four-membered ring

英 [fɔː(r) ˈmɛmbəd rɪŋ]

美 [fɔːr ˈmɛmbərd rɪŋ]

网络四元环,四原子环; 四元环; 四元坏; 四原子环

In EIMS there are many frame-rearrangement ion peaks. The cleavage of C-O, C-F. C-CF3 bonds and the formation of five-or four-membered heterocyclic ring ions containing nitrogen by losing CO are major mass spectrometric characters.
在EIMS中，均存在较多的骨架重排离子峰，其中CO，CF，CCF3，键断裂及失去CO形成的五元，四元含氮杂环离子是重要质谱特征。
This reaction includes the intermediates of the four-membered ring and the six-membered ring. And it indicated from the calculations that the step of β-H reductive elimination was the rate-determinating step.
具有四元环和六元环中间体，β&H（10）的还原消去反应是整个反应的速率决定步骤。
This paper designed and synthesized several chiral nitrogen-containing heterocyclic four-membered ring amide of chiral catalysts, studies its application in catalytic asymmetric Aldol reaction, and acquired better catalytic effect. 1.
本文设计合成了几种手性氮杂四元环酰胺类手性催化剂，研究了其在催化不对称Aldol反应中的应用，取得了较好的催化效果。