
TY  - JOUR
A1  - Riggs, NV 
T1  - An <i>ab initio</i> Study of Butyrolactone and 3-Hydroxybutyrolactone. Semiempirical Calculations on Proton Coupling Constants in These Molecules
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1985
VL  - 38
IS  - 11
SP  - 1575
EP  - 1583
KW  - 
UR  - https://doi.org/10.1071/CH9851575 
N2  - Optimization with the 3-21G basis set of the geometry of the envelope conformation of butyrolactone leads to a structure with an out-of-plane angle of 29.7&#176; for the flap. Similar optimization of the twisted-ring conformation leads to a structure lying only 0.2 kJ mol-1 higher in energy and having a twist angle of 18.7&#176;. These structures differ mainly in a vertical translation of C3 and C4 by c. 0.14 &#506; with respect to the C2-C1-O2 plane. The ring may be twisted or bent at low energy- cost, and the barrier to inversion via the planar-ring (CS) structure is only 4.7 kJ mol-1. It is suggested that the envelope conformation is but one of many transient structures in a rapid ring-inversion process. For 3-hydroxybutyrolactone, the optimized twisted-ring conformation with twist angle 22.0&#176; lies 0.3 kJ mol-1 below the optimized envelope conformation with out-of-plane angle 33.7&#176; again these structures differ mainly in a vertical translation of C 3 and C 4 by c. 0.15 &#506; with respect to the C 2-C 1-O2 plane. Moderate ring twisting and bending are rather more costly than in butyrolactone itself, and the hydroxy group clearly occupies the pseudo-axial position on C 3. Calculated bond lengths and angles for both molecules are mostly within the corresponding experimental ranges for a series of &#947;-lactones. Proton- proton spin coupling constants calculated by the FINITE/INDO method for the optimized 3-hydroxybutyrolactone structures are in moderate-to-good agreement with experimental values, and agreement is improved by application of a thermal population-averaging procedure. Thermally averaged values for butyrolactone are also presented. 
ER  -

