Abstract: Vinyl radiohalogenated small molecules shown in formulas I and II: ##STR1## wherein *X is a radiohalogen, C.dbd.C is a double bonded set of sp.sup.2 hybridized carbon atoms, and substituents R.sub.1, R.sub.2, and Y are as defined below. R.sub.1 and R.sub.2 are substituents independently selected from among hydrogen; alkyl or substituted alkyl, provided that any sp.sup.2 or sp carbon atom substituted on the alkyl is separated from C.dbd.C by at least one fully substituted sp.sup.3 carbon atom; aryl or substituted aryl, provided that the aryl is bonded directly to C.dbd.C; heteroalkyl, provided, first, that no heteroatom of the heteroalkyl bonds directly to C.dbd.C and, second, that any sp.sup.2 or sp hybridized carbon bonded to a heteroatom of the heteroalkyl is not bonded directly to or otherwise conjugated with C.dbd.C and, third, that where a single sp.sup.3 carbon intervenes between C.dbd.C and an sp.sup.2 or sp carbon bonded to a heteroatom, that intervening sp.sup.