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Shape Selective Catalysis
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
Most applications and manifestations of shape-selective catalysis involve acid-catalyzed reactions such as isomerization, cracking, dehydration, etc. Acid-catalyzed reactivities of primary, secondary, and tertiary carbon atoms differ. Tertiary carbon atoms form carbonium ions rather easily; therefore, they react much easier than secondary carbon atoms. Primary carbon atoms do not form carbonium ions under ordinary conditions and therefore do not react. Only secondary carbonium ions can form on normal paraffins; whereas, tertiary carbonium ions can generate on singly branched isoparaffins. Therefore, in most cases isoparaffins crack and isomerize much faster than normal paraffins. This order is reversed in most shape-selective acid catalysis; i.e., normal paraffins react faster than branched ones which sometimes do not react at all.
Synthesis, spectral characterization, and biological studies of Schiff bases and their mixed ligand Zn(II) complexes with heterocyclic bases
Published in Inorganic and Nano-Metal Chemistry, 2022
S. Vanitha, N. Sathish Kumar, K. Reddi Mohan Naidu, M. Balaji, A. Varada Reddy, N. Saritha
In the 13C NMR spectra (Figure 7) of Schiff base ligand L1, the peak at 26 ppm can be assigned to two methyl carbon atoms and the peak at 57 ppm can be assigned to methylene carbon atom. The tertiary carbon atom adjacent to imine group was seen at 75 ppm. The aromatic carbon atoms of the benzene and pyridine ring were seen in a wide range from 122 ppm to 160 ppm. The most important functional group carbon of the imine group was seen at 178 ppm. Likewise, for Schiff base L2, the methyl carbon atom adjusted to imine group can be seen at 14 ppm and methyl carbon atom on the benzene ring was given a signal at 21 ppm. The aromatic carbon atom of the benzene and pyridine ring can be seen in a range from 118 ppm to 162 ppm. The peak at 172 ppm can be assigned to imine group carbon atom.
Investigation of Aviation Lubricant Aging under Engine Representative Conditions
Published in Tribology Transactions, 2021
Abdolkarim Sheikhansari, Ehsan Alborzi, Christopher Parks, Spiridon Siouris, Simon Blakey
The antioxidant additives DODPA and α-NPA and antiwear additive TCP were identified in the fresh lubricant sample based on their mass spectra, as shown in Fig. 2. The mass spectrum of DODPA was characterized by the presence of signals m/z = 393, 322, 250, and 57. The signal corresponding to m/z = 393 is the molecular ion and the absence of pentyl group results in the base peak of m/z = 322. This fragmentation is in accordance with the probable molecular structure presented in the figure with a positive charge on a benzylic tertiary carbon. The loss of pentyl ions from the second octyl group generates the signal with m/z = 250. The signal with m/z = 57 is possibly pertained to the formation of an n-butyl group. The mass spectrum of α-NPA is predominantly characterized by only one molecular ion corresponding to m/z = 219 (15).
Selection of cross-seasonal heat collection/storage media for wood solar drying
Published in Drying Technology, 2020
Xiang Chi, Jing Xu, Guangping Han, Wanli Cheng, Bing Liu, Xinyuan Du, Haoyu Chen
The advantages of THO for heat collection were not reflected in the results. The experimental design considered that the collector system was a medium to low temperature collection system, regardless of the highest collection temperature. Second, THO is a mineral heat transfer oil with a mixture of long-chain alkanes, cycloalkanes, isoparaffins, and the like. Although the chemical properties were relatively stable, an oxidation reaction can occur at normal temperature. This can occur because the energy distribution of hydrocarbon molecules is not uniform, among which weaker bonds exist in higher energy molecules. Tertiary carbon atoms split hydrocarbon radicals under the influence of light and heat, and hydrocarbon radicals react with oxygen to form peroxide radicals. Peroxide radicals and hydrocarbon molecules have lower activation energies, thus oxidation could occur at room temperature.[28,29] There was also a thin liquid layer adjacent to the inner wall of THO in the beaker, called a laminar bottom layer. THO has low heat transfer efficiency in this thin layer.[30] W and W-EG collected more heat because W and W-EG have larger heat capacities. W took 80% longer time to collect heat at 20 °C than at an ambient temperature 5 °C because the structure of water clusters changed from solid hexagonal to tetrahedral at 15–20 °C, and more heat was required.[31]