From elewars@alchemy.chem.utoronto.ca Fri Aug 5 19:29:56 1994 Received: from alchemy.chem.utoronto.ca for elewars@alchemy.chem.utoronto.ca by www.ccl.net (8.6.9/930601.1506) id TAA05798; Fri, 5 Aug 1994 19:00:39 -0400 Received: (from elewars@localhost) by alchemy.chem.utoronto.ca (8.6.9/8.6.9) id TAA21684 for chemistry@ccl.net; Fri, 5 Aug 1994 19:05:13 -0400 Date: Fri, 5 Aug 1994 19:05:13 -0400 From: "E. Lewars" Message-Id: <199408052305.TAA21684@alchemy.chem.utoronto.ca> To: chemistry@ccl.net Subject: CALCS ON HCN/HNC ISOMERIZATION ipcake@iisc.ernet asked about the HCN/HNC isomerization. Here are the results of some calcs: H / \ N-----C H--N--C H--C--N TS linear linear Semiempirical AM1 method 118.5 kcal/mol 48.8 kcal/mol 31.0 kcal/mol ZPE 6.440 " " ZPE 10.747 " " ZPE 10.950 " " NC 1.217 NH 0.967 CH 1.069 NH 1.399 NC 1.178 CN 1.160 CH 1.298 HNC 59.0 NHC 53.5 NCH 67.6 -1 imag. freq -1407 cm Ab Initio, HF/3-21G -92.246 04 H -92.339 71 H -92.354 08 H ZPE 6.549 kcal/mol ZPE 11.022 ZPE 11.531 kcal/mol NC 1.183 NH 0.983 CH 1.050 NH 1.407 NC 1.160 CN 1.137 CH 1.213 HNC 55.1 NHC 53.0 NCH 71.9 -1 imag. freq -1216 cm Ab Initio, HF/6-31G* -92.791 95 H -92.855 33 -92.875 20 ZPE 7.287kcal/mol ZPE 10.70 kcal/mol ZPE 11.287 kcal/mol NC 1.169 NH 0.985 CH 1.059 NH 1.454 NC 1.154 CN 1.133 CH 1.155 HNC 50.8 NHC 51.7 NCH 77.5 -1 imag. freq -1227 cm The geom's of HCN and HNC have probably been measured by microwave spec. For an indication of the reliability of these calcs, see Hehre et al, "Ab Initio Molecular Orbital Calculations". For good quantitative estimates of relative energies, you probably should do MP2/6-31G* optimizations, and then maybe MP4/6-31G* single-points on these, or (best) G1 or G2 single-points. The HF geom's are likely not bad, and the energies are in the right order anyway. Errol Lewars =====