Joseph F. Chiang

Molecular structure of pyridine‐N‐oxide

The molecular structure of pyridine‐N‐oxide has been determined by gas phase electron diffraction. The internuclear distances and bond angles were obtained by applying a least squares analysis on the experimental molecular intensity. The bond distances (rg) and angles (ra) were N1–C2=1.384±0.011 A; C2–C3=1.381±0.009 A; C3–C4=1.393±0.008 A; N1–O7=1.290±0.015 A; C–H=1.070 A; ∠C2N1C6=120.9± 1.8°; ∠C3C4C5=114.1± 2.5°. The calculated moments of inertia agree with the microwave spectroscopic values.

Innovating e-waste management: From macroscopic to microscopic scales.

Waste electrical and electronic equipment (WEEE or e-waste) has become a global problem, due to its potential environmental pollution and human health risk, and its containing valuable resources (e.g., metals, plastics). Recycling for e-waste will be a necessity, not only to address the shortage of mineral resources for electronics industry, but also to decline environmental pollution and human health risk. To systematically solve the e-waste problem, more attention of e-waste management should transfer from macroscopic to microscopic scales. E-waste processing technology should be significantly improved to diminish and even avoid toxic substance entering into downstream of material. The regulation or policy related to new production of hazardous substances in recycled materials should also be carried out on the agenda. All the findings can hopefully improve WEEE legislation for regulated countries and non-regulated countries.

The molecular structure of norbornene as determined by electron diffraction and microwave spectroscopy

Abstract The molecular structure of norbornene has been investigated in the gas phase by combining electron diffraction data with microwave spectroscopic rotational constants. The interatomic distances (rg) and bond angles were obtained by applying a least squares program to the refined experimental molecular diffraction intensities. The CC bond length was found to be 1.336 ± 0.002 A while the ) bond length was 1. 529 ± 0.007 A. Other bond lengths and angles included (IUPAC numbering system was used for norbornene): C1-C6 = 1.550 ± 0.020 A, C1-C7 = 1.566± 0.005 A, C5-C6 = 1.556 ± 0.005 A, C-Have. = 1.103 ± 0.003 A, ∠C1C2C4 = 95.3°. The dihedral angle between planes C1C2C3C4 and C1C6C5C4 is 110.8 ± 1.5° while that between C1C2C3C4 and C1C7C4 is 122.3°. The moments of inertia calculated from ED structure are in good agreement with microwave spectroscopic values.

Molecular structures of 4-nitro-, 4-methyl- and 4-chloro-pyridine-N-oxides

Abstract The molecular structures of 4-nitro-, 4-methyl- and 4-chloro-pyridine- N -oxides have been determined by gas-phase electron diffraction. The structural parameters are obtained by least-squares fitting of the calculated molecular intensity functions to the observed intensities. A C 2v symmetry was assumed for 4-nitro- and 4-chloro-pyridine- N -oxides and C s for 4-methylpyridine- N -oxide. The deduced structural parameters are as follows: 4-nitropyridine- N -oxide; N 1 O 8 = 1.281 ± 0.022, N 7 O 13 = 1.262 (assumed), N 1 C 2 = 1.469 ± 0.066, C 2 C 3 = 1.386 ± 0.025, C 3 C 4 = 1.447 ± 0.019, C 4 N 7 = 1.628 ± 0.013, CH = 1.050 A (averaged); 4-methylpyridine- N -oxide; N 1 C 2 = 1.430 ± 0.034, C 2 C 3 = 1.354 ± 0.048, C 3 C 4 = 1.321 ± 0.062, C 4 C 7 = 1.577 ± 0.027, N 1 O 8 = 1.405, C 2 H 9 = 1.040, C 7 H 13 = 1.095 A; 4-chloropyridine- N -oxide; N 1 C 2 = 1.438 ± 0.017, C 2 C 3 = 1.363 ± 0.024, C 3 C 4 = 1.448 ± 0.027, N 1 O 8 = 1.262 ± 0.028, C 4 Cl 7 = 1.714 ± 0.025, CH = 1.10 A (averaged).

Recovery of rare and precious metals from urban mines—A review

Urban mining is essential for continued natural resource extraction. The recovery of rare and precious metals (RPMs) from urban mines has attracted increasing attention from both academic and industrial sectors, because of the broad application and high price of RPMs, and their low content in natural ores. This study summarizes the distribution characteristics of various RPMs in urban mines, and the advantages and shortcomings of various technologies for RPM recovery from urban mines, including both conventional (pyrometallurgical, hydrometallurgical, and biometallurgical processing), and emerging (electrochemical, supercritical fluid, mechanochemical, and ionic liquids processing) technologies. Mechanical/physical technologies are commonly employed to separate RPMs from nonmetallic components in a pre-treatment process. A pyrometallurgical process is often used for RPM recovery, although the expensive equipment required has limited its use in small and medium-sized enterprises. Hydrometallurgical processing is effective and easy to operate, with high selectivity of target metals and high recovery efficiency of RPMs, compared to pyrometallurgy. Biometallurgy, though, has shown the most promise for leaching RPMs from urban mines, because of its low cost and environmental friendliness. Newly developed technologies—electrochemical, supercritical fluid, ionic liquid, and mechanochemical—have offered new choices and achieved some success in laboratory experiments, especially as efficient and environmentally friendly methods of recycling RPMs. With continuing advances in science and technology, more technologies will no doubt be developed in this field, and be able to contribute to the sustainability of RPM mining.

The structure of hexafluorocyclopropane

The molecular structure of hexafluorocyclopropane has been determined by electron diffraction in the gas phase. The structural parameters were obtained by applying a least squares program on the experimental molecular intensity: CC = 1·505 ±0·003A, CF = 1·314 ±0·001A, and <FCF = 112·2 ± 1·0°. The CF bond length of hexafluorocyclopropane is in close agreement with the values found in CF4 and CF3CF3. The CC bond length is about that found in cyclopropane, while the FCF angle of the fluorocarbon is considerably smaller than the HCH angle in the hydrocarbon. The structure of hexafluorocyclopropane shows that the presence of the gem-difluoro groups causes a rehydridization of the Walsh or bent bond model sp2 hybrid carbon AOs to give more nearly sp3 hybridization. A complete discussion of the above reasoning will be made.

Molecular structure of 1,2,4-triazole

Abstract The molecular structure of 1,2,4-triazole has been determined by gas phase electron diffraction. The intemuclear distances and bond angles were obtained by applying a least-squares analysis to the experimental intensity. The bond distances ( r g ) and bond angles were N 1 -N 2 = 1.380 ± 0.010 A, N 2 C 3 = 1.329 ± 0.009 A, C 3 -N 4 = 1.348 ± 0.009 A, N 1 -C 5 = 1.377 ± 0.004 A, N 4 C 5 = 1.305 A (calculated value). N-H = 0.990 A, C-H = 1.054 A, ∠N 1 N 2 C 3 = 102.7± 0.5°, ∠N 2 C 3 N 4 = 113.8 ± 1.3°, ∠N 2 N 1 C 5 = 108.9 ± 0.8°, ∠H 1 N 1 N 2 = 110.9°, ∠H 2 C 3 N 4 = 119.2°, ∠H 3 C 5 N 1 = 131.0°, ∠C 3 N 4 C 5 = 105.7° (calculated value) and ∠N 4 C 5 N 1 = 108.7° (calculated value).

The average structures of 2,3-diazabicyclo[2.2.1]hept-2-ene and 2,3-diazabicyclo[2.2.2]oct-2-ene

Abstract The average molecular structures of 2,3-diazabicyclo[2.2.1]hept-2-ene and 2,3-diazabicyclo[2.2.2] oct-2-ene have been determined by electron diffraction in the gas phase. The structural parameters were obtained by applying a least squares analysis on the molecular scattering intensity functions. For 2,3-diazabicyclo[2.2.1]hept-2-ene, C s symmetry was assumed in calculating the geometry of the molecule. The parameters thus determined are: N 3 =N 2 = 1.221 A, N 3 - C 4 = 1.445 A, C 4 -C 5 = 1.538 A, C-H (ave.) = 1.112 A, 1 N 2 N 3 = 116.3°, 3 C 4 C 5 = 105.2°, 1 C 4 C 5 = 71.5°, C 4 -C 7 = 1.547 A, C 5 -C 6 = 1.530 A, 1 C 7 C 4 = 108.0°. For 2,3-diazabicyclo[2.2.2]oct-2-ene, C 2 v symmetry was assumed. The geometrical parameters are: N 3 = N 2 = 1.243 A, N 3 -C 4 = 1.473 A, C 4 -C 5 = 1.550 A, C 5 -C 6 = 1.516 A, C-H (ave.) = 1.119 A, 1 N 2 N 3 = 115.1°, 3 C 4 C 5 = 109.1°, 6 C 1 C 4 = 71.6°.

Structures of strained polycyclics: Bond distances and angles in tricyclo[3.3.0.02,6]oct-3-ene and in bicyclo[2.1.1]hexene-2

The structure of tricyclo[3.3.0.02,6]oct-3-ene in the gas phase has been determined by electron diffraction. From least squares fitting of theoretical to the experimental intensity function (range: 6 ⩽ q ⩽ 106), the CC bond lengths in the cyclobutane ring were found to be 1·580 ± 0·015 A. In the 5-member ring which contains the double bond, the CC distances are 1·503 ± 0·012 A, and in the other 5-membered ring, they are 1·505 ± 0·018 A on the sides and 1·579 ± 0·038 A at the base. The CC bond is 1·345 ± 0·010 A, and the average CH separation is 1·128 ± 0·010 A. The recorded patterns for the bicyclo[2.1.1]hexene-2 covered the angular range of q = 12−125 A−1. The interatomic distances and bond angles were obtained by applying a least squares analysis to the experimental molecular intensities. The CC double bond length was found to be 1·332 +- 0·005 A; CC single bond, adjacent to the double bond, is 1·537 ± 0·008 A, while the sp3-hybrid CC single bond is 1·549 ± 0·006 A. The dihedral angle of the 4-membered ring is 123·5 ± 1·3°. Comparison of the structures reported for this family of polycyclic hydrocarbons concludes this paper.

The molecular structures of mono-substituted cl-cyclohexene by gas-phase electron diffraction

Abstract The molecular structures of mono-substituted chlorocyclohexene are determined by gas-phase electron diffraction. The structural parameters are obtained by applying leastsquares analysis to the molecular scattering intensities. The bond distances ( r g ) and bond angles are: (1) 1-Cl-cyclohexene: C 1 C 2 = 1.336 ± 0.006 A. C 2 -C 3 = 1.500 ± 0.009 A, C 3 -C 4 = 1.533 ± 0.010 A, C 4 -C 5 = 1.537 A, C 5 -C 6 = 1.527 ± 0.010 A, C 1 -C 6 = 1.504 ± 0.009 A. C-Cl = 1.747 ± 0.005 A, C-H av = 1.138 ± 0.010 A, ∠Cl-cc = 126.3 ± 0.5°, ∠C 6 C 1 C 2 = 123.9 ± 0.8°. ∠C 1 C 2 C 3 = 124.6 ± 0.8°, ∠C 4 C 3 C 2 = 111.8 ± 1.2° and ∠-C 5 C 6 C 1 = 111.3 ± 1.1°; (2) 3-Cl-cyclohexene: C 1 =C 2 = 1.336 A, C 2 -C 3 = 1.501 ± 0.010 A, C 3 -C 4 = 1.513 ± 0.008 A, C 4 -C 5 = 1.542 A, C 5 -C 6 , = 1.516 ± 0.007 A, C 1 -C 6 = 1.505 ± 0.006 A, C-C1 = 1.801 ± 0.005 A, C-H av = 1.120 ± 0.008 A, ∠C 6 C 1 C 2 = 123.2 ± 1.0°, ∠C 1 C 2 C 3 = 124.1 ± 1.7°, ∠C 5 C 6 C 1 = 113.0 ± 1.3°, ∠C 2 C 3 C 4 = 112.5 ± 1.5° ∠ClC 3 C 2 = 110.3 ± 0.8°, ∠H-C=C = 123.0 ± 3.0° and ǒH-C-C = 109.5 ± 2.0°, with a mixture of 55% axial and 45% equatorial conformers; (3) 4-Cl-cyclohexene: C 1 =C 2 = 1.336 A, C 2 -C 3 = 1.507 ± 0.007 A, C 3 -C 4 = 1.516 ± 0.008 A, C 4 -C 5 = 1.544 A, C 5 -C 6 = 1.523 ± 0.010 A, C 1 - C 6 = 1-507 A, C-Cl = 1.799 ± 0.005 A, C-H av = 1.116 ± 0.005 A, ∠C 6 C 1 C 2 = 123.3 ± 1.5°, ∠C 5 C 6 C 1 = 113.0 ± 1.0°, ∠C 2 C 3 C 4 = 112.3 ± 1.0°, ∠ClC 4 C 3 = 110.2 ± 2.0°, ∠H-CC = 117.1 ± 4.5° and ∠H-C-C = 109.5 ± 1.0°, with a mixture of 45% axial and 55% equatorial conformers.