Theoretical Study Of Chiral Discrimination In Hydrogen-bonded Complexes

Chiral subject is widespread in nature. Chirality is one of the essential characteristics of nature. Chiral discrimination is the ability of a chiral molecule to distinguish between the two enantiomeric forms of another chiral molecule. On the molecular level, it is a great significance to understand the mechanism of chiral discrimination and its influence factors on the asymmetric synthesis, chiral detector of the design related to chirality.Chiral discrimination is classified into two groups. One group: A chiral molecule A* discriminates between the chiral forms, R and S, of a molecule B; the other group: Chiral self-discrimination lies in between two enantiomers of the same molecule A, either the same-ture self-discrimination or different. In this paper, we study on the chiral discrimination of the two chiral molecules.Theoretically, two kinds of energies are often used to study chiral discrimination. One is called chirodiastaltic energy, which is represented asΔEchir. The other kind of energy is named diastereofacial discrimination energy. When discussing chiral discrimination, one must take into account two aspects: one is the magnitude of chiral discrimination energy. The large value shows that the chiral discrimination ability is large; the small value shows that the chiral discrimination ability is small. The other is the sign of chiral discrimination energy (in the general case, which enantiomer of B, the R or S is preferred, and in self-discrimination which of the homo- or the heterodimer is the most stable). The sign ofΔEchir is positive or negative. A positive sign means that the heterochiral complex is preferred over the homochiral one and a negative sign means that the homochiral complex is favored over the heterochiral one.The other kind of energy is named diastereofacial discrimination energy which is defined as two diastereomers hydrogen bond complexes are formed both sides of the stereocenter in the host chiral molecule with the a pair of enantiomersof the guest chiral molecule.In this paper, the study system is the hydrogen bond complex of the chiral molecule butan-2-ol with hydrogen peroxide. Butan-2-ol is a catenulate chiral organic stable molecule. It has three monomer ("ga,""ag,"and"gg.") conformations from the highresolution microwave study and each of the monomers has three conformations:"h,""m,"or"e"(prefix). We use Leutwyler's method to study chiral discrimination for the hydrogen-bonded complexes of butan-2-ol (9 conformations) with hydrogen peroxide.In addition, we also extend chiral discrimination of the 2-methyl oxide and hydrogen peroxide formed the hydrogen bond complexes and study chiral discrimination for the hydrogen-bonded complexes 2-methylol oxirane (M-olOx) with hydrogen peroxide. We compare the results of the complexes between 2 - methyl oxide and 2-methylol oxiraneThe main contents in this paper is as follows:Chapter 1 Purpose and Significance, Present Situation and Development Trend for Chiral DiscriminationChapter 2 Study of Computational Method and TheoryChapter 3 Theoretical Study of Chiral Discrimination in Hydrogen-bonded Complexes of Butan-2-ol with Hydrogen PeroxideChapter 4 Chiral Discrimination in Hydrogen-bonded Complexes of 2-Methylol oxirane with Hydrogen PeroxideChapter 5 Summary and Prospect of the PaperThe main conclusions of this paper:We report a theoretical study on the chiral discrimination of different chiral formers of hydrogen-bonded complexes of butan-2-ol with hydrogen peroxide. Altogether, 36 minimum structures were located, and they are bound by intermolecular hydrogen bonds. For the 24 complexes of the h-form and m-form conformation, some complexes contain one primary hydrogen bond and several secondary hydrogen bonds; some complexes contain only secondary hydrogen bonds. For the 12 complexes of the e-form conformation, they are mainly bound by a single intermolecular hydrogen bond.For the h-form complexes, the value of the largest chirodiastaltic energy is -0.193 kcal mol-1 for SM-SP of"gg"(h), in favor of the SM complex in the"gg"conformation; the value of the largest diastereofacial energy is 3.491 kcal mol-1 for (SM-2)-SM of"gg"(h), in favor of the SM complex in the"gg"conformation. For the m-form complexes, the value of the largest chirodiastaltic energy is -0.238 kcal mol-1 for (SM-2)-(SP-2) of"gg"(m), in favor of the SM-2 complex in the"gg"conformation; the value of the largest diastereofacial energy is -3.763 kcal mol-1 for (SP-2)-SP of"ga"(m), in favor of the SP-2 complex in the"ga"conformation. For the e-form complexes, the value of the largest chirodiastaltic energy is 1.110 kcal mol-1 for SM-(SP-2) of"ga"(e), in favor of the SP-2 complex in the"ga"conformation; the value of the largest diastereofacial energy is -0.996 kcal mol-1 for (SP-2)-SP of"ga"(e), in favor of the SP-2 complex in the"ga"conformation.The number and strength of the hydrogen bond are different in the complexes of the different conformations in the flexible molecule butan-2-ol; there are also some different in the values and the signs of the largest chirodiastaltic energy and the largest diastereofacial energy.We compare and interpret the difference among the h-form, m-form and e-form conformations of butan-2-ol. The different positions (H, Me and Et) among the h-form, m-form, e-form and (H, Me and OH) among the"ga,""ag,"and"gg."determine the structure, energy, chirodiastaltic energy and diastereofacial energy multiplicity. Our study suggests that the mechanism of chiral discrimation on the system studied here is largely controlled by the primary hydrogen bond, and that the diastereofacial discrimation is mainly determined by the steric repulsion, that is, the driving force of the diastereofacial discrimation is mainly the steric repulsion of the ethyl group in the butan-2-ol.For the hydrogen-bonded complexes of 2-Methylol oxirane with hydrogen peroxide, we make a comparition and conclude: the difference between M-olOx and PO is that there is a methylol group in M-olOx which has a weak internal secondary hydrogen bond; there is a methyl group in PO which has not a intramolecular secondary hydrogen bond. For the syn complexes, there are double hydrogen bonds in M-olOx···HOOH; there is one single hydrogen bond in PO···HOOH. But for the anti complexes of M-olOx···HOOH and PO···HOOH, there is one single hydrogen bond; the hydrogen bond lengths are longer in M-olOx···HOOH than in PO···HOOH; these should attribute to the intramolecular secondary hydrogen bond. For the DM-olO···HOOH and DMO···HOOH complexes: the formers have double hydrogen bonds, the latters have one single hydrogen bond. The absolute value ofΔEchir in syn M-olOx···HOOH complexes is smaller than in PO···HOOH; but in anti M-olOx···HOOH and the DM-olO···HOOH complexes, the absolute value ofΔEchir are larger than in anti PO···HOOH and the DMO···HOOH complexes, that is, the chiral discrimination becomes large in anti M-olOx···HOOH and the DM-olO···HOOH complexes.