The Study On The Mechanism Of Hydrogen Abstraction Reaction Of The Skipped Diene

Research objective Two double bonds of the skipped dienes have the shortest distance in isolated dienes.Methylene between the two double bonds has attracted a lot of attention due to its high reactive activity.In our research,we use different types of hydrogen acceptor reacted with the skipped diene to further study the mechanisms of hydrogen abstraction reaction,to know whether configuration of hydrogen donor,types of hydrogen acceptor and substituent have effect on the thermodynamic properties and the kinetic parameters,further study on the relationship between structure and reaction and to revealing the nature of atom transfer reaction.Methods In this article,we use B3 LYP functional of DFT 6-31g(d)or 6-311++g(d,p)basis set to optimized the configuration of reactants and products,on the base of the calculation results,we obtain the interaction energyies.Correlative excited energies calculated according to M062 X functional 6-311++g(d,p)basis set.The reaction rate constants and tunneling factors were obtained by Ki SThel P program.According to the Gaussian results,Multiwfn could output electron density difference map and transition density matrix between ground state and excited state.Hydrogen abstraction reaction was selected as the object of study;we discussed the differences of linear TS and nonlinear TS,and probed whether rigidity and flexibility of hydrogen donor would affect the reactions.According to excited TXs reacted with MO and MLO,we also studied the reaction mechanisms of hydrogen abstraction reaction induced by triplet state of photo-activity reactants.The result of different types of hydrogen abstraction reactions can further understanding the reaction mechanisms of hydrogen transfer reaction.Using RT-IR to study,two systems(O-170,DDT with 1173 or BP)were chosen to study the influence of concentration of the reactants,photoinitiator type,radiation time,light intensity and monomer type on the polymerization kinetics of thiol-ene reaction.Results 2,5-heptadiene reacted with different types of BR were selected as a model,according to Boltzmann distribution we ensured the most stable configuration of donor was HD(account for 85.04% and its BDE was 68.7kcal/mol).BR often derived from the photolysis of cleavage PIs,such as 1173,184,2959 and so on,among them 2959 has the lowest BDE(61.3kcal/mol).TMBR often derived from the photolysis of acylphosphine oxide PIs,such as TPO,TPO-L,BAPO etc.,among them BAPO has the lowest carbonphosphorus BDE(59.6kcal/mol).Reactions of BR with hydrogen donors have pseudolinear TS as their angles of TS are over 170? or even 180?,while reactions of TMBR with hydrogen donors is nonlinear TS.The relationship of energies(activation energy,deformation energy,interaction energy)with the process of reaction were obtained based on IRC,the result implied that the activation energy and deformation energy were gradually increased along with IRC,while the interaction energies showed the opposite tendency.Activation energies and deformation energies of nonlinear TS were larger than that of pseudo-linear TS.On the basis of BEBO method,we found that nonlinear TS reaction had later TS than linear TS.Based on Evans-Polanyi relationship,the results showed that Polanyi factor of pseudo-linear TS bigger than nonlinear TS,it means the configuration of nonlinear TS is similar to its reactant compound,however the configuration of nonlinear TS is similar to its product compound..These results confirmed the result of BEBO,and the nonlinear TS occurred later than pseudo-linear TS.The results indicated that tunneling factor of hydrogen abstraction reactions triggered by free radicals were very large(3.5-4.0),while hydrogen abstraction reactions triggered by the triplet state of thioxanthone were much small(1.1-1.8)close to that of radical addition reaction(1.12).And the data also reveal that the rate constants of nonlinear TS were 3-4 orders of magnitude higher than pseudo-linear TS.Energies of excited state(vertical excitation energy,adiabatic excitation energy,reorganization energy)based on M062 X functional 6-311++g(d,p)basis set revealed that vertical excitation energy,adiabatic excitation energy of triplet state lower than that of the singlet,while reorganization energy of triplet higher than that of singlet,confirmed that triplet TXs have a higher reactivity.Electron density difference map and transition density matrix obtained by Multiwfn program suggested that the electron excitation from ground state to excited state was mainly the electron of carbonyl group;this means carbonyl chromophore was the reaction site.We also found that the bond angles and bond length of TXs were changed partly.We speculated it is the result from rearrangement of electronic structure.Compared of the reactions of TSs with MO or MLO,activated energy of the former is bigger than the latter and rate constant of the former was smaller.Calculational results displayed that all the TS angles were within linear range.Compared with hydrogen abstraction reactions triggered by radicals,interaction energies hydrogen abstraction reactions triggered by triplet were much higher in the saddle point,it is important part of activation energy.The activation energy of BP reacting with DDT was higher than that of BR who is photolysis product of 1173.According to the results of RT-IR,the reactant species,reactant concentration,light intensity,radiation time etc.have affect on final conversion and reaction rate.In the three component system of O-170,DDT and 1173/BP,the final conversion and reaction rate of the 1173 system reached the maximum,when the reaction molar ratio of O-170,DDT and 1173/BP was 2:2:4.The reaction rate and conversion rate were decreased when concentration of 1173 was too high or deficient.However,the conversion and reaction rate increased,when BP was excessive.If DDT was deficient,the conversion rate decreased with the decline of DDT concentration.But the effect of DDT concentration on the conversion and reaction rate,BP system was more obvious than 1173 system.If O-170 is less than the requirement of reaction molar ratio,the conversion rate will decrease,and effect of O-170 concentration on the conversion and reaction rate,the BP system was more obvious than 1173 system.The conversion rate of the 1173 system was higher than that of BP system with the same proportion.Conclusion From the distortion/interaction model and the BEBO method,we suggest that the nonlinear TS reaction has higher activation barrier and deformation energy than the quasilinear TS reaction.In addition,because of distortion limit,the TSs of flexible and rigid molecules appear at different times.We consider that the nonlinear TS cannot be treated as the traditional TS because they have different reaction mechanisms.Electronic excitation of TXs PIs were mainly concentrated in carbonyl between the two benzene rings,singlet excited state energy is higher than that of triplet state,and so the reorganization energy.Geometries of the ground state and triplet state were different,this leading to the capacity of capture hydrogen atom increased.Compared of reactions of TXs with different hydrogen donors,we found that TS of skipped diene functional group contained reactions appeared earlier than that of common methylene reactions,and the former reactions had lower activation energies and higher reaction rate constants.TSs of hydrogen extraction reaction induced by photo activity compounds are basically linear.The longer the radiation time,the faster the reaction rate,as well as the higher conversion rate and the greater intensity of radiation;BP was insoluble in O-170 and DDT mixtures.Therefore,the formula of O-170,DDT and 1173 is better than O-170,DDT and BP.