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Organic Synthesis
Published in Suresh C. Ameta, Rakshit Ameta, Garima Ameta, Sonochemistry, 2018
Chetna Ameta, Arpit Kumar Pathak, P. B. Punjabi
An aldol condensation is a condensation reaction in organic chemistry in which an enol or an enolate ion reacts with a carbonyl compound to form a P-hydroxyaldehyde or P-hydroxyketone, followed by dehydration to give a conjugated enone. Aldol condensations are important in organic synthesis, because they provide a smooth way to form carbon-carbon bonds (Carey and Sundberg, 1993). These reactions are usually catalysed by strong acids or bases, and a variety of different Lewis acids have been evaluated in this reaction (Reeves, 1966). Unfortunately, the presence of a strong acid or base promotes the reverse reaction (Hathaway, 1987) and this leads to the self-condensation of the reacting materials to give the corresponding byproducts in low yields (Nakano et al., 1987).
Alkenes and Alkynes: Structure, Nomenclature, and Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
An enol is an alkene alcohol, with the OH group attached to an sp2-hybridized carbon of the C=C unit. Most enols are very unstable and tautomerize to the isomeric ketone or aldehyde. What is keto–enol tautomerism?
Synthesis and characterization of lanthanide complexes as potential therapeutic agents
Published in Journal of Coordination Chemistry, 2020
FT-IR spectra of the coordinated compounds confirm the occurrence of complexation as shown in Supporting Information Figure S1. The characteristic spectral bands of N-H and C = O of hydrazone ligand [26] disappeared and the incoming bands of (C = N)enolic from 1559 to 1566 cm−1 [33–35] appeared in all complexes. These suggested the coordination via enol form instead of keto form by deprotonation of N-H proton during the tautomerization process. The shifting of stretching vibrations of azomethine group (C = N) agree with coordination of the central metal with nitrogen atom of azomethine group [36, 37]. A good indication of participation of nitrogen of azomethine group is appearance of a new band of ν(M–N) from 431 to 503 cm−1 [25, 38]. The coordination of sulfur atom with metal ions was confirmed by the shifting of υ(C-S) of thiophene in all the metal complexes to lower frequencies [39, 40]. From the FT-IR results, new bands of coordinated nitrate group were shown at 1239–1241 and 1079–1104 cm−1 due to asymmetric and symmetric stretches ν1 and ν2, respectively [41, 42]. Also, in the FT-IR data of all complexes, clear new bands appeared from 606 to 585 cm−1 assigned to ν(M–O) [43, 44]. It is concluded that the ligand behaves as a dianionic tetradentate ligand coordinated to metal ions via azomethine N, enolic O, hydroxyl O, and thiophene S.
Copper-assisted synthesis of five-membered O-heterocycles
Published in Inorganic and Nano-Metal Chemistry, 2020
Navjeet Kaur, Yamini Verma, Neha Ahlawat, Pooja Grewal, Pranshu Bhardwaj, Nirmala Kumari Jangid
Jiang et al.[67] described that alkenes underwent oxidative [3 + 2] cycloaddition with anhydrides and Cu catalyst. The carboesterification of alkenes with anhydrides delivered γ-lactones under reaction conditions though the formation of carbon–oxygen and Csp3–Csp3 bonds. Excellent yields were obtained from all substrates containing weakly or strongly electron-withdrawing or electron-donating groups. The conjugated dienes have exclusive selectivity for terminal olefin under optimized conditions. But the desired product was not obtained from internal olefins (Scheme 18). Initially, the Cu(OTf)2 coordinated with the enol and alkene of anhydride. Then, intermediate I was produced by a cis oxycupration. Subsequently, intermediate II was generated by an intramolecular insertion into enol. Finally, intermediate II furnished product with the assistance of molecular O2 and the catalytic cycle was completed with the regeneration of copper(II).[68]
Transition metal complexes with 2-acetylpyridine-ethylcarbazate: noncovalent interactions in their structures and antimicrobial studies
Published in Journal of Coordination Chemistry, 2020
Claudia C. Gatto, Eduardo de A. Duarte, Gabriela S. Liarte, Thayná S. Silva, Mariana B. Santiago, Carlos H. G. Martins
The ν(C = N) of HL at 1620 cm−1 shifts to 1617, 1601, 1635, and 1598 cm−1 for 1–4, respectively, suggesting the metal coordination of the azomethine nitrogen atom (N2) [28, 33, 36, 39]. The ν(C = O) absorption at 1717 cm−1 for HL shifts to 1653, 1644, and 1695 cm−1 for 1, 2, and 3, indicating that the coordination and interaction has also occurred via the carbonyl oxygen [28, 33, 39, 40]. The ν(N–H) are absent in the spectra of 4, suggesting the deprotonation of the N–H moiety with the coordination of HL in the enol form [41–43]. The ν(C = Npy) absorption is also shifted in the complexes spectra due to the coordination site (N1) of the pyridine groups. The ν(C = Npy) absorption of HL is at 1583 cm−1 and shifts to 1553, 1550, 1595, and 1562 cm−1 for 1–4, respectively [31, 36, 39, 44, 45]. The solvent water molecule of 1, 2, and 4 can be observed due to the presence of ν(O-H) absorption at IR spectra in the range of 3433–3451 cm−1.