The nature of the Reformatsky reagents derived from the ethyl and tert-butyl esters of bromoacetic acid has been studied by association measurements and NMR spectroscopy in various solvents. It appears that the reagents are dimeric in all but the most polar solvents. A dimeric structure containing both Zn-0 and Zn-C single bonds is present in the crystalline state of (BrZnCHzCOO-t-Bu. THF) 2, the final X-ray analysis of which is reported. Crystals ...