| Derivatives of cyclododecane have been synthesized in our laboratory and studied by X-ray crystal diffraction and NMR analysis. In this dissertation, preferred conformations of serial substituted cyclododecanones with different substituents were characterized by theoretical methods including molecular mechanics, molecular dynamics and quantum mechanics computation. For the first time, molecular dynamics mimeics was used for the conformational process of substituted cyclododecanone.1. Under the CVFF force filed and in DMSO, the conformations of a-monosubstituted cyclododecanones have been studied by means of molecular dynamics at room temperature. The results show that the ring skeleton of preferred conformation is [3333], with the carbonyl group present in the 2-C position, which is consistent with the experimental results. The interconversion between a-corner-syn-[3333]-2-one and a-side-exo-[3333]-2-one were analyzed using dynamics mimesis method. The calculated results show that their interconversion path is consistent basically, the preferred conformation is a-side-exo-[3333]-2-one and the interconversion energy barrier is increased along with the volume augmentation of the substituents. For a-chlorine (or bromine) cyclo-dodecanones the maxima barriers are 43.9 KJ/mol and 44.3 KJ/mol respectively and the corresponding conformation is a-side-exo-[31233]-2-one. For a-alkylcyclododecanone,the maximum barrier arrive at 53.9 KJ/mol, and the corresponding conformation is a-side-exo-[31233]-2-one. Fora-amino (orhydroxy) cyclododecacones, which contained active proton, the conformation of the maximum energy is a-side-exo-[3 1323]-1-one. For a-phenylthio(or benzyl) cyclododecanones, apart from a-side-exo-[3333]-2-one conformation, the more stable conformation is a-side-exo-[4332]-3-one instead of a-corner-syn-[3333]-2-one. The vibration frequencies of all the conformation were calculated by quantum mechanics AM3 method and in each case 3N-6 real vibrational frequencies were obtained.which indicated the true cnformations.2.The research result of a, a'-cis-bissubstitututed cyclododecanone by the same method at room temperature indicated that the preferred conformation still remained [3333]-2-one. The bigger substituent was present in a-side-exo position and the smaller substituent present in a-corner-syn position when the two substituents were different. Molecular dynamics analysis proved that the interconversion of preferred confomation was Cs-pseudorotation and the interconversion energy barrier were consistent with the volume and chemical quality of the substituents.The skeleton of preferred conformation changed into [4323]-3-one while the substituents were two same benzene ring or cyclehexane. The intercoversion energy barrier of [4323]-2-one skeleton conformation to [3333]-2-one is increased along with the volume of substituent. When the two substituents were other group, [4323]-2-one skeleton conformation was the second preferred conformation. For phenylsulfonyl or phenylthio group, [4323]-2-one skeleton conformation had high probability in solution because of it - it surface conjugating effect. When the two substituents were different, Cs-pseudorotation existed between the preferred conformationand its second preferred conformation. The interconversion energy barrier corresponded with the difference of the substituents.3.The third series were a, a-disubstituted cyclododecanone and a, a, a'-trisubstituted cyclododecanone. Molecular mechanics and molecular dynamics computation showed that the preferred cnformations ofa, a-disubstituted cyclododecanone were still [3333]-2-one with substituents present in a-corner-syn and a-corner-anti position. The preferred conformations of a, a, a'-trisubstituted cyclododecanone still remained [3333]-2-one when the substituents were small. When the substituents becomed big to some extent, the preferred conformatin changed to [3324]-2-one because of 1 ,3-nonbonding effect and extraconjugating effect. The theretical results above were consistent with experiments...
|
PDF Full Text Request