Why does bromination occur exclusively at the allylic position? Allylic H 360 kJ/mol (87 kcal/mol) H Alkyl 400 kJ/mol (96 kcal/mol) Vinylic 445 kJ/mol (106 kcal/mol) E2004 Thomson-Brooks/Cole H H R R H-C· R-C. R-C. R-C. H H H R Vinylic Methyl Primary Secondary < Tertiary Allylic (1) (2) (3) Less Stability More stable stable