[orgo814]

Looking at the solvochromatic solvent parameters, values beta (solvent as a H bond acceptor) and alpha (solvent as a H bond donor) were derived by looking at varying solvents interacting with p-nitroaniline and analyzing the UV lambda max.

I know for the alpha parameter, a good H bond donor ties up that NH2 group so that it can't conjugate nicely. Therefore, lower lambda max.

How does the beta parameter work though? Specifically, what's the effect on the conjugation of a good solvent H bond acceptor. Confused here.

[phth]

I think it is easier to understand the ability of a solvent to interact with a substrate is dependent of the substrate most importantly.  The lambda max will shift due to the properties of the solvent changing the relative energy levels. Dielectric constant is the best number to go off of in my opinion; the ability of separation of charge to be stabilized.  The other factor is the ability of hydrogen bonding.  It will tell you when separation of charge is stable (a dipolar solvent).  the ability of a solvent to hydrogen bond to a substrate is intrinsic to the substrate.  .  The dielectric constant of the solvent is affecting the n-->π*  energy level increasing the gap; It can be thought of as increasing the capacitance of the molecule.  It is directly related to the coordination to the amine by the solvent.  Things such a DMSO would be a good choice.     This is not the case when the preference for the molecule to interact with the solvent.  For example the s-trans cyclohexyldione enol will intereact with thesolvent and AcAcOEt will not):  edit*** the error in the picture is the equilibrium arrow for AcAcOEt should be flipped