Nh2

Chemical formula: C6H9O4N Molecular weight: 147.14

Crystal Structure

The a- and b-forms of the crystals belong to the orthorhom-bic crystal group, and the space group is P212121 with the crystal-lattice constant for both crystals as follows (25): a = 7.06, b = 10.3, and c = 8.75 A for the a-form and a = 5.17, b = 17.34, and c = 6.95 A for the b-form. The molecular arrangement obtained from an X-ray diffraction for two crystals are shown in Figure 5. From the crystal-structure analysis (25), L-glutamic acid in both forms exists as a zwitterion; a proton transfers from the a-carboxyl group to the amino group. The C(1)-O(1) and C(1)-O(2) distances of 1.24 and 1.27 A, for both crystal forms, are the values of the ionized carboxyl group. This discrepancy of 0.03 A found in both crystal forms can be attributed to differences in their intermolecular hydrogen bonds. O(2) makes a very short hydrogen bond with the OH group and a NH—O hydrogen bond with the NH^ group, while O(1) makes one NH—O bond with NH^.

In the y-carboxyl group, the length of C(5)-O(4) and C(5)-O(3), 1.21 and 1.37 A for the a-form, and 1.19, and 1.24 A for the b-form, respectively, indicate that it is un-ionized in both crystal forms.

The bond angles around C(2), C(3), and C(4) in the aform are significantly different from the corresponding ones in the b-form. This discrepancy may be a result of the steric repulsions that are due to the conformational differences. The OH—O bond seems to be most predominant of the four hydrogen bonds. It is reasonable to assume that considerable amounts of molecules are connected by OH— O hydrogen bonds to form chains in solution. The neigh-

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