Pyrrolizin-3-one and its 1,2-dihydro derivative: structures of the free molecules determined by electron diffraction and ab initio calculations and in the crystal by X-ray diffraction

Abstract

The molecular structures of pyrrolizin-3-one 1 and 1,2-dihydropyrrolizin-3-one 2 have been investigated in the gas phase by ab initio calculations (both compounds) and electron diffraction using the SARACEN method of structural analysis (parent compound only), and in the solid phase at 150 K by low-temperature X-ray diffraction. Important structural parameters (r_h1 structure) for a free molecule of 1 are: r(C–O) 1.215(4) and r[N–C(CO)] 1.437(4) Å. For 2 these (r_e structure) are: r(C–O) 1.2095 and r[N–C(CO)] 1.4068 Å. The corresponding values in the crystal for 1 are r(C–O) 1.207(2) and r[N–C(CO)] 1.408(2) Å, and for 2r(C–O) 1.216(2) and r[N–C(CO)] 1.392(2) Å.