Hedberg, Kenneth W. (1948) Part I. Investigations of the mechanism and kinetics of the formation of malchite green dye. A. Mechanism of the oxidation of leuco malachite green. B. Kinetics of the conversion of malachite green carbinol to dye. Part II. Determination of some molecular structures by the method of electron diffraction. A. Adamantane. B. 1,3,5,7,-cyclooctatetraene. Part III. The molecular structure of arsenobenzene. Determination of the unit cell and space group of the crystal. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-01312005-160036
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Part I. Investigations of the mechanism and kinetics of the formation of malachite green dye.
A. Mechanism of the oxidation of leuco malachite green.
The oxidation of leuco malachite green to malachite green dye is commonly considered to take place through the formation of malachite green carbinol: [...]. The present study shows that malachite green carbinol cannot be an intermediate in this process. The proof rests on the observation that the oxidation of leuco malachite green to dye occurs at a much more rapid rate than that at which malachite green carbinol is dehydrated to dye.
It is suggested that this result is evidence that the oxidation of ethanol does not take place through the formation of a gem-diol as intermediate.
B. Kinetics of the conversion of malachite green carbinol to dye.
The kinetics of the conversion of malachite green carbinol to dye have been studied in solutions of ionic strength approximately 2.84 over the pH range 2.5 - 4.9. The rate constants representing the rate of approach to equilibrium are first order with respect to carbinol and have the values 15.8, 13.4, 6.2, 8.7, 21.4 and 20.4 x [...] [...] at pH 4.88, 4.69, 4.08, 2.98, 2.25, and 1.65, respectively.
An attempt is made to account for the observed minimum in the curve which results when these values of the constant for the approach to equilibrium are plotted against pH. Part II. Determination of sole molecular structures by the method of electron diffraction.
An investigation of the structure of adamantane by electron diffraction has led to the following results for the structural parameters: [...], [...],[...]. (assumed), [...] (assumed) The molecular symmetry [...] was assumed. These results are in agreement with results obtained from x-ray diffraction studies of the crystal.
B. 1,3,5,7, - cyclooctatetraene.
The structure of cyclooctatetraene is of great theoretical importance to chemists because of the relationship between this molecule and the benzene molecule. From an earlier electron diffraction investigation of cyclooctatetraene it was concluded that all C - C bonded distances were equal and that the molecule has the symmetry [...]. This result is in complete disagreement with preliminary results from an x-ray diffraction investigation currently in progress in another laboratory; these results indicate cyclooctatetraene to have two different C - C bonded distances and the molecular symmetry [...].
The results of our electron diffraction investigation show that cyclooctatetraene has two C - C bonded distances, which are about equal to the normal double bond distance and to the conjugated single bond distance. The molecule has the symmetry [...] "tub" in agreement with the result from x-ray diffraction.
The positions of the double bonds in the molecule cannot be placed from the electron diffraction data; two different regions of parameter combinations, depending upon the position of the double bonds, give acceptable models. It is possible to make a choice between these regions, however, based upon considerations of strains induced by rotation about the double bond. The structural parameters for the best model in the chosen region are: [...] (assumed), and C - H = 1.098, (assumed).
Part III. The molecular structure of arsenobenzene determination of the space group and unit cell.
The molecular formula of arsenobenzene is commonly written as [...] although the true molecular formula is unknown. Determinations of the molecular weight of this substance indicate from 2 to 6 of the [...] units to be combined in solution. It was hoped that a determination of the space group and unit cell of the crystal would yield useful information regarding the structure of the molecule.
A tentative unit cell was determined from layer line measurements made from rotation photographs, and verified by a symmetrical Laue photograph. The arsenobenzene crystal was found to be monoclinic; and to contain 12 [...] units per cell. Accurate values of the lattice constants were obtained from oscillation photographs. These values are [...]. With the aid of Weissenberg photographs the probable space group of the crystal was determined to be [...].
The space group and unit cell of arsenobenzene together with considerations based on the chemistry of arsenic allow interesting deductions to be made regarding the molecules of this substance. One molecule may consist of 2,3, or 6 [...] units, giving 6,4, or 2 molecules per unit cell, respectively, There is, however, considerable qualitative evidence which indicates that discrete molecules of arsenobenzene do not exist in the crystal, and that instead the arsenic atoms are bonded together in infinite chains probably parallel to the monoclinic axis.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||1 January 1948|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||31 Jan 2005|
|Last Modified:||26 Dec 2012 02:29|
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