- A DFT and experimental study of the spectroscopic and hydrolytic degradation behaviour of some benzylideneanilines
-
The spectroscopic and hydrolytic degradation behaviour of some N-benzylideneanilines are investigated experimentally and theoretically via high quality density function theoretical (DFT) modelling techniques. Their absorption and vibrational spectra, accurately predicted by DFT calculations, are highly dependent on the nature of the substituents on the aromatic rings, hence, though some of their spectroscopic features are similar, energetic differences exist due to differences in their electronic structures. Whereas the o-hydroxy aniline derived adducts undergo hydrolysis via two pathways, the most energetically economical of which is initiated by a fast enthalpy driven hydration, over a conservative free energy (ΔG?) barrier of 53 kJ mol?1, prior to the rate limiting entropy controlled lysis step which occurs via a conservative barrier of ca.132 kJ mol?1, all other compounds hydrolyse via a slower two-step pathway, limited by the hydration step. Barriers heights for both pathways are controlled primarily by the structure and hence, stability of the transition states, all of which are cyclic for both pathways.
- Robertson, Tahjna I.,Nelson, Peter N.
-
-
- Effect of substituents on the UV spectra of supermolecular system: Silver nanoparticles with bi-aryl Schiff bases containing hydroxyl
-
Effect of substituents on the ultraviolet (UV) spectra of supermolecular system involving silver nanoparticles (AgNPs) and Schiff bases was investigated. AgNPs and 49 samples of model compounds (MC), bi-aryl Schiff bases containing hydroxyl (XBAY, involving 4-OHArCH?NArY, 2-OHArCH?NArY, XArCH?NAr-4′-OH, and XArCH?NAr-2′-OH), were synthesized. The size of AgNPs was characterized by transmission electron microscopy (TEM), and the UV absorption spectra of AgNPs, XBAYs, and MC-AgNPs mixed solutions were measured, respectively. The results show that (1) the size of AgNPs is larger in MC-AgNPs solutions than that in AgNPs solution due to the distribution of MC molecules on the surface of AgNPs; (2) the UV absorption wavelength of XBAYs changes in the action of AgNPs and their wavelength shift exists limitation between XBAY and MC-AgNPs solutions; and (3) the wavelength shift limit of MC-AgNPs (λWSL) is influenced by the substituents X and Y and the position of hydroxyl OH. The wavenumber ΔνWSL of λWSL can be quantified by employing the excited-state substituent constant σexCC and Hammett constant σ of substituents X and Y. Comparing with the 4-OH, the 4′-OH makes the ΔνWSL a red shift, whereas the 2′-OH, comparing with the 2-OH, makes the ΔνWSL a blue shift.
- Cao, Chao-Tun,Cheng, Shimao,Zhang, Jingyuan,Cao, Chenzhong
-
-
- Oxidative NHC Catalysis for the Generation of Imidoyl Azoliums: Synthesis of Benzoxazoles
-
N-Heterocyclic carbene (NHC)-catalyzed intramolecular cyclization of aldimines generated from 2-amino phenols and aromatic aldehydes leading to the synthesis of 2-arylbenzoxazoles under mild conditions is presented. The reaction proceeds via the generation of the aza-Breslow intermediates from imines and NHC, which under oxidative conditions form the key imidoyl azoliums and a subsequent intramolecular cyclization furnishes the product. The reaction tolerates a broad range of functional groups, and the products are formed in generally good yields.
- Patra, Atanu,James, Anjima,Das, Tamal Kanti,Biju, Akkattu T.
-
p. 14820 - 14826
(2019/01/03)
-
- Remarkable difference between five- and six- number-membered ring transition states for intramolecular proton transfer in excited state
-
In this study, a range of organic dyes were prepared to investigate difference between five- and six- number-membered ring transition states for internal proton transfer in excited state. Different strength intramolecular hydrogen bond in the target dyes
- Qin, Xiaozhuan,Ding, Ge,Wang, Zhenqiang,Zhang, Shengtao,Li, Hongru,Luo, Ziping,Gao, Fang
-
-
- Abnormal effect of hydroxyl on the longest wavelength maximum in ultraviolet absorption spectra for bis-aryl Schiff bases
-
Two sets of bis-aryl Schiff bases that contain 4(or 4′)-OH and 2(or 2′)-OH were synthesized. The first set consists of 4-HOArCH=NArY and XArCH=NArOH-4′, and the second set consists of 2-HOArCH=NArY and XArCH=NArOH-2′. Their ultraviolet absorption spectra were measured and investigated. A very interesting phenomenon was observed by analyzing their wave number νmax (cm?1) of longest wavelength maximum λmax (nm) of ultraviolet. Compared with the change regularity of the νmax of XArCH=NArY (where the X and Y excluded OH), the 4′-position hydroxyl (4′-OH) and 2′-position hydroxyl (2′-OH) have abnormal performance. The details are the following: the 4′-OH contributes an additional red shift to the νmax of XArCH=NArOH-4′ (λmax increase), whereas the 2′-OH contributes an additional blue shift to the νmax of XArCH=NArOH-2′ (λmax decrease). In addition, there are ortho steric effects of all 2-OH and 2′-OH on the νmax for 2-HOArCH=NArY and XArCH=NArOH-2′, and the ortho steric effect contributes a red shift to their νmax. These experimental facts can provide an important theoretical reference for us using aryl Schiff base compounds as optical materials and performing the molecular design.
- Cao, Chao-Tun,Zhou, Wei,Cao, Chenzhong
-
-
- Synthesis of 2-substituted pyrimidines and benzoxazoles via a visible-light-driven organocatalytic aerobic oxidation: Enhancement of the reaction rate and selectivity by a base
-
An efficient visible-light-driven photocatalytic oxidation of various 2-substituted dihydropyrimidines and phenolic imines has been achieved using an organic photocatalyst eosin Y bis(tetrabutyl ammonium salt) (TBA-eosin Y) and inexpensive oxidant molecular oxygen. With the aid of a base, significantly enhanced photoinduced electron transfer from substrates dihydropyrimidines or phenolic imines to the excited state of TBA-eosin Y has enabled the aerobic oxidation to yield 2-(methylthio)pyrimidines or 2-arylbenzoxazoles selectively. This journal is the Partner Organisations 2014.
- Wang, Lin,Ma, Zhi-Gang,Wei, Xiao-Jing,Meng, Qing-Yuan,Yang, Deng-Tao,Du, Shao-Fu,Chen, Zi-Fei,Wu, Li-Zhu,Liu, Qiang
-
supporting information
p. 3752 - 3757
(2014/08/05)
-
- Facile preparation of 2-substituted benzoxazoles and benzothiazoles via aerobic oxidation of phenolic and thiophenolic imines catalyzed by polymer-incarcerated platinum nanoclusters
-
Platinum nanoclusters supported on a polymer/carbon black composite material was found to be an excellent catalyst for the oxidative cyclization of phenolic and thiophenolic Schiff bases to 2-substituted benzoxazoles and benzothiazoles under ambient conditions. Copyright
- Yoo, Woo-Jin,Yuan, Hao,Miyamura, Hiroyuki,Kobayashi, Shu
-
supporting information; experimental part
p. 3085 - 3089
(2012/01/02)
-
- Efficient trapping of oxonium ylides with imines: A highly diastereoselective three-component reaction for the synthesis of β-amino-α-hydroxyesters with quaternary stereocenters
-
(Chemical Equation Presented) In one huge stride: The single-step construction of polyfunctionalized compounds with a quaternary stereocenter is possible through a highly diastereoselective multicomponent reaction of phenyldiazoacetates, alcohols, and imi
- Huang, Haoxi,Guo, Xin,Hu, Wenhao
-
p. 1337 - 1339
(2008/03/28)
-
- Highly enantioselective imine cinnamylation with a remarkable diastereochemical switch
-
The first general method for the enantioselective cinnamylation of aldimines is reported. The method utilizes a simple chiral cinnamylsilane reagent and is characterized by experimental simplicity and extraordinarily high levels of enantioselectivity. Fur
- Huber, John D.,Leighton, James L.
-
p. 14552 - 14553
(2008/09/19)
-