Sunday, 5 April 2015

organic chemistry - Doubts on IUPAC name 1,1'-methylenebis(4-isocyanatobenzene)


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Wikipedia states IUPAC name of the above compound as 1,1'-methylenebis(4-isocyanatobenzene) .


I have a confusion. Shouldn't isocyanate group be given preference over the methylene group? I assume the name as 4,4'-methylenebis(1-isocyanatobenzene) .


enter image description here


Similar is the case with DDT. Wikipedia states its IUPAC name as 1,1'-(2,2,2-Trichloroethane-1,1-diyl)bis(4-chlorobenzene) .



Why is the numbering of carbon with three chlorine atoms done $1$ ? Moreover, can it be $1,1'$ in the first place in place of $4,4'$ ? I guess the $\text{diyl}$ term indicates that it is connected to two different carbons(of benzene) .


To sum up, I want to know which chain should I select as parent chain and why .




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