偏光顕微鏡による尿素付加物の屈折率の測定

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Refractive indices of the hexagonal urea adducts were measured by the polarizing microscope, and they were compared with that of the tetragonal crystal of urea.<BR>In the tetragonal crystal of urea, the planes of the Y-shaped molecules are perpendicular to each other but parallel to the c axis; consequently this crystal is uniaxially positive (ω=1.483, ε=1.593). In the hexagonal urea adducts, although the oxygen atoms of urea molecules are superimposed along a vertical edges axis, the urea molecules are oriented 120° with respect to one another forming a helix spiral. The guest molecules are packed along c axis. As a result, the urea adducts are also uniaxially positive, and ω were constant (=1.492), but ε were changed by the forms of guest molecules (paraffins=1.566, saturated fatty acids =1.577, unsaturated fatty acids=1.5827).<BR>For the birefringence, therfore, the tetragonal urea was stronger than the hexagonal urea adducts.
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