ROTATIONAL BARRIERS ABOUT THE EXOCYCLIC C-N BOND IN 2-ARYL SUBSTITUTED 4-(N,N-DIMETHYLAMINOMETHYLENE)-2-OXAZOLIN-5-ONES - AN NMR-STUDY

The barriers to rotation about the exocyclic C-N bond in 2-aryl substi tuted 4-(N,N-dimethylaminomethylene) -2-oxazolin-5-ones have been dete rmined by complete line shape analysis of the NMR spectra of the N,N-d imethyl protons. The energy barriers are attributed to the long range electronic effect of p-substituents of 2-aryl ring. The barrier height s have been correlated with Hammett's substituent constant sigma. It h as been found that the electron withdrawing substituents (NO2, Cl) in the para-position of 2-aryl ring enhance the barrier heights. The oppo site has been observed with electron donating substituents.