File Extension RXN File Format MDL Reaction format RXN stands for MDL Reaction format. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question Info needed on QZDAOSINIT jobs How do I hide formatting symbols? Local clients loose connection to local SQL Server when system network drops connection to HQ.