scholarly journals A Theoretical and Experimental Study on Esterification of Citric Acid with the Primary Alcohols and the Hydroxyl Groups of Cellulose Chain (n = 1-2) in Parched Condition

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Dang T. Nguyen ◽  
Quan T. Pham
Keyword(s):  
Citric Acid ◽  
Ring Opening ◽  
Density Functional ◽  
Membered Ring ◽  
Hydroxyl Groups ◽  
Dehydration Reaction ◽  
Primary Alcohols ◽  
Reaction Step ◽  
Cellulose Chain ◽  
Ring Opening Reaction

Esterification of citric acid (CA) with the primary alcohols and the hydroxyl groups of cellulose chain (n = 1-2) in parched condition were investigated by using density functional theory (DFT) method and a two-layer ONIOM approach. Geometry and energy of reactants, products, and transition state (TS) structures were optimized at B3LYP/6-311g (d, p) level and ONIOM (B3LYP/6-311g (d, p):PM3MM) level. The computational results show that the esterification occurs in the two main steps: the first step is the dehydration reaction of CA to form anhydrides of 5-membered ring and 6-membered ring and the second step is the ring opening reaction with the hydroxyl –OH groups to form the ester products. The energy barrier of dehydration reaction step is much higher than that of ring opening reaction step. Effect of substituent R in primary alcohol R-CH2OH (R: CH=CH2, CH2NHCH3, CH2OCH3, CH2Cl) and cellulose chain (1G, 2G) on the reactivity, which has negative inductive effect –I, is significant. The combination of calculation data and experiment data were applied to make findings more rigorous. The activation energy of CA was determined by using differential scanning calorimetry (DSC) and thermal gravimetric (TG) analysis to be E a exp  = 47.8 kcal/mol; the experimental data favoured the dehydration reaction step of CA.

Thermal intramolecular reactions of Δ1-1,2,4-triazolines with extended exocyclic unsaturation

1988 ◽  
Vol 66 (3) ◽  
pp. 385-390 ◽  
Author(s):  
Adrian L. Schwan ◽  
John Warkentin
Keyword(s):  
Ring Opening ◽  
Hydrolysis Product ◽  
Sigmatropic Rearrangement ◽  
Membered Ring ◽  
Ring Closure ◽  
Experimental Results ◽  
First Order ◽  
Ring Opening Reaction ◽  
Intramolecular Reactions

Fumaratotriazoline (1) and amidotriazoline (3) undergo thermal first-order transformations in solution at 65 °C. The former affords the isomeric pyrrole 5 and its hydrolysis product 6. A mechanism involving opening of the initial five-membered ring to form 8, followed by closure to a new five-membered ring (9), is proposed. Amidotriazoline (3) loses N2 on heating to form 19. The experimental results are best accommodated in terms of a novel mechanism involving an electrocyclic ring closure, a [3 + 2] cycloreversion to form an ylide, a sigmatropic rearrangement of the ylide, and, finally, an electrocyclic ring-opening reaction.

Ring Opening of 1,1’-sulfonyl bis-aziridines Derived from L-Amino Acids and DFT Study on their Affinity Toward Different Nucleophiles

2021 ◽  
Vol 18 ◽  
Author(s):  
Nawel Khettache ◽  
Mohamed Dehamchia ◽  
Sihem Hessainia ◽  
Tahar Abbaz ◽  
Zine Régaïnia
Keyword(s):  
Ring Opening ◽  
Density Functional ◽  
Theoretical Study ◽  
Sodium Ethoxide ◽  
Aziridine Ring ◽  
Functional Theory ◽  
Cyanide Anion ◽  
Anionic Nucleophiles ◽  
Ring Opening Reaction ◽  
Selective Ring Opening

: We describe herein the ring-opening reaction of chiral 1,1’-sulfonyl bis-aziridines with various neutral and anionic nucleophiles, including benzylamine, piperidine, acetate, allyl thiolate, cyanide anion, and sodium ethoxide. These reactions afforded bis-opened or/and mono-opened compounds via a regioselective attack on the non-substituted methylene of aziridine ring. The structures of the products were confirmed based on spectral analysis (IR, 1H NMR, and 13C NMR). A theoretical study involving density functional theory (DFT) was used to rationalize the region-selective ring-opening of starting bis-aziridines.

Thiadiazoloquinoxalines

Synlett ◽  
2019 ◽  
Vol 30 (10) ◽  
pp. 1111-1124 ◽  
Author(s):  
Ben-Lin Hu ◽  
Martin Baumgarten
Keyword(s):  
Density Functional Theory ◽  
Small Molecules ◽  
Ring Opening ◽  
Density Functional ◽  
Membered Ring ◽  
Time Dependent ◽  
Functional Theory ◽  
Data Density ◽  
Td Dft ◽  
End Groups

In this account we summarized our work on the modification and extension of the thiadiazoloquinoxaline (TQ) as a strong acceptor unit for organic electronics. While also alternating conjugated copolymers with different donors were published, the focus here is the description of variation of the acceptor unit leading to many small molecules with different electronic properties as indicated from their optical absorptions, cyclic voltammetry (CV) data, density functional theory (DFT), and time-dependent (TD-DFT) calculations. The extension with ortho-diquinones seemed a promising way to enlarge the TQ molecules and further increase their electron affinity. At the end it is demonstrated how these units can be merged with other acceptors like naphthalenediimide (NDI) and be extended in an iterative way to extremely long condensed pyrene-fused heteroacenes with TQ end groups just by ring opening of the thiadiazole five-membered ring followed by further condensations in an iterative way.1 Introduction2 The Synthesis of TQ Cores3 The Extension of TQ3.1 The Extension at 4,9-Positions3.2 The Extension at 6,7-Positions3.3 The Extension on NDI3.4 The Extension with TQ for Endcapping (Bis TQ)4 Conclusions

A versatile synthesis of oligocrown compounds with hydroxyl groups at the hinge

1987 ◽  
Vol 52 (12) ◽  
pp. 2961-2970 ◽  
Author(s):  
Martin Bělohradský ◽  
Petr Holý ◽  
Ivan Stibor ◽  
Jiří Závada
Keyword(s):  
Ring Opening ◽  
Oxirane Ring ◽  
Hydroxyl Groups ◽  
Ring Opening Reaction

Oxirane ring-opening reaction of N-(2,3-epoxy-1-propyl) azacrowns Ia-Ic and 4,5-epoxy-2-oxapentylcrowns IIa-IIe with mono- and diamines (including mono- and diazacrowns) afforded array of new di-, tri-, and tetracrown compounds with hydroxyl groups placed at the hinge.

scholarly journals Theoretical Study on Epoxide Ring-opening in CO2/Epoxide Copolymerization Catalyzed by Bifunctional Salen-Type Cobalt(III) Complexes: Influence of Stereoelectronic Factors

Catalysts ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 328
Author(s):  
Karol Dyduch ◽  
Aleksandra Roznowska ◽  
Monika Srebro-Hooper ◽  
Bun Yeoul Lee ◽  
Artur Michalak
Keyword(s):  
Carbon Atom ◽  
Ring Opening ◽  
Density Functional ◽  
Model Systems ◽  
Conformational Space ◽  
Nucleophilic Attack ◽  
Epoxide Ring ◽  
Epoxide Ring Opening ◽  
The Real ◽  
Ring Opening Reaction

Propylene oxide (PO) binding and ring-opening reaction with the bifunctional CO2/epoxide copolymerization catalyst, based on the Co(III)-salcy complex including two quaternary ammonium salts with n-butyl substituents (N+-chains) were investigated by Density Functional Theory (DFT) calculations and compared with the model systems without the N+-chains. The importance of the different possible stereoisomers and the stereoselectivity of these processes for (S)- and (R)-enantiomers of PO were considered. To explore the conformational space for the real catalyst, a complex approach, developed previously was applied. The calculations for the model systems directly demonstrate that PO-ring opening proceeds preferentially in trans catalysts’ configuration and no participation of cis-β isomers is viable; nucleophilic attack at the methylene-carbon atom is preferred over that at methine-carbon atom. For the real bifunctional catalyst, with the (S,S)-configuration of cyclohexane, the results indicate a preference of (R)-PO ring-opening over (S)-PO ring-opening (ca. 6:5). Concerning stereoisomers resulting from the orientation of N+-chains in the real catalyst, different groups of structures participate in the ring-opening reaction for (R)-PO, and different for (S)-PO. The high population of nonreactive complexes of (R)-PO may be the key factor responsible for decreasing the activity of the analyzed catalyst in the epoxide ring-opening reaction.

scholarly journals C-C and C-H bond cleavage reactions in acenaphthylene aromatic molecule, an ab-initio density functional theory study

2019 ◽  
Vol 10 (4) ◽  
pp. 403-408 ◽  
Author(s):  
Muthana Abduljabbar Shanshal ◽  
Qhatan Adnan Yusuf
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Ring Opening ◽  
Density Functional ◽  
Bond Cleavage ◽  
Dft Method ◽  
Functional Theory ◽  
Ring Opening Reaction ◽  
Reaction Energies ◽  
Cleavage Reactions

The ab-initio DFT method (B3LYP) is applied to the study of the C-C and C-H bond cleavage reactions in acenaphthylene molecule. It is found that the C-C bond cleavage proceeds via a singlet aromatic transition state, compelled through a disrotatoric ring opening reaction. A sigmatropic H atom shift follows the transition state in some of these reactions, where the formation of a methylene -CH2,acetylenyl-, allenyl- or butadienyl moiety in the final product is possible. The calculated activation and reaction energies for the C-C ring opening are 164-236 and 52-193 kcal/mol, respectively. The calculated cleavage reaction energies for the C-H bonds are 117-122 kcal/mol and the activation energies are 147-164 kcal/mol.

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