13C and 1H NMR chemical shifts of 9‐alkyltriptycenes. Linear variations of 13C chemical shifts on successive substitution of the 9‐methyl hydrogen atoms by methyl groups

Abstract 13 C and 1 H NMR chemical shifts of 9‐methyltriptycene (2), 9‐ethyltriptycene (3), 9‐isopropyltriptycene (4) and 9‐ tert ‐butyltriptycene (5) were measured. The 13 C chemical shifts of the carbon atoms at each corresponding position in 2‐5 are proportional to the number of β‐methyl carbon atoms attached to the 9‐methyl (C‐α) carbon atom. Relatively small changes in the 13 C chemical shifts of C‐2, C‐3 and C‐4 carbon atoms and nearly constant values for the 1 H chemical shifts of the H‐2, H‐3 and H‐4 protons in 2‐5 suggest that the structures of the benzene rings in the 9‐alkyltriptycenes remain almost unaltered, resulting in linear variations of the 13 C chemical shifts of the 9‐alkyltriptycenes.