Drago constants

Strong absorption by C=0 from ester groiq) has been utilized. In this study the shift in frequency of carbonyl peak upon introduction of acceptor is used to detect molecular interactions. To complement our studies shifts in frequency of OH peaks upon interactions with various donor molecules were used. Such IR shifts can be calitetted with heat data and used to determine Drago constants, ch quantify the idic and basic characto of the epoxy resin as well as allow to predict strength of intoactions for molecules with I wn constants. 

To conq>are results fipom caiboiqi shift and hydroxyl peak diift we used a method tibat utilized hardness of base to determine Drago constants. This mediod has been presented before 14). The mediod is based on assunqition that the hardness, i.e. ratio C/E of bases with similar structure are equal. Thus, we assumed hardness of ester and cycloal hatic epoxy model molecules to be equal hardness of ethyl acetate, C p/E p==0.61, hardness of dicyclohexyl ketone to be equal to diat of acetone, C g/E g=0.72 and hardness of Bisphenol A aM F epoxies to be equal to that of cyclohexane oxide, C g/E g-l.S (17-20), Thus, relation (S) can be used to find Eb ... 

Table I. Collective results for model molecules In dilute cyclohexane solutions with Drago constants for acids (19).

Drago constants determined fiom C=0 peak shift are shown in Table HI. The results for acetone are with literature data see Table IV. 

Table HI. Drago constants for model molecules determined in tUs study from carbonyl peak shift in cyclohexane...

Drago constants for our model molecules are shown in Table V. In general, there is only slight dif rence between results obtain for HFIP and phenol and different solvents. In contrary to catbonjd peak shift data, OH peak shifts were large and did not display a concentration or solvent dependence. The comparison with literature data in Table IV with average constants presented in Table VI shows that values obtained for ketones and esters match literature data very well. 

The constants detennined for cycloaliphatic epoxy are close to those of esters. The data for epoxies (excluding cycloaliphatic one) are self-consistant, On the other hand, the Drago constants for cyclohexane oxide are 14% lower from those published in literature, however we have no knowledge about the method used to determine them. Upon these circumstances, we can consider om data to be very good. The hydroxyl peak shift seems to be valuable tool to assess molecular interactions and to quantify them. 

IR hydroxyl peak shifts have proven to be a convenient method for evaluatir site-specific interactions. IR peak shifts showed to be usefid tool to detect acid-base interactions between probe acids and model molecules containing carbonyl and other basic groiqrs. The calculated Drago constants based on OH peak shifts diowed to be more consistent widi literature data thoi constants derived from carbotQd peak drifts. Such constants allow the prediction of the strengdi of acid-base interaction. 

Table VI. Drago constants determined in this study...

In 1990, Drago and co-workers (104) had accumulated enough new information to warrant the assigning of improved values of the various Drago constants. The old iodine reference parameters (above) were changed to U = 0.5 (kcal/mol) and Ca = 2.0 (kcal/mol). This change expanded the Eb scale so that it covered a range comparable to the other parameters. 

Use of the Drago Constants in Adhesion Probiems Epoxies are widely used as adhesives. On polymerization, they obviously react with themselves, and, very importantly, react to some extent with the substrates to be adhered. 

The structures of the epoxy monomers, together with their model molecules, are shown in Figure 12.34 (106). The resulting Drago constants, together with the values of some classic molecules, are sununarized in... 

Table 12.10 Drago constants of epoxy and model molecules ...

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