Stereochemistry of (E)- and (Z)-1,1'-dichlorobifluorenylidenes, substituted overcrowded fullerene fragments.

Enantiomer Pub Date : 2002-11-01 DOI:10.1080/10242430215701
Sergey Pogodin, Shmuel Cohen, P Ulrich Biedermann, Israel Agranat
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引用次数: 5

Abstract

X-ray crystallographic and semiempirical PM3 and AM1 studies of 1,1'-dichlorobi-9H-fluoren-9-ylidene (5) are reported. The X-ray molecular structure of (Z)-5 indicated an approximately C2 symmetric conformation with pure twist around C9 = C9' of 40.4 degrees. The fjord regions are somewhat overcrowded: r(C8...C8') = 315.3 pm, r(Cl(1)...Cl(1') = 341.7 pm, r(C(8)...H(8')) = 259.0 pm. The four chlorine atoms of two neighboring molecules of (Z)-5 form a chain. The PM3 calculations showed that the global minimum of 5 is the C2 symmetric twisted conformation t(E)-5, which is 2.4 kJ/mol more stable than its diastereomer C2-t(Z)-5. The corresponding AM1 relative stability is reversed: C2-t(Z)-5 is 1.1 kJ/mol more stable than C2-t(E)-5. The pure twists of t(Z)-5 and t(E)-5 are 37.0 degrees and 37.2 degrees (PM3) and 40.5 degrees and 39.1 degrees (AM1). The corresponding (E) --> (Z) (PM3) and (Z) --> (E) (AM1) energy barriers of diastereomerization are 80.6 kJ/mol (PM3) and 75.8 kJ/mol (AM1). Two anti-folded local minima conformations C2-a(Z)-5 and C(i)-a(E)-5 were found to be 21.2 and 29.5 kJ/mol (PM3) and 25.8 and 35.2 kJ/mol (AM1) less stable than t(E)-5. The syn-folded conformations C(S)-s(Z)-5 and C2-s(E)-5 are transition states for the enantiomerization processes of C2-tz-5 and C2-tE-5, respectively, and lay 79.8 and 94.1 kJ/mol (PM3) and 108.3 and 107.4 kJ/mol (AM1) higher in energy than their corresponding twisted conformations. An alternative pathway for enantiomerization of C2-t(E)-5 via the anti-folded achiral intermediate C(i)-a(E) has a barrier of 56.0 kJ/mol (PM3) and 68.5 (AM1). An alternative pathway for enantiomerization of C2-t(Z)-5 via C2-t(E) and C(i)-a(E) has a barrier of 80.6 (PM3) and 75.8 (AM1) kJ/mol.

取代过满富勒烯片段的(E)-和(Z)-1,1'-二氯双氟乙烯基的立体化学。
报道了1,1'-二氯- 9h -芴-9-ylidene(5)的x射线晶体学和半经验PM3和AM1研究。(Z)-5的x射线分子结构为近似C2对称构象,C9 = C9′周围的纯扭为40.4度。峡湾地区有些拥挤:r(C8…C8') = 315.3 pm, r(Cl(1)…Cl(1') = 341.7 pm, r(C(8)…H(8')) = 259.0 pm。两个相邻的(Z)-5分子的四个氯原子形成一条链。PM3计算表明,5的全局最小值为C2对称扭曲构象t(E)-5,其稳定性比非对映体C2-t(Z)-5高2.4 kJ/mol。相应的AM1相对稳定性相反:C2-t(Z)-5比C2-t(E)-5稳定1.1 kJ/mol。t(Z)-5和t(E)-5的纯扭转度分别为37.0度和37.2度(PM3)和40.5度和39.1度(AM1)。对应的(E)—> (Z) (PM3)和(Z)—> (E) (AM1)非对映异构化能垒分别为80.6 kJ/mol (PM3)和75.8 kJ/mol (AM1)。两个反折叠的局部最小构象C2-a(Z)-5和C(i)-a(E)-5的稳定性分别为21.2和29.5 kJ/mol (PM3)和25.8和35.2 kJ/mol (AM1),比t(E)-5的稳定性差。C(S)-s(Z)-5和C2-s(E)-5是C2-tz-5和C2-tE-5对映异构化过程的过渡态,其能量分别比相应的扭曲构象高79.8和94.1 kJ/mol (PM3)和108.3和107.4 kJ/mol (AM1)。另一种通过抗折叠非手性中间体C(i)-a(E)对映异构化的途径具有56.0 kJ/mol (PM3)和68.5 kJ/mol (AM1)的势垒。通过C2-t(E)和C(i)-a(E)进行C2-t(Z)-5对映异构化的另一种途径的势垒分别为80.6 (PM3)和75.8 (AM1) kJ/mol。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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