Chemical shift assignments in N , N ‐disubstituted trifluoroacetamides

Due to hindered rotation about the central CN bond in N , N ‐disubstituted trifluoroacetamides, CF 3 CONR 1 R 2 , two resonance peaks are usually observed for each proton in R 1 and R 2 . Chemical shift assignments are made for the following amides: 1 , R 1 = R 2 = Me; 2 , R 1 = R 2 = Et; 3 , R 1 = Me, R 2 = 2‐Propyl; 4 , R 1 = Me, R 2 = 1‐Butyl; 5 , R 1 = Me, R 2 = Cyclohexyl; 6 , R 1 = R 2 = 2‐Propyl; 7 , R 1 = 2‐Propyl, R 2 = Cyclohexyl. Amides 6 and 7 show an inversion of the relative chemical shift for both the methine and methyl protons of the 2‐propyl group as compared with 3 . For non‐fluorinated amides, aromatic solvents shift the trans alkyl peaks to higher field faster than those cis (to the carbonyl oxygen atom); however, this generalization does not apply to all trifluoroacetamide proton peaks.