Conformational analysis. Part 39. A theoretical and lanthanide induced shift (LIS) investigation of the conformations of cyclopentanol and cis- and trans-cyclopentane-1,2-diol
Conformational analysis. Part 39. A theoretical and lanthanide induced shift (LIS) investigation of the conformations of cyclopentanol and cis- and trans-cyclopentane-1,2-diol
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DOI：
10.1039/b207841b
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发表时间：
2002-01-01
期刊：
影响因子：
--
通讯作者：
Sancassan, F
中科院分区：
文献类型：
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作者：
Abraham, RJ;Koniotou, R;Sancassan, F
用从头算和分子力学（MM）计算以及LIS技术研究了环戊醇和顺式和反式环戊烷-1，2-二醇的构象，用Yb（fod）（3）得到了分子中所有H-1和C-13核的诱导位移，以及用La（fod）（3）得到的络合位移。MM计算给出了环戊醇的两种优化几何构型。这些是包膜构象，在包膜瓣处具有羟基赤道（1A）和轴向（1B）。相比之下，高斯98在B3 LYP水平与6- 31 G ** 基组给出了优化的几何形状（1C），这是一个信封构象与羟基在轴向位置的折叠信封。Δ E（1A-1B）= 0.47 kcal mol（-1）（MM）和0.93 kcal mol（-1）（从头算），Δ E（1B = 1C）= 0.15 kcal mol（-1）（从头算）。用MM和从头计算方法对顺式1，2-环戊二醇进行了计算，得到了两种不同的包络构象（2A）和（2B），它们都含有一个赤道羟基和一个轴向羟基。对于反式-1，2-环戊二醇，两种计算给出了相同的几何形状，具有两个轴向羟基的包络构象（3A）和具有双赤道羟基的半椅构象（3B）。Δ E（3A - 3B）= 2.9 kcal mol（-1）（MM）和0.70 kcal mol（-1）（从头算）。LIRAS 4模型涉及一个sp（3）杂化氧原子与两个对称的孤对电子对被用于这些化合物。环戊醇的计算LIS与1A的观测数据的一致性较差，1B的一致性中等，但1C的一致性良好。结合1B和1C的LIS分析表明，在CHCl 3溶液中1C的群体> 80%。从头计算和LIS分析表明，溶液中的构象以不对称构象1C为主。环戊醇的这种构象与呋喃糖的构象之间的相似性表明，异头效应可能比迄今为止认识到的更为根本。在顺式-环戊烷-1，2-二醇中，观察到的数据与2A和2B的计算的LIS都很好地一致。在反式-环戊烷-1，2-二醇中，观察到的数据与3B的计算LIS吻合良好，但与3A的吻合较差。LIS允许分配的质子化学位移的个别亚甲基质子在这些分子中，这是以前没有给出。
The conformations of cyclopentanol and cis- and trans-cyclopentane- 1,2-diol have been studied by ab initio and molecular mechanics ( MM) calculations and by the LIS technique, using Yb(fod)(3) to obtain the induced shifts of all H-1 and C-13 nuclei in the molecule, together with complexation shifts obtained by the use of La(fod)(3). The MM calculations gave two optimised geometries for cyclopentanol. These were envelope conformations with the hydroxyl group equatorial (1A) and axial (1B) at the flap of the envelope. In contrast Gaussian 98 at the B3LYP level with the 6-31G** basis set gave an optimised geometry (1C) which was an envelope conformation with the hydroxyl group in ;an axial position at the fold of the envelope. DeltaE(1A-1B) = 0.47 kcal mol(-1) (MM) and 0.93 kcal mol(-1) (ab initio) and DeltaE (1B = 1C) = 0.15 kcal mol(-1) (ab initio). The MM and ab initio calculations for cis-1,2-cyclopentanediol gave different envelope conformations (2A) and (2B), both with one equatorial and one axial hydroxyl group. For trans-1,2- cyclopentanediol both calculations gave the same geometries, an envelope conformation with two axial hydroxyls (3A) and a half chair conformer with diequatorial hydroxyls (3B). DeltaE (3A - 3B) = 2.9 kcal mol(-1) (MM) and 0.70 kcal mol(-1) (ab initio). The LIRAS4 model involving an sp(3) hybridised oxygen atom with two symmetric lone pairs was used for these compounds. The calculated LIS for cyclopentanol gave poor agreement with the observed data for 1A, moderate agreement for 1B but good agreement for 1C. A LIS analysis combining 1B and 1C suggests that the population of 1C was > 80% in CHCl3 solution. The ab initio calculations and the LIS analysis agree that the unsymmetric conformer 1C is the major form in solution. The similarity between this conformer of cyclopentanol and that of the furanose sugars suggests that the anomeric effect may be more fundamental than hitherto realised. In cis-cyclopentane-1,2-diol the observed data were in good agreement with the calculated LIS for both 2A and 2B. In trans-cyclopentane-1,2-diol the observed data were in good agreement with the calculated LIS for 3B but in poor agreement for 3A. The LIS allowed the assignment of the proton chemical shifts of the individual methylene protons in these molecules which had not been given previously.