Knowledge Bank

Prompted by Molecular Mechanics calculations by Allinger and $coworkers,1$ we undertook a study of the microwave spectrum of $\delta$-valerolactone. In agreement with their calculations, we have found two conformers within a range of less than 1 kcal/mole.[FIGURE] R branch transitions in R band, K band and X band have been measured and used to determine the rotational constants. For the half-chair conformation the rotational constants (in MHz) are A = 4661.18, B = 2558.57, C = 1771.16. For the less abundant half boat conformer, A = 4547.06, B = 2595.87, C = 1867.86. A study of the Stark effect was only partially successful due to the nature of the spectrum. The presence of two conformers was further verified by disappearance of lines from the Raman spectrum when the sample was solidified and cooled to liquid nitrogen temperatures. Temperature studies of the Raman spectrum are in progress to attempt to determine the $\Delta H$ between the conformers.