Changes in the nitrogen functionality of N-15-enriched condensation products prepared from glucose and N-15-glycine were investigated during pyrolysis at 600-1000 degreesC. The structural changes in the condensation products were studied by means of solid-state C-13 and N-15 NMR spectroscopies. During pyrolysis, the aliphatic moieties of the condensation products decomposed and evolved as gas and tar. At pyrolysis temperatures above 600 degreesC, almost all the carbon in the chars were converted to aromatic carbon. After pyrolysis, large amounts of nitrogen remained in the chars as char nitrogen (char-N), and about 30% of the nitrogen was eliminated from the chars as HCN and NH3. With increasing temperature, the production of HCN and NH3 increased and the amount of char-N decreased. By combining X-ray photoelectron spectroscopy and NMR results, detailed results for nitrogen fractions in chars were obtained. During pyrolysis, the fraction of unsubstituted pyrrole-N decreased and the fraction of quatemary-N increased. The fraction of pyridine-N remained almost constant at temperatures below 800 degreesC, but at 900 degreesC and above, the fraction of pyridine-N decreased. The fraction of substituted pyrrole-N showed minimum at 800 degreesC. On the basis of these results, structural changes of nitrogen functional groups during pyrolysis are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.