1.
Dr.S.Aravamudhan FAMA2018

2. 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.
Dr.S.Aravamudhan
cis 1,4 diphenyl cyclobutane

3. 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.
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
Dr.S.Aravamudhan FAMA2018

4. PROPAGATION of Polymerization Reaction ϕ
POLYSTYRENE
Dr.S.Aravamudhan FAMA2018

5. 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.
Dr.S.Aravamudhan FAMA2018

6. 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.
Dr.S.Aravamudhan FAMA2018

7.
Dr.S.Aravamudhan FAMA2018

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

9.
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10.
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11. Even
though it is possible to visualize a cyclo- addition 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.
Dr.S.Aravamudhan FAMA2018

12. 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.
Dr.S.Aravamudhan FAMA2018

13.
Dr.S.Aravamudhan FAMA2018

14. 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.
Dr.S.Aravamudhan FAMA2018

15. Thank you End of Lecture
Hotlink below to a gif images construction set animation Movie
Dr.S.Aravamudhan FAMA2018