23-11-2018 Dr.S.Aravamudhan FAMA2018.

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Presentation transcript:

23-11-2018 Dr.S.Aravamudhan FAMA2018

cis 1,4 diphenyl cyclobutane In order to explain the measured Proton NMR spectrum of linear chain Polystyrene, a cyclic structure had to be invoked. In the preparation methods of polystyrene, that is during polymerization there does not seem any cyclization process occurring. 23-11-2018 Dr.S.Aravamudhan cis 1,4 diphenyl cyclobutane

Anion formed from initiator Anionic vinyl polymerization is a method of making polymers from small molecules containing carbon-carbon double bonds. It is a type of vinyl polymerization. In anionic polymerization, the process is begun by an initiator. In this case, the initiator is an anion; that is, an ion with a negative electrical charge. There are a lot of different initiators used in anionic vinyl polymerization, but the most often used is an unassuming little molecule called butyl lithium. http://pslc.ws/macrog/anionic.htm Now a little bit of the butyl lithium will always fall apart. Not a lot, but some. It falls apart to form a positive lithium cation and a negative butyl anion. We call an anion like this where the negative charge is on a carbon atom a carbanion Anion formed from initiator ϕ STYRENE Initiator initiates polymerization 23-11-2018 Dr.S.Aravamudhan FAMA2018

PROPAGATION of Polymerization Reaction http://pslc.ws/macrog/anionic.htm ϕ POLYSTYRENE 23-11-2018 Dr.S.Aravamudhan FAMA2018

cis 1,4 diphenyl cyclobutane In Proton NMR spectra generally four parameters determine spectral patterns Spectral line positions: Chemical shifts in ppm units τ or δ Line Intensities I ( Amplitudes of lines and line widths) 3. Spin-Spin Couplings J in Hz 4. Line widths LW-Δν in Hz When the cyclic structure is considered, there would be more J couplings between pairs than when the linear structure of polystyrene. Only with these additional parameter values the polystyrene PMR spectral pattern could be simulated. This is cis-1,4 biphenyl cyclobutane molecule. 23-11-2018 Dr.S.Aravamudhan FAMA2018

While the structure invoked for this instance is cis 1,4 diphenyl cyclobutane There is more information in the literature on cis and trans 1,2 diphenyl cyclobutane than can be found on the 1,4 analogue Hence arose this situation that a preliminary study on the possibility of cycloaddition (an addition to result in cyclization) with the computational chemistry software programs. 23-11-2018 Dr.S.Aravamudhan FAMA2018

23-11-2018 Dr.S.Aravamudhan FAMA2018

Distance between molecular units and Nature of Intermolecular Interaction Internet Link for 370796 mv01 Internet Link for 370796 mv01 With G.O. iterations the distance between units decrease.. Sign of convergence to result in single molecular unit Internet Link for 370806 mv02 With G.O. iterations the distance between units increase Internet Link for 370805 mv03 Even after G.O. converges the molecules remain two independent units 23-11-2018 Dr.S.Aravamudhan FAMA2018

23-11-2018 Dr.S.Aravamudhan FAMA2018

23-11-2018 Dr.S.Aravamudhan FAMA2018

Even though it is possible to visualize a cycloaddition by QM G.O. watching in the structure editor images, distinguishing the conformer structural features is not simple. For the GO results if by the QM methods PMR spectra are calculated the structural distinctions become more evident. 23-11-2018 Dr.S.Aravamudhan FAMA2018

CH2 protons CH protons These omplicated cpatterns occur because of J couplings between protons are also present The spectra in the previous slides are plots of Calculated Chemical shifts only. Even with simple pattern distinctions were evident. 23-11-2018 Dr.S.Aravamudhan FAMA2018

23-11-2018 Dr.S.Aravamudhan FAMA2018

Thus it seems certain correlation of structure-PMR spectral patterns can be obtained even for a context of a “fictitious spin system” and the structures invoked are arbitrary trial and effort approach. When coincidentally certain correlations are observed, QM theoretical software results give some support. However, a lot more detailed efforts are required to get lead into a situation, where structures not reported as synthesized compounds or any known compound are to be justified as responsible for observed spectral patterns. 23-11-2018 Dr.S.Aravamudhan FAMA2018

Thank you End of Lecture Hotlink below to a gif images construction set animation Movie http://saravamudhan.tripod.com/Animationwizard-60frames-20minutes.gif 23-11-2018 Dr.S.Aravamudhan FAMA2018