The same sequence of steps also was investigated for the CF3 analogue derived from 1j. Starting from CF3 substituted oalkynyl-ArylOBCl2 (SM1B), the process proceeds via closely comparable intermediate and transition states (Fig. ). Most notably for the CF3 derivative, the equivalent states to I1A, I3A TS2A and TS4A are all higher in energy (by between 2 -4 kcal mol -1 ), consistent with a build-up of positive charge at carbon in these intermediates/TSs, hence the electron withdrawing CF3 para to the alkyne retards the haloboration reaction. Indeed, the highest barrier to form the CF3 analogue of 2-Cl starting from the CF3-substituted o-alkynyl-ArOBCl2 is 25.0 kcalmol -1 . This is consistent with 1j requiring significantly longer at room temperature (> 12 h) for complete reaction when using just BCl3 to form 3j relative to 1a (which is converted to 3a in < 1 h).