China 
Africa 
Explore chapters and articles related to this topic
Greener Synthesis of Natural Products
Published in Ahindra Nag, Greener Synthesis of Organic Compounds, Drugs and Natural Products, 2022
Renata Kołodziejska, Renata Studzińska, Hanna Pawluk, Alina Woźniak
The reduction of a carbonyl compound by means of alcohol dehydrogenase (ADH) takes place when the transfer of one of the hydrogen atoms from the dihydropyridine ring of the cofactor (in most cases, it is nicotinamide adenine dinucleotide (NADH) or its phosphorylated derivative (NADPH)) to the particular face of the carbonyl group occurs. The pro-(S)- or pro-(R)-hydride (HS and HR, respectively) of the cofactor (NAD(P)H) attacks the si or re face of an sp2 hybridized carbon atom of the carbonyl group to form (R)- or (S)-alcohols. The reaction range comprises reduction of, for example, ketones, α- and β-keto esters, and α-keto acids by isolated enzymes or whole cells of microorganisms, plants, or animals – Figure 14.8.27–31
Nomenclature
Published in Steven L. Hoenig, Basic Chemical Concepts and Tables, 2019
A ketone is an organic compound that contains the carbonyl group (–C=O) on a carbon other than those on the end of a carbon chain (in the middle). the “e” ending of the parent hydrocarbon is changed to “one”.
Impact of Silane Treatment on the Properties of Kenaf Fiber Unsaturated Polyester Composites
Published in S.M. Sapuan, J. Sahari, M.R. Ishak, M.L. Sanyang, Kenaf Fibers and Composites, 2018
Md. Rezaur Rahman, Sinin Hamdan, Rubiyah bt Hj Baini
According to Coates (2000), the range for methyl C-H is 2970–2950 cm‑1 for asymmetry stretch or 2880–2860 cm‑1 for symmetry stretch. A weaker methyl or methylene band shows chain branching, and strong methyl bands indicates significant splitting (Coates 2000). As mentioned, there is carbonyl group in the composites. The carbonyl groups can be ketones, aldehydes, or esters. The carbonyl groups contain the C=O functional group. If ketones exist, the bond of C-H stretching is broader than the stretching of C-H bonds in aldehydes. From the results, the region shows the peaks at 1718.58 cm‑1 and 1720.50 cm‑1, which demonstrates that the ketones are present. However, according to Coates (2000), conjugations play as an important role when observing frequency of carbonyl. Which means the conjugations will determine that they either connect to aromatic rings or conjugate to C=C or C=O. Besides that, the level of carbonyl frequency also will help to differentiate the types of carbonyl compounds, in which it will determine if the carbonyl group will directly or indirectly attach to aromatic rings (Coates 2000).
An expedient carbon–sulfur bond formation explored through the cellulose sulfonic acid (CSA) catalyzed dithioacetal protection of carbonyl compounds
Published in Journal of Sulfur Chemistry, 2020
The carbonyl group is one of the most studied and highly appraised functional group in organic synthesis. Due to its’ high reactivity and wide range of transformations, it has been contributing more than any other functional group to organic synthesis [1]. In multi-step synthesis, its high reactivity often becomes an obstacle, especially where poly-functional groups are involved. In such cases it needs to be temporarily protected in a suitable form. Among the existing protecting groups, 1,1-dithioacetal protection is recognized as the most versatile due to its ease of formation, inherent stability towards acidic or basic conditions [2], and ability to revert the polarity of the carbonyl group [3]. Dithioacetals have been used as the precursor in alkylation [4], olefination [5], fluorination [6] hydrogenolysis [7], autoxidation [8] hydrodesulfurization [9] as well as in C–H or C–S bond activation [10,11]. Sulfur-containing compounds have found an important place in the synthesis of natural products [12], pharmaceuticals [13], structural diversifications [14] and in drug discovery [15] as well.
Comparative study of the nucleophilic attack step in the proteases catalytic activity: A theoretical study
Published in Molecular Physics, 2020
Sebastián A. Cuesta, José R. Mora, Cesar H. Zambrano, F. Javier Torres, Luis Rincón
When only one water molecule is considered in the calculation, a four-membered ring transition state is formed, where the carbon and the oxygen atoms of the carbonyl group and the hydrogen and oxygen atoms of the water molecule participate [Scheme 3 (i)]. An activation free energy of 47.3 kcal/mol was estimated for this step. In a second model [Scheme 3 (ii)], two water molecules were involved to form a six-membered transition state, for which an activation free energy of 44.9 kcal/mol was estimated, being slightly lower than the reaction with one solvent molecule. In the latter, the carbonyl group is protonated by extraction of a hydrogen atom of a first water molecule; at the same time, this deprotonated hydroxyl group activates a second water molecule, which finally attacks the carbon atom of the carbonyl group closing the ring in the transition state complex. The extra stabilisation of the transition state of the second system can be attributed to the lower structural tension of the six-membered ring in comparison to the four-membered one. Besides the differences between the transition states of the two reactions, it is clear that the spontaneous hydrolysis implies a high activation energy, suggesting the presence of a catalyst as requirement for the reaction to occur in nature. The spontaneous hydrolysis including more than two water molecules was considered in order to evaluate the presence of an oxyanion hole [76] around the carbonyl oxygen, which is expected to increase the electrophilicity of the carbon and consequently provide a lower activation free energy. In this sense, the activation free energy versus the number of water molecules was plotted in Figure 1, and as a result, it was observed that the activation energy decreases as the number of water molecules increases, being the minimum value associated to the system with four water molecules (ΔG‡ = 43.9 kcal/mol), while, the addition of a fifth water molecule results in an increase in the activation free energy, possibly due to steric effects. Based on this result, the model with four water molecules was defined as the reference to evaluate the catalytic action of the reactions simulated with the models depicted in Schemes 1 and 2. It is important to mention that the 3 extra water molecules added to the model simulate the presence of the oxyanion hole in the carbonyl group, which is further considered for the Cys- and Ser-protease because it stabilises the tetrahedral intermediate as well as the transition state making the carbon atom more susceptible for the nucleophilic attack [19,77,78].