Conformational Analysis of Marine Polyhalogenated ?-Chamigrenes Through Temperature-Dependent NMR Spectra
作者:Graziano Guella、Giuseppe Chiasera、Ines Mancini、Francesco Pietra
DOI:10.1002/hlca.19910740411
日期:1991.6.19
agreement, with (+)-9 and (+)-10, which have a trigonal C(2), two conformers can be directly observed by NMR. The kinetic barriers, which are seen to arise mainly from steric repulsions between Hax–C(14) and the axial H or halogen atoms at C(8) and C(10), are calculated and discussed with respect to well documented exocycliemethylidene-substituted cyclohexane(ene) systems. This helps to rationalize why in rogiolol
温度依赖性1 H-和13 C-NMR谱表明,多卤代海洋β-chamigrenes或其合成衍生物,其是反式-diequatorially,在C(8)和C(9)被取代的,如rogiolol(( - ) - 2),扁桃醇((+)- 3)和它们的乙酸酯(+)- 1和(-)- 4经历缓慢的振铃-椅子-椅子倒置。借助合成模型化合物和分子力学计算研究了构象平衡和动力学。因此,可以看到Br ax –C(2)和Heq –C(7)之间的空间排斥会不利于热力学构象异构体1b,2b,3b和4b,这只能通过交叉饱和转移来检测,而Me ax –C(1)和OH ax –C(3)之间的附加空间排斥使扁桃醇差向异构体的构象异构体8b几乎没有填充,因此可以无法检测到。与具有三角形C(2)的(+)- 9和(+)- 10一致,可以通过NMR直接观察到两个构象体。动力学障碍,主要是由于H ax之间的空间排斥而引起的–C(14)以及