The isonitrile-nitrile isomerization: kinetic parameters, reaction mechanism and relative photoionization cross-section of the HOMO. A HeI photoelectron spectroscopy study

The isomerisation reactions from CH3CH2CH2NC to CH3CH2CH2CN, (CH3)2CHNC to (CH3)2CHCN and (CH3)3CNC to (CH3)3CCN are found to be of first order by using HeI photoelectron spectroscopy (PES). The activation energies obtained by PES for the isomerisation of RNC, where R is −CH3, −CH2CH3, −CH2CH2CH3, −CH(CH3)2, and −C(CH3)3 are similar. This can be explained by the breaking of the RN bond and the making of the RC bond in the isomerisation reaction from RNC to RCN being essentially synchronous. A transition state is proposed. The photoionization cross-sections of the HOMO for the RNC are deduced from the intercept values in the kinetic equations obtained using PES, and related to the weight of the carbon atom in the isocyano group, because the HOMOs of the RNC mainly embody the 2s lone-pair electron of the carbon atom in the isocyano group.