Conformational Behaviour of Organic carbonyl Compounds. Part 2. Aldehydes and Acetyl Derivatives of Condensed Aromatic Hydrocarbons

The relative conformer stability in a number of acetyl and formyl derivatives of condensed hydrocarbons has been determined by the lanthanide induced shift (LIS) method and by simulating the experimental chemical shifts. For the aldehyde of naphtalene the conformational results were confirmed by examining the nmr spectra of model compounds with known probable conformation. In condensed hydrocarbons containing carbonyl substituents the behviour found may be substantially related to three distinct situations, those comparable to the alpha- and beta -positions of naphtalene and overcrowded positions comparable to position 4 in phenanthrene. Calculation of the conformational behaviour by the semi-empirical methods provide qualitative correct results only for systems where steric interactions are small.