A combined experimental and density functional theory investigation of the hydrogen bonding of 2-cyclohexen-1-one and 3-methyl- 2-cyclohexen-1-one in solvents

Solvent effects on the UV absorption and FT-Raman spectra of CHO and 3MCHO in solution phases were evaluated by using the UV and FT-Raman spectroscopies and B3LYP-TD/6-31++G(d, p) calculations employing SCIPCM solvent model in cyclohexane, acetonitrile and water solutions. The Raman intensity profiles in the νCO region of CHO and 3MCHO were affected strongly by solvents of different polarity and hydrogen bonding capability. The results indicated that nonpolar solvents favored CHO monomer, while protic solvents favored CHO-(H2O)n (n = 1,2) clusters. The new band at 1653 cm−1 for CHO and at 1643 cm−1 for 3MCHO in water were assigned respectively to CHO-(H2O)n clusters and 3MCHO-(H2O)n clusters. The hydrogen bonding of solvents and the π-σ superconjugation or π-p conjugation between CCCO and the neighbouring groups (such as CH3 and NH2) made the frequency of the νCO mode down-shift. The Raman spectra of CHO and 3MCHO were assigned.99