Conformational preference of the isocyanato-group

Abstract

The conformational free energy for the isocyanato-group (–ΔG°_NCO) in isocyanatocyclohexane is calculated from the n.m.r. spectrum by use of data obtained from the spectra of cis- and trans-4-t-butyl-1-isocyanatocyclohexane. From measurements of the chemical shift and the coupling constants in the spectrum at 35° values for ΔG°_NCO of 0·39 ± 0·02 and 0·48 ± 0·15 kcal./mole, respectively, are obtained; from the spectrum at –75° the value calculated for ΔG°_NCO is 0·60 ± 0·1 kcal./mole. An energy barrier for chair–boat interconversion in isocyanatocyclohexane of 10·8 kcal./mole is obtained from the coalescence temperature. The synthesis of the above cis- and trans-isomers is described.