Generation and characterization of distonic dehydrophenoxide radical anions under electrospray and atmospheric pressure chemical ionizations

We have explored the possibilities of generating radical anions under electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) conditions. By using different sets of ortho-, meta-, and para-isomers of nitrobenzoic acids, methylphenols, and nitrophenols, and m-, and p-isomers of hydroxybenzaldehydes and hydroxyacetophenones as the precursor molecules, we have successfully generated the isomeric distonic dehydrophenoxide radical anions (m/z 92) using the ESI process by applying relatively high capillary voltages, the in-source dissociation (ISD) condition. Under the same conditions, the o-hydroxybenzaldehyde and the o-hydroxyacetophenone yielded the even-electron dehydrophenoxide anion (m/z 93) due to the well-known ortho-effect. The distonic phenoxide radical anions at m/z 92 were also generated under APCI-ISD conditions by using m- and p-isomers of nitrobenzaldehydes and nitroacetophenones. While the o-nitrobenzaldehyde and the o-nitroacetophenone mainly yielded the phenoxide anion at m/z 93, due to the ortho-effect. The collision-induced dissociation (CID) experiments of all the anionic precursor molecules formed from either ESI or APCI produced comparable mass spectra as those observed in the ESI-ISD or the APCI-ISD experiments. The radical anions at m/z 92 reacted with CO₂ and O₂ to form the CO₂ adduct and the oxygen atom abstraction product, respectively, revealing the dual-character of the distonic radical anions, the phenide ion and the phenyl radical. Computational studies support the results of the ion-molecule reactions.     

Isobaric (vapour + liquid) equilibrium for N-methyl-2-pyrrolidone with branched alcohols

The (vapour + liquid) equilibrium (VLE) and boiling temperature measurements have been determined at 95.3 kPa as a function of composition for the binary liquid mixtures of N-methyl-2-pyrrolidone (NMP) with branched alcohols using a Swietoslawski-ebulliometer. The branched alcohols include 2-propanol, 2-butanol, 2-methyl-l- propanol, 2-methyl-2-propanol, and 3-methyl-l-butanol. The experimental temperature-composition (T–x) results were used to estimate Wilson parameters and then used to calculate the equilibrium vapour compositions and the excess Gibbs free energy at T = 298.15 K. The experimental temperature-composition (T, x) results were correlated with the Wilson, the NRTL and the UNIQUAC models. The experimental results are interpreted in terms of intermolecular interactions between constituent molecules.     

Excess molar volumes and ultrasonic studies of N-methyl-2-pyrrolidone with ketones at T = 303.15 K

Excess molar volumes (V^E) and ultrasonic studies at T = 303.15 K and atmospheric pressure have been measured over the whole composition range for the binary mixtures of N-methyl-2-pyrrolidone (NMP) with ketones. The ketones studied in the present investigation include methyl ethyl ketone (MEK), diethylketone (DEK), methyl propyl ketone (MPK), methyl isobutyl ketone (MIBK), and cyclohexanone (CH). The V^E values were measured using a dilatometer and were negative over the entire mole fraction range for NMP with MEK, DEK, MPK, and MIBK and were positive for NMP with CH. The ultrasonic sound velocities for the above systems were measured with a single crystal interferometer at a frequency of 3 MHz. The sound velocity (u) results have been used to calculate isentropic compressibility (K_s) and deviation in isentropic compressibility (ΔK_s) over the entire range of volume fraction. The sound velocity results have been predicted in terms of free length theory (FLT), collision factor theory (CFT), and Nomoto relation. The results reveal that all the theories gave a satisfactory estimate of the sound velocity. The deviation values of the isentropic compressibilities (ΔK_s) were negative over the entire range of volume fraction in all the binary liquid mixtures except in the binary system NMP with CH, where we observed positive ΔK_s values. The results are interpreted on possible molecular interactions between components.     

Liquid Draining Through Multiple Ports: An Investigation on Air Core Vortex Formation

Fluid Dynamics - The phenomenon of air core vortexing in liquid draining through cylindrical tanks can have serious adverse effects on many engineering systems. Hence, suppression of such vortices...     

Silver‐Catalyzed Isocyanide–Isocyanide [3+2] Cross‐Cycloaddition Involving 1,2‐Group Migration: Efficient Synthesis of Trisubstituted lmidazoles

Imidazole ring is an important five‐membered aromatic heterocycle that is widely present in natural products and synthetic molecules. The isocyanide–isocyanide [3+2] cross‐cycloaddition reaction constitutes a straightforward method to access imidazoles starting from the easily available chemicals. So far, only three successive reports are known and all lead to the formation of 1,4‐disubstituted imidazoles. Here, we report the first isocyanide–isocyanide [3+2] cross‐cycloaddition reaction allowing for the formation of 1,4,5‐trisubstituted imidazoles under silver catalysis. An unexpected 1,2‐migration of sulfonyl, alkoxycaybonyl, and carbamoyl groups took place during the cyclization process that is responsible for the formation of trisubstituted imidazoles. This report displayed a mechanistically novel synthetic method toward a variety of imidazole derivatives, which are otherwise difficult to access by conventional methods.     

Regioselective synthesis of isocoumarins by ruthenium-catalyzed aerobic oxidative cyclization of aromatic acids with alkynes

The highly regioselective aerobic oxidative cyclization of aromatic, heteroaromatic and alkenyl acids with alkynes in the presence of catalytic amounts of [{RuCl(2)(p-cymene)}(2)], AgSbF(6) and Cu(OAc)(2)·H(2)O providing isocoumarin derivatives was investigated.     

Control of stability through overlap matching: closo-carborynes and closo-silaborynes

The matching of ring and cap orbitals for overlap is used to arrive at the best carborynes among the many possibilities. Accordingly, 1,2-carboranes, 1,2-silaboranes (C2BnHn+2, and Si2BnHn+2, n = 4, 5, 8, and 10), and their dehydrogeno derivatives were studied with use of the Density Functional Theory (B3LYP/6-311+G*). The dehydrogenation of 2,3-C2B5H7 (6a) to 2,3-C2B5H5 (13a) is estimated to be even less endothermic than those of benzene and 1,2- C2B10H12 (1a) to benzyne and 1,2-C2B10H10 (8a) by more than 21 kcal/mol. This is due to the extra stabilization gained through better overlap of the C2B3H3 ring with the 2 BH caps. The relatively larger size of the Si atom leads to overlap requirements in silaboranes that are different from those in carboranes. The lower Si-Si single bond energy and the preference of Si for lower coordination result in unusual structures in dehydrogenosilaboranes. One of the Si atoms moves away from the surface in Si2B10H10 (15), Si2B8H8 (16, 17, and 18), and 1,2-Si2B5H5 (19). One Si atom forms a bridge to a trigonal surface in 2,3-Si2B5H5 (20) and 1,2-Si2B4H4 (21). Estimates of three-dimensional aromaticity with NICS calculations show that the exohedral double bond does not influence three-dimensional aromaticity.     

Effects of pitch-shift velocity on voice Fo responses

Previous studies have shown that voice fundamental frequency (F0) is modified by changes in the pitch of vocal feedback and have demonstrated that the audio-vocal control system has both open- and closed-loop control properties. However, the extent to which this system operates in closed-loop fashion may have been underestimated in previous work. Because the step-type stimuli used were very rapid, and people are physically unable to change their voice F0 as rapidly as the stimuli, feedback responses might have been reduced or suppressed. In the present study, pitch-shift stimuli, consisting of a disparity between voice F0 and feedback pitch of varying ramp onset velocities, were presented to subjects vocalizing a steady /ah/ sound to examine the effect of stimulus onset on voice F0 responses. Results showed that response velocity covaried with stimulus velocity. Response latency and time of the peak response decreased with increases in stimulus velocity, while response magnitude decreased. A simple feedback model reproduced most features of these responses. These results strongly support previous suggestions that the audio-vocal system monitors auditory feedback and, through closed-loop negative feedback, adjusts voice F0 so as to cancel low-level fluctuations in F0.     

Experimental and simulated validation of the energy dependence of saturation thickness of multiple scattered gamma rays

Saturation thickness for multiple scattering gamma rays from multiple sources has been measured experimentally and simulated using the Monte Carlo N-Particle (MCNP) Code. Experimental measurements were performed using a collimated beam of gamma-rays from ⁵⁷Co, ²⁰³Hg, ¹³³Ba, ²²Na, ¹³⁷Cs, ⁶⁵Zn and ⁶⁰Co sources. The gamma rays were directed at rectangular aluminium targets of varying thickness. A NaI (Tl) scintillation detector placed at a backscattering angle of 180° was used to detect the scattered photons. The measured and calculated saturation thickness increases with increasing energy of incident gamma-rays. Experimental and simulated values are compared and are in good agreement.