C2H6N (I'm going to assume as NITROGEN) - Cannot exist, as there would be too many hydrogens if all the electrons formed a covalent bond with another atom. You would think that you can make a atom like [CH3-CH](1+) where 1+ is the overall charge on the molecule (One of the hydrogens form a dative covalent bond with the lone pair on the nitrogen), but it is more likely that the C=N double bond will break, as it is more unstable. Also, in order for a ion to be made, high pressures will be needed, so (assuming you're in room temperature and pressure) it won't exist. Woo. essay, haha.
C3H5Br2 - Is unlikely to exist, because a carbocation (a positive carbon in a organic molecule) would exist. So it'll probably exist for a fraction of a second before a nucleophile (electron pair donator) will attack it and for a dative covalent bond with it, changing the structure.
I think it's right, but I'm only in A2 Chemistry, so hope this helped! =]