Ester-Linked Alkyl Chain Effect on the 2D Structures of Isobutenyl Compounds: Scanning Tunneling Microscopic Study
作者:Yoshihiro Kikkawa、Manami Ishitsuka、Kazuhiro Omori、Ayumi Kashiwada、Seiji Tsuzuki、Kazuhisa Hiratani
DOI:10.1246/bcsj.20150018
日期:2015.6.15
Various lengths of alkyl chains were introduced to the basic skeleton of isobutenyl ether compounds via ester bond (D1-OCn), and the 2D structures were investigated by using scanning tunneling microscopy at a solid/liquid interface. In the D1-OCn, two naphthalene units with ester-linked alkyl chains were connected with the isobutenyl group. The D1-OCn possessing C18–21 alkyl chains displayed alternate changes in the 2D structures, in which the alkyl chains were oriented in the same direction to form an interdigitation, whereas those with C15–17 chains showed the same dumbbell-shaped structures, suggesting that there is a specific alkyl chain length range exhibiting the odd–even effect. After the thermal reaction of tandem Claisen rearrangement (TCR), ether functions in the D1-OCn were converted to hydroxy groups accompanied by a new C–C bond formation (D2-OCn). Then, odd–even effect in the D1-OCn was completely cancelled to show only linear alignment in which the alkyl chains turned to the opposite direction, regardless of the alkyl chain length in the rearranged compounds (D2-OCn). This result indicates that various 2D structures of the isobutenyl compounds with ester groups can be transformed to the same linear alignment by the TCR. However, odd–even effect and structural transformation due to the Claisen rearrangement were unavailable for the “half” molecule containing a single naphthalene unit with an alkyl chain and an allyl moiety. Therefore, it can be concluded that dual alkyl chains connected to the naphthalene units are necessary for the isobutenyl ether compounds to reveal the odd–even effect and structural transformation by the TCR.
通过酯键(D1-OCn)将不同长度的烷基链引入异丁烯基醚化合物的基本骨架,并在固/液界面上使用扫描隧道显微镜研究其二维结构。在 D1-OCn 中,两个带有酯键烷基链的萘单元与异丁烯基相连。具有 C18-21 烷基链的 D1-OCn 在二维结构上显示出交替变化,烷基链在同一方向上取向,形成相互咬合,而具有 C15-17 烷基链的 D1-OCn 则显示出相同的哑铃状结构,这表明存在一个特定的烷基链长度范围,显示出奇偶效应。经过串联克莱森重排(TCR)热反应后,D1-OCn 中的醚官能团转化为羟基,同时形成新的 C-C 键(D2-OCn)。然后,D1-OCn 中的奇偶效应被完全消除,只显示出烷基链转向相反方向的线性排列,而与重排化合物(D2-OCn)中烷基链的长度无关。这一结果表明,带有酯基的异丁烯基化合物的各种二维结构都可以通过 TCR 转变为相同的线性排列。然而,对于含有单个萘单元、一个烷基链和一个烯丙基的 "半 "分子来说,奇偶效应和由于克莱森重排引起的结构转变是不存在的。因此,可以得出结论,异丁烯醚化合物要通过 TCR 显示奇偶效应和结构转变,与萘单元相连的双烷基链是必要条件。