環状スルフランの構造,結合エネルギーおよび反応性
スポンサーリンク
概要
- 論文の詳細を見る
A series of 10-S-3 type sulfuranes, tetraazathiapentalenes (10a-i, 11a-f, 12, and 17) fused with pyrimidine ring and/or pyridine ring, were prepared by oxidation of the corresponding thioureas. The restricted internal rotation of the pyrimidine ring was observed by temperature dependent <SUP>1</SUP>H NMR spectrum which gave the kinetic parameters of Δ<I>G</I><SUP>298</SUP><SUP>_??_</SUP>=16.6kcal/mol, Δ<I>H</I>=15.9kcal/mol, and Δ<I>S</I><SUP>_??_</SUP>=-2.4 eu at 25°C for the rotational barrier in 10a. The substituent effect to the kinetic data can be reasonably explained in terms of electronic balance of the N-S-N hypervalent bond or the different degree of contribution of resonance canonical structures. Comparison of the rotational barrier of 10a with that of model compounds (18 and 24) suggests that hypervalent N-S-N stabilization in 10a is more than 6kcal/mol. Methylation of these 10-S-3 type sulfuranes (10a, 10d, and 11a) was investigated to clarify the electronic effect in these molecules. The crystal structure of the neutral symmetric sulfurane 10a reveals to be a planar molecule in which the sulfur atom was found to be in the same plane of the two pyrimidine rings. The S-N bond lengths 1.948(3) and 1.938(3) Å are longer than the sum of the covalent bond radii, consistent with a bond order less than unity. The crystal structures of the dicationic symmetric sulfurane 17 and the unsymmetrical sulfurane 11a also show to be planar molecules. The S-N distances in 11a were different each other due to the electronic imbalance between the apical ligands. Semi-empirical calculation (AM 1) of these systems (10a and 17) indicate the expected electronic features of the hypervalent molecules (10-S-3 sulfuranes) and the small contribution of π-overlapping in the N-S-N bonds.
- 1995-08-01
著者
関連論文
- 環状スルフランの構造,結合エネルギーおよび反応性
- トリフェニルアンチモンジブロミドによるα-ケトアルコ-ル類の酸化反応--5価有機アンチモンの関与 (ヘテロ原子の有機化学) -- (トリス(イソシアン酸)リンの合成とその反応性)
- タイトル無し