In there compounds, the cyclopentadiene ring has only four hydrogens . 在这些化合物里，环戊二烯环只有4个氢。
2.
A novel ring - enlargement oxidation of polyphenyl substituted cyclopentadienes in air ( or molecular oxygen ) promoted by perchloric acid was described , in which an oxygen atom was inserted into the cyclopentadiene - ring , forming a six - membered pyrylium salts 摘要报导了空气（或氧气）存在的条件下，由高氯酸引发多苯基取代环戊二烯发生新颖的碳碳键断裂扩环反应，在此反应中，氧原子插人到环戊二烯环中形成相应的六元环吡喃盐类化合物。
3.
E - learning provides a friendly contact surface , a image direct - viewing learning environment , and provides the chart , the article , the sound , the picture cyclopentadiene multiple sense organ stimulating , it is advantageous to the scene establishment and the gain and maintenance of massive knowledge , it also can organizes each kind of study information and various disciplines knowledge deferring to the text and the ultra link , this is extremely advantageous to the learners ’ knowledge structure formating and the developing , also has the advantage extremely to construct the current knowledge significance , this is other learning environments is unable to achieve E - learning能够提供界面友好,形象直观的学习环境,提供图、文、声、像并茂的多重感官综合刺激,有利于情景创设和大量知识的获取和保持,还能够按照文本、超链接的方式组织各种学习信息和各学科知识,这非常有利于学习者知识结构的形成和发展,对当前知识的意义建构非常有好处,这是其他学习环境无法做到的。
