Force field parameters for use in MM2 modelling programs have been dev
eloped for the diazoketone function, from a combination of X-ray cryst
allographic data, IR spectroscopy, and ab initio and semi-empirical ca
lculations. These parameters have been applied to study the accessible
conformations and structure of two diazoketone containing molecules,
for which X-ray crystallographic data is available. Comparison of X-ra
y data and calculated geometry was only possible after allowance was m
ade for the effect of crystal packing forces.