Identification of conjugated diolefins in fossil fuel liquids by ¹H n.m.r. two-dimensional correlated spectroscopy

Conjugated diolefins in fossil fuel liquids were identified by a two-dimensional (2D) ¹H n.m.r. chemical shift correlated spectroscopy (COSY) experiment. The trans-terminal, trans-internal and (cis, trans)-internal conjugated diolefin isomers were clearly identified in the olefinic region of the 2D COSY spectrum by comparison with the 2D COSY spectra of model compounds. At 11.7 T, the cross peaks due to conjugated diolefins are well resolved from the cross peaks of non-conjugated olefins and styrene-like compounds. The resonance peaks corresponding to conjugated diolefins in the one-dimensional (1D) ¹H n.m.r. spectrum were assigned based on the positions of cross peaks in the 2D COSY spectrum. Quantitation of conjugated diolefins from the 1D ¹H n.m.r. spectra showed that conjugated diolefins were easily detected in the 2D COSY spectra when present at about 0.01 mmol of diene per gram of sample. For lower levels (0.001 mmol of diene per gram of sample) verification of the presence of diolefins was done by a 1D ¹H n.m.r. homodecoupling experiment.