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Type of Document	Dissertation
Author	Hamilton, Walter Clark
URN	etd-12152003-090535
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-12152003-090535
Title	The crystal structure of dimethyl phosphino-borine trimer. The method of least squares in electron diffraction. Some structural studies by the electron diffraction by gas molecules
Degree	PhD
Option	Chemistry
Advisory Committee	Advisor Name Title Verner Schomaker Committee Member
Keywords	None
Date of Defense	1954-01-01
Availability	unrestricted
Abstract NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The crystal structure of dimethyl phosphino-borine trimer, [(CH[subscript 3][subscript 2]PBH[subscript 2][subscript 3], has been determined by analysis of its x-ray diffraction maxima. Use was made of a three-dimensional Patterson function, least squares on the structure factors, and a three-dimensional electron-density difference map. The space group is P[subscript nma]; the unit cell constants are a = 11.16 [angstroms], b = 13.16 [angstroms], and c = 10.53 [angstroms]. There are four molecules per unit cell. The molecule has a cyclohexane-like ring of alternating phosphorus and boron atoms, with two methyl groups attached to each phosphorus atom. It has a plane of symmetry, and the environment of each phosphorus atom is C[subscript 2v]. The following average structural parameters were found: [...].ome attention is given to the determination of temperature factors from the difference map and to fitting of atomic form factors by Gaussians. The R factor for the final structure is 0.169. The advantages of the method of least squares, as contrasted to the usual correlation treatment, in electron diffraction investigations of molecular structure are outlined. Special attention is given to visual data and to the weighting of observations, including remarks on the use of a non-diagonal weight matrix and the derivation of weights from the goodness of fit, and to obtaining reliable estimates of error, and of error correlation, for the parameters. The method of least squares has been applied to electron diffraction photographs of bicycloheptadiene, C[subscript 7]H[subscript 8], and bicyclo-octane, C[subscript 8]H[subscript 14]. In the case of bicyeloheptadiene, a simple valence-force potential function adequately explains the values found for the structural-parameters. The structure of difluoromethane has been reinvestigated by electron diffraction.
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