Ester-Linked Alkyl Chain Effect on the 2D Structures of Isobutenyl Compounds: Scanning Tunneling Microscopic Study

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.