dynamics simulations of both serine and sulfoserine were performed at multiple collision energies and theoretical mass spectra obtained. Comparisons to experimental results are favorable for both systems. Peaks related to the sulfo group are identified and the reaction dynamics explored. In particular, three significant peaks (m\z 106, 88, and 81) seen in the theoretical mass spectrum directly related to the sulfo group are analyzed as well as major peaks shared by both systems. Our analysis shows that the m\z 106 peaks result from intramolecular rearrangements, intermolecular proton transfer among complexes composed of initial fragmentation products, and at high energy side-chain fragmentation. The \mz 88 peak was found to contain multiple constitutional isomers, including a previously unconsidered, low energy structure. It was also seen that the RM1 semi empirical method was not able to obtain all of the major peaks seen in experiment for sulfoserine. In contrast, PM6 did obtain all major experimental peaks.

Theoretical investigation of Ramachandran plot of N-formyl-L-alanine-amide

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Genetic Algorithm ◽  
Theoretical Investigation ◽  
Energy Analysis ◽  
Empirical Method ◽  
Conformational Space ◽  
Ramachandran Plot ◽  
Global Minima ◽  
Reasonable Time ◽  
Semi Empirical

The full conformational space of N-formyl-L-alanine-amide was explored by the semi-empirical method AM1 coupled to the Multi Niche Crowding (MNC) genetic algorithm implemented in a package of programs developed in our laboratory. The structural and energy analysis of the resulting conformational space E(,ψ) exhibits 5 regions or minima ɣL, ɣD, ɛL, D and αD. The technique provides better detection of local and global minima within a reasonable time.

scholarly journals How Good Is the STW Sensor? An Account from a Larger Shipping Company

2021 ◽  
Vol 9 (5) ◽  
pp. 465
Author(s):  
Angelos Ikonomakis ◽  
Ulrik Dam Nielsen ◽  
Klaus Kähler Holst ◽  
Jesper Dietz ◽  
Roberto Galeazzi
Keyword(s):  
High Frequency ◽  
Additional Data ◽  
Empirical Method ◽  
Influential Factor ◽  
Sensor Data ◽  
Sea State ◽  
Shipping Company ◽  
Frequency Sensor ◽  
Semi Empirical

This paper examines the statistical properties and the quality of the speed through water (STW) measurement based on data extracted from almost 200 container ships of Maersk Line’s fleet for 3 years of operation. The analysis uses high-frequency sensor data along with additional data sources derived from external providers. The interest of the study has its background in the accuracy of STW measurement as the most important parameter in the assessment of a ship’s performance analysis. The paper contains a thorough analysis of the measurements assumed to be related with the STW error, along with a descriptive decomposition of the main variables by sea region including sea state, vessel class, vessel IMO number and manufacturer of the speed-log installed in each ship. The paper suggests a semi-empirical method using a threshold to identify potential error in a ship’s STW measurement. The study revealed that the sea region is the most influential factor for the STW accuracy and that 26% of the ships of the dataset’s fleet warrant further investigation.

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