High resolution electronic spectroscopy is demonstrated in the study of the electronic structure of para-alkyl substituted phenols (p-cresol, p-ethylphenol, p-isopropylphenol, p-propylphenol, p-sec-butylphenol, p-tert-butylphenol, and p-pentylphenol) and 2,2,4,4-tetramethyl cyclobutane-1,3-dione (TMCBD). The study on p-alkyl substituted phenols performed by laser induced fluorescence in a supersonic jet provided rich information of the electronic and vibrational structures of p-alkyl substituted phenols in the excited state as well as in the ground state. This study also provided a convenient method for the identification of conformational isomers of molecules in the excited state by observing fluorescence excitation spectra of the molecules to be studied;The study of TMCBD performed by fluorescence and low temperature polarized absorption spectroscopies provided an alternative technique for the study of electronic structures of molecules which cannot be studied in the gas phase under high resolution conditions due to the low fluorescence quantum yields or low vapor pressures of the molecules to be studied. These studies along with polarized infrared spectroscopy provided enough information about the electronic structure of TMCBD to resolve and confirm several arguments on the S[subscript]1 ([superscript]1A[subscript] u) leftharpoons S[subscript]0 ([superscript]1A[subscript] g) transition. These experiments confirm the point symmetry group change to TMCBD upon excitation to the first excited singlet state (S[subscript]1), the symmetry of progression forming modes, the observation of C-H stretching vibrations in the S[subscript]1 state, and the existence of a double minimum potential in the S[subscript]1 state. Additionally, a complete vibrational analysis in the excited state (S[subscript]1) as well as in the ground state was performed. ftn[superscript] aDOE Report IS-T 1367. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.