Reaction Field Models for the Solvent Influence upon the Fundamental Carbonyl Vibrational Peak of 2-Butanone in Aprotic Media

Abstract

The solvent-induced shift of the fundamental vibrational mode of the carbonyl group in 2-butanone was measured in 27 solvents using FTIR techniques. Eight model formulations for the reaction field of the solvent in which the dielectric continuum is specified in terms of dielectric constant ( ), optical dielectric constant (n 2 ), and effective dielectric constant ( p ) were applied to the solvent dependence of the carbonyl band. The critical tests for these models included both their statistical fit and their predicted value for the ν j gas for the carbonyl band. Most of the f( ) and f( ,n 2 ) functions including the Kirkwood, McRae, and Block-Walker parameters clearly demonstrate that solvent dipolarity-polarizability is the dominant effect upon ν j(CdO) in 21-23 aprotic solvents. However, a two-term MO perturbation statement in both f( ) and a cross-product function proved to be a better overall model than those using only a single parameter. The poorest fits to the ν j(CdO) data were encountered with continuum statements in terms of the p quantity.

Influence of the Dielectric Medium on the Carbonyl Infrared Absorption Peak of Acetylferrocene

“…Here, and are the cavity and the reaction field, respectively, a is the spherical solvent cavity dimensions, is dipole moment vector, is a function that depends of bulk dielectric constant and f ( ε ) is the Onsager dielectric continuum function of the reaction field with dependence in bulk dielectric constant and gives a measurement of the strength of the reaction field [ 44 ]. In terms of molecular orbital theory (MO) [ 43 , 44 , 45 , 46 ], the electrostatic solute-solvent interaction is considered as an additional term in the Hamiltonian of the isolated molecule H 0 and then, the Hamiltonian for the molecule with the reaction field of the solvent ( H p ) is represented by the standard perturbation statement as [ 3 , 4 ] where, is the dipolar operator and f ( ε ) is the Onsager reaction field function, however, it can be considered as a general dielectric continuum function in terms of bulk dielectric constant ( ε ) and/or optical dielectric constant ( n 2 ), according to an alternative reaction field model proposed by Kolling formulated in terms of a simplified molecular orbital treatment for the influence of a polar solvent upon the IR absorption for the carbonyl group of 2-butanone, ethyl acetate and tetramethylurea [ 3 , 4 , 29 ]. In this model, different dielectric continuum functions has been used, such as the Kirkwood-Bauer [ 47 ], Block-Walker [ 48 ], Brady-Carr [ 49 ], McRae [ 50 ], London-Onsager [ 44 ], Marcus [ 51 ], Born [ 52 ] and Bekarek-Kolling [ 1 , 53 ] and can be seen in Table 1 .…”

“…In this context, Kolling proposed an alternative solvent reaction field perturbation model (SCRF-MO), based on dielectric continuum concepts, which incorporates several reaction field functions and a molecular orbital treatment that permits estimation of these solvent-induced shifts for carbonyl species in aprotic, aliphatic and monofunctional solvents (“select solvents”). His results clearly demonstrate that solvent dipolarity-polarizability is the dominant effect upon ( C ≡ N ) of benzonitrile and ( C = O ) of 2-butanone, ethyl acetate and tetramethylurea in a wide variety of aprotic solvents [ 1 , 3 , 4 , 29 ]. However, to our knowledge, this model has not been applied for interpreting the solvent dependence of the carbonyl band of organometallic compounds, although linear solvation energy relationships (LSER) have been used to explain solvent effects on various free-energy-based properties in diverse systems such as coordination and organometallic compounds [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ].…”

“…The electronic and vibrational properties of a substance are affected by several microscopic and macroscopic properties of the medium. Consequently, there is considerable interest in the study of solvent-induced perturbations on characteristic infrared absorption peaks and linear and nonlinear optical properties of organic compounds [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. In effect, a number of semiempirical solvatochromic parameters representing “solvent polarity” have been applied to the quantification of medium effects on these properties [ 13 , 27 , 28 ].…”

“…In effect, a number of semiempirical solvatochromic parameters representing “solvent polarity” have been applied to the quantification of medium effects on these properties [ 13 , 27 , 28 ]. It is known that vibrational frequencies for a molecule dissolved in a liquid depend principally on the dielectric nature of medium (solvent polarity-dipolarity) when specific local interactions are absent [ 1 , 3 , 4 , 23 , 27 ]. It was shown for solute molecules having large permanent dipole moments, that the solvent effect can be explained well by the Onsager reaction field model [ 16 , 24 ].…”

“…This organometallic compound was selected due to its importance for the synthesis of medicines, optical and electronic materials with exceptional properties [ 38 , 39 , 40 , 41 , 42 ] and because this anisotropic molecule contains an acetyl group conjugated with a cyclopentadienyl ring of the organometallic electron donor ferrocenyl group. Besides, in this work we intend to probe the validity in this organometallic system of the polarity-polarizability model proposed by Kolling [ 1 , 3 , 4 , 29 ] and constructed from simplified molecular orbital arguments and reaction field theory as an alternative to interpreting the solvent-induced spectral shift for maximum frequency carbonyl band in small organic molecules.…”