syn-Substituted cyclopropanes (syn-I) (R, R1, and X are above the plane) and anti-I (X is below the plane) are prepd. from R1R3C:CRR2 and :CHF (from Br2CHF and BuLi). syn- and anti-I(X = Cl) are also prepd.; the syn-anti ratios for I(X = F and X = Cl) are similar. The formation of syn-transition states is discussed. [on SciFinder (R)]