It's not a joke, you would have to have been there when that book was being written to really understand it     The reason for that statement is simply that the cis and trans isomers do have slightly different properties    For example a photoamination does result in different reaction products and would demonstrate this phenomenon as was brought up by drone 342 at the time    That was a long time ago and many things have changed greatly since then    The statement is wrong in most cases but there are times when it can make a difference     This is simply a case when Strike's old bromide about not asking a question would have probably been the best course    It's very unlikely that anyone else could even answer this properly unless they were around back then and could remember what was posted on the Hive at that time     You people need to start thinking a lot more before you touch a keyboard, the thread that discussion occurred in was locked and so this one is going to bee too