The Spiral Structure Of The Chiral Molecules And The Theory Of Optical Rotation

In material world, properties are determined by structure, so is optical activity. The chirality is an abstract concept but not a molecular structure itself. The helical structure exists in all organic molecule. It has definite directional character and many characteristic parameters. The helical structure can be correlate with the rotatory direction and the value of optical rotation. The helical structure is just the essential cause resulting in the optical activity.The rotatory direction determined under different conditions will be change for some optically active molecules. Because their conformations have been changed under different conditions. The change of the helical direction in molecular structure, so that it results in change of the rotatory direction. This does not disagree with the rule of helix theory. When the changes of conditions applied to determine can not have influence on the conformation in molecular structure, the rotatory direction will not change.By using the optical theory and analyzing the stereostructure of optically active substances can be connected with the value of their mole rotation. A range of more rotation of optically active compounds can be deduced from the structure. Thereby the fundamental theory of stereochemistry is further improvedOn the basis of these theories, we have studied the relationship between configuration and conformation of glycine amide, cysteine and uracil, thymine and 5-halouracils and their rotatory direction is specially analysed. Seven stable conformers of the neutral glycine amide and six conformers of cysteine have been studied at the B3LYP/6-311++G** level of the theory. The natural optical rotation of the seven conformers has been calculated using Hartree-Fock and density-functional theory with B3LYP functional at the sodium D line. The magnitudes of the optical rotation of the mirror-image conformers I, II, III are approximate same, while the signs of the optical rotation are reversed. For the glycine amide, the dependence of the optical rotation on the orientation of theamino, carboxyl and amide groups and for cysteine, the dependence of the optical rotation on the orientation of the amino, carboxyl, hydroxyl and thiol groups have been systematically investigated. We have described the implementation of DFT and HF theory for calculation of the optical rotation of uracil, thymine and 5-halouracils at 589.3 nm. It has previously shown that the HF and DFT values for the optical rotation of the same organic molecules are very different, and the difference is strongly depending on the conformer. The optical rotations have been carried out for uracil, thymine and 5-halouracils for a diverse set of eight solvents. The variation of the optical rotation with solvents is highly molecule-dependent.Their rotatory direction and optical rotation are both determined by the molecular stereostructure. The rotatory direction of amino-acid can be predicted from its structure. On the other hand, the configuration and conformation can also be deduced from its rotatory direction.