BacI mechanism

Of fhe eight mechanisms, seven have actually been observed in hydrolysis of carboxylic esters. The one that has not been observed is the BacI mechanism. 

The terminology used for mechanisms in this section is based on the Ingold system (reference 112). The lUPAC nomenclature (reference 161) for alkaline hydrolyses of esters is as follows The BacI mechanism is Dm + + A hDh- The Bac2 reaction is termed An + Dn + A hDh. For... 

See the lUPAC rules Guthrie, R.D. Pure Appl. Chem., 1989, 61, 23. As given here, the lUPAC designations for BacI and BalI are the same, but Rule A.2 adds further symbols so that they can be distinguished Su-AL for BalI and Su-AC for BacI- por reviews of the mechanisms of ester hydrolysis and formation, see Kirby, A.J. in Bamford Tipper, Ref 193, vol. 10, 1972, p. 57 Euranto, E.K. in Patai, Ref 216, p. 505. This is an Sn 1 mechanism with OR as leaving group, which does not happen. 

Fig. 12. Dynamic mechanical analysis of BACY-based glass laminate composites. (—) BA-...

Table 3. Mechanical properties of glass laminate composite of BACY [146]...

Assuming co-reaction, the cure reaction of a mixture of bis(4-maleimido phenyl) methane and BACY was followed by FTIR [221]. The reaction kinetics, studied by DSC, suggested dependency of cure mechanism on blend composition. The apparent activation energy computed by the Prime method increased with BMI content. The rate maximum at a fractional conversion range of 0.32-0.33 indicated an autocatalytic nature of the reaction. The different pattern of activation energy with fractional conversion for two different blend compositions indicated non-identical cure mechanisms for the two compositions. The cyclot-rimerization of BACY occurred during the cure of a 1 2 molar ratio of BMI and BACY. Since activation parameters derived from DSC method are generally not consistent, and since the cyanate cure can be catalyzed by impurities present in BMI, which was not taken into consideration, the authors conclusions on the cure mechanism based on DSC kinetics can be erroneous. 

Table 8. Mechanical properties of neat resin moldings of BACY/BMIP blend [235]...

Fig. 20. Dynamic mechanical spectrum of the BACY/BMIP neat resins. 1 Hz. Heating rate 10 °C/min, in N2. (—)BACY/BMIP-70/30, ( )BACY/BMIP-60/40, (—-)BACY/BMIP-70/ 30/CPM-20%...

The study of the interaction mechanism of thin films of BACY prepolymer on different surface states of Si and oxidized Al employing advanced techniques such as XPS, UPS, MIES, IR reflection spectroscopy, and AFM was undertaken by Possart and Dieckhoff [364]. The trioxy triazine was the only moiety identified to have adhesive interaction with the substrate. On a Si surface, the mechanism was identified as donor-acceptor interaction where the lone pairs of electrons on N and O atoms of trioxy triazine were involved in the electron donor process for the Si cation. On aluminum oxide, the Lewis acidic OH groups act as electron acceptors, withdrawing electron density from the lone pairs of O and N of the trioxy triazine. Back donation of electron density from Al metal to the organic layer is operative beneath the oxide layer. The dicyanate monomer doesn t adhere at all and desorbs quickly out of the interphase region on the substrate. It was concluded that thermosetting reaction of the prepolymer is thus hampered and the resulting network will be less dense near the substrate than in the bulk. 

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