The evolution of the principle of circumscribing

Circumscribing benzenoid polycyclic aromatic hydrocarbons was first introduced in 1982 under the topic of a periodic table for benzenoid hydrocarbons and isomer enumeration. This circumscribing process was rendered on benzene to successively generate coronene, circumcoronene, dicircumcornene, and so on as the first constant-isomer series. Subsequently, numerous benzenoid constant-isomer series were uncovered because of the coupling of the benzenoid periodic table (Table PAH6) and circumscribing. Circumscribing even carbon monocyclic polyenes produced [n]cyclacenes (n = number of hexagonal rings) which are monotier nanotubes. Starting with [n]cyclacenes and successive circumscribing generates (n,0) Zigzag nanotubes of increasing length. Successive circumscribing cycloparaphenylenes leads to (n,n) Armchair nanotubes of increasing length. Successive supercircumscribing cycloparaphenylenes leads to total-resonant-sextet Armchair nanotubes of maximum stability. Circumscribing polycyclic conjugated systems was subsequently introduced for other ring sizes. Circumscribing polycyclic hydrocarbons with a combination of pentagonal and hexagonal rings leads to fullerenes when 12 pentagonal ring is reached. Generation of altans is a specialised type of circumscribing in which the encircling annulene is attached via its alternate degree-2 vertices to the degree-2 vertices of the core structure. We show that monocapped nanotubes are circumscribed altans.苯系多环芳烃（benzenoid polycyclic aromatic hydrocarbons）的环绕构建方法最早于1982年，伴随苯系烃周期表与异构体计数的研究主题被提出。该环绕构建过程以苯为起始底物，依次生成蔻（coronene）、包覆蔻（circumcoronene）、双包覆蔻（dicircumcornene）等化合物，构成首个恒定异构体系列。后续，得益于苯系烃周期表（PAH6表）与环绕构建方法的结合，大量苯系恒定异构体系列被发掘。对偶数碳单环多烯烃进行环绕构建，可得到[n]环省（[n]cyclacenes，其中n为六元环数目），此类化合物属于单层纳米管。以[n]环省为起始底物，经连续环绕构建可得到长度递增的(n,0)型锯齿形（Zigzag）纳米管。对环对苯撑（cycloparaphenylenes）进行连续环绕构建，可得到长度递增的(n,n)型扶手椅形（Armchair）纳米管。对环对苯撑进行连续超环绕构建，可得到稳定性最优的全共振六隅体（total-resonant-sextet）扶手椅形纳米管。后续，环绕构建方法被拓展应用于其他环尺寸的多环共轭体系。对同时含有五边形与六元环的多环烃进行环绕构建，当结构中存在12个五边形环时，即可得到富勒烯（fullerenes）。阿尔坦（altans）的生成是一种特殊的环绕构建方式：环绕形成的轮烯（annulene）通过其交替的二度顶点，与核心结构的二度顶点相连。本研究证实，单封端纳米管属于环绕构建型阿尔坦结构。