Conventional analytical methods such as H-1 NMR, vapor pressure osmometry (VPO) and elemental analysis were used to characterize the soot precursor material represented by the chloroform extractable fractions of the young soot gathered at different heights of an ethylene inverse diffusion flame in terms of average structural parameters. The results indicate that the soot soluble fraction obtained at a 6 mm height has a relatively large molecular weight and has long aliphatic chains which later disappear with an increase in height above the burner base, especially in the region where the temperature is high (1200 K). This behavior is also accompanied by an increase in the aromaticity (f(a)) of the samples. (c) 2006 Elsevier Ltd. All rights reserved.